Effects of Warm and Dry Conditions on Ozone Deposition and Biogenic VOC Emissions in the Eastern Mediterranean

Climate change is expected to significantly alter 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 enhance biogenic volatile organic compound (BVOC) emissions and surface ozone (O₃) concentrations, while simultaneously suppressing dry ozone deposition via 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 by synthesizing results from multiple field campaigns conducted between 2013 and 2023 in the eastern Mediterranean. Using eddy covariance and branch-level enclosure measurements, we quantified fluxes and mixing ratios of O₃, VOCs (dominated by BVOCs and measured using PTR-ToF-MS), and nitrogen oxides (NOₓ) across forested, urban, and coastal environments.

Our observations show that under very dry conditions (RH < 30%), the occurrence of positive (upward) O₃ fluxes increases, while the downward ozone deposition velocity increases logarithmically with RH in both urban and rural settings, driven by enhanced surface evaporation and dry air intrusion events from the upper troposphere¹,². Canopy- and branch-level measurements further reveal that under severe drought, instantaneous intraday variations in meteorological parameters serve as better proxies for BVOC emission rates than absolute meteorological values³,⁴. Additional coastal observations indicate substantial marine contributions to isoprene mixing ratios inland, consistent with recent increases in sea surface temperature in the Levantine Basin ⁵.

Collectively, these results point toward enhanced ozone formation and reduced surface removal under future warmer and drier climates, while providing new insights into the modeling of dry ozone deposition and BVOC emissions under warm and dry conditions.

 

 

 

References

1. Choi, D. et al., Sci. Total Environ., 2025. https://doi.org/10.1016/j.scitotenv.2025.180347

2. Li, Q. et al., Sci. Total Environ., 2019. https://doi.org/10.1016/j.scitotenv.2018.12.272

3. Li, Q. et al., Biogeosciences, 2024. https://doi.org/10.5194/bg-21-4133-2024, 2024

4. Li, Q. et al., Sci. Total Environ., 2025. https://doi.org/10.1016/j.scitotenv.2025.180423

5. Dayan, Chen, et al., Atmos. Chem. Phys.,2020. https://doi.org/10.5194/acp-20-12741-2020