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.