Impact of Regulations of Traffic Emissions on  PAH Level in the Air

Contents

Foreword

Summary and Conclusions

Background and implementationv
Air pollution levels and trends

Resume og Konklusioner

Undersøgelsens baggrund og forløb
Luftforureningsniveauer og trend

1 Introduction
1.1 Air pollution with PAH and other mutagens from traffic and other sources
1.2 Reduction of emissions
1.3 Recommended limit values
1.4 Toxicological evaluation of PAH and other mutagens in air

2 Measuring programme, locations, sampling and analysis
2.1 Measuring programme and locations
2.2 Sampling and analysis

3 Results and discussions
3.1 The general air pollution situation
3.2 Air pollution of PAH and other mutagenic PAC
3.3 Comparison of N-PAC and PAH
3.4 Correlations with other parameters
3.5 Trend analysis
3.6 The influence of ambient temperature and global radiation

4 Conclusions

Acknowledgements

References
 

Foreword

In the period 1992-1994 The Danish Environmental Protection Agency supported a project that evaluated the contribution of traffic to the emissions of PAH and mutagens in cities, the PAH-levels in Denmark and evaluation of the health aspects of PAH and other mutagens. It was concluded, that motor vehicles were main sources to PAH-pollution in streets in Copenhagen, and that 2/3 of the PAH-emission originated from diesel driven motor vehicles.

The measurements indicated significantly lower levels of PAH and mutagens in 1993 as compared to 1992. One theory put forward was that this improvement could be related to a concomitant change in the quality of diesel used in buses. The main objective of this project has been to complement the previous observations with additional data in order to proof or disproof the theory.

The results from the project will contribute to the ongoing discussions about the need for a further improvement of the diesel quality in cities.

The report has been presented for a group of experts with the following members:

DEPA:
Erik Iversen (chairman)

NERI:
Finn Palmgren

IFT:
John Chr. Larsen

DTU:
Jesper Schramm

All the authors were participating in the meeting with the expert group.
 

Summary and Conclusions

Background and implementation

PAH emissions

Emissions of PAH (polycyclic aromatic hydrocarbons) originate from several sources. Traffic is an important contributor, especially in streets. A little more than half of the fuel consumption used for road transport in Denmark is made of petrol. The second important fuel is diesel oil. During the nineties severe emission standards have been introduced, both for petrol and diesel driven motor vehicles. In October 1990 legislation was introduced in Denmark which required the closed loop 3-way catalysts on all new petrol driven passenger cars. This new technology was expected to result in a significant reduction in the emission of PAH and to reduce the emission of CO, hydrocarbons and nitrogen oxides from the individual car with 70-80%. During the measuring campaign in 1992 about 10% of the petrol-driven passenger cars were equipped with catalysts. This proportion increased to about 40% during the 1996 measurements. Petrol makes up about 55% of the fuels used for road transport in Denmark. Most of the remaining part is diesel oil. The introduction of new diesel qualities for buses from July 1992 was also expected to reduce the PAH and soot emissions. The new diesel fuels have a lower distillation end point implicating a lower fuel content of hydrocarbons with high molecular weight including PAH.

Previous investigations

The Danish Environmental Protection Agency (DEPA) supported in 1992-1994 a project with the following main objectives (Nielsen et al. 1995b and c):

1. Evaluation of the contribution of traffic to PAH-emissions, including a distinction between petrol and diesel driven vehicles.
2. Determination of the PAH levels at different locations in Denmark.
3. Evaluation of the health effects of PAH and other POM (polycyclic organic matter).

Previous results

Most of the measurements were made in the period January to March 1992, i.e. before the introduction of the new diesel fuel qualities. The investigation showed that the highest levels of PAH in air were found in street air. The range was as follows: Street > city background suburbs > village > country sites. The levels of benzo(a)pyrene in city air (street: 4.4 ± 1.2 ng/m³, city background: 1.4 ± 0.6 ng/m³) appeared to be between the tolerable level of 5 ng/m³ (annual average) and the acceptable level of 0.5 ng/m³ applied as air quality criteria in the Netherlands. In Denmark it is the policy that the levels of PAH and other PAC should be as low as possible, and the outdoor air levels are regulated by means of emission limits for the various sources. The traffic emissions were the major PAH source in street air. The contribution was estimated to be 80%. The weekdays distribution was as follows: Working days: 90% and weekends: 40%. The diurnal variation showed peaks in the morning and afternoon rush hours and lowest concentrations in the night hours. The contribution from diesel vehicles was estimated to be twice the contribution from petrol cars (Nielsen 1996).

1992 to 1993 trend

The background for this project was the trend observed from 1992 to 1993 in the air levels of mutagenicity and PAH. A very strong decrease was observed in the air levels of mutagenicity, but a decrease was also observed for PAH. This may suggest that the effect of legislation in reducing the traffic emissions is more effective for PAH and other mutagenic compounds than for CO, nitrogen oxides and soot. The levels of the latter were applied as internal standards. The decreases in the levels of PAH and mutagenicity were calculated relative to these three types of compounds. However, the interpretation of the results was not unambiguous, as the meteorological conditions were different in the two sets of measurements, and the emissions of PAH and other mutagens might perhaps also have been affected by the ambient temperatures (Nielsen, 1996, Nielsen et al., 1995b and c).

Measuring programme

Measurements of 24-h levels of particulate PAC (mainly PAH) and mutagenicity were performed at a busy street in the central Copenhagen (H.C. Andersens Boulevard). At this location measurements have been performed on a daily basis of NO, gas NO_y, SO₂, CO, ozone, soot, particulate matter and inorganic elements. The traffic intensity in the street is in the magnitude of 60,000 cars each day, and the streets in the neighbourhood have also high traffic intensities. Most of the 1996 samples for PAH analyses and mutagenicity testing were collected in the winter (40%) and the spring (45%) as the major part of the 1992-1993 samples were obtained in the months January-March. The particulate phase PAC measurements include 28 PAH (3-6 rings), 2 oxy-PAH (3-4 rings), 2 S-PAC (3-4 rings) and 17 N-PAC (2-5 rings). The mutagenicity assays included the following tester strains: TA98+S9, TA98-S9 and TA98NR. In a limited number of cases a test was performed on a basic extract in addition to the total extract.

Air pollution levels and trend

PAC levels

The levels of PAC in the street air were lower in 1996 than in 1992. The 1996 level of benzo(a)pyrene was 2.2±0.6 ng/m³ and that of benzo(e)pyrene was 3.1±0.7 ng/m³ compared to 4.6±1.4 ng/m³ and 4.4±0.8 ng/m³ respectively in 1992. However, the results are questioning the application of benzo(a)pyrene as a reliable indicator for the air pollution with mutagenic and carcinogenic PAC as discussed later in this section. The levels of the two oxy-PAH, anthraquinone and benzanthrone, were of the same magnitude as the most abundant PAH, fluoranthene, pyrene, benzofluoranthenes, benzo(c)phenanthrene, chrysene/triphenylene, benzopyrenes, benzo(ghi)perylene and coronene. The concentrations of S- and N-PAC were about one order of magnitude lower than those of PAH. The mean mutagenic activity seen in TA98+S9 was 48±41 rev./m³. The direct mutagenic activity measured in TA98-S9 was 70% of the activity seen with metabolic activation. The level of direct acting mutagenic nitro compounds ((TA98-S9)-(TA98NR)) constituted 56% of the total level of direct acting mutagenicity, which is a typical result for air samples. The TA98+S9 mutagenic activity in the basic extracts was about 3% of the activity in the total extracts in those samples collected on days with low activity of atmospheric photochemistry. However, the photochemical processes may produce water soluble, polar indirect acting mutagens ending up in the basic extract, as the mutagenicity of this fraction increased significantly with increasing atmospheric ozone concentrations. The lowest-level of 3% is ascribed to be caused mainly by N-PAC.

PAH composition

The higher concentrations of airborne particulate matter in the 1996 samples compared to the 1992-93 seems to have samples caused a higher proportion of the lighter PAH relative to the heavier ones. The lighter PAH are distributed in the atmosphere between the gas phase and particles. The heavier PAH are only associated with particles. The particle association of the lighter PAH increases, when the amount of airborne particulate matter increases. Atmospheric chemistry of the reactive PAH (cyclopenteno(cd)pyrene, benzo(a)pyrene, perylene and anthanthrene) was another factor affecting the PAH composition in the 1996 samples relative to that in the 1992-1993 samples. Thus, the 1996 to 1992-93 ratio for the four PAH (0.42±0.05) was significantly lower than the ratio for the stable PAH, benz(a)anthracene, triphenylene, chrysene, benzo(a)-, benzo(b)-, benzo(j)- and benzo(k)fluoranthene, benzo(e)pyrene, indeno(1,2,3-cd)pyrene, benzo(ghi)perylene and coronene, (0.60±0.08) (t-test, p<0.01).

