Emissions of aerosols and gases from fires have been shown to adversely affect US air quality at local to regional scales as well as downwind regions far away from the source. In addition, smoke from fires negatively affects humans, ecosystems, and climate. Recent observations have shown an upward trend of area burned over western US resulting from increasing fire activity, most likely related to climate change. Climate-driven changes in fire emissions may result in an increase of carbonaceous aerosol, and a significant increase in annual mean PM2.5 and haze. This project provided an integrated assessment of the effects of fires under different future climate and population scenarios on fine particulate matter mass (PM2.5) and ozone (O3) at global scale, with a particular focus on the United States. The objectives of this study, most of which were met, were: 1) use of climate projections to predict changes in fire activity in 2050, 2) identify potential changes in vegetation and fuels resulting from changes in climate and their implications in fire activity, 3) identify changes in fire occurrence and severity resulting from changes in future climate and vegetation and fuels, and 4) predict impacts on air quality resulting from changes in fire activity and climate on the mid-21st century. We employed the global Community Earth System Model (CESM) with the RCP climate, anthropogenic emissions and land use, and the SSP population projections (i.e., RCP4.5/SSP1 and RCP8.5/SSP3). Within CESM, we used a complex-based fire parameterization to project future climate- and human-driven fire emissions, and considered landscape, deforestation, agricultural and peat fires. Our study showed that on a global scale fire area burned is predicted to increase about 8% in 2050 and 30% at the end of the 21st century compared to present day as a result of climate and population density changes. When we isolated climate changes, we found more dramatic increases in area burned throughout the century, with 20-30% in 2050 and 28-77% in 2100, which shows the important role that fire suppression may play on a regional scale. Across the world, PM2.5 concentrations are predicted to increase significantly as a result of increased fire activity. These increases are most prominent over North America, EuroAsia and Equatorial regions, in which fire-driven PM2.5 may potentially offset anticipated reductions in anthropogenic emissions. During the summertime, fire emissions will dominate PM2.5 concentrations almost entirely across the US. The number of annual mortalities attributed to PM2.5 as well as visibility degradation are similar to the PM2.5 changes, with increases in fire PM2.5 offsetting benefits from anthropogenic PM2.5 reductions. Changes in fire emissions will also significantly impact future O3 air quality, with increases up to 9 ppb to the daily maximum 8-hour average over western US. Our study illustrates the need to consider the effects of fires in future air quality management and planning and emission policy making, as controlling anthropogenic emissions may not be enough to attain future air quality targets.