AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Instantaneous Secondary Organic Aerosol Formation from M-xylene Photooxidation: Quantification of NOx and NO3 Radical Effects on SOA Yield
LIJIE LI, Ping Tang, Chia-Li Chen, Mary Kacarab, David R. Cocker III, University of California, Riverside
Abstract Number: 552 Working Group: Aerosol Chemistry
Abstract Observations from recent field studies indicate that the formation of secondary organic aerosol (SOA) from anthropogenic sources is considerably underestimated in current models. Aromatic hydrocarbons have been recognized as a major anthropogenic SOA precursor gases. Further, it has been widely reported that SOA formation from aromatic hydrocarbon photooxidation is highly sensitive to the NO$_x level. In this study, instantaneous aerosol yield (IAY) and a modified SOA growth curve are introduced and applied during data mining of 89 classic m-xylene photooxidation experiments with HC/NO$_x ratios ranging from 1.3 to 71.6. It is observed that IAY trend is categorized into two types. For low NOx experiments (initial NO$_x lower that 100 ppb), NO$_(2)/NO ratio higher than 70 could serve as a threshold to the substantial formation of SOA. When the initial NO$_x concentration is higher than 100 ppb, the IAY of SOA formation is lower even though NO$_(2)/NO ratio is higher than 70. For these high initial NO$_x experiments, the product of NO$_2 and O$_3 is comparatively high indicating the potential effects of NO$_3 radical when using black lights as a light source for photooxidation. Next, radical experiments are carried out to study the effect of NO$_3 radical. NO$_3 radical experiments are realized by injecting N$_(2)O$_(5) in the middle of photooxidation experiment. m-Xylene, H$_(2)O$_(2) and O$_3 are injected into the chamber to initialize the SOA formation and black lights are still used as light sources. The effect of NO$_3 radical on SOA yield, volatility and density will be reported. Mz43 (C$_(2)H$_(3)O$^(+))/mz44 (CO$_(2)$^(+)) ratio determined by ToF-HR-AMS is used to demonstrate the difference in SOA chemical composition. This study facilitates the understanding of potential mechanism that is critical to the SOA formation from aromatics.