His main interests are the study of urban and regional air quality problems with an emphasis on the size and composition of atmospheric particles and gas-to-particle conversion processes. Professor Kleeman's research program balances experiment, theory, and modeling to approach air quality problems from multiple directions. Current projects include the development of a source-oriented external mixture model for application in central California, and an evaluation of the impact that climate change will have on urban / regional PM2.5 concentrations.