Summertime (2020) Source Apportionment of Organic Aerosols in relation with their gaseous precursors, Volatile Organic Compounds, in the Paris region, France
Résumé
Organic aerosol (OA) particles are key pollutants in
atmospheric chemistry, and have impacts on public
health and climate (IPCC report, 2021). While their
primary sources are rather well identified and quantified,
the formation processes of secondary OA are still poorly
understood, due to their complexity and high spatial and
temporal variability.
In the Paris region (France), the main primary
sources of OA are traffic and residential wood burning,
which have higher contributions at fall and wintertime.
In summertime, secondary formation involving gaseous
precursors (Volatile Organic Compounds, VOCs) is more
important, due to their biogenic source being more
abundant and meteorological conditions leading to more
oxidation and condensation.
As a matter of fact, an OA source apportionment
study conducted on Aerosol Chemical Speciation
Monitor (ACSM) measurements for the period 2012-
2018 at the SIRTA ACTRIS facility (located about 20km
south-west Paris city center) highlighted 4 main factors:
Hydrocarbon-like OA (HOA), Biomass-Burning OA (BBOA)
as primary factors and Less-Oxidized Oxygenated OA (LOOOA)
and More-Oxidized Oxygenated OA (MO-OOA) as
secondary factors (Zhang et al, 2019). LO-OOA showed a
seasonal pattern with higher levels in summer,
suggesting being mostly from biogenic precursors’
oxidation.
Knowledge on key organic gaseous precursors can
help resolving the origins, notably using combined
aerosol and VOCs mass spectra in receptor modeling
approach such as Positive Matrix Factorization (PMF). For
instance, Crippa et al. (2013) retrieved OA origins from
AMS (Aerosol Mass Spectrometer) and PTRMS data from
July 2009 and January-February 2010 in Greater Paris,
including 2 primary and 4 secondary factors: LV-OOA, 2
SV-OOA – one from daytime processes and the other
from nighttime processes – and a marine OA factor.
Together with decennial continuous ACSM
observations, VOCs are monitored since January 2020 at
SIRTA using a Proton-Transfer-Reaction Quadrupole
Mass-Spectrometer (PTR-Q-MS).
In the present study, the ACSM and PTR-MS
datasets are used to try and refine SOA sources during
the summer season (2020).
Results notably allow to investigate the links
between the primary HOA-traffic factor and expected
gaseous co-emissions. Among secondary factors, a
daytime biogenic OOA factor could be mainly driven by
isoprene OH-oxidation. A nighttime OOA factor could
also be obtained, involving primary contributions from
monoterpenes - which are mainly from biogenic origin
but could also have anthropogenic sources, even in
summer (Panopoulou et al, 2020) - and their oxidation by
NO3 enhanced at lower temperatures.
Furthermore, the comparison with results from
Crippa et al. (2013) illustrate the temporal evolution of
OA sources and pollution in the Paris region at a 10-years
interval.
This work was supported by H2020 Research
Infrastructures ACTRIS projects (ACTRIS 2 (grant no.
654109)), the National Center for Scientific Research
(CNRS), the French alternatives energies and Atomic
Energy Commission (CEA), the French Ministry of
Environment, the DIM-R2DS program from the Ile-de-
France region and the long-term monitoring aerosol
program SNO-CLAP. We gratefully thank Roland Sarda-
Estève, Nicolas Bonnaire and Dominique Baisnée for
their contribution in maintaining data acquisition at
SIRTA.