Abstract
Apportionment of urban particulate matter (PM) to sources is central for
air quality management and efficient reduction of the substantial public
health risks associated with fine particles (PM2.5). Traffic is an important
source combustion particles, but also a significant source of resuspended
particles that chemically resemble Earth's crust and that are not affected by
development of cleaner motor technologies. A substantial fraction of urban
ambient PM originates from long-range transport outside the immediate urban
environment including secondary particles formed from gaseous emissions of
mainly sulphur, nitrogen oxides and ammonia. Most source apportionment studies
are based on small number of fixed monitoring sites and capture well
population exposures to regional and long-range transported particles.
However, concentrations from local sources are very unevenly distributed and
the results from such studies are therefore poorly representative of the
actual exposures. The current study uses PM2.5 data observed at population
based random sampled residential locations in Athens, Basle and Helsinki with
17 elemental constituents, selected VOCs (xylenes, trimethylbenzenes, nonane
and benzene) and light absorbance (black smoke). The major sources identified
across the three cities included crustal, salt, long-range transported
inorganic and traffic sources. Traffic was associated separately with source
categories with crustal (especially Athens and Helsinki) and long-range
transported chemical composition (all cities). Remarkably high fractions of
the variability of elemental (R2 > 0.6 except for Ca in Basle 0.38) and
chemical concentrations (R2 > 0.5 except benzene in Basle 0.22 and nonane in
Athens 0.39) are explained by the source factors of an SEM model. The RAINS
model that is currently used as the main tool in developing European air
quality management policies seems to capture the local urban fraction (the
city delta term) quite well, but underestimates crustal particle levels in the
three cities of the current study. Utilizing structural equation modelling
parallel with traditional principal component analysis (PCA) provides an
objective method to determine the number of factors to be retained in a model
and allows for formal hypotheses testing.
Original language | English |
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Pages (from-to) | 77-92 |
Journal | Science of the Total Environment |
Volume | 384 |
Issue number | 1-3 |
DOIs | |
Publication status | Published - 2007 |
MoE publication type | A1 Journal article-refereed |
Keywords
- Urban air
- Particulate matter
- Source apportionment
- Population exposures
- SEM
- VOC
- Benzene