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Spatial differentiation in LCA impact assessment
7. Photochemical ozone formation
Background information for this chapter can be found in:
- Chapter 3 of the "Environmental assessment of products. Volume 2: Scientific background" by Hauschild and Wenzel (1998a).
- Chapter 6 of the "Background for spatial differentiation in life cycle impact assessment – EDIP2003 methodology" by Potting and Hauschild (2005).
7.1 Introduction
When solvents and other volatile organic compounds are released to the atmosphere, most of them are degraded within a few days to weeks. Initiated by sunlight, nitrogen oxides (NOx) and volatile organic
compounds (VOCs) react to form ozone. The nitrogen oxides are not consumed during the ozone formation, but have a catalyst-like function. Depending on the nature of the VOCs, the reactions may take
hours or days. Since the process is initiated by sunlight, it is called photochemical ozone formation. It takes place in the troposphere, the lower layers of the atmosphere, where it is the primary source of
ozone.
The formed ozone is an unstable gas but nevertheless, it has a half-life of a few weeks in the troposphere. This does mean, however, that the ozone formed in the troposphere cannot rise to the stratosphere
and remedy the thinning of the ozone layer there. In the troposphere, it is widely dispersed, and ozone measured at a particular location may have arisen from VOC and NOx emissions many hundreds of
kilometres away. The ozone concentration in the troposphere rises by about 1% a year over most of the northern hemisphere, where the largest emissions of VOC and NOx occur. Over the southern
hemisphere, the ozone concentration in the troposphere is practically constant.
Due to its high reactivity, ozone attacks organic substances present in plants and animals or materials exposed to air. This leads to an increased frequency of humans with problems in the respiratory tract
during periods of photochemical smog in cities, and the steadily increasing tropospheric concentration of ozone causes a reduced agricultural yield. For Denmark, the loss is estimated to cost about 10% of
the total agricultural production.
7.2 Classification
The substances contributing to photochemical ozone formation are:
- volatile organic compounds (VOC)
- nitrogen oxides (NOx)
- carbon moNOxide (CO)
- methane (CH4)
Volatile organic compounds
Applying the definition of EDIP97, a volatile organic compound is defined as
an organic compound with a boiling point below 250° C. In addition to being volatile, the compound must contain hydrogen or double bonds between carbon atoms to be able to undergo oxidation
with ozone formation. Due to the exceptionally long lifetime of methane (CH4) and consequent low ozone formation potential, a distinction is often made between this compound and the rest of the VOCs
which are sometimes referred to as NMVOCs (non-methane VOCs). If nothing else is specified, in this Guideline, VOCs should be taken as non-methane VOCs. VOCs may be reported in life cycle
inventories as individual substances or as mixtures. The main sources of VOC emissions are combustion processes and use of organic solvents.
Nitrogen oxides
NOx designates the sum of NO and NO2. The two oxides are easily interconverted through oxidation or reduction and their relative prominence depends on the redox conditions of the surrounding air.
Therefore, they are usually reported as the sum; NOx. The main source of NOx is combustion processes where it is formed from atmospheric nitrogen N2and oxygen O2.
Carbon moNOxide
Even though it is not an organic compound, CO also contributes to photochemical ozone formation. The main source of CO is incomplete combustion.
Methane
The contribution of CH4 to ozone formation is important at the global scale rather than the regional scale, due to its long life time in the troposphere, and methane is considered an important greenhouse gas.
The main man-made sources of methane are combustion processes and biogenic sources like rice paddies and the digestive systems of livestock.
7.3 EDIP97 characterisation factors
Most current life cycle impact assessment methodologies apply photochemical ozone creation potentials, POCPs, to characterise the photochemical ozone formation potential of VOCs. The POCP factors
applied in EDIP97 express the potential for formation of ozone during the first 4-9 days after emission at standard concentrations of hydroxyl radical and NOx and at typical atmospheric conditions. The
POCP factors are found in Table 23.3 and 23.4 in Wenzel et al., 1997. The ozone formation potential of a substance is expressed relative to that of ethylene (C2H4) which is used as a reference compound.
As discussed in Hauschild and Wenzel, 1998e, ozone formation is strongly dependent on local conditions like the simultaneous presence of other VOCs and NOx, and the solar radiation intensity, all of
which may vary strongly from location to location. This is the reason why a preliminary spatial differentiation was introduced in EDIP97 through the distinction between emissions occurring in regions with low
and high background levels of NOx.
The definition of the POCP factors excludes the possibility of representing the contribution of NOx to photochemical ozone formation. This means that only the contribution from VOCs is considered. As
mentioned already in the documentation of EDIP97, this is quite unfortunate since NOx may in some cases be the main contributor to the formation of photochemical ozone. Nonetheless the contribution
from NOx can not be represented using the EDIP97 methodology.
7.4 EDIP2003 characterisation factors
The inability to give a satisfactory representation of the spatial variability of the ozone formation is the main motivation behind developing the new spatial characterisation factors which allow a much higher
degree of spatial differentiation revealing rather large differences which are averaged out in the EDIP97 approach.
In addition, the EDIP2003 factors hold the following advantages over the POCP approach employed in EDIP97:
- the resulting impact potential is more straightforward to interpret in terms of environmental damage since it is modelled further along the impact chain to include exposure of human beings and vegetation
instead of just predicting the potential formation of ozone
- the dependence on surrounding conditions means that the potential for ozone formation must be expected to vary from year to year. The EDIP2003 factors are calculated for the emission levels of three
different years (1990, 1995 and predicted emission levels for 2010) for average meteorological conditions which allows judging their sensitivity to this temporal variation. Only the factors for 1995 are shown
here – the others can be found in Hauschild et al., 2005.
