Xin Huang, Professor, Nanjing University
Aerosols in the atmosphere could perturb the energy balance of the Earth-atmosphere system, and hence influence regional or even global climate change. Our recent studies have highlighted the importance of aerosols on local and regional meteorological conditions, especially the evolution of the planetary boundary layer (PBL) and synoptic weather.
Based on model simulations and multiple observations, we found that the suspended aerosols could greatly reduce incoming solar radiation, decrease the surface heat flux, heat the atmosphere and stabilize the temperature stratification, thereby suppressing daytime PBL development and then enhancing haze pollution. Such positive feedback could be of great importance in both megacity and regional scales, especially in highly polluted regions like China. In such kind of aerosol‐PBL interaction, black carbon (BC) has been identified to play the key role in modifying the PBL meteorology. It is demonstrated that BC induces heating in the PBL, particularly in the upper PBL, and the resulting decreased surface heat flux substantially depresses the development of PBL and consequently enhances the occurrences of extreme haze pollution episodes. In addition, comparison between long-term radiosonde observations and reanalysis data also confirmed the meteorological feedback. Statistically, under polluted conditions, a significant heating in upper-PBL with a maximum temperature change of about 0.7 °C and a substantial dimming near the surface with a mean temperature drop of -2.2 °C in Beijing.
Furthermore, on a regional scale, aerosol‐PBL interactions also amplified transboundary haze pollution across eastern China. Severe haze events frequently strike many megacities in China despite strict local emissions reduction efforts in winter. We find that long-range transport and aerosol-PBL feedback may interact with each other rather than act as two isolated processes as traditionally thought by investigating typical regional haze events in 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-PBL interaction in China and suggest the importance of coordinated cross-regional emission reduction with a focus on radiatively active species like black carbon.