Impact of heatwaves on sources and transformations of ambient volatile organic compounds

Abstract. Heatwaves are increasingly frequent, intense, and prolonged under climate change, affecting atmospheric chemistry and secondary air pollution. Volatile organic compounds (VOCs) are key precursors of ozone (O₃) and secondary organic aerosol (SOA), yet the impacts of heatwaves on VOC-related processes remain not fully integrated. This review synthesizes advances in heatwave impacts on VOC emissions, source contributions, transformation, and secondary pollution. Based on 287 publications (~67% from 2020–2026), observations show that heatwaves increase total ambient VOCs, but dominant compounds vary by city and reflect local emissions. Temperature-sensitive anthropogenic sources (solvent use, volatile chemical products, fuel storage, vehicle evaporation) increase strongly, whereas combustion sources are less temperature-dependent. Biogenic VOC emissions, especially isoprene and monoterpenes, respond nonlinearly to temperature and are modulated by plant physiology, water stress, and species-specific storage/synthesis. Heatwaves also enhance atmospheric oxidation through increased photolysis and radical production, altering VOC oxidation, radical cycling, O₃ formation regimes, and gas-particle partitioning. Enhanced emissions and oxidation can promote O₃ and SOA formation, but net responses depend on VOC-NO_x sensitivity, peroxyacetyl nitrate (PAN) chemistry, product volatility, partitioning, reactive uptake, and particle-phase diffusion. Observations, experiments, emission parameterizations, source apportionment, inverse modeling, and chemical transport models provide complementary evidence, but uncertainties remain in temperature-dependent emissions, semi-volatile/intermediate-volatility organic compounds (S/IVOCs) oxidation, multiphase chemistry, and observational constraints. Future research should integrate high-resolution measurements, source apportionment, inverse modeling, and process-based models across heatwave events to quantify source-specific temperature responses and improve predictions of VOC-driven secondary pollution.