Effect of emission sources

Both the emissions from diesel cars as well as the emissions from petrol driven passenger cars were reduced in 1996 compared to 1992. The effects of the introduction of light diesel and those of catalysts for petrol passenger cars were estimated to be about 2:1. It was estimated for the 1992 samples that about 2/3 of the traffic PAH contribution originated from diesel vehicles and about 1/3 originated from petrol driven cars. The changes in the emission sources did not cause any major changes in the PAH composition in 1996 compared to 1992. The 1996 to 1992 ratios of phenanthren (0.61) and methylphenanthrenes (0.63) were very close to each other and the 1996 to 1992-93 ratios of benzo(ghi)perylene (0.64) and coronene (0.64) were not significantly different from the ratio of the other stable PAH (0.60±0.08). It is therefore concluded, that the diesel-to-petrol contribution ratio is still about 2:1 in 1996, and that the ratio of the effects of the introduction of light diesel and those of catalysts for petrol cars also must have been about 2:1. The 2:1 ratio is supported by the finding that the PAH reduction was almost three times larger than the reduction in carbon monoxide. The effect of the catalysts is expected to be the same for PAH and CO, and most of the CO in the street air originates from petrol engines. In addition, the differences between the PAH 1993 to 1992 ratio and the CO 1993 to 1992 ratio were almost the same as the differences in the corresponding 1996 to 1992 ratios suggesting that the effect on diesel emissions took place between the 1992 and 1993 measurements. The trends from 1992 to 1996 is further discussed later.

Mutagenicity and atmospheric chemistry

Atmospheric processes may affect the composition of mutagenic PAC in the polluted air masses by increasing the mutagenic activities and decreasing the benzo(a)pyrene concentrations. Therefore the health risk arising from air pollution may be underestimated if only pollution indicator concentrations are used without taking the impact of atmospheric processes into consideration. This imply that the human health risk ratio between the countryside site and the city is higher than the ratio calculated on the basis of the benzo(a)pyrene level alone. The relative mutagenicity estimated by the ratio between the content of mutagens and PAH increased strongly with the chemical age of the polluted air masses. The chemical age was estimated by the ratio between 2-nitrofluoranthene and 1-nitropyrene. The former is formed by atmospheric processes and the second one is emitted directly into the atmosphere. The increase in direct acting mutagens was larger than that of indirect mutagens. The increase in direct acting nitro-PAC and other PAC ones was the same.

Mutagenicity and long-range transport

In addition, on the 22 April 1996 the air pollution in the air at H.C. Andersens Boulevard originated from both local sources and from polluted air masses transported from the Continent. The levels of mutagenic activities increased with a factor of 5-7 compared to the mean levels of the period. The level of the traffic gases, NO, gas NO_y and CO, originating mainly from the local sources were normal (increased by a factor of 1.1-1.3). Although not comparable with the mutagenic activities, the long range transport contribution caused an increase in SO₂ (factor: 2.5), S-PAC (2.0) and benzanthrone (2.0). Most of the stable heavier PAH increased with a factor of 1.6-1.8. The increases were minor for benzo(ghi)perylene (1.4) and coronene (1.2) and close to the factor for the traffic gases. Benzo(ghi)perylene and especially coronene has a high contribution from traffic sources.

Oxy-PAH

The oxy-PAH, benzanthrone, is mainly associated with particles. Two or maybe three sources contribute to its presence in ambient air: Emission, atmospheric chemistry and perhaps resuspension. If so the identification of the last source is new, while there are conflicting data in the literature on whether atmospheric processes may be a source or not. However, considering

(1) that the summer half year level of benzanthrone is 1.5 times higher than the winter half year level,

(2) that the concentration of benzanthrone was elevated by a factor of 2.0 in the long-range transport incidence,

(3) that the relative benzanthrone content (benzanthrone/Sum PAH) is anticorrelated (r=-0.52, p<0.05) to the relative benzo(a)pyrene content (benzo(a)pyrene/Sum PAH), it is evident that a significant part of benzanthrone is formed by atmospheric processes. Resuspension of aged particles is perhaps an additional source for benzanthrone and other oxy-PAH, even though resuspension appears to be a negligible source for the presence of PAH in street air. The background for this may be, that the resuspended particles are aged and exposed to sun light and reactive atmospheric gases for a longer time. Under these circumstances the PAH may be oxidised and transformed to oxy-PAH, e.g. benzanthrone. Thus the ratio of benzanthrone to the sum of PAH (sum of benzo(e)pyrene, benzo(bjk)fluoranthene and indeno(1,2,3-cd)pyrene) increased when the amount of airborne soil dust elements, Fe, Ti, Si and Ca increased (r=0.52-0.64, p<0.05). The four soil dust elements are considered to be an indicator for the up whirling of settled particles.

Trend analysis

The variations in PAH and other mutagens were related to those of the air pollutants measured on a daily basis each year in order to limit the influence of the different meteorological conditions. The comparisons indicate that the regulations of traffic emissions induced by the environmental authorities have had a greater impact on the levels of PAH and other airborne mutagens than on the levels of nitrogen oxides, CO and soot. Thus taking all data into consideration the PAH decreased 19±12% from 1992 to 1993 and 38±8% from 1992 to 1996. The decrease in mutagenicity was 42±18% from 1992 to 1996. The decreases of the four reference components, NO, gas NO_y, CO and soot, were 3±6% from 1992 to 1993 and 18±5% from 1992 to 1996. The decreases in PAH concentrations and mutagenicity levels were significantly larger (t-test, p<0.01) than the decreases of the four reference components. The regulations of traffic emissions appear to have a greater impact on the mutagenicity levels than on the PAH levels confirming the observations in 1993. Disclosing the long-range transport incidence the decrease from 1992 to 1996 of the 7 PAH (benzo(bjk)fluoranthene, benzo(a)- and benzo(e)pyrene, benzo(ghi)perylene and coronene) was 40±7% and the decrease in the mutagenic activity in the three different tester strains were as follows: TA98+S9 59%, TA98-S9 54% and TA98NR 71%. Applying the 1992 data set where measurements of inorganic elements also were available the PAH concentrations decreased with 50±9% and the mutagenicity levels with 42±18% from 1992 to 1996. The six reference inorganic elements, S, K, V, Ni, Zn and Cu, increased in the same period with 22±16%. The comparison includes data from the long-range transport episode.

Seasonal variation

The summer to winter variation in PAC showed different patterns depending on the type of compounds and their source relations. The oxy-PAH, benzanthrone, had higher atmospheric concentrations in the summer half-year than the winter half-year. The reactive PAH, cyclopenteno(cd)-pyrene and benzo(a)pyrene showed the opposite tendency having the highest concentrations at winter-time. The photolytic degradation of benzo(a)pyrene was also confirmed by the anticorrelation between the global radiation and the ratio of benzo(a)pyrene to the PAH sum (r=-0.56, p<0.05). There were no major difference in the summer and winter levels of the stable PAH reference components, benzo(e)pyrene, benzo(bjk)fluoranthene and indeno(1,2,3-cd)pyrene.

Health risk

The most significant health risk of ambient air pollution with PAH and other mutagens is expected to be an excess lung cancer. The risk assessment made in a previous study (Nielsen et al., 1995c) was based upon estimates assuming that the PAC composition is similar in country air, street air, source emissions and in the working environment and that differences can be disregarded. For residents in Copenhagen and other heavily urbanised areas it was estimated that the air pollution with PAH and other mutagens would cause, as a maximum, five extra lung cancer cases each year among one million individuals. The risk will be lower for individuals living at country sites. The observations that atmospheric processes during the transport of PAC influence the formation of mutagenic compounds might imply that the above mentioned maximum estimate could be higher.
 

Resume og Konklusioner

Undersøgelsens baggrund og forløb

Emission af PAH

Flere typer af forbrændingskilder medfører luftforurening med polycycliske aromatiske kulbrinter (PAH). Trafik er en vigtig forureningskilde, specielt i gader. I løbet af halvfemserne er der derfor indført strengere emissionsstandarder. Fra og med oktober 1990 påbød lovgivningen således, at alle nye biler, der anvendte benzin som brændstof, skulle være forsynet med en lukket tre-vejs katalysator. Denne teknologi forventes at reducere emissionen af PAH. Anvendelsen forventes tilsvarende at reducere emissionen af CO, kulbrinter og nitrogenoxider med 70-80% fra den enkelte bil. Omkring 10% af personbilerne var forsynet med katalysator under målekampagnen i 1992. Denne andel steg til omkring 40% under 1996 målingerne. Benzin udgør omkring 55% af det brændstof, der anvendes til vejtransport i Danmark. Diesel olie udgør hovedparten af resten. Indførelsen af kvaliteter for diesel til busser fra juli 1992 forventes ligeledes at reducere emissionen af PAH og sod-partikler. De nye diesel brændstoffer har en lavere slut destillations temperatur, således at brændstoffet får et lavere indhold af kulbrinter med høj molekylvægt inkl. PAH.

