Under the Lens: Visualizing Ammonia Air Pollution 


It’s summer,  and in Wisconsin, that means peak season for dangerous ammonia air pollution. A new analysis of satellite imagery by Clean Wisconsin shows monthly concentrations of ammonia air pollution in our state are worst in May but last all summer long. 

“Emissions peak around May in the agricultural areas of the state, particularly in southwestern Wisconsin, coinciding with fertilizer application season,” says Clean Wisconsin Science Program Director Paul Mathewson. “It’s something we can often smell where we’re outdoors this time of year, but satellite imagery shows just how high those concentrations really are in the air we breathe.”

Hotspots of ammonia concentrations in Wisconsin in May and July. Red areas indicate top 10% of ammonia concentrations in the state (data source: Wang et al. 2021). Green circles indicate locations of concentrated animal feeding operations (data source: Wisconsin DNR)

Mathewson says ammonia pollution is concerning because once it’s airborne, it transforms into fine particulate matter, one of the most dangerous types of air pollution. These very small particles can penetrate deeply into the lungs and make their way into the bloodstream, triggering numerous health impacts such as heart attacks and asthma. Fine particulate matter is the leading environmental risk factor for premature death. 

Monthly ammonia concentrations in the air as measured by satellite data. Dark purple indicates low concentrations and warmer colors indicate higher concentrations, with bright yellow indicating the highest concentrations. All data are from Wang et al. 2021

Clean Wisconsin’s analysis also reveals that ammonia pollution hot spots tend to become more localized in mid-summer, occurring in parts of the state where concentrated animal feeding operations (CAFOs) are located. 

“As summer progresses, ammonia hotspots shift towards the northeast part of the state, often occurring near higher densities of large livestock operations. Warm temperatures cause livestock manure to release ammonia, so that becomes a more significant source of this air pollution in the middle of summer.” 

Manure and fertilizer are often cited as major sources of water contamination in Wisconsin and are also recognized as contributors to climate change due to releases of methane and nitrous oxide, respectively, which are potent greenhouse gases. But it’s been hard to visualize air quality impacts until now. 

“We know that improving manure and fertilizer management is critical to protect our lakes, streams and drinking water. But as these satellite data help us to visualize, better management can also have important benefits from an air quality perspective.” 

According to Mathewson, practices that can reduce ammonia emissions include: using animal feed that produces minimal nitrogen waste and applying fertilizer and manure only up to the amount of nitrogen that crops need. Nitrogen that plants can’t take up will end up in our water or in the air such as in ammonia emissions