Impact of Urban, Agricultural and Industrial Emissions on the Atmospheric Reactive Nitrogen in the Columbia River Gorge Scenic Area

Abstract:

Secondary inorganic aerosol (SIA) formation is not fully characterized due to inadequate knowledge of pre-cursor emissions (ammonia, NH_3, and nitrogen oxides, NOx) and from incomplete understanding of reactions in model predictions involving the precursors and the chemical products such as nitric acid (HNO₃). The Columbia River Gorge (CRG), located between Oregon and Washington states, has unique sources of reactive nitrogen located at both ends and experiences bimodal winds: winter easterlies and summer westerlies. Because of the unique winds, this project will utilize the CRG as an environmental flow tube as we monitor for atmospheric reactive nitrogen species at two locations within the CRG: one located on the western side and one on the east. Measurements will include total oxidized nitrogen, NOx, NH₃ and HNO₃ using annular denuders, and a novel method using ion exchange resins for particulate ammonium, nitrate, and sulfates. In addition, an ozone gas analyzer and meteorological conditions of temperature, relative humidity, wind speed and direction will be measured. Our December 2012- June 2014 NOx measurements located near the eastern end of the CRG show significantly different (p<<0.05) levels of NO₂ with easterly (8.1 ppb) versus westerly (5.7 ppb) wind conditions. This suggests an eastern NOx source – potentially the 550 megawatt Boardman Coal Power Plant 100 km to the east. These measurements in the near-source environment will provide insight into uncertainties in HNO₃ formation, regional ammonia levels, and the best strategy for managers to reduce NOx or NH₃ emissions to minimize SIA formation.