Heat and continental transport shape the variability of volatile organic compounds in the Eastern Mediterranean: insights from multi-year observations and regional modeling

Abstract

Volatile organic compounds (VOCs) are key precursors of tropospheric ozone and secondary organic aerosol formation, yet multi-year observations in the Eastern Mediterranean and Middle East (EMME) remain limited. This study presents multi-year (April 2022–June 2024) high-resolution measurements of 76 VOCs using PTR-ToF-MS at a rural background site in Cyprus, combined with HYSPLIT air-mass analysis to examine the effects of regional transport on VOCs variability. Oxygenated VOCs (OVOCs) dominated the VOCs burden (∼ 79 %), followed by aliphatic hydrocarbons, aromatic hydrocarbons, and terpenes. Most VOCs exhibited clear diurnal patterns, observed highest during 08:00–14:00 UTC, varying by species, due to enhanced photochemical activity and temperature-driven emissions. Terpenes, particularly isoprene, increased exponentially with temperature upto 35–38 °C but decreased beyond this threshold, indicating heat-stress inhibition. Monoterpenes showed elevated levels both day and night, reflecting contributions from both biogenic and anthropogenic sources. OVOCs, including acetone, acetaldehyde, methanol, and acetic acid, showed sharp enhancement above 35 °C, consistent with intensified primary emissions and secondary formation under extreme heat. Aromatic hydrocarbons were mainly higher during winter, linked to combustion processes, but benzene levels were highest during summer particularly when temperature rose above 35 °C from evaporative and potential stress-related biogenic sources. HYSPLIT air-mass trajectory analysis revealed dominant contributions from Europe and Northwest Asia (∼ 68 %), transporting aged OVOCs, while Middle East winter inflows enhanced aromatic hydrocarbons. While WRF-Chem captured seasonal trends, most VOCs were underestimated, highlighting under-representation of emission sources and oxidation pathways in the model. Overall, the study emphasizes temperature and regional transport as key drivers of VOC variability in the Eastern Mediterranean.