Accelerating growth in the transport sector, a booming construction industry, and a growing industrial sector are responsible for worsening air pollution in Indian cities. While estimates of health impacts are effective in raising overall concern about air quality, they do not specifically answer the question of what are the sources of air pollution and and what is their contribution. Further uncontrolled growth will lead to more pollution and require large recurring investments to control pollution. This study under the SIM-air program was initiated with support from the Climate Works Foundation (USA) and the Shakti Sustainable Energy Foundation (India) to better understand the sources of air pollution in six cities in India, to support an integrated dialogue between local pollution management and climate policy in a co-benefits framework.