Modeling secondary organic aerosol formation from isoprene oxidation under dry and humid conditions CEREA, Joint Laboratory Ècole des Ponts ParisTech/EDF R&D, Université Paris-Est, 77455 Marne la Vallée, France
31 Jan 2011
Received: 22 July 2010 – Published in Atmos. Chem. Phys. Discuss.: 30 August 2010 Abstract. A new model for the formation of secondary organic aerosol (SOA)
from isoprene was developed. This model uses surrogate molecular
species (hydroxy-hydroperoxides, tetrols, methylglyceric acid,
organic nitrates) to represent SOA formation. The development
of this model used available experimental data on yields and
molecular composition of SOA from isoprene and methacrolein
oxidation. This model reproduces the amount of particles measured
in smog chambers under both low-NOx and high-NOx
conditions. Under low-NOx conditions, the model reproduces the
transitional formation of hydroxy-hydroperoxides particles, which are photolyzed
and lead to SOA mass decrease after reaching a maximum. Under high-NOx
conditions, particles are assumed to be formed mostly from the photo-oxidation of a
PAN-type molecule derived from methacrolein (MPAN). This model successfully reproduces
the complex NOx-dependence of isoprene oxidation and suggests a possible
yield increase under some high-NOx conditions. Experimental data correspond
to dry conditions (RH < 10%). However, particles formed from
isoprene are expected to be highly hydrophilic, and isoprene
oxidation products would likely partition between an aqueous
phase and the gas phase at high humidity in the atmosphere.
The model was extended to take into account the hydrophilic
properties of SOA, which are relevant under atmospheric conditions,
and investigate the effect of particulate liquid water on SOA
formation. An important increase in SOA mass was estimated
for humid conditions due to the hydrophilic properties.
Experiments under high relative humidity conditions should
be conducted to confirm the results of this study, which
have implications for SOA modeling.
Revised: 01 December 2010 – Accepted: 14 January 2011 – Published: 31 January 2011
Citation: Couvidat, F. and Seigneur, C.: Modeling secondary organic aerosol formation from isoprene oxidation under dry and humid conditions, Atmos. Chem. Phys., 11, 893-909, doi:10.5194/acp-11-893-2011, 2011.