Tidligere undersøgelser

Miljøstyrelsen (MST) støttede derfor i 1992-1994 et projekt, som havde følgende hovedformål (Nielsen et al., 1995b og c):

1. Vurdering af trafikbidraget til den samlede emission af PAH, inklusiv en differentiering mellem benzin- og dieselkøretøjer.
2. Bestemmelse af forureningsniveauet med PAH på forskellige lokaliteter i Danmark.
3. Vurdering af de sundhedsskadelige effekter af PAH og andre PAC (polycyclic aromatic compounds).

Tidligere resultater

De fleste af målingerne blev udført i perioden januar - marts 1992, d.v.s. inden indførslen af de nye diesel-brændstofs kvaliteter. Undersøgelsen viste, at de højeste PAH niveauer forekom i gadeluft. Rækkefølgen var som følgende: Gade > bybaggrund forstad > landsby > landbrugsområde. Niveauerne af benz(a)pyren i byluften (gade: 4,4 ±1,2 ng/m³, bybaggrund: 1,4 ± 0,6 ng/m³) syntes at ligge imellem den tolerable grænseværdi på 5 ng/m³ (årsmiddelværdi) og den acceptable grænseværdi på 0,5 ng/m³, der anvendes som luftkvalitetskriterium i Holland. I Danmark er det Miljøstyrelsens opfattelse, at niveauerne af PAH i luft skal være så lave som mulige, og luftforureningsniveauet reguleres derfor vha. emissions-grænseværdier for de enkelte kilder. Trafikemissionerne var hovedkilden til forekomsten af PAH i gadeluft. Bidraget blev beregnet til at være 80%. Ugefordelingen var som følgende: Hverdage: 90% og weekender: 40%. Døgnvariationen viste toppe i morgen- og eftermiddagsmyldretiden og de laveste niveauer om natten. Emissionsbidragene fra henholdsvis dieselbiler og benzinbiler blev vurderet til at være 2 til 1 (Nielsen, 1996).

1992 til 1993 trend

Baggrunden for iværksættelsen af dette projekt var trenden i luftforureningsniveauerne for mutagenicitet og PAH fra 1992 til 1993. Niveauet af mutagenicitet-luftforureningsniveauet faldt kraftigt fra 1992 til 1993, og der var ligeledes et fald i PAH-niveauerne. Resultaterne synes derfor at indikere, at de lovgivningsmæssige initiativer for at reducere emissionerne fra biler virker mere effektivt for PAH og andre mutagene forbindelser end for CO, nitrogenoxider og sod. Niveauerne af de tre sidstnævnte blev anvendt som interne standarder i 1992-1993 sammenligningen, og faldet i PAH og mutagenicitet var således relativt til de tre typer af forurening. Fortolkningen af resultaterne var imidlertid ikke entydig, da de meteorologiske forhold i de to måleserier var væsentlig forskellige, og emissionerne af PAH og andre mutagener kan muligvis også påvirkes af vejrliget, specielt lufttemperaturen (Nielsen, 1996, Nielsen et al., 1995b og c).

Måleprogram

Målingerne af døgnniveauerne af partikulært PAC (især PAH) og mutagenicitet blev udført på trafikeret gade i det centrale København (H.C. Andersens Boulevard). Miljøkontrollen udfører hver dag på denne lokalitet målingerne af luftkvaliteten af NO, gas NO_y, SO₂, CO, ozon, sod og i samarbejde med Danmarks Miljøundersøgelser ligeledes af partikelindholdet og uorganiske elementer. Trafikintensiteten i gaden er af størrelsesordenen 60.000 biler pr. døgn. De fleste af prøverne til PAC og mutagenicitet-analyserne blev samlet op i vinterperioden (40%) og foråret (45%) af hensyn til, at hovedparten af 1992-1993 målingerne blev udført i månederne januar-marts. Målingerne af partikulært PAC omfattede 28 PAH (3-6 ringe), 2 oxy-PAH (3-4 ringe), 2 S-PAC (3-4 ringe) og 17 N-PAC (2-5 ringe). Mutagenicitets-testene blev udført med følgende teststammer med og uden metabolisk aktivering (±): TA98+S9, TA98-S9 og TA98NR. I enkelte tilfælde blev der desuden udført tests på et basisk ekstrakt i tillæg til testene på det totale ekstrakt.

Luftforureningsniveauer og trend

PAC niveauer

PAC niveauerne i gadeluft var reduceret i 1996 sammenlignet med 1992. 1996 niveauet af benz(a)pyren var 2,2±0,6 ng/m³ og niveauet af benz(e)pyren var 3,1±0,7 ng/m³ sammenholdt med 1992 niveauer på 4.6±1.4 og 4.4±0.8 ng/m³. Resultaterne sætter også spørgsmål ved anvendeligheden af benz(a)pyren som en pålidelig indikator for luftforureningen med mutagene og carcinogene PAC som diskuteret senere i dette afsnit. Niveauerne af de to oxy-PAH, anthraquinon og benzanthron, var i den samme størrelsesorden som de mest almindelig forekommende PAH, fluoranthen, pyren, benzfluoranthener, benz(c)phenanthren, chrysen/triphenylen, benzpyrener, benz(ghi)perylen og coronen. Koncentrationerne af S- og N-PAC var omkring en størrelsesorden lavere end niveauerne af PAH. Middelmutageniciteten bestemt vha. af TA98+S9 var 48±41 rev./m³. Den direkte mutagene aktivitet målt vha. TA98-S9 var 70% af aktiviteten, som blev målt med metabolisk aktivering. Det mutagene niveau af direkte virkende nitro-PAC ((TA98-S9)-(TA98NR)) udgjorde 56% af det totale niveau for direkte virkende mutagenicitet, hvilket er et typisk resultat for luftprøver. TA98+S9 mutagen-aktiviteten i de basiske ekstrakter var omkring 3% af aktiviteten i de totale ekstrakter i de prøver, som var opsamlet på dage med lav aktivitet af atmosfærisk fotokemi. De fotokemiske processer danner imidlertid muligvis vandopløselige polære indirekte virkende mutagene forbindelser, som ender i de basiske ekstrakter. Mutageniciteten af den basiske fraktion øges således væsentlig med tiltagende koncentrationer af ozon i atmosfæren. Bundniveau-værdien på 3% tilskrives således hovedsageligt at være forårsaget af N-PAC.

Sammensætning af PAH

De højere svævestøvskoncentrationer i 1996-prøverne sammenlignet med 1992-93 prøverne syntes at have medført en relativ højere andel af de lette PAH i forhold til de tunge PAH. De lette PAH er fordelt i atmosfæren mellem gasfase og binding til partikler, hvorimod de tunge PAH udelukkende er partikel-bundne. Der er derfor en større andel af de lette PAH, der er bundet til partikler, når koncentrationen af svævestøv forøges. Atmosfærekemi af de reaktive PAH (cyclopenten(cd)pyren, benz(a)pyren, perylen og anthanthren) var en anden faktor, som påvirkede PAH-sammensætningen i 1996-prøverne i forhold til 1992-93 prøverne. Således var 1996 til 1992-93 forholdet mellem koncentrationerne af de fire PAH (0,42±0,05) signifikant lavere end forholdet for de stabile PAH, benz(a)anthracen, triphenylen, chrysen, benz(a)-, benz(b)-, benz(j)- og benz(k)fluoranthen, benz(e)pyren, inden(1,2,3-cd)pyren, benz(ghi)perylen og coronen, (0,60±0,08) (t-test, p<0,01).

Effekt af emissionskilderne

Både emissionerne fra dieselkøretøjer såvel som emissionerne fra de benzindrevne personbiler blev reduceret i 1996 sammenlignet med 1992. Effekten af indførelsen af let diesel og effekten af katalysatorer for personbiler blev vurderet til at være omkring 2:1. Forholdet mellem methylphenanthrener og phenanthren og forekomsten af benz(ghi)perylen og coronen er blevet anvendt til at estimere bidraget fra dieselbiler og benzindrevne biler. Det blev estimeret for 1992-prøverne, at dieselbidraget udgjorde ca. 2/3 af PAH-bidraget fra trafik, og at 1/3 skyldtes benzinbiler. Ændringerne i kilderne medførte ikke ændringer i PAH-sammensætningen i luften i 1996 sammenlignet med 1992. 1996 til 1992 forholdene af phenanthren (0,61) og methylphenanthrener (0,63) var næsten ens og 1996 til 1992-1993 forholdene af benz(ghi)perylen (0,64) og coronen (0,64) var ikke signifikant forskellige fra forholdet for de andre stabile PAH (0,60±0,08). Som følge heraf kan det konkluderes, at forholdet mellem diesel- og benzinbidragene er omtrent uændrede i 1996, samt at effekten af indførelsen af let diesel og effekten af katalysatorer for personbiler har været omtrent 2:1. . Effektforholdet på 2:1 støttes af, at PAH-reduktionen var næsten 3 gange større end reduktionen af kulilte. Effekten af katalysatorer forventes at være den samme for PAH og CO, og hovedparten af CO i gadeluften stammer fra benzinbilernes udstødningsgasser. Desuden var forskellen mellem 1993 til 1992 forholdet for PAH og forholdet for CO næsten det samme som forskellen i de tilsvarende 1996 til 1992 forhold. Dette resultat indikerer, at dieseleffekten er sket mellem 1992 og 1993 målingerne i overensstemmelse med, at den ultralette diesel blev indført i denne periode. 1992 til 1996 trenden vil blive diskuteret videre i et senere afsnit.

