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

• Main Authors: D. C. Anderson, J. Pavelec, C. Daube, S. C. Herndon, W. B. Knighton, B. M. Lerner, J. R. Roscioli, T. I. Yacovitch, E. C. Wood
• Format: Article
• Language: English
• Published: Copernicus Publications 2019-03-01
• Series: Atmospheric Chemistry and Physics
• Online Access: https://www.atmos-chem-phys.net/19/2845/2019/acp-19-2845-2019.pdf

<p>Observations of total peroxy radical concentrations ([<span class="inline-formula"><i>X</i>O₂</span>]&thinsp;<span class="inline-formula">≡</span>&thinsp;[<span class="inline-formula">RO₂</span>]&thinsp;<span class="inline-formula">+</span>&thinsp;[<span class="inline-formula">HO₂</span>]) 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 [<span class="inline-formula">O₃</span>] was 48&thinsp;ppbv at the site downwind of central San Antonio. Higher concentrations of NO and <span class="inline-formula"><i>X</i>O₂</span> at the downwind site also led to median daytime ozone production rates <span class="inline-formula">(<i>P</i>(O₃))</span> of 4.2&thinsp;ppbv&thinsp;h<span class="inline-formula">⁻¹</span>, a factor of 2 higher than at the two upwind sites. The 95th percentile of <span class="inline-formula"><i>P</i>(O₃)</span> at the upwind site was 15.1&thinsp;ppbv&thinsp;h<span class="inline-formula">⁻¹</span>, significantly lower than values observed in Houston. In situ observations, as well as satellite retrievals of HCHO and <span class="inline-formula">NO₂</span>, suggest that the region was predominantly <span class="inline-formula">NO_<i>x</i></span>-limited. Only approximately 20&thinsp;% of observations were in the VOC-limited regime, predominantly before 11:00&thinsp;EST, when ozone production was low. Biogenic volatile organic compounds (VOCs) comprised 55&thinsp;% of total OH reactivity at the downwind site, with alkanes and non-biogenic alkenes responsible for less than 10&thinsp;% 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 <span class="inline-formula">NO_<i>x</i></span> emissions. Observations in the urban center of San Antonio are needed to determine whether this policy is true for the entire region.</p>