High concentrations of organic aerosol (OA) often occur in Asian countries, leading to great health burdens. The severity and frequency of heatwaves are expected to rise with climate change. However, little is known about the heatwave impacts on OA formation. Here we deployed a long time-of-flight aerosol mass spectrometer (LTOF-AMS) to measure the real-time chemical composition of submicron aerosols in urban Beijing during summer of 2023 along with advanced chemical ionization mass spectrometers to detect gaseous and particulate oxidation products. During the heatwave episode, SOA, ozone, and sulfate concentrations increased by 21%, 75%, and 41%, respectively, compared to the non-heatwave episode with similar air mass origin, indicating significantly enhanced secondary formation. We further applied machine learning methods to identify the key drivers of the SOA enhancement during the heatwave episode. Our results suggest that the SOA enhancement during the heatwave episode will be increasingly important in the future. 

SOA