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Atmospheric Deposition Modeling in the Chesapeake Bay Watershed
Citation:
Benish, S., J. Bash, K. Foley, C. Hogrefe, Keith Appel, S. Napelenok, L. Linker, G. Shenk, AND G. Bhatt. Atmospheric Deposition Modeling in the Chesapeake Bay Watershed. Chesapeake Bay Quarterly Meeting, Virtual, Virtual, April 05 - 06, 2022.
Impact/Purpose:
Source apportionment techniques implemented in photochemical models are critical tools for policymakers to develop optimal emission control strategies. Here, we discuss important revisions included in the Integrated Source Apportionment Method (ISAM) available in the Community Multiscale Air Quality (CMAQ) model version 5.3 platform that increases user flexibility and improves model estimated source attribution. Our evaluation focuses on applying ISAM to a case study assessing nitrogen (N) deposition in the Chesapeake Bay watershed, a region that experiences high nutrient loading from a variety of urban and agricultural sources. Comparison to National Atmospheric Deposition Program (NADP) NH4 and NO3 wet deposition observations reveal slight model underestimates with strong correlations (R=0.40-0.70). Source apportionment results to the watershed suggest boundary conditions contribute a quarter to both total oxidized and total reduced N deposition. Mobile (23%), electric generating units (9%), and nonroad (6%) emissions are found to contribute significantly to total oxidized N deposition, while bidirectional ammonia (NH3) (21%), non-poultry animal manure (33%), and poultry manure (11%) constitute the majority towards total reduced N deposition in the Watershed. While targeting local NH3 emissions for control will help reduce total reduced N deposition within the Watershed, our results suggest emission controls outside the Watershed will significantly decrease reduced N deposition at some locations more so than local efforts. Brute-force simulations zeroing out mobile emissions estimate slightly larger oxidized and reduced N deposition amounts than ISAM with strong correlations (r2=0.56-0.87). The estimated mobile total N budget is comparable, only 0.13-0.31 kg-N/ha larger in the Brute Force compared to the ISAM, providing confidence the accuracy of the estimated source contributions. Appropriate source apportionment approaches in photochemical modeling to aid decisionmakers require improving emissions estimation techniques, such as incorporating satellite data in areas of temporal and spatial NH3 variability.
Description:
Source apportionment techniques implemented in photochemical models are critical tools for policymakers to develop optimal emission control strategies. Here, we discuss important revisions included in the Integrated Source Apportionment Method (ISAM) available in the Community Multiscale Air Quality (CMAQ) model version 5.3 platform that increases user flexibility and improves model estimated source attribution. Our evaluation focuses on applying ISAM to a case study assessing nitrogen (N) deposition in the Chesapeake Bay watershed, a region that experiences high nutrient loading from a variety of urban and agricultural sources. Comparison to National Atmospheric Deposition Program (NADP) NH4 and NO3 wet deposition observations reveal slight model underestimates with strong correlations (R=0.40-0.70). Source apportionment results to the watershed suggest boundary conditions contribute a quarter to both total oxidized and total reduced N deposition. Mobile (23%), electric generating units (9%), and nonroad (6%) emissions are found to contribute significantly to total oxidized N deposition, while bidirectional ammonia (NH3) (21%), non-poultry animal manure (33%), and poultry manure (11%) constitute the majority towards total reduced N deposition in the Watershed. While targeting local NH3 emissions for control will help reduce total reduced N deposition within the Watershed, our results suggest emission controls outside the Watershed will significantly decrease reduced N deposition at some locations more so than local efforts. Brute-force simulations zeroing out mobile emissions estimate slightly larger oxidized and reduced N deposition amounts than ISAM with strong correlations (r2=0.56-0.87). The estimated mobile total N budget is comparable, only 0.13-0.31 kg-N/ha larger in the Brute Force compared to the ISAM, providing confidence the accuracy of the estimated source contributions. Appropriate source apportionment approaches in photochemical modeling to aid decisionmakers require improving emissions estimation techniques, such as incorporating satellite data in areas of temporal and spatial NH3 variability.