Fjerntransport

Kemiske processer i atmosfæren kan påvirke sammensætningen af mutagene PAC i de forurenede luftmasser og forøge den mutagene aktivitet og reducere indholdet af benz(a)pyren. Derfor kan sundhedsrisikoen ved luftforurening blive undervurderet, hvis man kun anvender koncentrationer af forureningsindikatorer uden at tage hensyn til indflydelsen af de atmosfærekemiske processer. Dette medfører, at den helbredsmæssige risiko for landboere i forhold til risikoen for byboere er højere end det atmosfæriske benz(a)pyren-forhold mellem de to lokalitets-typer indikerer. Den relative mutagenicitet (forholdet mellem mutagener og PAH) steg således kraftigt med den kemiske alder af de forurenede luftmasser. Den kemiske alder blev vurderet vha. forholdet mellem 2-nitrofluoranthen og 1-nitropyren. Den førstnævnte nitro-PAH dannes ved kemiske processer i atmosfæren og den sidstnævnte emitteres direkte til luften fra f.eks. udstødningsgasser. Forøgelsen af de direkte mutagener var kraftigere end forøgelsen af de mutagener, som kræver metabolisk aktivering. Forøgelsen af direkte nitro-PAC og andre direkte mutagene PAC var den samme.

Mutagenicitet og fjerntransport

22. april 1996 hidrørte luftforurening på H.C. Andersens Boulevard både fra lokale kilder og fra forurenede luftmasser fjerntransporteret fra kontinentet. Niveauerne af de mutagene aktiviteter steg med en faktor 5-7 i forhold til middelniveauet i samme periode. Niveauerne af trafikgasserne, NO, gas NO_y og CO, var normalt. Forøgelsesfaktoren for disse var 1.1-1.3. Fjerntransporten medførte desuden en forøgelse af niveauet for SO₂ (faktor: 2,5), S-PAC (2,0) og benzanthron (2,0), men forøgelsesfaktorerne for disse var væsentlig mindre end for de mutagene aktiviteter. De fleste af de stabile højere PAH blev forøget med en faktor 1,6-1,8. For benz(ghi)perylen (1,4) og coronen (1,2) var forøgelsen mindre og tæt på faktoren for trafikgasser. Benz(ghi)perylen og især coronen har et højt bidrag fra trafikale kilder.

Oxy-PAH

Oxy-PAH-en, benzanthron, er hovedsaligt bundet til svævestøv. Tre kilder synes at bidrage til benzanthron´s forekomst i atmosfæren: Emission, atmosfærekemi og resuspension. Identifikationen af den sidste kilde er ny, medens der er modstridende data i litteraturen om, hvorvidt atmosfærekemi er en kilde eller ej. Imidlertid synes det indlysende fra vores data, at en væsentlig del af benzanthron i atmosfæren har hidrørt fra atmosfærekemiske processer, eftersom:

(1) Sommerhalvårsniveauet af benzanthron er 1,5 gange større end vinterhalvårsniveauet.

(2) Koncentrationen af benzanthron var forhøjet med en faktor 2,0 under fjerntransportepisoden.

(3) Det relative benzanthron indhold (benzanthron/Sum PAH) er antikorreleret (r=-0,52, p<0,05) til det relative indhold af benz(a)pyren (benz(a)pyren/Sum PAH).

Resuspension er måske også en kilde til benzanthron og andre oxy-PAH. Selvom resuspension kan negligeres som kilde til forekomsten af PAH i gadeluften. Baggrunden for dette kan være, at de genophvirvlede partikler er ældet og har været udsat for sollys og reaktive atmosfæriske gasser i en længere periode. Under disse omstændigheder kan PAH blive oxideret og omdannet til oxy-PAH, f. eks. benzanthron. Baggrunden for hypotesen er, at forholdet mellem benzanthron og sum af PAH (sum af benz(e)pyren, benz(bjk)fluoranthen og inden(1,2,3-cd)pyren) steg, når mængden af jordstøvselementer, Fe, Ti, Si og Ca, i atmosfæren steg (r=0,52-0,64, p<0,05). Forekomsten af de fire jordstøvselementer er her anvendt som indikator for betydningen af genophvirvlingen af deponerede partikler.

Trendanalyse

Variationerne i koncentrationerne af PAH og andre mutagener blev relateret til variationerne i koncentrationerne af de luftforureningskomponenter, som måles hver dag, for at begrænse indflydelsen af forskelle i de meteorologiske forhold. Sammenligningerne indikerer, at de reduktionsbegrænsende initiativer introduceret af Miljøstyrelsen har haft en større begrænsende effekt på forekomsten af PAH og andre mutagener end på niveauerne af nitrogenoxider, CO og sod-partikler. PAH indholdet faldt således 19±12% fra 1992 til 1993 og 38±8% fra 1992 til 1996, hvis man tager alle data i betragtning. Indholdet af mutagen aktivitet af svævestøvspartikler faldt med 42±18% fra 1992 til 1996. Til sammenligning faldt indholdet af de fire referencekomponenter 3±6% fra 1992 til 1993 og 18±5% fra 1992 til 1996. Faldet i indholdet af PAH og mutagenicitet var signifikant større (t-test, p<0,01) end faldet for de fire referencekomponenter. Reguleringerne af trafikemissionerne synes at have en større effekt på det total indhold i at atmosfæren af mutagener end på PAH-indholdet, som også 1993-resultaterne indikerede. Således var faldet 40±7% for PAH fra 1992 til 1996 og faldet for mutagenicitet-testene som følgende: TA98+S9 59%, TA98-S9 54% og TA98NR 71%, hvis man udelukker data fra fjerntransportepisoden. 1992 til 1996 faldet for PAH var 50±9% og mutagenicitet-faldet var 42±18%, hvis man anvender det data sæt fra 1992, hvor der er tilgængelige data for partikulære uorganiske elementer. Til sammenligning steg de seks referencekomponenter, S, K, V, Ni, Zn and Cu, fra 1992 til 1996 med 22±16%. Sammenligningen inkluderer data fra fjerntransport-episoden.

Årstidsvariation

Sommer til vinterforholdet af PAC viste forskellige mønstre betinget af stoftypen og deres kilderelationer. Oxy-PAH-en, benzanthron, havde højere koncentrationer i atmosfæren om sommeren end om vinteren. De reaktive PAH, cyclopenten(cd)pyren og benz(a)pyren, viste den modsatte tendens med de højeste koncentrationer om vinteren. Den fotolytiske nedbrydning af benz(a)pyren blev også bekræftet gennem antikorrelationen mellem den global stråling og forholdet af benz(a)-pyren til PAH-summen (r=-0,56, p<0,05). Der var ingen væsentlige forskelle i sommer og vinterniveauerne af de stabile reference-PAH forbindelser, benz(e)pyren, benz(bjk)fluoranthen og inden(1,2,3-cd)pyren.

Sundhedsmæssige risici

Den væsentligste sundhedsmæssige risiko ved luftforureningen med PAH og andre mutagener forventes at være risikoen for lungekræft. Det blev estimeret ved risikovurderingen, som udførtes i en tidlige undersøgelse (Nielsen et al., 1995c), at for beboere i København og andre større byer ville luftforureningen med PAH og andre mutagener maksimalt medføre fem ekstra lungekræfttilfælde pr. år pr. 1 million indbyggere. Vurderingen var dels baseret på skøn, som antager, at PAC sammensætningen er sammenlignelig i land- og byluft, udstødnings- og røggasser og i arbejdsmiljøer, og at benz(a)pyren kan anvendes som markør for PAC niveauet, og dels baseret på indholdet af mutagen aktivitet. Risikoen ville være lavere for personer, der lever på landet, baseret på skøn over benz(a)pyren-niveauerne. Det faktum at de atmosfærekemiske processer under transporten kan have indflydelse på dannelsen af mutagene forbindelser kan måske tyde på, at det tidligere skøn er for lavt.
 

