Remotely sensed BC columns over rapidly changing Western China show significant decreases in mass and inconsistent changes in number, size, and mixing properties due to policy actions

Abstract

Abstract Rapid economic and energy growth in Asia has led to change in the loadings of black carbon (BC) in the last two decades. This work uses remotely sensed column absorbing aerosol optical depth to quantify BC loading day-by-day and grid-to-grid. Variance maximization is used to uniquely compute an unbiased set of observations of remotely sensed NO2 in space and time of urban and suburban sources, including regions with changing energy and industry. An inversely applied probabilistic MIE algorithm constrains the size, mixing state, and number of BC using four spectral observations. Significant differences in the particle size and mixing state are identified and attributed including: a drop around 2012 when China’s national air pollution policies were adopted, a drop ahead of the 2008 Olympics, and flattening from 2015 onward. A case of simultaneous reduction in BC mass and increase in BC number demonstrates PM2.5 controls may not fully control BC.