Photolytic Mass Loss of Secondary Organic Aerosol Derived from Photooxidation of Biomass Burning Furan Precursors.

Direct photolysis as a potentially important chemical loss pathway for atmospheric organic aerosol (OA) is increasingly recognized but remains highly uncertain, particularly for secondary organic aerosol (SOA) derived from biomass burning (BB) precursors. We present the measurements of the photolytic mass change of SOA derived from photooxidation of three furan precursors, 3-methylfuran, 2-methylfuran, and furfural, in an environmental chamber under both dry and humid conditions. Each type of SOA was collected on crystal sensors, and the mass losses by photolysis under 300 or 340 nm light were continuously monitored using a quartz crystal microbalance (QCM). By incorporation of measurements and modeling, 10-40% of furan SOA masses can be lost by direct photolysis under solar radiation over their typical atmospheric lifetime. The mass loss fraction is well correlated with the mass fraction of nitrogen-containing compounds (NOC) in the SOA, possibly because these species can largely enhance the light absorption cross section and readily undergo photodissociation under UV light.