The EDIP2003 characterisation factors for photochemical ozone formation have been developed using the RAINS model which was also used for development of characterisation factors for acidification
and terrestrial eutrophication. Site-generic factors have been established (see Table 7.1), as well as site-dependent factors for 41 European countries or regions (see Annex 7.1 to this chapter). The
photochemical ozone formation factors relate an emission by its region of release to the ozone exposure and impact on vegetation or human beings within its deposition areas. The principles of the RAINS
model are described in Section 4.4. It was originally developed for modelling of acidification (N- and S-compounds) and air-borne eutrophication (N-compounds) but it is intended to support the
development of cost-effective European abatement strategies for different types of air pollution and has therefore recently been expanded to include the precursors of photochemical ozone formation (NOx
and VOCs). For the modelling of ozone formation, RAINS applies a meta-model which has been statistically derived from a mechanistic model of the highly complex reaction schemes behind the formation
of ozone and other photo-oxidants.
Such highly complex models are used for calculation of the POCPs which are used as characterisation factors in EDIP97 but they will not be feasible in an integrated assessment model where
source-receptor relationships must also be modelled well. Instead, RAINS builds on a computationally efficient `reduced-form' model of ozone formation which acts as a meta-model based on the complex
mechanistic model, using statistical regression methods to summarise the behaviour of the a more complex model.
The ozone formation is influenced by the presence of other VOCs as determined by the concomitant emission patterns of the European countries. The factors may therefore vary in time and in order to reveal
temporal variation, they are calculated for the registered or projected emissions of three reference years 1990, 1995 and 2010. The factors based on the 1995 emissions are chosen as the default EDIP2003
characterisation factors but the factors for the other years are given in Hauschild et al., 2005 to allow checking the temporal sensitivity of the factors and, if wanted, to allow temporal differentiation for those
emissions of the product system, which will take place in the future (e.g. from the late use stage of long-lived products or from the disposal stage). The site-generic factors only show minor temporal
variations but for some countries, the change in the site-dependent factors may be considerable over time, for exposure of humans.
The ozone formation is also influenced by the meteorological conditions which may fluctuate from year to year. To reduce the influence of annual variations in meteorological conditions, the characterisation
factors for each of the emission years 1990, 1995 and 2010 are derived as the average of five different calculations using the meteorological data for the years 1989, 1990, 1992, 1993 and 1994
respectively.
Due to its long life time, the contribution of methane to ozone creation is rather low on a regional level. This is why it is not included in the RAINS model, which has been adapted for calculating the
EDIP2003 characterisation factors. Instead, it is suggested to base the characterisation factors for methane on the site-generic factors developed for VOCs and correct for the fact that due to the long
lifetime of methane, a large part of the ozone formed will expose ocean areas and hence not contribute to exposure of vegetation or humans. A correction factor of 0.5 is proposed.
Human health and ecosystem health are the LCA protection areas which can be influenced by the photochemical ozone formation. Human beings and vegetation show clear differences in their sensitivity and
thresholds to ozone exposure, and the exposure of humans and vegetation is therefore modelled separately. The damage to materials caused by ozone is not modelled explicitly but it is taken to be reflected
by the exposure of humans since the geographical distribution of man-made materials will follow the distribution of humans.
As part of the new methodology for characterisation of photochemical ozone formation, the impact category is thus divided into two subcategories which represent the exposure of human beings and
materials, and the exposure of vegetation above their respective thresholds. For each of these two subcategories, an impact potential is calculated.
The impact potential for vegetation exposure is expressed as the AOT40, the product of the area of vegetation exposed above the threshold of chronic effects, 40 ppb (m2), the annual duration of the
exposure above the threshold (hours), and the exceeding of the threshold concentration (ppb). The unit of the impact potential for vegetation is m2?ppm?hours. The impact potential for human exposure is
expressed as the AOT60, the product of the number of persons exposed above the threshold of chronic effects, 60 ppb (pers), the annual duration of the exposure above the threshold (hours), and the
exceeding of the threshold concentration (ppb). The unit of the impact potential for human exposure is pers?ppm?hours.
What do the impacts express?
The site-generic and the site-dependent EDIP2003 photochemical ozone formation potentials of an emission are expressed in the same units. For vegetation, the impact is expressed as the AOT40, the
accumulated exposure (duration times exceedance of threshold) above the threshold of 40 ppb times the area that is exposed as a consequence of the emission. The threshold of 40 ppb is chosen as an
exposure level below which no or only small effects occur. The unit for vegetation exposure is m2?ppm?hours. For humans the impact is expressed as the AOT60, the accumulated exposure above the
threshold of 60 ppb times the number of persons which are exposed as a consequence of the emission. No threshold for chronic exposure of humans to ozone has been established. Instead, the threshold of
60 ppb is chosen as the long-term environmental objective for the EU ozone strategy proposed by the World Health Organisation, WHO. The unit for human exposure is pers?ppm?hours.
In comparison, the EDIP97 photochemical ozone formation potential is expressed as the emission of C2H4 that would lead to the same potential formation of ozone in the environment.
7.5 Site-generic characterisation
The site-generic characterisation factors have been developed as emission-weighted European averages of the site-dependent.
