Photolytic Mass Loss of Secondary Organic Aerosol (SOA) Derived from Biomass Burning Precursors in Different Relative Humidity

NARA SHIN, Yuchen Wang, Taekyu Joo, Pengfei Liu, Nga Lee Ng, Georgia Institute of Technology

     Abstract Number: 256
     Working Group: Biomass Combustion: Outdoor/Indoor Transport and Indoor Air Quality

Abstract
Biomass burning (BB) is one of the major sources of organic aerosol (OA) and volatile organic compounds (VOCs) in the atmosphere. The atmospheric oxidation of the emitted BB VOCs can lead to the formation of secondary organic aerosol (SOA). The SOA formed in the atmosphere undergoes multiple loss processes, such as photochemical processes (including photolysis and photooxidation), hydrolysis, and wet and dry deposition. However, the photolysis behaviors of biomass burning SOA (BBSOA) and their impact on aerosol lifetime have not been well constrained. Previous studies have shown that furan species are important sources contributing to BBSOA formation. In this work, we investigated the effect of photolysis on BBSOA formed by photooxidation of furan compounds (2-methylfuran, 3-methylfuran, and furfural) at high NOx conditions. BBSOA was produced in chamber experiments under dry (<5%) and humid (~50%) conditions. The formed BBSOA was deposited onto a quartz crystal substrate and the mass-loss rates of SOA under specific UV lights (300 and 340 nm) were measured using a Quartz Crystal Microbalance (QCM). The results indicate 15-35% and 3-10% mass losses under UV illumination of 300 and 340 nm, respectively. The BBSOA produced from 2-methylfuran and 3-methylfuran at dry condition (< 5%) has relatively a higher mass-loss rate from both 300 and 340 nm lights compared to those formed at humid condition (~50%). On the other hand, furfural BBSOA formed under dry and humid conditions shows a similar mass-loss rate (33%). The observed photolytic mass losses are linked to the chemical composition of BBSOA formed under different RH conditions, as a result of differing gas- and particle-phase chemistry. Overall, this study highlights changes in the lifetime of BBSOA induced by photolysis, which indicates that photolysis can be a potential fate and loss mechanism of BBSOA in the ambient environment.