This study quantifies the source contributions to PM2.5 in three major Chinese cities of Beijing, Tianjin, and Shanghai during the period of June to August 2016. The sensitivity analysis is employed by individually eliminating each sector to identify their respective contributions. The numerical simulations reveal that industry is the dominant contributor to PM2.5 pollution in all three cities with contributions ranging from 41.01% to 53.42%. The contributions of residential-commercial, energy and transportation are in the range of 11.25% to 27.21%, 17.45% to 20.61%, and 5.89% to 15.02%, respectively. Agriculture and deforestation-wildfire are found to contribute 4.23% to 7.28% and 2.60% to 5.30%, respectively.