Satellite-based separation of climatic and surface influences on global aerosol change

Both climatic and surface factors affect aerosol change. It is crucial to separate these influences for environment management and air pollution controlling. Though numerous models have been applied to assess contributions of climatic and surface influences, the results were great controversy because of the models' avoidable uncertainties from initial conditions, model error, and prediction scenarios. Here, we separate the contribution of climatic and surface influences on global aerosol change through satellite observations and statistical methods. Satellite and ground observation data sets of global aerosol, climatic (precipitation, windspeed, temperature, and relative humidity) and surface (land cover and terrain) factors are collected for the investigation. Methodologically, a multilinear regression (MLR) model is first built to simulate the theoretical influence of climatic factors under conditions with a fixed surface influence. Then, the actual surface influence is estimated by measuring the residual trend between observed and MLR-simulated results. Our results show that global aerosol was reduced in the past decade (2001-2016), represented by a temporal trend of -0.00105 a(-1) in the aerosol optical depth (AOD). Both climatic and surface factors tend to enhance the reduction of global aerosol. Specifically, the climatic and surface influences are -0.00041 a(-1) and 0.00064 a(-1), which contribute 39.05% and 60.95% of global aerosol reduction, respectively. Spatially, surface influence is more heterogeneous compared to climatic influence due to the spatial variability of surface properties. Meanwhile, the interaction of climatic and surface factors plays a significant effect on the magnitude and sign of the individual influence, with extreme climate strongly disturbing surface influence. It could be concluded that surface influence acts as the primary contribution to global aerosol change, which fluctuates with the interaction of climate change.