Recent research suggests that safety regulators may have drastically underestimated the severity of the ammonia emissions produced by cars and other vehicles. According to a report by Streetsblog, it turns out that vehicles may release five times more ammonia than previously believed, a level of pollution primarily affecting cities like New York.
As the report describes, ammonia gas, or NH3, “is a relatively understudied vehicle emission” that nonetheless poses real environmental and health risks. The gas “combines with nitrogen oxides in the air to form the fine particulate matter that has a major impact on human health,” with research suggesting links to “15,000 premature deaths across the United States each year.”
In March 2020, as the coronavirus pandemic lockdowns cleared streets and highways across the US, a team of researchers at the University of Colorado, Boulder saw a chance to measure how much ammonia gas levels declined in turn. As a press release by the university explains, they wanted to answer the question: “How much do vehicles in a city like Los Angeles add to the ammonia emissions that can hang in the air and sicken residents?”
The study’s findings were published last month in Environmental Science and Technology Letters. In short, what it found is that in Los Angeles alone, cars—as opposite to other sources, like agriculture runoff—produce the vast majority of the NH3 gas in the city, as much as 95%. Said the study’s lead author, Hansen Cao, “Our estimates for vehicle ammonia emissions are higher than federal and state inventories by a factor of two to five.”
The study’s methodology involved using the “accidental before and after picture” provided by the pandemic, allowing them to track ammonia concentrations in Los Angeles’s air in satellite images taken before and after March 2020. They settled on two locations: downtown LA, and an area north of Riverside, described as “a hub for livestock and agriculture.” The ammonia “hotspot” above LA had pretty much cleared up by the end of March 2020, the study found, indicating that “vehicles produce at least 60% of the ammonia emissions in urban Los Angeles.” Previous estimates by regulatory agencies at both the state and federal levels were under 25%.
As Streetsblog notes, the study’s findings about Los Angeles don’t necessarily mean that other cities suffer similar proportions of ammonia gas pollution. The study’s authors plan to hope to apply the question to other cities as well, noting that the results may have meaningful implications for car safety regulators. “Vehicles can be the dominant sources of ammonia emissions over urban areas,” Cao said in the CU Boulder press release. “If we’re underestimating those emissions, then previous estimates of premature deaths owing to ammonia emissions might also be underestimated.”