1 Introduction

1.1 Air pollution with PAH and other mutagens from traffic and other sources

Definition of PAH and POM

Polycyclic aromatic hydrocarbons (PAH) consists of carbon and hydrogen and can be conceived as consisting of fused rings of benzene. PAH belongs to the group of polycyclic aromatic compounds (PAC). PAC cover azaarenes, oxaarenes, thiaarenes and transformation products of these and PAH, e.g. nitro derivatives and quinones besides PAH. Azaarenes, thiaarenes and oxaarenes can be conceived as a PAH, where a carbon atom in the ring system is replaced by a nitrogen, sulphur or an oxygen atom, respectively. The S- and O-PAC can be identified and determined in the PAH fraction of a sample as the chemical and physico-chemical properties of S- and O-PAC are very similar to those of PAH (Nielsen, 1983). The concern of the presence of PAH and other PAC in the environment is caused by the fact that several of them are carcinogens and present in polluted air. The compounds are formed by combustion, e.g. of petrol, oil and wood (Finlayson-Pitts and Pitts, 1986).

Particle/gas distribution

The larger PAH (5 - 7 rings), covering most of the carcinogens are associated with particles in the atmosphere. Part of the 3 and 4 rings PAH is also present in ambient air in vapour phase (Nielsen and Pilegaard, 1990). O- and S-PAC show similar distribution as their analogue PAH. The nitrogen atom in N-PAC causes a minor reduction in the vapour pressure, thus the gas phase to particulates ratio of three rings N-PAC (Mw = 179) corresponds to the ratio of fluoranthene and pyrene (Mw = 202) (Adams et al., 1982, Chen and Preston, 1997). Substituted PAH, e.g. nitro derivatives, have lower volatility than the parent PAH (Feilberg et al., 1998). Therefore, a larger proportion of the 3 and 4 ring members of these is associated with particles. The major part of the mutagens in ambient air has been shown to be particle-associated (Fenger et al., 1990).

Indicator for carcinogenicity

Previous investigations (Nielsen, 1989, Nielsen et al., 1995b and c and 1996, Ostenfeldt, 1989) have shown that PAH as well as mutagenic activity are applicable as indicators to investigate the content of carcinogens in ambient air. Several sources may contribute to the air pollution, e.g. traffic, oil heating, wood stoves, municipal incinerators and industry. In addition, long-range transport of pollution from other countries may occur. In order to determine the importance of different sources, the relative PAH composition of ambient air samples has been compared with that of exhaust and stack gases. Thus, Sawicki (1962) and Brasser (1983) applied the ratio of pyrene to benzo(a)pyrene (BaP), that of benzo(ghi)perylene to BaP and that of coronene to BaP to discriminate between the contributions from traffic sources and from domestic coal heating. The application of compositional differences to source identification has also been suggested by others (Daisey and Lioy, 1981, Daisey et al., 1986, Gordon and Bryan, 1973). In recent years, PAH have also replaced lead as a tracer for traffic pollution after the phase-out of lead in petrol (Daisey et al., 1986). In Denmark it is agreed that traffic, domestic heating and long-range transport are important sources of PAH and other mutagens (Fenger et al., 1990, Gudmundsson, 1988, Kemp, 1989, Nielsen, 1989, Nielsen and Pilegaard, 1990, Nielsen et al., 1993, Ostenfeldt, 1989). The traffic sources are, however, the dominant PAH sources in street air (Nielsen et al. 1995b and c, Nielsen 1996). In a smaller number of incidents PAH contribution from wood-stoves has been recognised in suburban areas (Nielsen, 1989, Nielsen and Pilegaard, 1990, Nielsen et al., 1993, Ostenfeldt, 1989).

Objective

The objective of this investigation was to determine whether the application of diesel fuel having a low distillation end point had affected the air levels of PAH and mutagens. These new diesel qualities are expected to reduce the emissions of particulates and soot (Karonis et al., 1998) and therefore, probably also the emissions of PAH and other mutagens (Westerholm and Egebäck, 1994). Most of the PAH in the diesel exhaust is carried over from the fuel and not formed by pyrosynthesis during the combustion process (Williams et al., 1989). After the introduction of the new diesel fuel quality a significant reduction in the levels of PAH and especially the mutagens was observed (Nielsen, 1996, Nielsen et al. 1995b and c). However, the results were not unambiguous, as the meteorological conditions were different in the two set of measurements, and the emissions of PAH and other mutagens also might have been affected by the ambient temperature (Nielsen, 1996, Nielsen et al. 1995b and c).

1.2 Reduction of emissions

Introduction of catalysts

Catalysts were introduced on vehicles in the seventies in USA. These catalysts were oxidation catalysts for vehicles equipped with petrol engines. The oxidation catalyst reduces the amount of CO and hydrocarbons in the exhaust gas. In the eighties 3-way catalysts were introduced, also for petrol engines. In 3-way catalysts there are neither oxidising nor reducing conditions. This is because CO and hydrocarbon removal needs oxidising conditions while NOx removal requires reducing conditions. Therefore, the 3-way catalyst has to operate in the border area.

National legislation

In October 1990 legislation was enforced in Denmark which required the closed loop 3-way catalysts on all new petrol driven passenger cars. In the EU similar legislation has been in force since January 1993. It is estimated that this new technology will reduce the emission of CO, HC (hydrocarbons) and NOx from the individual car by 70-80%. The use of catalysts will probably also result in a significant reduction in the emission of PAH (Rogge et al., 1993a). The proportion of petrol passenger cars equipped with catalysts was about 10% during the 1992 measurements. This proportion increased to about 15% during the 1993 measurements and to 40% in 1996. Petrol makes up about 55% of the fuel used for road transport in Denmark. Diesel oil is the second next dominating fuel. Another legislative change that might influence the PAH-emission from motor vehicles is the introduction of new diesel qualities as discussed in the end of the introduction. In July 1992 the sulphur content in autodiesel in Denmark was reduced from 0.2% to 0.05%. At the same time a special diesel quality with low distillation end point was introduced in buses. The new diesel qualities will reduce the emission of particulates and thereby probably the emission of PAH. The reduction in sulphur content to 0.05% has been mandatory in the EU from October 1996.

Formation of PAH

The introduction of catalytic converters raised the question to what extent unregulated compounds like PAH would be formed in the converter. The majority of the investigations show that the converters are very efficient and in almost every case produce a reduction of about 90%. However, most measurements are valid for new catalysts only. There are almost no data for used catalysts. Furthermore, it has been shown that engine technology like exhaust gas recirculation, which was introduced to reduce NOx emissions, will have a dramatic increasing effect on the PAH conversion efficiency of the catalyst. Therefore it seems not plausible to expect 90% conversion efficiency of a catalyst under real conditions. Furthermore, the application of catalysts appears to change the PAC composition in favour of oxygenated PAC (Rogge et al., 1993a). This could either be due to a lower efficiency of the catalyst towards oxy-PAH or because PAH are converted to oxy-PAH by the catalyst.

1.3 Recommended limit values

Various national and international authorities have established standards or limit values for air pollution components. With respect to the occurrence of carcinogenic PAH and other mutagens in air the regulators are faced with an extremely difficult situation as these compounds are present in complex mixtures with widely varying compositions and carcinogenic potencies depending on different sources and locations. Most often benzo(a)pyrene is used as a marker substance for the total carcinogenic potency present in ambient air.

The Netherlands

In the Netherlands a draft (annual average) tolerable level of 5 ng/m³ and an acceptable level of 0.5 ng/m³ for the benzo(a)pyrene content in the outdoor air has been given in the Environmental Programme 1988-1991 (Montizaan et al., 1989).

Germany

In Germany The Umwelt Bundes Amt has stated that "Since dose-effect relationships for man do not exist, the recommended value is based on technical and economic feasibility". In view of the concentrations occurring in Western European cities an annual average of 10 ng/m³ benzo(a)pyrene is used as an "orientating value". This value should be feasible, considering the values in other countries (Montizaan et al., 1989).

US-EPA

The US-EPA in 1984 has proposed to regulate PAH in the outdoor air by means of emission limits instead of determining a recommended value for PAH in the outdoor air.

WHO

The WHO (1987) states that because of the carcinogenic properties of PAH a safe level cannot be recommended. Various risk assessments are given using benzo(a)pyrene as an indicator. Based on benzene soluble fractions of cokeoven emissions, a risk of lung cancer is given of 9x10-5 per ng benzo(a)pyrene per m³ at lifetime exposure. It is clearly stated that this estimation is related to a mixture of PAH and other carcinogens similar to that occurring in coke emissions.

Denmark

The Danish Environmental Protection Agency has not established standards for PAH in ambient air. As PAH are carcinogenic compounds the levels should be as low as possible, and the Danish EPA regulates PAH in the outdoor air by means of emission limits for the various sources.

