Department of Environmental Sciences , University of Virginia , Charlottesville , Virginia 22904 , United States.
Department of Earth and Environment , Boston University , Boston , Massachusetts 02215 , United States.
Environ Sci Technol. 2019 May 7;53(9):4695-4706. doi: 10.1021/acs.est.8b04852. Epub 2019 Apr 10.
Drought conditions affect ozone air quality, potentially altering multiple terms in the O mass balance equation. Here, we present a multiyear observational analysis using data collected before, during, and after the record-breaking California drought (2011-2015) at the O-polluted locations of Fresno and Bakersfield near the Sierra Nevada foothills. We separately assess drought influences on O chemical production ( PO) from O concentration. We show that isoprene concentrations, which are a source of O-forming organic reactivity, were relatively insensitive to early drought conditions but decreased by more than 50% during the most severe drought years (2014-2015), with recovery a function of location. We find drought-isoprene effects are temperature-dependent, even after accounting for changes in leaf area, consistent with laboratory studies but not previously observed at landscape scales with atmospheric observations. Drought-driven decreases in organic reactivity are contemporaneous with a change in dominant oxidation mechanism, with PO becoming more NO -suppressed, leading to a decrease in PO of ∼20%. We infer reductions in atmospheric O loss of ∼15% during the most severe drought period, consistent with past observations of decreases in O uptake by plants. We consider drought-related trends in O variability on synoptic time scales by analyzing statistics of multiday high-O events. We discuss implications for regulating O air pollution in California and other locations under more prevalent drought conditions.
干旱条件会影响臭氧空气质量，可能会改变 O 质量平衡方程中的多个项。在这里，我们利用在加利福尼亚创纪录干旱（2011-2015 年）之前、期间和之后在内华达山麓丘陵附近弗雷斯诺和贝克斯菲尔德的 O 污染地点收集的数据，进行了多年的观测分析。我们分别评估了干旱对 O 化学产生（PO）的影响，从 O 浓度的角度来看。我们表明，异戊二烯浓度（一种形成 O 的有机反应性来源）对早期干旱条件相对不敏感，但在最严重的干旱年份（2014-2015 年）下降了 50%以上，恢复情况取决于地点。我们发现干旱-异戊二烯效应与温度有关，即使在考虑叶面积变化之后也是如此，这与实验室研究一致，但以前在大气观测的景观尺度上没有观察到。有机反应性的干旱驱动下降与主导氧化机制的变化同时发生，PO 变得更加受 NO 抑制，导致 PO 减少约 20%。我们推断，在最严重的干旱期间，大气 O 损失减少了约 15%，这与过去观察到的植物对 O 吸收减少的情况一致。我们通过分析多日高 O 事件的统计数据来研究干旱对天气尺度 O 变异性的相关趋势。我们讨论了在加利福尼亚和其他干旱条件更为普遍的地区调控 O 空气污染的意义。
