Abstract Description: It is well-established that the Cache Valley in northern Utah has wintertime PM2.5 problem and that the local PM2.5 is compositionally-dominated by ammonium nitrate (NH3NO3). Studies in 2006, 2016, and 2017 found Valley-wide ambient, wintertime ammonia (NH3) concentrations of 42, 56, and 75 ppb, respectively. There has historically been a very clear concentration maxima in the northern central part of the valley near the location of a large poultry egg producer. Further, since 2011, Cache Valley is also the location of NADP AMoN site UT01, which has consistently reported the highest NH3 concentrations in the entire nation-wide network. Additional studies have found that the Cache Valley airshed has historically been NH3-rich by a factor of 2-6x, owing mostly to the abundance of agriculturally-derived NH3. In April 2022, due to an outbreak of Avian Influenza (AI), the large local poultry facility had to depopulate more than 1.4 million birds. The sudden removal of one of Cache Valley’s more significant NH3 sources allows for an unusual opportunity to assess the atmospheric impacts of such an unplanned source reduction scenario, in terms of valley-wide atmospheric gas-phase NH3 and the potential for resultant changes in particulate-phase ammonium nitrate (NH4NO3). As such, a study has been initiated for the winter of 2022/2023 to determine the spatial variability of ambient NH3 using a network of 20-25 Ogawa passive NH3 samplers and to examine potential changes in the area’s PM2.5 mass concentrations and ionic contributions via filter-based collection using AirMetrics MiniVols to be collocated at the Utah Division of Air Quality’s local regulatory site (Smithfield, SM). The results will be presented and discussed in terms of absolute magnitudes and in relation to previous, pre-AI conditions.
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