1.4 Toxicological evaluation of PAH and other mutagens in air

Single compounds

The variety of complex mixtures of PAH and other mutagens in ambient air at different locations are composed of many hundreds of different mutagenic and presumably carcinogenic compounds with varying potencies. Besides the limited number of PAH measured in this study, many other PAH and a variety of other mutagenic compounds contribute to the overall mutagenicity of ambient air samples. These may include alkylated PAH, oxygenated PAH such as PAH-ketones, carboxaldehydes and quinones, heterocyclic PAH such as azaarenes and thiophenes, and nitro-PAH (and their oxygenated derivatives) which has attracted interest due to their exceptionally high specific mutagenicity in the Ames test. However, when it comes to hard facts on the toxicological properties of these compounds, only a few of the PAH, some heterocyclic PAH and some nitro PAH have been studied to any greater extent. One compound, namely benzo(a)pyrene, which is one of the most carcinogenic PAH known, has been used in numerous biochemical and toxicological studies of mainly mechanistic nature, as a prototype of a chemical carcinogen. In spite of the many studies available on benzo(a)pyrene it is noteworthy that no adequate long-term carcinogenicity studies conducted according to modern standard and quality have been published yet.

Potency and risk

A summary of the toxicological properties of PAH with emphasis on mutagenicity and carcinogenicity has been given previously (Nielsen et al. 1995c and 1996). Potency estimates relative to the carcinogenic potency of benzo(a)pyrene were presented for those compounds for which sufficient data were available. In addition various risk assessments of benzo(a)pyrene were discussed.

Complex mixtures

Complex mixtures of PAH and other mutagens are inherent constituents of many heavier petroleum fractions and coal liquefaction products. For ambient air the significant sources of complex mixtures of PAH and other mutagens are the solid and gaseous combustion products of practically any organic product including fuels (gasoline, diesel, kerosene, heavy fuel oils, wood, alcohols), plastics, tobacco, organic wastes etc. The composition of these mixtures vary considerably depending on their source, the temperatures at which they are formed and several other variables. A large number of reported experimental work has been concerned with the biological effects of POM, especially the relation between the known constituents and the mutagenicity and carcinogenicity of POM from various sources. As discussed previously (Nielsen et al., 1995c and 1996) the 4-7 ring PAH fraction of condensate from car exhaust (petrol, diesel), domestic coal stove emissions and tobacco smoke contains nearly all the carcinogenic potential of PAH. This has been found after skin painting, subcutaneous injection and intrapulmonary implantation of fractions (WHO, 1987). The role of diesel particulates in the possible lung carcinogenicity of diesel exhaust was also discussed (Nielsen et al. 1995c and 1996).

Potency and risk

A summary of potency and risk assessment methods was given for complex mixtures of PAH (Nielsen et al. 1995c and 1996). Four different approaches were discussed. The specific marker substance approach, the maximum potency approach and the relative potency approach all use benzo(a)pyrene as a hall-mark in the expression of the carcinogenic potency of a given complex mixture of PAH. The comparative potency approach use data from human studies which have been correlated to data from animal bioassays and indirectly to results from in vitro mutagenicity tests, such as the Ames test.
 

2 Measuring programme, locations, sampling and analysis

2.1 Measuring programme and locations

Street station

The programme covered measurements at a busy street in Copenhagen (H.C. Andersens Boulevard). This allows a comparison of the measurements of PAH and other mutagens with the results obtained for the same site in 1986, 1987, 1992 and 1993 (Nielsen, 1989 and 1996, Nielsen et al. 1995b and c and 1996, Ostenfeldt 1989). In addition, NO, gas NOy, SO₂, CO, ozone, soot, particulate matter and particulate inorganic elements have been performed for many years on a daily basis on the location (HLU, 1993, Jensen et al. 1993, Municipality 1990). The traffic intensity in the street is in the magnitude of 60,000 cars each day, and the streets in the neighbourhood have also high traffic intensities. The street is situated north-south. The measuring station was at the eastern side of the street. The summer amusement park, Tivoli, is situated on the western side of the street. The station has for many years been applied in Communality and regional air quality programmes (HLU, 1993, Jensen et al., 1993, Municipality, 1990). Most of the samples for PAH analyses and mutagenicity testing were collected in the winter (40%) and spring (45%) as the major part of the previous measurements were performed in the months January-March.

Meteorological conditions

The average meteorological conditions for the 1996 samples were comparable with those for the 1992-1993 samples. Thus, the mean temperature and wind speed outside the city was 3.5 ± 2.9 °C and 5.9 ± 1.3 m/s, respectively, for the 1996 samples compared to 2.7 ± 0.6 °C and 5.5 ± 0.6 m/s, respectively, for the 1992 - 1993 samples. Despite the average temperature was almost the same the temperature variation for the 1996 samples (range: -6.4 to 21.7 °C) was larger than for the 1992 - 1993 samples (range: -4.4 to 7.5 °C). A few of the samples in 1996 were collected in the summer and autumn. The wind direction distribution for the 1996 samples was different from the average conditions as almost the same number of samples was collected from each wind sector. In contrast to the 1996 samples the wind direction distribution for the 1992 - 1993 samples was typical for Danish conditions (Larsen and Jensen, 1983) having the dominant wind direction from west (51 %), followed by winds from south (22 %), north (16 %) and east (10 %).

Local wind directions

The local wind directions at H. C. Andersens Boulevard were determined by the topography of the city and the dominant wind directions were from south and north. The roughness of the surfaces caused the local wind speeds to be 3 - 4 times lower than that measured outside the city.

2.2 Sampling and analysis

PAC sampling

24-hour samples of airborne particulate matter were collected using conventional Hi-Vol samplers with glass fibre filters. The sampling volumes were typical about 2000 m³. The filters were stored in a freezer (-18 °C) until the analysis.

Extraction

The filters were cut into small pieces and extracted ultrasonically, 30 min. each time, with dichloromethane (p.a. Merck) (2 times) and finally with acetone (p.a. Merck). The samples were protected against light both in this step and the following ones in order to avoid photolysis of the PAC. The combined extracts were divided in two equal parts. One part was concentrated to 5 ml and applied to the mutagenicity tests (see later).

Cleaning up

The other part was added known amounts of d8-dibenzothiophene, d12-triphenylene, d12-perylene and d12-coronene (internal standards) and concentrated to 1 ml. Two ml of cyclohexane (p.a. Merck) was added and the samples were concentrated to 1.0 ml. The PAH fraction of the solution was isolated by means of liquid-liquid extraction with a cyclohexane-dimethylformamide-water system (Nielsen et al., 1986) as follows:

The PAC including PAH was isolated from the aliphatic hydrocarbons by extraction of the cyclohexane with 3 times 1.0 ml of a mixture of 90% dimethylformamide (p.a. Fluka) and 10% water (MilliQ). The three dimethylformamide-water phases were collected and 2.4 ml water was added. Thus the ratio of dimethylformamide and water was 1:1 diminishing the solubility of PAH and medium polar PAC, such as oxy-PAC, but not the solubility of polar organic compounds. The PAH and oxy-PAC were extracted from the dimethylformamide-water mixture by 3 aliquots of 3.0 ml cyclohexane. The combined cyclohexane phases were extracted with 2.0 ml water in order to remove traces of dimethylformamide. After this the cyclohexane phase was dried with sodium sulphate to remove traces of water and concentrated to about 1 ml.

Recovery

The recoveries were determined to be 85-100% for a range of representative PAC, including the internal standards.

GC-MS analysis

The PAH samples were analysed by capillary gas chromatography (Varian STAR 3400 CX) using temperature programmable splitless injection, a fused silica RTX5-MS column (Restek) and ion trap mass spectrometric detection (Varian Saturn 4D).

Mutagenicity test

One ml of the 5 ml dichloromethane extract (see above under extraction) was used for gravimetric analyses. The remaining 4 ml was evaporated to almost dryness under a gentle stream of nitrogen. 3 ml of dimethyl sulfoxide (DMSO) was then added followed by evaporation of the remaining dichloromethane by means of nitrogen. The DMSO dissolved extracts were tested for mutagenic activity in the Salmonella/mammalian microsome assay. The assays were carried out by the standard plate incorporation method described by Maron and Ames (1983) using the strains TA98 and TA98NR. The tests were performed with and without a rat liver homogenate (S9-mix) with the TA98 strain and without S9-mix with the TA98NR strain. The S9-mix (1 mg protein/plate) was prepared from Arochlor 1254 induced male Wistar rat liver. The extracts of the air particulates were tested at the following concentrations: 1) undiluted (corresponding to 10-18 m³ air pr. plate, 2) 3 times diluted, 3) 9 times diluted, 4) 27 times diluted and 5) pure DMSO (negative control). Each concentration was tested in triplicate except the undiluted extract, where only one plate was used, due to the limited test material. All extracts were tested at least twice at two independent days. The number of his+ revertants were scored manually after 48 hours incubation at 37 °C. The mutagenic activities (revertants/m³) of all extracts were calculated by linear regression analyses of the linear part of the dose response curve. Positive controls were made applying 2-aminoanthracene (TA98 with S9), 2-nitrofluorene (TA98 without S9) and 1,8-dinitropyrene (TA98NR).

