We interpret here the variability of levels of carbonaceous
aerosols based on a 12 yr database from 78 monitoring
stations across Spain specially compiled for this article.
Data did not evidence any spatial trends of carbonaceous
aerosols across the country. Conversely, results show marked
differences in average concentrations from the cleanest, most
remote sites (around 1 μgm−3 of non-mineral carbon (nmC),
mostly made of organic carbon (OC) with very little elemental
carbon (EC), around 0.1 μgm−3; OC/ EC = 12–15),
to the highly polluted major cities (8–10 μgm−3 of nmC; 3–
4 μgm−3 of EC; 4–5 μgm−3 of OC; OC/ EC = 1–2). Thus,
urban (and very specific industrial) pollution was found to
markedly increase levels of carbonaceous aerosols in Spain,
with much lower impact of biomass burning and of biogenic
emissions. Correlations between yearly averaged OC/ EC
and EC concentrations adjust very well to a potential equation
(OC = 3.37 EC0.326, R2 = 0.8). A similar equation is obtained
when including average concentrations obtained at
other European sites (OC = 3.60EC0.491, R2 = 0.7).
A clear seasonal variability in OC and EC concentrations
was detected. Both OC and EC concentrations were higher
during winter at the traffic and urban sites, but OC increased
during the warmer months at the rural sites. Hourly equivalent
black carbon (EBC) concentrations at urban sites accurately
depict road traffic contributions, varying with distance
from road, traffic volume and density, mixing-layer height
and wind speed. Weekday urban rush-hour EBC peaks are
mimicked by concentrations of primary gaseous emissions
from road traffic, whereas a single midday peak is characteristic
of remote and rural sites. Decreasing annual trends
for carbonaceous aerosols were observed between 1999 and
2011 at a large number of stations, probably reflecting the
impact of the EURO4 and EURO5 standards in reducing
the diesel PM emissions. This has resulted in some cases in
an increasing trend for NO2 / (OC + EC) ratios as these standards
have been much less effective for the abatement of NOx
exhaust emissions in passenger diesel cars. This study concludes
that EC, EBC, and especially nmC and OC+ EC are
very good candidates for new air quality standards since they
cover both emission impact and health-related issue
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