The impact of aerosol-meteorology feedback on the effectiveness of emission reduction for PM2.5: A modeling case study in Northern China

The quantification of the effectiveness of anthropogenic emission control measures is crucial for future air quality policies. Meteorology plays a vital role in haze pollution, and the interactions between aerosol and meteorology have been widely studied. However, it is not fully clear how aerosol-meteorology feedback affects the effectiveness of emission reduction for PM2.5, which limits our ability of optimizing anti-pollution policies. Here, with the two-way atmospheric chemical transport model WRF-Chem, the effects of aerosol-meteorology feedback on the effectiveness of emission reduction for PM2.5 during a winter severe haze event in 2016 over the Northern China Plain (NCP) are studied. In the more polluted area of NCP (MP_NCP) during the daytime, 20% emission reduction over NCP increases near-surface downward shortwave radiation by 4.62 W/m2, 2 m temperature by 0.08 degrees C, boundary layer height by 7.19 m and reduces 2 m relative humidity by 0.31% and thereby alleviates worsened meteorological conditions caused by aerosol effect. As a result, in MP_NCP, 20% emission reduction without aerosol-meteorology feedback leads to a decrease of 40.49 & mu;g/m3 of near-surface PM2.5 and the above meteorological changes decrease near-surface PM2.5 concentration by 7.82 & mu;g/m3, indicating that aerosol-meteorology feedback strengthens the effectiveness of emission reduction by 19%. In the less polluted area (LP_NCP), aerosol effect induced meteorological changes decrease PM2.5 concentration by 7.57 & mu;g/m3 and 20% emission reduction without aerosol-meteorology feedback leads to a decrease of 13.15 & mu;g/m3 in near-surface PM2.5. This reveals a remarkable enhancement of 58% in the effectiveness of emission reduction, which is much larger than that in MP_NCP. Such difference can be attributed to the presence of more clouds in LP_NCP, where the decrease in liquid water path, along with the increase in the planetary boundary layer height, jointly contributes to the PM2.5 decrease. Moreover, the effect of aerosol-meteorology feedback on the effectiveness of emission reduction for PM2.5 is nonlinear. With increasing PM2.5 concentration, the aerosol-meteorology feed-back induced PM2.5 reduction first increases and then stabilizes once the PM2.5 concentration exceeds 350 & mu;g m-3. This study can provide reference for air pollution control strategies.

Automated summary

This study investigates the effects of aerosol-meteorology feedback on the effectiveness of emission reduction for PM2.5 during a severe winter haze event in the Northern China Plain in 2016. The results show that the feedback can enhance the efficiency of emission reduction, especially in more polluted areas, where emission reduction can decrease near-surface PM2.5 concentration and improve meteorological conditions. This study provides reference for air pollution control strategies.