Modeling of a severe dust event and its impacts on ozone photochemistry over the downstream Nanjing megacity of eastern China

Dust aerosols could affect tropospheric photochemistry by interacting with solar radiation or providing reactive surfaces for heterogeneous reactions. This study examines the effects of a typical springtime dust storm (16-18 March, 2014) on ozone photochemistry over the downstream Nanjing megacity in eastern China. The on-line coupled Weather Research and Forecasting-Chemistry (WRF-Chem) model is used, with the inclusion of eight heterogeneous reactions on dust surfaces. Comparisons with satellite data and visibility record indicate that the model is capable of reproducing the onset time and downstream transport of this dust event. Dust particles act as a sink for all these trace gases examined here. The net decreases of O3, NO2, NO3, N2O5, HNO3, OH, HO2 and H2O2 in the atmosphere are estimated as −6.1%, −16.0%, −37.4%, −13.9%, −47.7%, −6.0%, −9.2% and −29.7%, of which more than 80% can be explained by heterogeneous chemistry on dust surfaces. The decreases in ground photolysis rate and OH concentration, along with changes in other weather variables induced by dust aerosols (i.e., radiation and temperature) lead to lower photochemical activity and a small decrease of O3 mixing ratio by roughly 0.5%. This study highlights the importance of dust interaction with ozone photochemistry, and also sets the stage for further investigation of the complicated dust impacts on tropospheric aerosol chemistry.