The Spatial and Temporal Distribution of Atmospheric Ammonia in Northern Colorado

As an unregulated compound, ammonia is not well characterized in many regions as measurements are often limited in time and space. In northeastern Colorado, ammonia emissions impact sensitive ecosystems in Rocky Mountain National Park (RMNP). In an effort to improve our understanding of the spatial and temporal trends in the region, passive ammonia samplers have been deployed across northern Colorado in the summer from 2010 to 2017. In 2017 18 sites were part of the network. These data provide insight into how the average ammonia concentration varies from sites in close proximity to and at sites removed from the main ammonia sources. This data set also provides information on the trends in ammonia concentration from 2010-2017. The summer average ammonia concentration exceeded 30 µg/m³ at the sampling site nearest to confined animal feeding operations (CAFOs) during all sampling years. Concentrations rapidly decrease away from CAFOs and no other site exceeded 16 µg/m³ for the summer average concentration. Along the Front Range urban corridor ammonia concentrations are typically 3-5 µg/m³_. From 2010-2015 concentrations were relatively steady at the majority of sites with increases observed near CAFOs and small decreases at the easternmost site. In 2016 a significant decrease in ammonia was observed across the entire network. Possible reasons for this observed region-wide decrease will be discussed along with sampling handling and quality control.