Scientific knowledge on the chemical compositions of fine particulate matter (PM 2.5 ) is essential for properly assessing its health and climate effects, and for decisionmakers to develop efficient mitigation strategies. A high-resolution PM 2.5 chemical composition dataset (CAQRA-aerosol) is developed in this study, which provides hourly maps of organic carbon, black carbon, ammonium, nitrate, and sulfate in China from 2013...