Evidence for significant particulate organic nitrate formation in the Los Angeles Basin at night
Abstract
Oxidn. of biogenic volatile org. compds. (BVOCs) by the nitrate radical (NO₃) represents a potentially efficient secondary org. aerosol (SOA) formation pathway. However, the contribution of nighttime NO₃-BVOC chem. to urban OA prodn. remains poorly constrained. Here, we present measurements of submicrometer aerosol compn. obtained at Caltech (Pasadena, CA) with an Aerodyne HR-ToF-AMS in May-June 2020. At night (19:00-6:00), a majority (>70%) of AMS-derived aerosol nitrate is org., and particulate org. nitrates (pONs) constitute up to 20-30% of total AMS-derived OA. Notably, clear increases in pON mass loadings are obsd. after sunset that correlate strongly with the prodn. rate of NO₃. The mass spectral signature of a pON-assocd. org. aerosol factor extd. using pos. matrix factorization (PMF) is compared to lab. SOA formed from NO₃ oxidn. of individual monoterpenes to aid source identification. Box model simulations reproduce obsd. overnight pON formation using reasonable SOA yields from NO₃ oxidn. of monoterpenes (~40%). Comparison to data collected in 2010 suggests that a major shift in the dominant nighttime nitrate aerosol formation pathway has occurred in the last decade. The observation of substantial NO₃-derived pON prodn. highlights the increasing importance of biogenic emissions to urban aerosol loadings and NO_x loss processes.
Additional Information
© 2021 American Chemical Society.Additional details
- Eprint ID
- 112462
- Resolver ID
- CaltechAUTHORS:20211215-163227176
- Created
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2021-12-15Created from EPrint's datestamp field
- Updated
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2021-12-15Created from EPrint's last_modified field
- Caltech groups
- Division of Geological and Planetary Sciences