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By disrupting normal societal activities, such as driving, COVID-19 lockdowns gave a unique opportunity to study their impacts on the environment. Satellite data shows that vehicles are the main source of urban airborne ammonia (NH3), which forms small particles that contribute to air pollution and harm human health.
NH3 is converted into tiny particles of compounds when it is released into the atmosphere. Most NH3 pollution comes from agricultural sources. The side-effect of producing ammonia emissions is what contributes to the problem, because vehicles' catalytic converters are designed to reduce emissions of NOx pollutants. In cities, it's difficult to tell if traffic emits more NH3 or if it's agriculture that's causing it, and the assumption has been that agriculture is the culprit. Daven K. Henze and colleagues wanted to see if satellite data could be used to answer this question for the first time from space, since such an approach could be applied more broadly to urban areas throughout the world.
In western Los Angeles, previous on-the-ground measurements found that vehicle emissions of NH3 were being underestimated. Satellite readings of NH3 and NO2 were analyzed by the team. The main source of NO2 in the region is on-road transportation, so the compound can serve as a proxy for changes in traffic volume and an indicator of vehicular emissions. The team took meteorological effects into account to calculate the amount of ammonia emissions that can be traced to vehicles. They found that vehicles accounted for a majority of the NH3 emissions at this urban location, but that they were much higher than the estimates by government agencies. The health impact of ammonia may be comparable to NOx, yet it has been largely under-recognized.
The first satellite-based confirmation that vehicles are an under-recognized source of urban NH3 pollution is provided by COVID-19 Lock Downs.
Environmental Science & Technology Letters is a journal.
Vehicles are an under-recognized source of urban ammonia pollution.
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