Ammonia emission controls as a cost-effective strategy for reducing atmospheric particulate matter in the eastern United States

Current regulation aimed at reducing inorganic atmospheric fine particulate matter (PM2.5) is focused on reductions in sulfur dioxide (SO2) and oxides of nitrogen (NOx equivalent to NO + NO2); however, controls on these pollutants are likely to increase in cost and decrease in effectiveness in the future. A supplementary strategy is reduction in ammonia (NH3) emissions, yet an evaluation of controls on ammonia has been limited by uncertainties in emission levels and in the cost of control technologies. We use state of the science emission inventories, an emission-based regional air quality model, and an explicit treatment of uncertainty to estimate the cost-effectiveness and uncertainty of ammonia emission reductions on inorganic particulate matter in the Eastern United States. Since a paucity of data on agricultural operations precludes a direct calculation of the costs of ammonia control, we calculate the ammonia savings potential, defined as the minimum cost of applying SO2 and NOx emission controls in order to achieve the same reduction in ambient inorganic PM2.5 concentration as obtained from a 1 ton decrease in ammonia emissions. Using 250 scenarios of NH3, SO2, and NOx emission reductions, we calculate the least-cost SO2 and NOx control scenarios that achieve the same reduction in ambient inorganic PM2.5 concentration as a decrease in ammonia emissions. We find that the lower-bound ammonia savings potential in the winter is $8,000 per ton NH3; therefore, many currently available ammonia control technologies are cost-effective compared to current controls on SO2 and NOx sources. Larger reductions in winter inorganic particulate matter are available at lower cost through controls on ammonia emissions.