Aerosol Acidity Modulated by Temperature Through Semi-Volatile Species

James Campbell, Rodney J. Weber, JINGQIU MAO, University of Alaska Fairbanks

     Abstract Number: 417
     Working Group: Aerosol Processes and Properties in Changing Environments in the Anthropocene

Abstract
Temperature modulates aerosol pH through several ways. While the increased solubility (Henry’s law constant) of semi-volatile gases at lower temperatures is well recognized, the temperature dependence of acid dissociation constants has received less attention. More importantly, the simultaneous increase in both Henry’s law constant and acid dissociation constant at lower temperatures amplifies volatility shifts for species like NH3 and HNO3. In our recent work by Campbell et al. (2024), we show that reduced NH3 volatility at extremely cold conditions (< -30 ℃) enhances aerosol neutralization in ammonium-sulfate aerosols. Building on this, we investigate pH behavior across a broad temperature range in ammonium-sulfate-nitrate aerosols. Our results highlight that aerosol pH is governed by the interplay between NH3 and HNO3 volatility, modulated by ambient temperature and the relative abundance of total NH3, total HNO3 and total H2SO4. These findings provide key insights into aerosol acidity and secondary aerosol chemistry on a global scale.