N-PAC

A few samples were analysed for N-PAC and nitro-N-PAC and the basic extracts of the samples were tested for mutagenicity in order to test whether the outstanding observations of Sera et al. (1994) also could be extrapolated to Danish conditions. Sera et al. (1994) has detected and identified strong potent mutagenic nitro-N-PAC in atmospheric samples and samples from diesel exhaust in Japan. Twenty-five % of the collected dichloromethane-acetone extracts were added known amounts of d7-quinoline, d9-acridine and 10-azabenzo(a)pyrene and concentrated to 1.0 ml. Two ml toluene (p.a. Merck) was added and the mixture was concentrated to 2.0 ml. The basic N-PAC in the toluene solution was extracted with 2x2.0 ml 8.25 M phosphoric acid (p.a. Merck) (Nielsen et al., 1986). The two phosphoric acid phases was combined and adjusted to a pH of about 14 with ca. 9 ml of 11 M potassium hydroxide (p.a. Merck) in an ice bath. The N-PAC were extracted from the alkaline aqueous phase with 3x2.0 ml proportions of dichloromethane. The combined dichloromethane phases were dried with sodium sulphate and concentrated to 1.0 ml and analysed by GC-MS. The solutions for the mutagenicity tests of the N-PAC fraction were prepared in the same manner except that no internal standards were added.

Inorganic gases

CO was determined by means of infrared light absorption in a two-channels instrument (Fuji Electric, ZRC) each 30 min. Measurements of NO and volatile NO_y were performed by a two chamber chemiluminescence monitor (Monitor Labs, 8840) each 30 min. NO_y was converted to NO by passing the filtered gas sample through 315 °C molybdenum chips. All NO_y species should be reduced to NO (Nielsen et al., 1995a). SO₂ was determined by its fluorescence emission by irradiation of the polluted air sample with UV light (Monitor Labs, 8850). Ozone was determined by means of its UV-absorption.

Particles and elements

Particles were sampled on a cellulose nitrate/acetate membrane filter (Millipore RA) having a pore size of 1.2 mm during 24-h periods with an air flow volume of 60 m³. The exposed spot of the filter had a diameter of 40 mm. The particle size cut in the inlet depended on the wind speed in the surroundings (Barrett, 1984), but it corresponded in average to an aerodynamical diameter of around 20 mm. The soot content on the filters was determined by reflectometric measurements. The membrane filters were also used for the determinations of TSP (total suspended particulate matter) and elements with atomic number higher than 13 (Al). The amount of TSP was determined by weighing. This was performed in a climate room with a relative humidity of 52 ± 2 % and a temperature of 23 ± 0.5 °C (Miljøministeriet, 1986). The exposed filters were kept for at least 7 days in the climate room for conditioning prior to the weighing. After weighing one fourth of the filters were punched out for the analysis of the elements by means of PIXE (Proton Induced X-ray Emission spectroscopy) (Jensen et al., 1993, Johanson and Campbell, 1988). In the PIXE analysis the particle filter part was exposed to protons of high energy (2.5 MeV). The amounts of the elements were determined by means of the composition and intensity of the emitted X-rays.
 

3 Results and discussions

3.1 The general air pollution situation

Inorganic components

Table 3.1.1 shows the 24-h levels of airborne inorganic components in the street in the 1996 samples and the 1992 - 1993 samples. The levels appeared to be typical for street stations in Copenhagen (Jensen et al., 1993).

1996 to 1992-93 ratios

The major change from 1992-1993 to 1996 is the one order of magnitude decrease of in particulate lead and bromine. Pb and Br are formed by the thermal decomposition of tetraalkyl lead compounds and the lead scavenger, ethylene dibromide, and therefore emitted from vehicles using leaded petrol (Nielsen, 1984a). The phase-out of leaded petrol and consequently also the lead scavengers, is the background for the strong decrease in lead and bromine. Sulphur dioxide has decreased by almost a factor of three as a result of limiting the content of sulphur in oil and diesel fuels and a decrease in the application of oil burners for local house heating. Also the annual average of SO₂ in 1996 is a factor of three lower than in 1992 (Jessen, 1998). The introduction of catalysts should reduce the emission of NO, gas NO_y, CO and soot from passenger cars, and a minor reduction in the levels is indicated by the results. The annual average of CO in 1996 was 30% lower than that in 1992 (Jessen, 1998). A significant part of soot, NO and gas NO_y originates from diesel vehicles, while diesel vehicles are of minor importance as a source for CO. It is expected that the application of the new diesel fuels for buses also may reduce the emission of soot. However, recent results (Karonis et al., 1998) perhaps suggest that the application of these diesel fuels for buses also have a positive effect on the emission of NO_y compounds.

Manganese

The strong increase in particulate manganese from 1992-1993 to 1996 is unique for the measuring station at H. C. Andersens Boulevard and does not appear to have any relation to the traffic. The source for manganese appears to be soil dust, but if the soil dust in the area is enriched with manganese, the reason for this is unknown (Kaare Kemp, private communication, 1998).

Resuspension

When the 1996 and 1992 mean concentrations (Table 3.1.1) of the particulate inorganic elements were compared, the variation of in the levels of the other elements, including particulate matter, were less than that of lead, bromide and manganese. However the contributions of soil dust elements (aluminium, calcium, silicon and titanium) and particulate matter were higher in the 1996 samples by a factor of 1.3-2.3. Also, other particulate inorganic elements had increased 1996 to 1992 ratios, e.g. sulphate (1.09), potassium (1.4), vanadium (1.04), nickel (1.03), copper (1.4) and zinc (1.4). A possible explanation is a higher impact of resuspension processes in the 1996 than 1992 samples. This explanation is supported by the increased soil dust contribution in the 1996 samples.

Table 3.1.1. Particulate polycyclic aromatic compounds (PAC) (ng/m³), mutagenic activity (rev./m³) and inorganic components in street air in 1996 and 1992-1993.

3.2 Air pollution with PAH and other mutagenic PAC

1996 and 1992-93

The 1996 mean levels of some of the major PAC are shown in Fig. 3.2.1. Table 3.1.1 compares the levels of particle associated PAH and other mutagenic PAC in 1996 with those in 1992-1993. Both for the PAH and the mutagenicity the 1996 levels were about 40-50% lower than the 1992-93 levels. Thus the average of the 1996 to 1992-93 ratios for the different PAH was 0.61 ± 0.09 and that for the different mutagenicity tests was 0.50 ± 0.22 (see also Fig. 3.2.2). The difference between the PAH ratios and the mutagenicity ratios was not significant (p = 0.22). The 1996 measurements include two oxygenated PAH, anthraquinone (C₁₄H₈O₂) and benzanthrone (C₁₇H₁₀O). The levels of these are of the same magnitude as the most abundant PAH, i.e. fluoranthene, pyrene, benzofluoranthenes, benzo(c)phenanthrene, chrysene/triphenylene, benzopyrenes, benzo(ghi)perylene and coronene (see Fig. 3.1.1). Recently a polar benzo(a)pyrene oxidation product has been reported to be present in the same levels as benzo(a)pyrene in street air dust (Ismail et al., 1998).

(Figur 3.2.1 - 4 kb)

Figur 3.2.1 The mean levels of some PAH, S-PAC, N-PAC and oxy-PAH. Legends for the four groups: PAH: Ph: phenanthrene, MePh: methylphenanthrenes, CP: cyclopenteno(cd)pyrene, BbjkF: benzo(b)- + benzo(j)- + benzo(k)fluoranthene, BeP: benzo(e)pyrene, BaP: benzo(a)pyrene, Per: perylene, IP: indeno(1,2,3-cd)pyrene, BghiP: benzo(ghi)perylene, Anthan: anthanthrene, Cor: coronene. S-PAC: DBT: dibenzothiophene, BNT: benzo(b)naptho(2,1-d)thiophene. N-PAC: BfQ: benzo(f)quinoline, BcA: benz(c)acridine. Oxy-PAH: AnO: anthraquinone, BAO: benzanthrone.

Benzo(a)pyrene

The mean value of BaP was 2.2±0.6 in 1996 compared to 4.4±1.2 ng m^-3 in 1992-93, but as discussed later in this section part of the reduction is caused by atmospheric degradation. Thus, the results are questioning the reliability of the application of benzo(a)pyrene as a trustworthy indicator for the air pollution with mutagenic and carcinogenic PAC. The questioning is supported by the observations of others (Matsumoto et al., 1998).

Mutagenicity

The mean mutagenic activity seen in TA98+S9 was 48±41 in 1996 and 59±29 revertants m^-3 in 1992-93. The direct mutagenic activity measured in TA98-S9 was 70-75% of the activity seen with metabolic activation. The mutagenicity level of direct acting nitro compounds ((TA98 - S9) - (TA98NR - S9)) constitute 56% in 1996 and 27% in 1992-93 of the total level of direct acting mutagenicity as discussed later in this section. The level of direct acting nitro compounds is typically about 50% of the total direct acting mutagenicity in air samples (see Table 3.1.1 and Fig. 3.2.2).

