Atmospheric ammonia can double the number of atmospheric particles over high emission regions and lead to the potential for increased cloud formation, a study finds. Anthropogenic ammonia emissions, which primarily stem from agricultural activities such as fertilizer application, are projected to double by 2100. While much is known about ammonia’s effects on surface air quality, less is known about how much reaches the upper atmosphere and its effects there. Christos Xenofontos and colleagues modeled the effect of anthropogenic ammonia emissions on particle formation in the upper troposphere and lower stratosphere. The authors compared two global simulations of atmospheric chemistry, one with anthropogenic ammonia emissions included and a baseline with no human-caused emissions. The model shows that convection carries ammonia above the surface layer, strongly enhancing aerosol formation and growth, resulting in changes in aerosol composition and abundance over high emission regions.  These aerosol particles increase cloud condensation nuclei by 2.5 times compared to baseline. Aerosol optical depth increased by 80% which affects the absorption of light by particles in the atmosphere and potentially climate. According to the authors, ammonia is projected to reach the upper troposphere in high enough concentrations that its effects should be included in climate models and projections.