In a recent peer-reviewed study, a team including AER Principal Scientist Karen Cady-Pereira showed that COVID-19 lockdowns provide a unique opportunity for making the first satellite-based constraints on vehicle NH3 emissions for an entire urban region (western Los Angeles), which they found made up 60−95% of total NH3 emissions, substantially higher than the values of 13−22% in state and national inventories. This provides a new means of constraining a component of transportation emissions whose impacts may rival those of NOx, yet which has been largely under-recognized and uncontrolled.
In situ measurements have suggested vehicle emissions may dominate agricultural sources of NH3 in many cities, which is alarming given the potential for urban NH3 to significantly increase human exposure to ambient particulate matter. However, confirmation of the prevalence of vehicle NH3 throughout a city has been challenging because of mixing with agricultural sources, and the latter are thus routinely assumed to dominate.
This figure shows the fraction of NH3 emitted over West LA by vehicles estimated from four bottom-up inventories (NEI11, NEI17, CARB20, FIVE) and from this study, which applied a top-down approach with TROPOMI NO2 and CrIS NH3 as inputs. The impact of changing meteorological conditions for this approach was estimated using both TROPOMI NO2 changes (blue) and the GEOS-Chem model (pale green).
Citation / Link: COVID-19 Lockdowns Afford the First Satellite-Based Confirmation That Vehicles Are an Under-recognized Source of Urban NH3 Pollution in Los Angeles
Hansen Cao, Daven K. Henze, Karen Cady-Pereira, Brian C. McDonald, Colin Harkins, Kang Sun, Kevin W. Bowman, Tzung-May Fu, and Muhammad O. Nawaz
Environmental Science & Technology Letters 2022 9 (1), 3-9 DOI: 10.1021/acs.estlett.1c00730