Can Acid-Base Aerosol Nucleation Be Applied to All Urban Settings in the World?

Lee Tiszenkel, James Flynn, Alana Dodero, SHANHU LEE, University of Alabama Huntsville

     Abstract Number: 274
     Working Group: Urban Aerosols

Abstract
Aerosol nucleation is an extremely complex atmospheric process that produces new particles directly from gas phase species, impacting air quality, human health, and climate. The current understanding of urban aerosol nucleation is mostly based on the measurements made in Chinese megacities that suggested that sulfuric acid and dimethylamine contribute to urban nucleation, without organics. An important question is whether this acid-base nucleation process can be applied to all urban sites in the world, regardless of vastly different urban vegetations and different emissions of urban VOCs (e.g., emerging VCPs). Here, we conducted comprehensive measurements of nucleation precursors at the urban center in Houston, the 4th most populated and highly polluted urban site in the United States. Our observations and box model simulations show that sulfuric acid, base, and low-volatility OOMs contribute to urban aerosol nucleation in Houston. The chemical composition analyses of OOMs and box model simulations show that under the typical urban Houston conditions, low-volatility OOMs form from autoxidation of VOCs, as well as multigenerational OH oxidation of aromatic compounds; autoxidation and dimerization reactions are not suppressed by NOx. Our findings thus contrast with previous urban studies made in Chinese megacities, where OOMs are too volatile to contribute to urban aerosol nucleation, demonstrating distinctively different roles of organics in urban aerosol nucleation due to different chemical compositions of OOMs. With increasing emissions of emerging air pollutants in the United States and Europe, this multicomponent nucleation process will be crucial for mitigating air pollution in the evolving urban climate.