Hidden Cost of U.S. Agricultural Exports: Particulate Matter from Ammonia Emissions

Abstract

We use a model of agricultural sources of ammonia ((NH_3)) coupled to a chemical transport model to estimate the impact of U.S. food export on particulate matter concentrations ((PM_{2.5})). We find that food export accounts for 11% of total U.S. (NH_3) emissions (13% of agricultural emissions) and that it increases the population-weighted exposure of the U.S. population to (PM_{2.5}) by (0.36 \mu g m^{–3}) on average. Our estimate is sensitive to the proper representation of the impact of (NH_3) on ammonium nitrate, which reflects the interplay between agricultural ((NH_3)) and combustion emissions ((NO, SO_2)). Eliminating (NH_3) emissions from food export would achieve greater health benefits than the reduction of the National Ambient Air Quality Standards for (PM_{2.5}) from (15 to 12 \mu g m^{–3}). Valuation of the increased premature mortality associated with (PM_{2.5}) from food export (36 billion US$ (2006) per year) amounts to 50% of the gross food export value. Livestock operations in densely populated areas have particularly large health costs. Decreasing (SO_2) and (NO_x) emissions will indirectly reduce health impact of food export as an ancillary benefit.