The site-generic photochemical ozone formation impacts of a product can be calculated according to the following formulas:
Click here to see the Formula
(7.1)
Where:
sg EP(po,veg) is the site-generic photochemical ozone formation impact on vegetation expressed as area exposed above threshold (in m2?ppm•hours/f.u.)
sg EP(po,hum) is the site-generic photochemical ozone formation impact on human health expressed as persons exposed above threshold (in pers?ppm?hours/f.u.)
sg CF(po,veg)VOC is the site-generic photochemical ozone formation factor from Table 7.1 that relates emission of VOCs or CO to the impact on vegetation in the deposition area (in m2•ppm•hours/g).
sg CF(po,veg)NOx is the site-generic photochemical ozone formation factor for from Table 7.1 that relates emission of NOx to the impacts on vegetation in the deposition area
(in m2•ppm•hours/g).
sg CF(po,hum)VOC is the site-generic photochemical ozone formation factor from Table 7.1 that relates emission of VOCs or CO to the impacts on human health in the deposition area (in
pers•ppm•hours/g).
sg CF(po,hum)NOx is the site-generic photochemical ozone formation factor from Table 7.1 that relates emission of NOx to the impacts on human health in the deposition area
(in pers•ppm•hours/g).
sg CF(po,veg)CH4 is the site-generic photochemical ozone formation factor for from Table 7.1 that relates emission of CH4 to the impacts on vegetation in the deposition area
(in m2•ppm•hours/g).
sg CF(po,hum)CH4 is the site-generic photochemical ozone formation factor from Table 7.1 that relates emission of CH4 to the impacts on human health in the deposition area
(in pers•ppm•hours/g).
ηi is a substance-specific efficiency factor from Annex 7.2 expressing the ozone creation potential of the individual volatile organic compound or CO (s) relative to the ozone creation potential of the
European average VOC (dimensionless).
Ei is the emission of NOx, CH4 or individual or source-specified VOC or CO (s) according to index (in g/f.u.)
For each of the two sub categories, the procedure for calculating the site-generic impact potential is:
- multiply the NOx emission by the relevant site-generic characterisation factor for NOx from Table 7.1
- multiply the emissions of individual VOCs, source-specified VOC mixtures or CO by their efficiency factor from Annex 7.2 and add them to the emissions of unspecified VOCs to get the sum-VOC
emission
- multiply the sum-VOC emission by the site-generic characterisation factor for VOCs and CO from Table 7.1
- multiply the CH4 emission by the site-generic characterisation factor for CH4 from Table 7.1
- Sum the impact potentials thus calculated for NOx, VOC, CO and CH4 to get the impact potential for each of the two sub categories.
The spatially determined variation which potentially lies hidden in the site-generic photochemical ozone impacts, can be estimated from the standard deviation given in Table 7.1 for each substance.
7.6 Site-dependent characterisation
The photochemical ozone formation impact from a product is often dominated by a few processes. To avoid unnecessary work, applications where a site-dependent assessment is desired, may therefore
start with calculation of the site-generic photochemical ozone formation impacts of the product as described in the previous section. Based on the site-generic impact, the processes with the dominating
contributions can then be identified (step 1) and their site-generic impacts be adjusted with the relevant site-dependent characterisation factors (step 2 and 3) using the procedure described below. This
procedure can be seen as a sensitivity analysis-based reduction of those uncertainties in the site-generic impact which are posed by refraining from site-dependent characterisation.
Step 1
For each of the sub categories calculate the site-generic photochemical ozone formation impact as described in the previous section, and on this basis identify the processes with the dominating contributions
or decide to do site-dependent characterisation for all processes. Order the contributions from the largest to the smallest and select the process with the largest photochemical ozone formation contribution.
Table 7.1. Factors for site-generic characterisation of photochemical ozone formation impacts on vegetation and human health
| Substance |
Impacts on vegetation
(m2•ppm•hour/g) |
Impacts on human
health(pers•ppm•hour/g) |
| |
Factor |
standard deviation |
Factor |
standard deviation |
| NOx |
1.8 |
2.9 |
1.2•10-4 |
2.7•10-4 |
| VOC. CO |
0.73 |
1.2 |
5.9•10-5 |
1.3•10-4 |
| CH4 |
0.36 |
0.6 |
2.9•10-5 |
6.3•10-5 |
Step 2
Reduce each of the two site-generic photochemical ozone formation impacts of the product calculated in step 1 with the contribution of the process selected in step 1. Calculate the site-dependent impact
potentials from the emissions of this process with the relevant site-dependent characterisation factors from Annex 7.1 using the following formulas:
Click here to see the Formula
(7.2)
Where:
sd EP(po,veg)p is the site-dependent photochemical ozone formation impact on vegetation expressed as area exposed above threshold by the selected process (p)
(in m2•ppm•hours/f.u.)
sd EP(po,hum)p is the site-dependent photochemical ozone formation impact on human health expressed as persons exposed above threshold by the selected process (p)
(in pers•ppm•hours/f.u.)
sd CF(po,veg)NOx,i is the site-dependent photochemical ozone formation factor from Annex 7.1 that relates emission of NOx from country or region (i), where the selected process (p) is located, to the
impacts on vegetation in the deposition area (in m2•ppm•hours/g).
