AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Emergence of a New Chemical Regime: Growing Abundance of Water Soluble Organics in Cloud Water Associated with a Growing Ion Imbalance
CHRISTOPHER LAWRENCE, Sara Lance, James Schwab, James Dukett, Kevin Civerolo, Oliver Rattigan, Dan Kelting, Elizabeth Yerger, Hunter Favreau, Paul Casson, Richard Brandt, University at Albany, SUNY
Abstract Number: 675 Working Group: Aerosol Chemistry
Abstract Long-term reductions in anthropogenic sulfate in the eastern U.S. have been captured by observations spanning several decades across New York State, including cloud water composition measurements at Whiteface Mountain (WFM). These observations reflect one of the major goals of the Clean Air Act: dramatic reductions in sulfuric acid deposition. Concomitant long-term reductions in nitrate and ammonium have also been recorded, associated with reduced particulate mass loadings. Altogether, these outcomes are considered one of the greatest success stories in the history of U.S. air pollution regulation.
Due to the historical impetus for cloud water monitoring in the eastern U.S., measurements at WFM began with inorganic ion speciation, which has continued largely unchanged to the present day. Measurements of Water Soluble Organic Carbon (WSOC) were added in 2009. In the past decade cloud water samples have become increasingly anion deficient, leading to a growing number of samples considered “invalid” due to ion imbalance. While most published literature on cloud water composition does not include “invalid” samples, in the present day “invalid” samples outnumber “valid” samples. The growing ion imbalance suggests that there is a growing abundance of anions that are not detected with the traditional suite of measurements. When choosing not to apply these ion balance criteria in the data analysis, a striking increase in WSOC emerges over the past decade. A growing abundance of ammonium in cloud water has also reached a new milestone, surpassing both sulfate and nitrate combined. Thus, while the acidity of cloud water has decreased dramatically, these observed changes in cloud water composition suggest that we are entering a new chemical regime in the northeastern U.S., which is not necessarily “clean”.
We report on the re-evaluation of these long-term trends and describe the addition of an important constituent to our cloud water monitoring efforts: organic acids.