Observations show increased nitrate in coastal cloud droplet residuals from large-particle activation and N 2 O 5 hydrolysis

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Abstract
Clouds change the chemical composition of aerosols, yet observations characterizing these processes are quite limited. Ground-based in-cloud measurements in coastal Southern California show that the highest nitrate to sulfate ratio (2.5 ± 1.7) in droplet residuals is near cloud base where cloud liquid water content and droplet number concentration are below the observed 20th percentile. The number size distribution of nitrate-rich particles peaks at a larger diameter than sulfate-rich particles, supporting growth to droplets of nitrate-rich particles at lower supersaturations than for sulfate-rich particles. Nitrate mass concentrations are up to three times higher in-cloud compared to pre-cloud and correlated with statistically significant reductions in ozone concentrations, consistent with contributions from in-cloud nitrate formation by N 2 O 5 hydrolysis. This study provides quantitative relationships of cloud properties to nitrate production in droplet residuals and associated ozone reduction, illustrating the impacts of aqueous reactions in clouds.
Funding Information
  • National Science Foundation (AGS-2133441)
  • National Science Foundation (AGS-1852977)
  • U.S. Department of Energy (DE-SC0022958)
  • Triad National Security (89233218CNA000001)
  • Triad National Security (89233218CNA000001)

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