Novel Analysis to Quantify Plume Crosswind Heterogeneity Applied to Biomass...

Decker, Z., S. Wang, I. Bourgeois, Campuzano Jost, M. Coggon, J. P. DiGangi, G. S. Diskin, F. Flocke, A. Franchin, C. Fredrickson, G. Gkatzelis, S. R. Hall, H. Halliday, K. Hayden, C. D. Holmes, L. G. Huey, J. Jimenez-Palacios, Y. R. Lee, J. Lindaas, A. Middlebrook, D. D. Montzka, J. A. Neuman, J. B. Nowak, D. Pagonis, B. B. Palm, J. Peischl, F. Piel, P. Rickly, M. Robinson, A. Rollins, T. B. Ryerson, K. Sekimoto, J. Thornton, G. Tyndall, K. Ullmann, P. Veres, C. Warneke, R. Washenfelder, A. Weinheimer, A. Wisthaler, C. Womack, and S. S. Brown (2021), Novel Analysis to Quantify Plume Crosswind Heterogeneity Applied to Biomass Burning Smoke, Environ. Sci. Technol., 55, 15646-15657, doi:10.1021/acs.est.1c03803.

We present a novel method, the Gaussian observational model for edge to center heterogeneity (GOMECH), to quantify the horizontal chemical structure of plumes. GOMECH fits observations of short-lived emissions or products against a long-lived tracer (e.g., CO) to provide relative metrics for the plume width (wi/wCO) and center (bi/wCO). To validate GOMECH, we investigate OH and NO3 oxidation processes in smoke plumes sampled during FIREX-AQ (Fire Influence on Regional to Global Environments and Air Quality, a 2019 wildfire smoke study). An analysis of 430 crosswind transects demonstrates that nitrous acid (HONO), a primary source of OH, is narrower than CO (wHONO/wCO = 0.73−0.84 ± 0.01) and maleic anhydride (an OH oxidation product) is enhanced on plume edges (wmaleicanhydride/wCO = 1.06−1.12 ± 0.01). By contrast, NO3 production [P(NO3)] occurs mainly at the plume center (wP(NO3)/wCO = 0.91−1.00 ± 0.01). Phenolic emissions, highly reactive to OH and NO3, are narrower than CO (wphenol/wCO = 0.96 ± 0.03, wcatechol/wCO = 0.91 ± 0.01, and wmethylcatechol/wCO = 0.84 ± 0.01), suggesting that plume edge phenolic losses are the greatest. Yet, nitrophenolic aerosol, their oxidation product, is the greatest at the plume center (wnitrophenolicaerosol/wCO = 0.95 ± 0.02). In a large plume case study, GOMECH suggests that nitrocatechol aerosol is most associated with P(NO3). Last, we corroborate GOMECH with a large eddy simulation model which suggests most (55%) of nitrocatechol is produced through NO3 in our case study.

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Tropospheric Composition Program (TCP)