AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Instantaneous NO Effect on Secondary Organic Aerosol Formation during m-Xylene Photooxidation
LIJIE LI, Ping Tang, Chia-Li Chen, David R. Cocker III, University of California, Riverside
Abstract Number: 274 Working Group: Aerosol Chemistry
Abstract SOA formation from aromatic hydrocarbon photooxidation is highly sensitive to NO concentration. Instantaneous NO effect on SOA formation from m-xylene photooxidation has been investigated in this work by data mining 10 years of aromatic hydrocarbon chamber experiments conducted in the UCR chamber. First, sub-ppb level NO effect on SOA formation is studied by modifying classical aromatic SOA growth curves based on NO$_2/NO ratio. Relationships among SOA growth rate, hydrocarbon consumption, HC/NO, absolute NO concentration, NO$_3 radical concentration and OH radical concentration are demonstrated. Second, five NOx injection schemes are applied to chamber photooxidation experiments to simulate continuous NO sources in urban areas. Radical concentrations are estimated using the SAPRC-11 photochemical model. Influence of NO$_x injection schemes on radical concentrations (OH, HO$_2 and RO$_2), SOA formation, aerosol volatility and aerosol density is explored. An mz43 (C$_(2)H$_(3)O$^(+))/mz44 (CO$_(2)$^(+)) ratio determined by ToF-HR-AMS is used to explore SOA chemical composition differences arising from these injection schemes. It is expected SOA formation was suppressed at high NO concentrations as reported by many studies. Interestingly, however, enhanced SOA formation is also observed when low NO levels (~1ppb) were artificially maintained by continuous or step-wise injection. A mechanism for promoting SOA formation at ~1ppb NO concentration is proposed. This study facilitates the understanding of NO effect on SOA formation under atmospherically relevant conditions.