Seminar

Abstract

Ammonia (NH₃) from agricultural and urban sources effects terrestrial ecosystems and atmospheric composition, and some of these sources have increased substantially in recent decades. Over the last 50 years world usage of NH₃-derived fertilizers has increased by an order of magnitude, resulting in a major increase of NH₃ to the ecosystem from agriculture. Major NH₃ sources from agricultural activity include animal waste and crop fertilization. In urban areas automobiles equipped with three-way catalytic converters have become a source of atmospheric NH₃. These anthropogenic sources increase the burden of NH₃ to the atmosphere, where NH₃ is the dominant gas-phase base. NH₃ in the atmosphere contributes to particle formation. For example, emissions of NH₃ and NOx (NO + NO₂), which can be oxidized in sunlight to form nitric acid (HNO₃), can react to form atmospheric ammonium nitrate particles.

NH₃ from agricultural activity and urban centers results in ammonium nitrate formation in both the Los Angeles-South Coast Air Basin (SoCAB) and the San Joaquin Valley (SJV) of California. These regions are designated by the US Environmental Protection Agency (EPA) as being in non-attainment of the National Ambient Air Quality Standards (NAAQS) for both PM2.5 and PM10. Since formation of fine aerosol nitrates from NH₃ and HNO3 accounts for a significant fraction of the PM2.5 mass, quantifying the sources of NH₃ in theses regions is important for developing aerosol control strategies. Fast-time resolution observations of NH₃ and traces gases and aerosols made aboard the NOAA WP-3D aircraft during the CalNex 2010 campaign are used to quantify and compare NH₃ sources in California, evaluate their representation in emissions inventories, and determine their impact on particle formation.