Impacts of Heatwaves on Characteristics of Atmospheric Methylglyoxal in a Suburban Area in Eastern China

Methylglyoxal (Mgly) is a ubiquitous yet poorly constrained atmospheric volatile organic compound significantly contributing to the formation of ozone and secondary organic aerosols. Global warming increases heatwaves frequency, affecting sources and sinks of Mgly. Thus, studies on Mgly observations during heatwaves become increasingly urgent. Here, we combined field measurements using Vocus proton transfer reaction time-of-flight mass spectrometry (Vocus PTR-ToF-MS), box model, and the Weather Research and Forecasting model with Chemistry (WRF-Chem) to investigate the impacts of heatwaves on Mgly at a suburban site in eastern China during a prolonged heatwave influenced summer in 2022. After verifying that Vocus PTR-ToF-MS accurately detects Mgly and eliminating ion fragmentation artifacts of isoprene, we discovered that the heatwave doubled Mgly concentrations. This was attributed to a significant rise of isoprene—the dominant precursor of Mgly as confirmed by box modeling. The heatwave also altered photolysis and oxidation of Mgly and emission characteristics of isoprene, leading to an earlier peak and then a sudden drop of Mgly in the morning. This was different from the consistent peaks with air temperatures observed during non-heatwave period. The concentrations of Mgly and isoprene showed positive correlations with air temperatures below 33°C, whereas both species' concentrations decline as temperatures exceeded 35°C. Additionally, WRF-Chem underestimated isoprene and slightly overestimated Mgly. It could not capture the trends of Mgly and the discrepancies between model and measurements exacerbated when heatwave occurred. This study highlights the significant impact of heatwaves on Mgly and provides a benchmark for future model optimization.