Climate change is expected to significantly alter atmospheric photochemical activity through its impact on biosphere–atmosphere gas exchange. In particular, higher air temperatures and lower relative humidity (RH) over land are projected to increase biogenic volatile organic compound (BVOC) emissions and surface ozone (O₃) concentrations while simultaneously suppressing dry ozone deposition through both stomatal and non-stomatal pathways.
This study investigates the effects of warm and dry conditions on dry ozone deposition and BVOC emissions from terrestrial vegetation using observations from multiple field campaigns conducted between 2013 and 2023 in the eastern Mediterranean. Measurements were conducted across a sharp climatic gradient in Israel and at an urban site in Beijing. Using eddy covariance and branch-level enclosure techniques, we quantified fluxes and mixing ratios of O₃, BVOCs, and nitrogen oxides (NOₓ) across forested, urban, and coastal environments.
Our observations show that downward ozone deposition velocity decreases logarithmically with decreasing relative humidity under dry conditions (RH < 30%) in both urban and rural settings, a response associated with increased surface evaporation and episodes of dry-air intrusion from the upper troposphere. Both canopy- and branch-level measurements further reveal that short-term (intraday) changes in meteorological conditions are better proxies for drought-related changes in BVOC emission rates than the corresponding absolute values, with relative humidity emerging as the dominant controlling factor. Additional coastal observations indicate substantial marine contributions to inland isoprene mixing ratios, while increases in sea surface temperatures have been reported in the Levantine Basin.
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