AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Ammonium and Ammonia: Concentration Trends in the Northeast United States
JAMES SCHWAB, Hesham Hassan, Matthew Ninneman, Joseph P. Marto, Jie Zhang, Sara Lance, Christopher Lawrence, Fangqun Yu, Gan Luo, Arshad Nair, Kevin Civerolo, Oliver Rattigan, University at Albany, SUNY
Abstract Number: 501 Working Group: Remote and Regional Atmospheric Aerosol
Abstract Gas phase ammonia and its condensed phase counterparts – particulate ammonium and aqueous ammonium – comprise a critically important pool of reduced nitrogen compounds in the earth’s atmosphere and biogeosphere as a whole. Ammonia is the most abundant base species in the atmosphere, playing critical roles in both aerosol nucleation and secondary aerosol growth, and providing a major nutrient input to terrestrial and aquatic ecosystems. For all these reasons it is important to understand changes in concentrations of both ammonia and ammonium; and the factors that influence their concentration trends. PM2.5 ammonium has been decreasing since around 2000, reflective of the similar trends in PM2.5 sulfate concentrations and sulfur dioxide emissions. While PM2.5 ammonium concentrations have been decreasing, gas phase ammonia concentrations have been increasing, an expected compensating effect given the largely stable NH3 emissions reported by EPA inventories. Aqueous phase ammonium in precipitation and cloud water is more complicated, and recent data for the Northeast U.S. indicate it has been increasing over the past decade as well. These contrasting trends have produced a new regime in the aqueous phase charge balance in the Northeast U.S., with an ammonium cation surplus over the combined nitrate and sulfate anion strength emerging as the typical condition of cloud and rain water in the past couple years. This presentation will explore these trends, the factors contributing to them, and their implications for aerosol formation, atmospheric chemistry, and ecosystem response.