The effect of meteorological conditions during drought on BVOC mixing ratios over an Eastern Mediterranean Forest

Biogenic volatile organic compounds (BVOCs) influence photochemical air pollution and climate change, with emissions strongly affected by meteorological conditions. However, the impact of drought on BVOC emissions remains poorly characterized, limiting the predictive power of this feedback on climate change and air quality. This study hypothesized that under severe drought, instantaneous intraday variations in meteorological parameters serve as a better proxy for BVOC emission rates at the forest scale than absolute meteorological values. To test this hypothesis, we employed proton transfer reaction time-of-flight mass spectrometry to quantify the mixing ratios of a suite of soluble and insoluble VOCs under severe drought conditions in a natural Eastern Mediterranean forest in autumn 2016. To assess processes other than emissions from the forest on observed mixing ratios, we applied planetary boundary layer height (PBLH) simulations using the Weather Research and Forecasting (WRF) model, chemical kinetic calculations, and short-lived species analysis, accounting for variations in mixing height, VOC oxidation, and transport out of the fetch, respectively. Under prolonged drought conditions, instantaneous changes in temperature (∆T∆t) and particularly in relative humidity (∆RH∆t) correlated more strongly with BVOC mixing ratios than absolute meteorological values and PBLH. On a daily scale, ∆T∆t and particularly ∆RH∆t correlated significantly (p < 0.01) with the vast majority of the investigated BVOCs mixing ratios. However, unsegmented daytime analysis revealed weak correlation between BVOCs mixing ratios and meteorological parameters, including temperature, relative humidity, and solar radiation. These findings highlight the importance of analyzing meteorological effects on BVOC emissions under drought at daily-or shorter-timescales.