Characterization of ozone production in San Antonio, Texas, using measurements of total peroxy radicals

Anderson, Daniel C.; Pavelec, Jessica; Daube, Conner; Herndon, Scott C.; Knighton, Walter B.; Lerner, Brian M.; Roscioli, J. Robert; Yacovitch, Tara I.; Wood, Ezra C.

Observations of total peroxy radical concentrations ([inline-formulaXO2] inline-formula≡ [inline-formulaRO2] inline-formula+ [inline-formulaHO2]) made by the Ethane CHemical AMPlifier (ECHAMP) and concomitant observations of additional trace gases made on board the Aerodyne Mobile Laboratory (AML) during May 2017 were used to characterize ozone production at three sites in the San Antonio, Texas, region. Median daytime [inline-formulaO3] was 48 ppbv at the site downwind of central San Antonio. Higher concentrations of NO and inline-formulaXO2 at the downwind site also led to median daytime ozone production rates inline-formula(P(O3)) of 4.2 ppbv hinline-formula−1, a factor of 2 higher than at the two upwind sites. The 95th percentile of inline-formulaP(O3) at the upwind site was 15.1 ppbv hinline-formula−1, significantly lower than values observed in Houston. In situ observations, as well as satellite retrievals of HCHO and inline-formulaNO2, suggest that the region was predominantly inline-formulaNOx-limited. Only approximately 20 % of observations were in the VOC-limited regime, predominantly before 11:00 EST, when ozone production was low. Biogenic volatile organic compounds (VOCs) comprised 55 % of total OH reactivity at the downwind site, with alkanes and non-biogenic alkenes responsible for less than 10 % of total OH reactivity in the afternoon, when ozone production was highest. To control ozone formation rates at the three study sites effectively, policy efforts should be directed at reducing inline-formulaNOx emissions. Observations in the urban center of San Antonio are needed to determine whether this policy is true for the entire region.

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Anderson, Daniel C. / Pavelec, Jessica / Daube, Conner / et al: Characterization of ozone production in San Antonio, Texas, using measurements of total peroxy radicals. 2019. Copernicus Publications.

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