AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Comparison of NO2 Effects on Secondary Organic Aerosol (SOA) Formation from Ozonolysis of Four Monoterpenes
DANIELLE C DRAPER, Delphine Farmer, Yury Desyaterik, James N. Smith, Juliane L. Fry, Reed College
Abstract Number: 250 Working Group: Aerosol Chemistry
Abstract The effect of NO$_2 on secondary organic aerosol (SOA) formation from ozonolysis of alpha-pinene, beta-pinene, Delta-carene, and limonene was investigated in unseeded experiments using a dark flow-through reaction chamber. Each monoterpene exhibited different aerosol formation trends from pure ozonolysis compared to ozonolysis with increasing NO$_2 concentrations: number concentrations and mass yields both systematically decreased with increasing [NO$_2] for alpha-pinene; number concentrations decreased with increasing [NO$_2] for beta-pinene and Delta-carene while mass yields remained comparable; and both number concentrations and mass yields increased with increasing [NO$_2] for limonene. Kinetics modeling of the first generation gas-phase chemistry suggests that differences in observed aerosol yields at different NO$_2 concentrations is likely caused by the formation of NO$_3, which competes with O$_3 to oxidize the monoterpene and has been shown to produce different aerosol yields. SOA from each experiment was collected and analyzed offline by HPLC-ESI-MS, enabling comparisons between aerosol product distributions for each system. For all monoterpenes studied except for alpha-pinene, experiments influenced by NO$_3 oxidation contained more high molecular weight products (MW > 400 amu) relative to ozonolysis, suggesting the importance of oligomerization mechanisms in NO$_3-initiated SOA formation. The lack of oligomers observed from alpha-pinene may explain its anomalously low aerosol yield with NO$_3. Through direct comparisons of mixed-oxidant systems, this work suggests that NO$_3 is likely to dominate nighttime oxidation pathways in most regions with both biogenic and anthropogenic influences.