Miljøprojekt, 1003 – The indoor and outdoor concentrations of particulate air-pollution and PAHs in different size fractions and assessment of exposure and health impacts in the Copenhagen population

The indoor and outdoor concentrations of particulate air-pollution and PAHs in different size fractions and assessment of exposure and health impacts in the Copenhagen population

1.1 Background

Epidemiological studies have shown a relationship between increased mass concentrations of urban air-pollution and increased hospitalisation for respiratory symptoms and mortality rates (e.g.,Künzli et al. 2000; Schwartz et al. 2001; Schwartz et al. 2002; Pope, III et al. 2002; Nafstad et al. 2004)). These adverse health effects are better correlated to fine particles (PM₁ and PM_2.5) ^[1] than coarser particle measures (e.g., PM₁₀).

However, adverse health effects from air-pollution are not related to particle mass-concentrations alone. Long-term exposure to specific Hazardeous Air-Pollution Substances - often referred to as HAPS or air toxics - can also result in negative health effects of which cancer appears to be the most important outcome. In the USA, 188 HAPS' have been identified under the Clean Air Act Amendments of 1990 (http://www.epa.gov/ttn/atw/188polls.html). Among these air toxics, benzene and PAH's (Polycyclic Aromatic Hydrocarbon) are some of the most important carcinogenic compounds.

Combustion of fossil fuels (coal, oil, diesel and gasoline) is generally the most important source of PAHs in ambient air. Increased use of wood-burning stoves for domestic heating in Denmark has additionally re-introduced wood burning as an important PAH source in local environments . PAHs also exist as constituents in emissions from typical indoor sources such as cooking, smoking and indoor emissions from wood-burning stoves. Hence, human exposure to particulate matter and PAHs in indoor environments is a mixture of the contribution from outdoor air and that emitted from indoor sources.

The transport properties and biological effects from exposure to particulate air-pollution strongly depend on particle size distribution. Submicrometer particles can easily penetrate into the indoor environment, especially if air-filtration does not occur.

PAH's mainly occur in the fine particle fraction (Schnelle et al., 1995). A recent study has shown that the size distribution of PAH's at the 20 m roof-top in Saitama (Japan) was unimodal with a peak concentration at 480-680 nm . On the other hand, the maximum in relative PAH-contents was found in the particulate matter smaller than 200 nm. This is consistent with observations in exhaust from combustion of fossil fuels, where it has been found that PAHs form individual particles or adsorb onto especially the ultra-fine combustion particles during cooling of the flue gas or exhaust. Hence, owing to the size of combustion particles and production of volatile PAHs from e.g. traffic and other outdoor sources, PAHs may be an important constituent of the particulate air pollution indoors. Several studies have already been completed to quantify the degree of particle infiltration. However, owing to particle phase transformations and potential influence of indoor sources, it is still unclear to what extent urban air-pollution de facto penetrates into the indoor environment. Indoor-outdoor ratios of specific urban air-pollution compounds, such as PAHs, may yieL_D better estimates.

In addition to the infiltration efficiency into Buildings, particle size also determines the deposition efficiency of particles in the respiratory system. In humans, coarse particles deposit in the upper respiratory system, whereas the fine (PM₁ and PM_2.5) and ultrafine particles ( ≤ 100 nm) predominantly are retained in the deeper bronchioalveolar region of the lung. Some ultrafine particles also deposit in the nose and throat owing to their high diffusion rates. Consequently, since indoor particulate air-pollution and vehicle exhaust including particle-bound PAHs mainly occur in the submicrometer range, they are predicted to deposit mainly in the gas-exchange region in the deeper respiratory tract with lesser amounts in the nose and throat. Therefore, bias may occur in causal studies using coarser mass-dose estimates

1.2 Purpose of the study

The purpose of this study was to:

Determine the concentrations and indoor-outdoor relationship for PM₁, PM_2.5 and inhalable dust indoors and outdoors of an uninhabited apartment at Jagtvej in the centre of Great Copenhagen combined with roof-top measurements of urban background concentrations at the National Institute of Occupational Health (Copenhagen, Denmark).
Determine the concentrations and indoor-outdoor relationships for specific volatile and semivolatile PAH's in PM_2.5 at the three sample sites with focus on the influence from traffic air-pollution on indoor air.
Evaluate the potential adverse health effects induced by the particulate air-pollution and the carcinogenic risk induced by the observed PAH-concentrations in the indoor and outdoor environments in Copenhagen.

The project was funded by the Danish Environmental Protection Agency and conducted in synergy with the TRIP-project (Centre for Traffic Research on environmental and health Impacts and Policy) funded by the Strategic Environmental Research Program (http://www.akf.dk/trip/index.htm) and a parallel study of the characterization, inflammatory potential and genotoxic effect of the particulate air-pollution in Copenhagen funded by the Danish Ministry of the Interior and Health, Research Centre for Environmental Health (J.nr. 383-29-2001).

Footnotes

[1] PM is short for Particulate Matter. PM₁ is the mass concentration of particles up to 1 m-size.