Six-year source apportionment of submicron organic aerosols from near-continuous highly time-resolved measurements at SIRTA (Paris area, France)
2019
Abstract. Organic aerosol (OA) particles are recognized as key factors influencing air
quality and climate change. However, highly time-resolved long-term
characterizations of their composition and sources in ambient air are still
very limited due to challenging continuous observations. Here, we present an
analysis of long-term variability of submicron OA using the combination of
an aerosol chemical speciation monitor (ACSM) and a multiwavelength Aethalometer
from November 2011 to March 2018 at a peri-urban background site of the
Paris region (France). Source apportionment of OA was achieved via partially
constrained positive matrix factorization (PMF) using the multilinear engine
(ME-2). Two primary OA (POA) and two oxygenated OA (OOA) factors were
identified and quantified over the entire studied period. POA factors were
designated as hydrocarbon-like OA (HOA) and biomass burning OA (BBOA). The
latter factor presented a significant seasonality with higher concentrations
in winter with significant monthly contributions to OA (18 %–33 %) due to
enhanced residential wood burning emissions. HOA mainly originated from
traffic emissions but was also influenced by biomass burning in cold
periods. OOA factors were distinguished between their less- and
more-oxidized fractions (LO-OOA and MO-OOA, respectively). These factors
presented distinct seasonal patterns, associated with different atmospheric
formation pathways. A pronounced increase in LO-OOA concentrations and
contributions (50 %–66 %) was observed in summer, which may be mainly
explained by secondary OA (SOA) formation processes involving biogenic
gaseous precursors. Conversely, high concentrations and OA contributions
(32 %–62 %) of MO-OOA during winter and spring seasons were partly
associated with anthropogenic emissions and/or long-range transport from
northeastern Europe. The contribution of the different OA factors as a
function of OA mass loading highlighted the dominant roles of POA during
pollution episodes in fall and winter and of SOA for highest springtime and
summertime OA concentrations. Finally, long-term trend analyses indicated a
decreasing feature (of about −175 ng m −3 yr −1 ) for MO-OOA, very
limited or insignificant decreasing trends for primary anthropogenic
carbonaceous aerosols (BBOA and HOA, along with the fossil-fuel and biomass-burning black carbon components) and no statistically significant trend for
LO-OOA over the 6-year investigated period.
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