Abstract
Biogenic volatile organic compounds (BVOCs) play an important role in atmospheric ozone and aerosol formation. While BVOC emissions are influenced by a range of environmental stressors, field-based understanding of how environmental variability, particularly prolonged drought followed by rewetting, modulates ambient BVOC concentration in urban environments remains limited. With the projected increase in the frequency of drought events in future, investigating the effects of post-drought impacts on BVOC emissions become crucial, particularly in regions with poor air quality and non-compliance with air quality standards. In this study, we compare in-situ BVOC and oxidized VOC (OVOC) observations from two San Antonio Field Study (SAFS) campaigns conducted in the spring of 2017 and 2021. Initial analysis revealed substantial differences in ambient BVOC and OVOC concentrations between 2017 and 2021, while changes in anthropogenic VOCs were comparatively minor. This prompted further investigation into the environmental factors driving the observed variability in BVOCs and OVOCs. We found that the 2021 campaign coincided with a period of severe drought, followed by a substantial rainfall event early in the sampling period, conditions different than in 2017. This post-drought rewetting in 2021 led to pronounced enhancements in BVOC emissions, with isoprene and monoterpenes increasing by factors of 2 and 8.6, respectively, compared to the non-drought year. OVOCs also showed marked increases under these conditions, exemplified by a ∼14-fold rise in hydroxyacetone concentrations. In the post-drought rewetting scenario, the OH reactivity associated with BVOCs increased, particularly with monoterpenes, signifying its potential role in secondary organic aerosol formation and urban air quality.
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•VOCs and trace gases were measured in San Antonio during 2017 and 2021.•Sampling duration in 2017 and 2021 had contrasting drought and rainfall conditions.•Rewetting after drought led to sharp increases in BVOC and OVOC concentrations.•OH reactivity increased significantly in drought year due to enhanced BVOC and OVOC.