sd CF(po,veg)VOC,i is the site-dependent photochemical ozone formation factor from Annex 7.1 that relates emission of VOCs or CO from country or region (i), where the selected process (p) is located,
to the impact on vegetation in the deposition area (in m2•ppm•hours/g).
sg CF(po,veg)CH4 is the site-generic photochemical ozone formation factor CH4 from Table 7.1 that relates emission of CH4 to the
impacts on vegetation in the deposition area
(in m2•ppm•hours/g).
sd CF(po,hum)NOx,i is the site-dependent photochemical ozone formation factor from Annex 7.1 that relates emission of NOx from country or region (i), where the selected process (p) is located, to the
impacts on human health in the deposition area (in pers•ppm•hours/g).
sd CF(po,hum)VOC,p is the site-dependent photochemical ozone formation factor from Annex 7.1 that relates emission of VOCs or
CO from country or region (i), where the selected process (p) is located, to the impacts on human health in the deposition area (in pers•ppm•hours/g).
sg CF(po,hum)CH4 is the site-generic photochemical ozone formation factor from Table 7.1 that relates emission of CH4 to the impacts on human health in the deposition area (in pers•ppm•hours/g).
ηi is a substance-specific efficiency factor from Annex 7.2 expressing the ozone creation potential of the individual volatile organic compound or CO (s) relative to the ozone creation potential of the
European average VOC (dimensionless).
Ep,i is the emission of NOx, CH4 or individual or source-specified VOC or CO (s), according to index, from process (p) (in g/f.u.)
For both sub categories, the procedure for calculating the site-dependent impact potential is:
For each process:
- determine in which country the process is located to select the relevant site-dependent characterisation factors in Annex 7.1
- multiply the NOx emission by the relevant site-dependent characterisation factor for NOx from Annex 7.1
- multiply the emissions of individual VOCs, source-specified VOC mixtures or CO by their efficiency factor from Annex 7.2 and add them to the emissions of unspecified VOCs to get the sum-VOC
emission for the process
- multiply the sum-VOC emission by the relevant site-dependent characterisation factor for VOCs and CO from Annex 7.1
- multiply the CH4 emission by the site-generic characterisation factor for CH4 from Table 7.1
- sum the impact potentials thus calculated for NOx, VOC, CO and CH4 to find the impact potential for the process for each of the two photochemical ozone formation sub categories
As a first approach, also the emissions from a non-European or unknown region can be calculated with the site-generic factors from Table 7.1. The standard deviations on the site-generic factors in Table
7.1 give a range of potential spatial variation for the application of the site-generic factor within Europe. Given the size of the variation in emissions and sensitivities within Europe, the site-dependent factor is
expected to lie within this range for most regions, also in the rest of the world. Expert judgement may be used in the interpretation to assess whether the factor for emissions from processes in non-European
regions should be found in the lower or upper end of the range.
Step 3
Add the site-dependent contributions from the process selected in step 1 to the adjusted site-generic contribution from step 2. Repeat step 2 until the site-dependent contribution of the selected processes is
so large that the spatially determined variation in the photochemical ozone impact score can no longer influence the conclusion of the study (e.g. when the site-dependent share is larger than 95% of the total
impact score)
7.7 Normalisation
The EDIP2003 person equivalents for photochemical ozone formation are:
Impacts on vegetation: 1.4•105 m2•ppm•hours/person/year Impacts on human health
and materials: 10 pers•ppm•hours/person/year
Following the EDIP97 approach, the normalisation references for photochemical ozone impact on vegetation and human health are based on the impacts caused by the actual emission levels for 1995 (see
Hauschild and Wenzel 1998e and Stranddorf et al., 2005). Applying the EDIP2003 characterisation factors for photochemical ozone formation, the total exposure of vegetation and humans above the
respective threshold values in Europe is 5.3•1013 m2?ppm•hours and 3.7•109 pers?ppm?hours respectively. The person equivalent is calculated as an average European impact per person assuming a total
European population of 3.70•108 persons.
Due to lack of national European emission estimates for the emissions of CO and CH4, these have not been included in the normalisation references. Based on data collected for Europe and Denmark for the
EDIP97 normalisation references, they are not expected to contribute more than 5% altogether.
7.8 Interpretation
The EDIP2003 photochemical ozone formation impact potentials are improved in two aspects compared to the impact potentials calculated using the EDIP97 characterisation factors; the environmental
relevance is increased, and a part of the spatial variation in sensitivity of the receiving environment is now taken into account.
Environmental relevance
The environmental relevance is increased because the exposure of the sensitive parts of the environment (vegetation or human beings) is included in the underlying model which now covers most of the
causality chain towards the LCA protection areas: Ecosystem health and human health. This is particularly important because it increases consistency with weighting factors based on the environmental
relevance.
The EDIP default weighting factors for photochemical ozone formation are based on political reduction targets. These targets are also aimed partly at protecting human and ecosystem health. In comparison,
the EDIP97 factors only cover the potential for formation of ozone.
In addition, the contribution of NOx is now included in the impact potentials. The significance of this novelty depends for a specific product system on the quantities of NOx and VOCs emitted. From the
calculation of the normalisation references, it is known that on a European level, NOx contributes around twice as much as VOC to photochemical ozone formation, and on average the characterisation
factor for NOx is more than three times as high as the characterisation factor of VOCs.
