A study of the effect of aerosols on surface ozone through meteorology feedbacks over China

摘要

Interactions between aerosols and gases in the atmosphere have been the focus of an increasing number of studies in recent years. Here, we focus onaerosol effects on tropospheric ozone that involve meteorological feedbacks induced by aerosol–radiation interactions. Specifically, we study theeffects that involve aerosol influences on the transport of gaseous pollutants and on atmospheric moisture, both of which can impact ozonechemistry. For this purpose, we use the UK Earth System Model (UKESM1), with which we performed sensitivity simulations including and excluding theaerosol direct radiative effect (ADE) on atmospheric chemistry, and focused our analysis on an area with a high aerosol presence, namely China. Bycomparing the simulations, we found that ADE reduced shortwave radiation by 11 % in China and consequently led to lower turbulent kineticenergy, weaker horizontal winds and a shallower boundary layer (with a maximum of 102.28 m reduction in north China). On the one hand, thesuppressed boundary layer limited the export and diffusion of pollutants and increased the concentration of CO, SO2, NO,NO2, PM2.5 and PM10 in the aerosol-rich regions. The NO/NO2 ratio generally increased and led to more ozonedepletion. On the other hand, the boundary layer top acted as a barrier that trapped moisture at lower altitudes and reduced the moisture at higheraltitudes (the specific humidity was reduced by 1.69 % at 1493 m on average in China). Due to reduced water vapour, fewer clouds wereformed and more sunlight reached the surface, so the photolytical production of ozone increased. Under the combined effect of the two meteorologyfeedback methods, the annual average ozone concentration in China declined by 2.01 ppb (6.2 %), which was found to bring the model intocloser agreement with surface ozone measurements from different parts of China.