Evaluating the impacts of brick-kiln emissions on fine particles.

Observed winter fine particle (PM2.5) concentrations in Bangladesh tend to be high with monthly mean concentrations ranging between 182-229 μg m-3. To evaluate the model skill in reproducing the high observed concentrations, we apply the Community Multi-scale Air Quality (CMAQv5.4) model and compare model predicted PM2.5 concentrations with observed data in Bangladesh in January 2019. We use anthropogenic emissions estimates from the Hemispheric Transport of Air Pollution (version 3) mosaic inventory, supplementing them with brick kiln emissions estimates over Bangladesh, and replacing them with emissions from the Speciated MultipOllutant Generator for India. The model reproduces monthly mean observed PM2.5 concentrations to within -27% to -2% in Bangladesh and successfully tracks the day-to-day and diurnal variation of observed PM2.5 concentrations. Both model and observed data show higher night-time PM2.5 concentrations than daytime concentrations due to shallow boundary layers, lower temperature, lower wind speed, and higher relative humidity at night. We find brick kiln emissions contribute monthly mean PM2.5 concentrations of 31-46 μg m-3 (18-27%) in Bangladesh. A substantial portion of the contribution of brick kiln emissions to PM2.5 concentrations originate from secondary organic aerosols due to the large amount of volatile organic compounds emissions. A 50% reduction of brick kiln emissions can improve PM2.5 concentrations in Bangladesh by 14-20 μg m-3. Organic mass is the largest component of PM2.5 in Bangladesh representing over 50% of the PM2.5 mass.