Spatial variation
The spatial variation in exposure for photochemical ozone formation can be large, even at the very local scale. The variation in sensitivity between European regions is now presented on a national scale
showing a factor 15-20 of difference between least and the most sensitive emission countries for exposure of vegetation, and a factor of around 400 times of difference for exposure of humans (the latter
reflecting the variation in population density in the deposition areas). This variation is hidden when the EDIP97 factors or similar site-generic factors are used for characterisation.
7.9 Example
Applying the EDIP2003 factors, characterisation is performed on the inventory presented in Section 1.6.
Site-generic characterisation
As described in Section 7.5, first, the site-generic impacts are calculated. The photochemical ozone formation impacts on vegetation and human health in Table 7.2 and 7.3 are determined using the
site-generic factors from Table
7.1 and the substance-specific efficiency factors for different VOCs and CO from Annex 7.2.
Table 7.2. Site-generic photochemical ozone impacts on vegetation for one supporting block made from plastic or zinc (mean and standard deviation representing spatial variation)
| | Emission to air fromplastic part |
Emission to air from zinc part |
Site-generic ozonimpact, vegetation,
Table 7.1 |
Efficiency factor,Annex 7.1 |
| Substance |
g/f.u. |
g/f.u. |
m2ppm•hour/g |
|
|
| |
|
|
mean |
std. dev |
|
| Hydrogen chloride |
0.001163 |
0.00172 |
|
|
|
| Carbon moNOxide |
0.2526 |
0.76 |
0.73 |
1.2 |
0.075 |
| Ammonia |
0.003605 |
0.000071 |
|
|
|
| Methane |
3.926 |
2.18 |
0.36 |
0.6 |
0.018 |
| VOC, power plant |
0.0003954 |
0.00037 |
0.73 |
1.2 |
1.3 |
| VOC, diesel engines |
0.02352 |
0.0027 |
0.73 |
1.2 |
1.5 |
| VOC, unspecified |
0.89 |
0.54 |
0.73 |
1.2 |
1 |
| Sulphur dioxide |
5.13 |
13.26 |
|
|
|
| Nitrogen oxides |
3.82 |
7.215 |
1.8 |
2.9 |
|
| Lead |
8.03•10-5 |
0.000260 |
|
|
|
| Cadmium |
8.66•10-6 |
7.45•10-5 |
|
|
|
| Zinc |
0.000378 |
0.00458 |
|
|
|
| Total |
|
|
|
|
|
| |
Site-generic ozoneimpac,
|
Site-generic ozone impact, |
| |
vegetation, plastic |
vegetation, zinc part |
| Substance |
m2ppm•hour/f.u. |
m2ppm•hour/f.u. |
| |
Mean |
std.dev. |
Mean |
std.dev. |
| Hydrogen chloride |
|
|
|
|
| Carbon moNOxide |
0.014 |
0.023 |
0.042 |
0.068 |
| Ammonia |
|
|
|
|
| Methane |
0.025 |
0.042 |
0.014 |
0.024 |
| VOC, power plant |
3.8•10-4 |
6.2•10-4 |
3.5•10-4 |
5.8•10-4 |
| VOC, diesel engines |
0.026 |
0.042 |
0.0030 |
0.0049 |
| VOC, unspecified |
0.65 |
1.1 |
0.39 |
0.65 |
| Sulphur dioxide |
|
|
|
|
| Nitrogen oxides |
6.9 |
11.1 |
13.0 |
20.9 |
| Lead |
|
|
|
|
| Cadmium |
|
|
|
|
| Zinc |
|
|
|
|
| Total |
7.66 |
12.33 |
13.44 |
21.77 |
Table 7.3. Site-generic photochemical ozone impacts on human health for one supporting block made from plastic or zinc (mean and standard deviation representing spatial variation)
| |
Emissionto air from plastic part |
Emissionto air from zinc part |
Site-generic ozone impact, human health,
Table 7.1 |
Efficiency factor,Annex 7.1 |
| Substance |
g/f.u. |
g/f.u. |
pers•ppm•hours |
|
|
| |
|
|
mean |
std.dev. |
|
| Hydrogen chloride |
0.001163 |
0.00172 |
|
|
|
| Carbon moNOxide |
0.2526 |
0.76 |
5.9•10-5 |
1.3•10-4 |
0.075 |
| Ammonia |
0.003605 |
0.000071 |
|
|
|
| Methane |
3.926 |
2.18 |
2.9•10-5 |
3.6•10-5 |
0.018 |
| VOC, power plant |
0.0003954 |
0.00037 |
5.9•10-5 |
1.3•10-4 |
1.3 |
| VOC, diesel engines |
0.02352 |
0.0027 |
5.9•10-5 |
1.3•10-4 |
1.5 |
| VOC, unspecified |
0.89 |
0.54 |
5.9•10-5 |
1.3•10-4 |
1 |
| Sulphur dioxide |
5.13 |
13.26 |
|
|
|
| Nitrogen oxides |
3.82 |
7.215 |
1.2•10-3 |
2.7•10-4 |
|
| Lead |
8.03•10-5 |
0.000260 |
|
|
|
| Cadmium |
8.66•10-6 |
7.45•10-5 |
|
|
|
| Zinc |
0.000378 |
0.00458 |
|
|
|
| Total |
|
|
|
|
|
| |
Site-generic ozone impact,
human health, plastic part |
Site-generic ozone impact,
human health, zinc part |
| Substance |
pers•ppm•hours/f.u |
pers•ppm•hours/f.u |
| |
mean |
std.dev. |
mean |
std.dev. |
| Hydrogen chloride |
|
|
|
|
| Carbon moNOxide |
1.1•10-6 |
2.5•10-6 |
3.4•10-6 |
7.4•10-6 |
| Ammonia |
|
|
|
|
| Methane |
2.0•10-6 |
2.5•10-6 |
1.1•10-6 |
1.4•10-6 |
| VOC, power plant |
3.0•10-8 |
