10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Linked Response of Aerosol Acidity and Ammonia to SO2 and NOx Emissions Reductions in the US
ABIOLA LAWAL, Xinbei Guan, Cong Liu, Lucas Henneman, Vasudha Bhogineni, Rodney J. Weber, Athanasios Nenes, Armistead G. Russell, Georgia Institute of Technology
Abstract Number: 519 Working Group: Aerosol Modeling
Abstract Reductions in sulfur (SO2) and nitrogen oxides (NOx) emissions have led to considerable improvements in air quality such as lower particulate matter (PM2.5) concentrations. However, similar responses in aerosol acidity have not been observed. Aerosol acidity is an important characteristic of particulate matter (PM2.5) that has far wide-reaching implications in atmospheric heterogeneous chemistry, biogeochemical cycles, climate forcing and adverse health effects. Studying the impact of the reduction of SO2 and NOx emissions, both of which can ultimately constitute a large portion of inorganic aerosol mass fraction, is important to understanding the environmental impacts of future emissions reductions on acidity. Previous spatially limited studies have shown that effects of these precursor emission reductions have had minimal impact on aerosol acidity1. Other studies involving a thermodynamic analysis into the neutralizing effectiveness of ammonia (NH3(g)) on aerosols have shown limited impact of high ammonium concentrations on aerosol acidity2. This study expounds upon previous aerosol acidity analysis by conducting a longer temporal and wider spatial study over the continental United States using data from three nationwide ambient concentration networks; the Ammonia Monitoring Network (AMoN), the Clean Air Status and Trends network (CASTNET) and the Southeastern Aerosol Research and Characterization Network (SEARCH) together with a chemical transport model (CMAQ). Further, as aerosol pH is not readily measured, the aerosol thermodynamic model, ISORROPIA II is utilized here to characterize aerosol pH. Results of the study show that aerosol acidity has not responded to nationwide reductions in SO2 and NOx, with all observed increases yielding changes in pH of less than 1 unit over varying periods of time. Additional results also show no significant changes in particulate nitrate or atmospheric gaseous ammonia concentrations in response to these reductions. In effect, our study finds nationally, what has been reported for the southeast US1; the significant emission reductions in SO2, NOx did not significantly impact aerosol acidity. What are the implications of these findings? Maybe a more important question is when, if ever, will the aerosol system become more sensitive or respond differently to these emission reductions.
References [1] Weber, R.J., et al., High aerosol acidity despite declining atmospheric sulfate concentrations over the past 15 years. Nature Geosci, 2016. 9(4): p. 282-285. [2] Guo, H.Y., R.J. Weber, and A. Nenes, High levels of ammonia do not raise fine particle pH sufficiently to yield nitrogen oxide-dominated sulfate production. Scientific Reports, 2017. 7.