Characterization of Ozone Production in San Antonio, Texas Using Observations of Total Peroxy Radicals

Abstract

9Observations of total peroxy radicals (XO2  RO2 + HO2) made by the Ethane CHemical 10 AMPlifier (ECHAMP) and concomitant observations of additional trace gases made onboard the 11 Aerodyne Mobile Laboratory (AML) during May 2017 were used to characterize ozone production at 12 three sites in the San Antonio, Texas region. Median daytime [O3] was 48 ppbv at the site downwind of 13 central San Antonio. Higher concentrations of NO and XO2 at the downwind site also led to median 14 daytime ozone production rates (P(O3)) of 4.2 ppbv hr −1 , a factor of two higher than at the two upwind 15 sites. The 95 th percentile of P(O3) at the upwind site was 15.1 ppbv hr −1 , significantly lower than values 16 observed in Houston. In situ observations, as well as satellite retrievals of HCHO and NO2, suggest that 17 the region is NOX limited for times after approximately 9:00 local time, before which ozone production is 18 VOC-limited. Biogenic volatile organic compounds (VOC) comprised 55% of total OH reactivity at the 19 downwind site, with alkanes and non-biogenic alkenes responsible for less than 10% of total OH 20 reactivity in the afternoon, when ozone production was highest. To control ozone formation rates at the 21 three study sites effectively, policy efforts should be directed at reducing NOX emissions. Observations in 22 the urban center of San Antonio are needed to determine whether this policy is true for the entire region. 23Atmos. Chem. Phys. Discuss., https://doi.radicals from three sites in the San Antonio area, characterizing the XO2 (XO2  RO2 + HO2) 91 distribution in the region. We use these XO2 measurements, along with observations of NO and 92 other trace gas species, to quantify ozone production in regions up-and downwind of the urban 93 core. Though there have been many prior determinations of P(O3) using measurements of a 94 subset of peroxy radicals (i.e., using laser-induced fluorescence measurements of HO2 and a 95 fraction of RO2) (e.g. Ren et al., 2013), this is one of the few determinations of ozone production 96 using the direct observation of total peroxy radicals (Sommariva et al., 2011). Combined with 97 quantification of the primary production of ROX radicals (P(ROX)) and satellite retrievals of 98 HCHO and NO2, we determine the ozone production regime in San Antonio. Finally, we explore 99 the main contributors to OH reactivity in the region. 100 2.Methodology 101 2.

Peroxy Radical Measurements by Ethane – Nitric Oxide Chemical Amplification and Laser-Induced Fluorescence/Fluorescence Assay by Gas Expansion during the IRRONIC field campaign in a Forest in Indiana

“…Although the calibration comparison was favorable, due to the time required to conduct successful calibrations with the acetone photolysis method and its overall inconvenience (Wood and Charest, 2014) we have discontinued its use. For subsequent field measurements we have used the water vapor photolysis method and another method based on methyl iodide photolysis (Anderson et al, 2018;Clemitshaw et al, 1997;Liu and Zhang, 2014). All three calibration methods do indicate that a humidity-dependent calibration must be used for both CObased and ethane-based chemical amplifiers.…”

“…compounds (VOCs), photolysis of oxygenated VOCs, and decomposition of peroxyacetylnitrate (PAN) (Atkinson, 2000). VOCs, and secondary aerosol particles (Kroll and Seinfeld, 2008;Ng et al, 2008;Atkinson and Arey, 2003;Akimoto, 2016;Claeys et al, 2004). The chemical identity and concentrations of peroxy radicals can provide important information on atmospheric oxidation processes such as ozone production, the removal efficiency of primary pollutants, and radical budgets.…”

Improved Chemical Amplification Instrument by Using a Nafion Dryer as an Amplification Reactor for Quantifying Atmospheric Peroxy Radicals under Ambient Conditions

“…5,17 The mechanisms for the formation of peroxy radicals are not the part of this work; however, the diel results show clear nocturnal production. 31,32 Understanding the oxidation chemistry in the daylight as well as in the night time will improve the understanding of the roles of nature and anthropogenic emission precursors in severe ozone pollution, 33 especially in the PRD region where photochemistry is active. 34 For most ambient conditions, the RH of the sample was smaller than 90%.…”