6.7•10-8 |
2.8•10-8 |
6.3•10-8 |
| VOC, diesel engines |
2.1•10-6 |
4.6•10-6 |
2.4•10-7 |
5.3•10-7 |
| |
|
|
|
|
| VOC, unspecified |
5.3•10-5 |
1.2•10-4 |
3.2•10-5 |
7.0•10-5 |
| Sulphur dioxide |
|
|
|
|
| Nitrogen oxides |
4.6•10-3 |
1.0•10-3 |
8.7•10-3 |
1.9•10-3 |
| Lead |
|
|
|
|
| Cadmium |
|
|
|
|
| Zinc |
|
|
|
|
| Total |
4.66•10-3 |
1.22•10-3 |
8.77•10-3 |
2.00•10-3 |
Using site-generic characterisation factors, the largest impacts are found to be caused by the zinc supporting block for both of the two photochemical ozone sub categories. In both cases, the impacts are 2-3
times higher for the zinc supporting block than the impacts calculated for the plastic block. However, the potential spatial variation is so large (as revealed by the spatially determined standard deviation) that
the conclusion is highly uncertain. Therefore, a site-dependent characterisation is performed for those processes which contribute the most to the site-generic impacts, in order to reduce the spatially
determined uncertainty and strengthen the conclusion.
Site-dependent characterisation
Table 7.2 and 7.3 show that the impacts on vegetation as well as on human health are dominated by the contribution from NOx, while an emission of unspecified VOCs is also noticeable. The main NOx
sources for the zinc component, are identified as the production of zinc from ore which takes place in Bulgaria, the casting of the component which takes place in Yugoslavia and that part of the transport of
the component, which takes place by truck through Germany (data not shown). For the plastic component, the main sources for NOx are found to be the production of plastic polymer in Italy, the flow
injection moulding of the supporting block in Denmark and the transportation of the component by truck, mainly through Germany (idem). The unspecified VOC-emission from the plastic component is
caused by the plastic polymer production in Italy, and for the zinc component, it comes from the casting process in Yugoslavia (data not shown). The emissions from these processes contribute more than
99% for the zinc component and 75% for the plastic component for impacts on vegetation (Table 7.2) as well as impacts on human health (Table 7.3).
In the calculation of the site-dependent impacts for these key processes, the relevant factors from Annex 7.1 (photochemical ozone formation) are applied. The results are shown in Table 7.4.
Table 7.4. Site-dependent photochemical ozone impacts on vegetation and human health for key processes from either product system.
| Zinc part |
Emission |
Ozone formation factor,
vegetation, Annex 7.2 |
Ozone formation factor, human health,Annex 7.2 |
Impact, vegetation |
Impact, human health |
| |
g/f.u. |
m2ppm•hours/g |
pers•ppm•hours/g |
m2ppm•hours/f.u. |
pers•ppm•hours/f.u. |
| NOx emissions |
|
|
|
|
|
| Zinc production, Bulgaria |
0.97 |
1.4 |
2.20•10-6 |
1.4 |
2.1•10-6 |
| Zinc casting, Yugoslavia |
1.65 |
1.6 |
2.20•10-6 |
2.6 |
3.6•10-6 |
| Transport, mainly Germany |
4.56 |
2.9 |
1.70•10-4 |
13.2 |
7.8•10-4 |
| VOC emissions |
|
|
|
|
|
| Zinc casting, Yugoslavia |
0.53 |
0.2 |
1.40•10-5 |
0.1 |
7.4•10-6 |
| Total. zinc part |
|
|
|
17.33 |
7.99•10-4 |
| Plastic part |
Emission |
Ozone formation factor,
vegetation, Annex 7.2 |
Ozone formation factor, human health,Annex 7.2 |
Impact, vegetation |
Impact, human health |
| |
g/f.u. |
m2 ppm•hours/g |
pers•ppm•hours |
m2 ppm•hours/f.u. |
pers•ppm•hours/f.u. |
| NOx emissions |
|
|
|
|
|
| Plastic production, Italy |
0.63 |
1.5 |
2.00•10-4 |
0.9 |
1.3•10-4 |
| Flow injection moulding, Denmark |
0.48 |
1.5 |
3.40•10-5 |
0.7 |
1.6•10-5 |
| Transport, mainly Germany |
1.74 |
2.9 |
1.70•10-4 |
5.0 |
3.0•10-4 |
| VOC emissions |
|
|
|
|
|
| Plastic polymer production, Italy |
0.87 |
0.7 |
1.00•10-4 |
0.6 |
8.7•10-5 |
| Total. plastic part |
|
|
|
7.33 |
5.33•10-4 |
The site-generic impacts from the key processes are subtracted from the original site-generic impacts in Table 7.2 and 7.3, and the site-dependent impacts from the key processes calculated in Table 7.4 are
added. The photochemical ozone impacts thus corrected are found in Table 7.5, and the differences to the original site-generic impacts of Table 7.2 are illustrated in Figure 7.1.