(Figur 3.2.2 - 6 kb)

Figur 3.2.2 Variation in the concentrations of different air pollution components in 1992, 1993 and 1996 normalised to 1992 levels. Abbreviations: see the legend to Fig. 3.1.1. TA98+S9: Indirect mutagenicity, TA98-S9: Direct mutagenicity, TA98NR: Mutagenic activity of direct acting non-nitro PAC, gas NO_y: total gas phase nitrogen oxides. CO: carbon monoxide.

PAH composition changes gas particle ratio

Some of the differences in the 1996 PAH composition compared to the 1992-93 composition can be related to the physical and chemical processes in the atmosphere, even though the PAH composition in the two sets of samples is very close to each other. The larger PAH (Mw > 250) as mentioned in Section 1.1 is almost exclusively associated with particles (Nielsen and Pilegaard, 1990, Yamasaki et al., 1982)). The particle associated proportion is 70-95% for cyclopenteno(cd)pyrene, benz(a)anthracene, chrysene and triphenylene (Mw 226-228), 50-60% for benzo(b)naptho(2,1-d)thiophene, benzo(ghi)fluoranthene and benzo(c)phenanthrene (Mw = 226-234), 30-40% for pyrene and fluoranthene (Mw = 202) and 3-15% for phenanthrene, anthracene and methylphenanthrenes (Mw = 178-192). The gas phase proportion decreases with decreasing ambient temperature but also with increasing amounts of airborne particulate matter. The higher atmospheric particle concentrations in the 1996 samples ( see Section 3.1) are probably the reason for the significantly (p< 0.05) lower decrease of the lighter PAH (1996 to 1992-93 ratio: 0.73 ± 0.21) in the 1996 samples compared to the heavier PAH (0.54 ± 0.04). This is considered due to the effects of the ambient temperature had not been considered to be the reason, as the average value was almost the same in the two data sets (see Section 2.1).

Atmospheric chemistry

Atmospheric decomposition of the reactive PAH (Nielsen, 1984b and 1988) (cyclopenteno(cd)pyrene, benzo(a)pyrene, perylene and anthanthrene) was significant in the 1996 samples. Thus, the 1996 to 1992-93 ratio of the four PAH (0.42±0.05) was significantly lower than the ratio for the stable PAH, benz(a)anthracene, triphenylene, chrysene, benzo(a)-, benzo(b)-, benzo(j)- and benzo(k)fluoranthene, benzo(e)pyrene, indeno(1,2,3-cd)pyrene, benzo(ghi)perylene and coronene, (0.60±0.08) (t-test, p<0.01). Fig. 3.2.3 shows the 1996 to 1992 ratio for some of the major PAH.

(Figur 3.2.3 - 5 kb)

Figur 3.2.3 PAH composition in 1996 normalised to 1992. Abbreviations: See the legend to Fig. 3.2.1. Phe: phenanthrene (reference component for MePh), MePh (indicator for diesel exhaust), BghiP and Cor (both indicator for traffic emissions, BaP, CP, Per and Anthan (all four reactive PAH) and Other PAH: benzo(b)- + benzo(j)- + benzo(k)fluoranthene + benzo(e)pyrene + indeno(1,2,3-cd)pyrene (reference components).

Emission sources

The changes in the emission sources did not appear to cause any major changes in the atmospheric PAH composition. The reason for this may be that both the emissions from diesel cars as well as the emissions from petrol driven passenger cars are reduced. The ratio between methyl-phenanthrenes and phenanthrene and the presence of benzo(ghi)perylene and coronene were previously applied to estimate the contributions from diesel and petrol engines (Nielsen 1996, Nielsen et al. 1995b and c and 1996). For the 1992-93 results it was estimated that 80% of the PAH originates from traffic sources with the following weekdays distribution: Working days 90% and weekends 40%. Approx. 2/3 of the total traffic contribution originated from the diesel traffic applying benzo(e)pyrene as indicator for PAH (Nielsen, 1996). For 1996 the total traffic contribution appears to be in the magnitude of 80-90% on working days and the ratio between diesel and petrol emissions appears still to be about 2 to 1. The 1996 to 1992 ratios of phenanthrene (0.61) and methylphenanthrenes (0.63) were very close to each other and the 1996 to 1992-93 ratios of benzo(ghi)perylene (0.64) and coronene (0.64) were not significantly different from the ratio of the stable PAH (0.60±0.08). Our estimate of the ratio of emissions from either diesel vehicles or cars running on petrol is based on the ratio of methylphenanthrenes and phenanthrene as the alkylated PAH in our view are the only PAH which can be applied to distinguish between these types of sources. In the literature a number of PAH emission profiles from both types have been presented (see e.g. Li and Kamens, 1993, Miguel et al., 1998, Staehlin et al., 1998, Strandell et al., 1994) including tunnel studies and chassis dynamometer tests both from Europe and USA. None of the five data sets included alkylated PAH. The test of the emission profiles on our data revealed that one should be cautious in the application and interpretation of these kind of studies. The 1992 to 1996 reduction of PAH from diesel vehicles appeared to be twice the reduction from petrol cars, i.e. that the 35% reduction of BbjkF and BeP in 1996 relative to 1992 can be split into a reduction on 22% caused by the decrease from diesel vehicles and 13% by petrol cars. Similar numbers are achieved if one compares the PAH reduction with that of CO as discussed later.

Mutagenicity

The mutagenicity of the extracts of the particles were determined applying the Salmonella strains TA98 and TA98NR. TA98NR is devoid of the enzyme (nitroreductase) making the bacteria able to reduce the nitro-group in nitro-PAC (Ar-NO₂) to a hydroxylamine (Ar-NHOH). The hydroxylamine is acetylated by acetyltransferase, which is present both in TA98 and TA98NR. An electrophile reactive transformation product (a nitrene (Ar-N) or nitrenium ion (Ar-NH+)) of the acetylated hydroxylamino derivative causes the mutagenicity ascribed to the nitro-PAC. Thus nitro-PAC are direct acting mutagens towards TA98 in the TA98-S9 test, but not towards TA98NR in the analogue test. The results indicate that the composition of mutagenic compounds has changed significantly from 1992 to 1996. The 1996 to 1992 ratio for TA98NR-S9 (0.40) was much lower than the ratios for TA98+S9 and TA98-S9 (both 0.67) indicating that a higher proportion of the direct mutagenicity was caused by nitro-PAC in the 1996 samples than in the 1992 samples. However, the mutagenicity of the nitro-PAC in the 1992-1993 samples appeared to be a factor two lower than that observed typically. As the relative increase of direct mutagenic nitro-PAC also appears to be associated with a relative decrease of direct mutagenic non-nitro-PAC, one should be cautious in the interpretation of the TA98NR 1992-1993 results.

3.3 Comparison of N-PAC and PAH

Background

The background for including determination of the basic N-PAC and testing for mutagenicity in a few samples was as mentioned in Section 2.2. the outstanding observations of Sera et al. (1994). Sera et al. (1994) reported identification and detection of strong mutagenic nitro-N-PAC in atmospheric samples and samples of diesel exhaust. In a historical perspective the presence of particle-associated N-PAC and PAH have been compared previously in samples from roof level in the inner city and in samples from a suburban area both from the period 1976-82 (Nielsen et al. 1986).

N-PAC

The concentrations of N-PAC (Table 3.3.1) are about one order of magnitude lower than those of PAH (Fig. 3.2.1 and Table 3.3.2). N-PAC may be a more serious problem than the PAH in other context, e.g. the contamination of soil with tar and creosote as well as contamination of freshwater and marine sediments (Feilberg and Nielsen, 1998, Osborne et al., 1997). But in relation to air pollution N-PAC can be considered to be a minor problem compared to the PAH unless the N-PAC is a source for the formation of very potent mutagenic and carcinogenic compounds. The carcinogenic and mutagenic potencies of N-PAC are comparable with those of PAH (Nielsen et al., 1997). The dominant N-PAC associated with particles have 2-4 rings. A significant fraction of the 2 ring N-PAC will also be present in gas phase. Therefore, only the N-PAC having Mw > 178 are included in the comparisons between the 1996 measurements and the previous measurements, i.e. benzoquinolines, acridine, phenanthridine, benz(c)acridine and other dibenzoquinolines (C₁₇H₁₁N) and dibenzacridines.

Table 3.3.1. Comparison of the concentrations (±2s) of particulate azaarenes (N-PAC) (ng/m³), the particulate mutagenic activity (rev./m³) and inorganic components at different locations and different years at winter time.

Table 3.3.2. Comparison of the concentrations (±2s) of particulate PAH* (ng/m³) and particulate (rev./m³) and inorganic components at different locations and different years.

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