Abstract View
Aerosol Acidity as a Driver of Aerosol Formation and Nutrient Deposition to Ecosystems
ATHANASIOS NENES, Spyros Pandis, Maria Kanakidou, Armistead G. Russell, Shaojie Song, Petros Vasilakos, Rodney J. Weber, LAPI/EPFL, Switzerland; ICE-HT/FORTH, Greece
Abstract Number: 611
Working Group: Urban Aerosols
Abstract
Nitrogen oxides (NOx) and ammonia (NH3) are central contributors to particulate matter (PM) concentrations worldwide. Ecosystem productivity can be modulated by the atmospheric deposition of this inorganic "reactive nitrogen". PM and nitrogen deposition responses to changes in the emissions of both compounds is complex and typically studied on a case-by-case basis.
Here we present a simple but thermodynamically consistent approach that expresses the chemical domains of sensitivity of aerosol particulate matter to NH3 and HNO3 availability in terms of aerosol pH and liquid water content. From our analysis, four policy-relevant regimes emerge in terms of sensitivity: i) NH3-sensitive, ii) HNO3-sensitive, iii) combined NH3 and HNO3 sensitive, and, iv) a domain where neither NH3 and HNO3 are important for PM levels (but only nonvolatile precursors such as NVCs and sulfate). When this framework is applied to ambient measurements or predictions of PM and gaseous precursors, the “chemical regime” of PM sensitivity to NH3 and HNO3 availability is directly determined.
The same framework is then extended to consider the impact of gas-to-particle partitioning, on the deposition velocity of NH3 and HNO3 individually, and combined affects the dry deposition of inorganic reactive nitrogen. Four regimes of deposition velocity emerge: i) HNO3-fast, NH3-slow, ii) HNO3-slow, NH3-fast, iii) HNO3-fast, NH3-fast, and, iv) HNO3-slow, NH3-slow. Conditions that favor strong partitioning of species to the aerosol phase strongly delay the deposition of reactive nitrogen species and promotes their accumulation in the boundary layer and potential for long-range transport.
With this new understanding, aerosol pH and associated liquid water content can be understood as control parameters that drive PM formation and dry deposition flux and arguably can catalyze the accumulation of aerosol precursors that cause intense haze events throughout the globe.