Table 7.5. Photochemical ozone impacts from either product system with site-dependent characterisation of key process emissions
| | Ozone, vegetation |
Ozone, human health |
| | m2ppm•hours/f.u. | pers•ppm•hours/f.u. |
| Zinc component | 17.6 | 8.80•10-4 |
| Plastic component | 10.9 | 2.90•10-3 |
For photochemical ozone formation impact on vegetation, more than 99% of the impacts for the zinc component in Table 7.5 include the spatial information. Even if the site-dependent characterisation was
performed for all the remaining processes in the product system, the result will thus not change significantly, given their modest share in the total and the standard deviation. The spatially conditioned
uncertainty of the impact has largely been cancelled. For the plastic component, however, the figure is 85% for impacts on vegetation and for impacts on human health it is as low as 60%. This means that for
the plastic component, particularly the figure for impacts on human health may still change if further spatial characterisation is performed. More key processes need thus to be included in order to cancel the
spatially determined uncertainty of the conclusion.
Click here to see the Figure
Figure 7.1 summarises the difference between the site-generic and the site-dependent impacts.
Figure 7.1 Site-generic and site-dependent photochemical ozone impacts on vegetation and human health from the two product systems. For the site-dependent impacts, the site-dependent characterisation
factors have only been applied for key processes as described above.
As seen from Figure 7.1, the inclusion of spatial differentiation at the level of country of emission reverses the dominance in ozone impact on human health. When a major part of the spatial variation in the
dispersion patterns and sensitivity of the exposed environment (i.e. population density) is eliminated, the impact from the plastic component is larger than the impact from the zinc component. For ozone
impacts on vegetation, the ranking of the two alternatives remains the same also after spatial characterisation. Considering that for the plastic component, the ozone impact on human health still comprises a
significant potential for spatial variation, no conclusion can be drawn yet for this impact category
Annex 7.1: Site-dependent photochemical ozone formation factors
Factors for site-dependent characterisation of photochemical ozone formation impacts on vegetation and human health
| Country | Vegetation | Human health |
| | NOx | VOC | NOx | VOC |
| | m2•ppm•hours/g | pers•ppm•hours/g |
| Albania | 1.1 | 0.2 | 9.40E-06 | 4.00E-06 |
| Austria | 3 | 0.5 | 7.00E-05 | 4.70E-05 |
| Belarus | 1.6 | 0.4 | 2.50E-06 | 7.20E-09 |
| Belgium | 1.6 | 1.1 | 3.80E-04 | 2.20E-04 |
| Bosnia/ Herzegovina | 1.6 | 0.2 | 1.30E-05 | 3.50E-05 |
| | | | | |
| Bulgaria | 1.4 | 0.3 | 2.20E-06 | 2.20E-06 |
| Croatia | 2.4 | 0.3 | 3.80E-05 | 1.20E-04 |
| Czech Republic | 2.4 | 0.9 | 2.10E-04 | 6.20E-07 |
| Denmark | 1.5 | 0.8 | 3.40E-05 | 2.70E-05 |
| Estonia | 0.2 | 0.6 | 1.20E-06 | 9.40E-06 |
| Finland | 0.4 | 0.3 | 8.50E-07 | 5.20E-07 |
| France | 3.4 | 0.9 | 2.20E-04 | 1.20E-04 |
| Germany-new | 2.9 | 1.5 | 1.70E-04 | 1.10E-04 |
| Germany-old | 2 | 1.3 | 3.30E-04 | 1.90E-04 |
| Greece | 0.5 | 0.1 | 1.90E-05 | 1.10E-05 |
| Hungary | 4.3 | 0.8 | 3.00E-05 | 2.40E-05 |
| Ireland | 0.2 | 0.1 | 1.20E-05 | 8.50E-06 |
| Italy | 1.5 | 0.7 | 2.00E-04 | 1.00E-04 |
| Latvia | 0.4 | 0.3 | 2.50E-06 | 1.00E-06 |
| Lithuania | 1.1 | 0.6 | 4.20E-06 | 1.30E-06 |
| Luxemburg | 0.8 | 0.1 | 1.10E-04 | 5.80E-05 |
| Macedonia | 0.5 | 0.2 | 4.30E-06 | 3.80E-05 |
| Moldova | 0.7 | 0.5 | 1.50E-06 | 1.80E-06 |
| Netherlands | 0.8 | 0.9 | 2.30E-04 | 1.30E-04 |
| Norway | 0.2 | 0.1 | 2.10E-06 | 1.50E-06 |
| Poland | 2.5 | 1.2 | 1.10E-04 | 6.90E-05 |
| Portugal | 3.5 | 1.1 | 1.30E-04 | 6.70E-05 |
| Romania | 2.1 | 0.3 | 5.00E-06 | 5.00E-06 |
| Russia-Kaliningrad | 0.2 | 0 | 3.60E-06 | 4.70E-06 |
| | | | | |
| Remaining Russia | 0.9 | 0.2 | 2.10E-06 |
