Leveraging Passive Sampling and Satellite Data to Understand Ammonia in Northeast Colorado

The Colorado Front Range and the plains to the east are important source regions of ammonia (NH₃). NH₃ is an unregulated pollutant primarily emitted in this region from animal feeding and other agricultural activities. Upslope flows driven by the mountain-plains circulation periodically transport these emissions into Rocky Mountain National Park located 50 km west of the Front Range, where they can be deposited by wet and dry deposition processes. Excess reactive nitrogen (N) deposition in RMNP is a well-documented problem with impacts including changes in soil biogeochemistry, enhanced microbial activity, and increased N in freshwater bodies. Biweekly passive NH₃ concentration measurements from 2010 to 2023 across 12 sites in northeast Colorado will be used to assess the temporal and spatial variability in NH₃ concentration across three distinct regions: urban/suburban, agricultural, and rural areas. Previous work indicates that 2010-2015 represents a stable baseline for NH₃ concentration in the region. By extending the concentration data set through 2023, we can further examine whether any changes in NH₃ concentrations are evident, especially in the agricultural source region where a variety of best management practices have been under discussion to reduce emissions. This analysis of passive NH₃ network data will be complemented by review of 2007 to 2023 NH₃ total column retrievals from the Infrared Atmospheric Sounding Interferometer (IASI) satellite. We will evaluate spatial and temporal consistency between these in situ and remote sensing data sets and consider periods where elevated NH₃ from transported wildfire plumes might be present in the satellite column measurements but not reflected in the surface measurements.