A near-explicit mechanistic evaluation of Isoprene photochemical seecondary organic aerosol formation and evolution: simulations of multiple chamber experiments with and without added NOx

Journal Article · Thu Jul 16 00:00:00 EDT 2020 · ACS Earth and Space Chemistry

DOI:https://doi.org/10.1021/acsearthspacechem.0c00118· OSTI ID:1657208

Thornton, Joel A. ^[1]; Shilling, John E. ^[2]; Shrivastava, ManishKumar B.  ^[2]; D'Ambro, Emma ^[1]; Zawadowicz, Maria A. ^[2]; Liu, Jiumeng  ^[2]

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1. University of Washington
2. BATTELLE (PACIFIC NW LAB)

Experimentally determined yields of secondary organic aerosol (SOA) from the photochemical oxidation of isoprene in the absence of aqueous acidic aerosol vary substantially, both within a given experiment and across different environmental chamber conditions. The underlying mechanisms driving this variation remain poorly evaluated, leading to significant uncertainty in how to extrapolate laboratory chamber results to the atmosphere. Herein, we compare SOA predictions from a near-explicit gas-phase chemical mechanism of isoprene oxidation by the hydroxyl radical (OH) in the presence and absence of nitrogen oxide radicals (NOx), to multiple chamber experiments on non-aqueous isoprene photochemical SOA (ipSOA) conducted by different groups in different chambers. SOA is predicted by volatility-driven gas-particle partitioning of hundreds of individual reaction products. The mechanism includes simplified descriptions of particle-phase organic chemistry, including organic hydroperoxide photolysis, and organic nitrate hydrolysis and accretion reactions. The model has good skill (mean normalized bias typically within 25%) at predicting the observed formation and evolution of ipSOA across a range of chambers and conditions at low NOx. The model has much less skill at describing the observed non-linear response of ipSOA to elevated NOx. Organic nitrate hydrolysis is unable to explain significant ipSOA at high NOx, whereas particle-phase accretion reactions of tertiary nitrates may play a role. Uncertainties in the chamber radical environment and fate of key organic peroxy radicals (RO2) remain as or even more important than vapor losses to chamber walls in determining how best to extrapolate chamber-based yields to the atmosphere. Implications for likely atmospheric yields of ipSOA and recommendations for future chamber experiments are discussed.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1657208
• Report Number(s): PNNL-SA-153144
• Journal Information: ACS Earth and Space Chemistry, Vol. 4, Issue 7
• Country of Publication: United States
• Language: English