Amplified transboundary transport of haze by aerosol–boundary layer interaction in China

Although air quality in China has substantially improved since 2013 as a consequence of the clean air action, severe haze events still frequently strike megacities despite strict local emissions reduction efforts. Long-range transport and local accumulation as well as chemical transformation have been deemed as key factors of heavy haze pollution; however, the formation mechanisms of regional long-lasting haze and the physical and chemical connections between different megacities clusters are still poorly understood. Here we present that long-range transport and aerosol–boundary layer feedback may interact rather than act as two isolated processes as traditionally thought by investigating typical regional haze events in northern and eastern China. This interaction can then amplify transboundary air pollution transport over a distance of 1,000 km and boost long-lasting secondary haze from the North China Plain to the Yangtze River delta. Earlier emission reduction before the pollution episodes would provide better air pollution mitigation in both regions. Our results show an amplified transboundary transport of haze by aerosol–boundary layer interaction in China and suggest the importance of coordinated cross-regional emission reduction with a focus on radiatively active species like black carbon. Secondary air pollution events are enhanced in the Yangtze River delta, China, due to the interaction of long-range transport and aerosol–boundary layer feedback, according to a combination of observations and simulations of haze events from 2013 to 2018.