Modeling secondary organic aerosol formation from isoprene oxidation under dry and humid conditions

FLORIAN COUVIDAT (1), Christian Seigneur (1)

(1) CEREA, Joint Laboratory Ecole des Ponts ParisTech/EDF R&D, Université Paris-Est

     Abstract Number: 222
     Last modified: April 30, 2010

Abstract
A new model for the formation of secondary organic aerosol (SOA) from isoprene has been developed. This model uses surrogate molecular species (hydroxy-hydroperoxides, tetrols, methylglyceric acid, organic nitrates) to represent SOA formation. Pathways for the formation of SOA were introduced in the atmospheric chemical model RACM2. 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 Caltech experimental chamber under both low-NO$_x and high-NO$_x conditions. Under low-NO$_x conditions, the model reproduces the transitional formation of hydroxy-hydroperoxides particles which are photolysed and lead to SOA mass decrease after reaching a maximum. Under high-NO$_x conditions, particles were supposed to be formed mostly from the photooxidation of a PAN-type molecule derived from methacrolein (MPAN). This model successfully reproduces the complex NO$_x-dependence of isoprene oxidation and suggests a possible yield increase under some high-NO$_x 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 then extended to take into account the hydrophilic properties of isoprene SOA and investigate the effect of particulate liquid water on SOA formation.