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Influence of Continuous NOX Injection on SOA Yield from Biogenic Precursors: Comprehensive Branching Ratio Study
SAHAR GHADIMI, David Cocker, University of California, Riverside
Abstract Number: 256
Working Group: Aerosol Chemistry
Abstract
α-Pinene plays an important role in atmospheric pollution due to its high SOA yield and it’s global prevalence as the most abundant emitted monoterpene (C10H16) worldwide. α-Pinene undergoes photooxidation reactions to generate highly reactive RO2. species. Depending on atmospheric NOx levels (and specifically NO levels), these RO2. species undergo further reaction via two competing mechanistic pathways (HO2. or NO), the extent of which reaction occurs is referred to as the “branching ratio (β)”. Under low-NOx conditions, RO2. radicals tend to react more with HO2. radicals to yield gas-phase products with lower volatility leading to higher SOA formation. Contrary, under high-NOx conditions, RO2. radicals react with NO molecules resulting in the formation of the high volatile organic nitrates leading to lower SOA yields.
In this study, the correlation between SOA formation yield from α-Pinene precursor and β value was investigated in an atmospheric chamber. A series of experiments were designed using SAPRC modeling to oxidize α-pinene while maintaining constant β values throughout the experiment via continuous NO injection. The results will be compared to “classical” SOA yield experiments in which the NO and VOC was injected at the start of the experiment with β increasing throughout the experiment from near 1 to near 0. The outcomes of this novel study are critical for the development of more accurate atmospheric SOA models.