Biogenic emissions-related ozone enhancement in two major city clusters during a typical typhoon process

Typhoons could influence air quality via multiple chemical and physical process and has attracted much scientific attention. A typical typhoon, In-Fa, passed through Yangtze River Delta (YRD) and Jing-Jin-Ji (JJJ) after it made a landfall in China. Under such influences, two city clusters both experienced high ozone (O₃) concentrations, with JJJ about 5 days earlier than YRD. Data from several environmental monitoring sites indicated that cross-regional transport and biogenic emissions both played an important role in O₃ formation. During the typhoon process, O₃ precursors were first transported from YRD and its surrounding areas to JJJ due to the summer monsoon. After that, air masses from northern China returned to YRD due to the peripheral winds of typhoon. High O₃ was concentrated in downwind regions, causing fast secondary formation. The peripheral winds and downdrafts of typhoon led to high temperature and stagnant weather, favorable for biogenic emissions. The modeling results showed the contribution of BVOCs to O₃ could reach 10 ppb in JJJ when the typhoon made its landfall in YRD. When the typhoon moved to JJJ, the cross-transport of air masses from northern China to YRD contributed half of biogenic-emission-related O₃. Our research extends the knowledge into the importance of biogenic emissions to O₃ and cross-regional transport during a typhoon process.