Science Inventory

Monthly Patterns of Ammonia Over the Contiguous United States at 2-km Resolution

Citation:

Wang, R., X. Guo, D. Pan, J. Kelly, J. Bash, K. Sun, F. Paulot, L. Clarisse, M. Van Damme, S. Whitburn, P. Coheur, C. Clerbaux, AND M. Zondlo. Monthly Patterns of Ammonia Over the Contiguous United States at 2-km Resolution. GEOPHYSICAL RESEARCH LETTERS. American Geophysical Union, Washington, DC, 48(5):e2020GL090579, (2021). https://doi.org/10.1029/2020GL090579

Impact/Purpose:

Ammonia (NH3) contributes to the formation of particulate matter, which is known to degrade air quality and impact human health. The largest source of ammonia is from agricultural activities in non-urban areas and in the United States, yet the current knowledge of NH3 emissions from agriculture is limited due to the lack of observational data. With daily measurements, satellite-based observations provide a new possibility to better understand the spatiotemporal distribution of NH3. We have developed high spatial resolution (2 km) satellite maps of NH3 on a monthly scale in the United States. The areas with the highest ambient NH3 concentrations are generally very localized with gradients in ambient concentrations spanning several orders of magnitude several km downwind from emission sources, suggesting that monitoring sites need to be co-located with sources in order to better constrain emission inventories. Observed seasonal patterns varied dramatically based upon the underlying agricultural activities. Areas with significant animal husbandry had peak abundances in mid-summer, whereas cropland-dominated regions had peak abundances in spring with a shoulder in autumn. A comparison of satellite observations with model results showed that these high-resolution satellite maps can be used to help to improve the seasonalities of NH3 emission inventories.

Description:

Monthly, high‐resolution (∼2 km) ammonia (NH3) column maps from the Infrared Atmospheric Sounding Interferometer (IASI) were developed across the contiguous United States and adjacent areas. Ammonia hotspots (95th percentile of the column distribution) were highly localized with a characteristic length scale of 12 km and median area of 152 km2. Five seasonality clusters were identified with k‐means++ clustering. The Midwest and eastern United States had a broad, spring maximum of NH3 (67% of hotspots in this cluster). The western United States, in contrast, showed a narrower midsummer peak (32% of hotspots). IASI spatiotemporal clustering was consistent with those from the Ammonia Monitoring Network. CMAQ and GFDL‐AM3 modeled NH3 columns have some success replicating the seasonal patterns but did not capture the regional differences. The high spatial‐resolution monthly NH3 maps serve as a constraint for model simulations and as a guide for the placement of future, ground‐based network sites.