Jacobson specializes in computer modeling and analysis of air pollution, weather, and climate and the impact of energy technologies on the atmosphere. Some goals of his research are to understand physical, chemical, and dynamical processes in the atmosphere better through numerical modeling and to improve the simulation of air pollution, weather, and climate. Some topics he has studied include near-source pollutant evolution, the effects of aerosols on climate and ultraviolet radiation, the effects of aerosol mixing state on radiative heating, the effects of black carbon and biomass burning on climate, gas- and aqueous-phase air pollution chemistry, cloud formation and evolution, aerosol microphysics and chemistry, wind energy resources, the effect of hydrogen fuel cells on the atmosphere, and the relationship between different energy sources and climate. As part of his research, he has developed and applied numerical algorithms that simulate gas, aerosol, cloud microphysical, radiative, and land/ocean-surface processes. He has also developed an air-pollution-weather-climate model that he has applied to study scientific problems from the freeway scale to the global scale.