2.90E-0 |
| Slovakia | 3.4 | 0.7 | 5.60E-05 | 1.50E-06 |
| Slovenia | 1.2 | 0.2 | 2.60E-05 | 2.70E-06 |
| Spain | 2.3 | 0.6 | 4.60E-05 | 2.40E-05 |
| Sweden | 1 | 0.4 | 1.20E-05 | 8.30E-06 |
| Switzerland | 2.2 | 0.4 | 9.80E-05 | 6.10E-05 |
| Ukraine | 2 | 0.7 | 3.70E-06 | 2.10E-07 |
| United Kingdom | 1 | 1.3 | 9.90E-05 | 6.00E-05 |
| Yugoslavia | 1.6 | 0.2 | 2.20E-06 | 1.40E-05 |
| Atlantic Ocean | 0.5 | 0 | 1.40E-05 | 0.00E+00 |
| Baltic Sea | 0.5 | 0 | 1.50E-06 | 0.00E+00 |
| North Sea | 1.1 | 0.2 | 7.80E-05 | 0.00E+00 |
Annex 7.2: Efficiency factors for individual VOCs and source-specified VOCs
| Individual VOCsand methane |
Efficiencyfactor ηs |
Individual VOCs,carbon moNOxide and source specified VOCs |
Effiencyfactor ηs |
| Alkanes |
1 |
Aldehydes |
1.5 |
| |
|
formaldehyde |
1.1 |
| ethane |
0.21 |
acetaldehyde |
1.3 |
| propane |
1.1 |
propionaldehyde |
1.5 |
| n-butane |
1 |
butyraldehyde |
1.4 |
| isobutane |
0.79 |
isobutyraldehyde |
1.6 |
| n-pentane |
1 |
valeraldehyde |
1.7 |
| isopentane |
0.74 |
acrolein |
2 |
| n-hexane |
1.1 |
Ketones |
1 |
| 2-methylpentane |
1.3 |
acetone |
0.45 |
| 3-methylpentane |
1.1 |
methyl ethyl ketone |
1.1 |
| 2.2-dimethylbutane |
0.63 |
methyl isobutyl ketone |
1.6 |
| 2.3-dimethylbutane |
0.96 |
Alcohols |
0.66 |
| n-heptane |
1.3 |
methanol |
0.31 |
| 2-methylhexane |
1.2 |
ethanol |
0.67 |
| 3-methylhexane |
1.2 |
isopropanol |
0.5 |
| n-octane |
1.2 |
butanol |
1 |
| 2-methylheptane |
1.2 |
isobutanol |
0.75 |
| n-nonane |
1.2 |
butan-2-diol |
0.75 |
| 2-methyloctane |
1.3 |
Ethers |
1 |
| n-decane |
1.2 |
dimethyl ether |
0.75 |
| 2-methylnonane |
1.1 |
propylene glycol methyl ether |
1.3 |
| n-undecane |
1.1 |
Esters |
0.51 |
| n-dodecane |
1 |
methyl acetat (=dimethyl ester) |
0.06 |
| Alkenes |
2.2 |
ethyl acetate |
0.55 |
| ethylene |
2.5 |
isopropyl acetate |
0.54 |
| propylene |
2.6 |
n-butyl acetate |
0.81 |
| 1-butene |
2.4 |
isobutyl acetate |
0.83 |
| 2-butene (trans) |
2.5 |
Propylene glycol methyl ether-acetate |
0.25 |
| Isobutene |
1.5 |
Chloro-alkanes |
0.011 |
| 2-pentene (trans) |
2.3 |
methylen chloride |
0.023 |
| 1-pentene |
2.6 |
chloroform |
0.0075 |
| 2-methylbut-1-ene |
1.9 |
methyl chloroform |
0.0025 |
| 3-methylbut-1-ene |
2.2 |
Chloro-alkenes |
0.64 |
| 2-methylbut-2-ene |
1.9 |
trichloroethylene |
0.17 |
| 2-methylpropene |
1.6 |
tetrachloroethylene |
0.01 |
| Isoprene |
2 |
allyl chloride |
1.8 |
The dimensionless efficiency factor is representing the efficiency of individual VOCs relative to the European average VOC in contributing to ozone formation. It is derived as the quotient between the
respective POCP-factors for 4-9 days in high NOx-areas (the EDIP97 characterisation factors for high NOx-areas).
Annex 7.2: Efficiency factors for individual VOCs and source-specified VOCs
| Individual VOCsand methane | Efficiencyfactor ηs | Individual VOCs, carbon moNOxide andsource specified VOCs | Efficiencyfactor ηs |
| Alkynes | | Inorganic compounds | |
| acetylene | 0.42 | carbon moNOxide | 0.075 |
| Aromatics | 1.9 | | |
| benzene | 0.47 | Source-specified VOC mixtures | |
| toluene | 1.4 | Petrol-powered car, exhaust | 1.5 |
| o-xylene | 1.7 | Petrol-powered car, vapour | 1.3 |
| m-xylene | 2.5 | Diesel-powered car, exhaust | 1.5 |
| p-xylene | 2.2 | Power plants | 1.3 |
| ethylbenzene | 1.5 | Combustion of wood | 1.5 |
| n-propylbenzene | 1.2 | Food industry | 1 |
| isopropylbenzene | 1.4 | Surface coating | 1.3 |
| 1.2.3-trimethylbenzene | 2.9 | Chemical cleaning of clothes | 0.75 |
| 1.2.4-trimethylbenzene3 | | Refining and distribution of oil | 1.3 |
| 1.3.5-trimethylbenzene | 2.9 | Natural gas leakage | 0.05 |
| o-ethyltoluene | 1.7 | Coal mining | 0.018 |
| m-ethyltoluene | 2 | Farming | 1 |
| p-ethyltoluene | 1.8 | Landfilling of household waste | 0.018 |
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Version 1.0 january 2006, © Danish Environmental Protection Agency
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