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- Title
Evaluating the Impacts of Cloud Processing on Resuspended Aerosol Particles After Cloud Evaporation Using a Particle‐Resolved Model.
- Authors
Yao, Yu; Dawson, Matthew L.; Dabdub, Donald; Riemer, Nicole
- Abstract
Aerosol particles undergo physical and chemical changes during cloud processes. In this work, we quantified the changes in aerosol mixing state using a particle‐resolved model. To this end, we coupled the particle‐resolved aerosol model PartMC‐MOSAIC with the aqueous chemistry module CAPRAM 2.4 and designed cloud parcel simulations that mimicked several cloud cycles that a particle population may be exposed to in polluted urban environments. With ammonium nitrate and ammonium sulfate added to the activated particles, after the cloud evaporated, the activation potential of the resuspended aerosol particles increased for supersaturation thresholds lower than the maximum supersaturation attained in the cloud. Formation of sulfate and nitrate increased the internally mixed state of all particle populations, quantified by the mixing state index χ. The change of aerosol mixing state due to aqueous‐phase chemistry was related to the fraction of activated particles. For a case with low aerosol number concentration, where the activated fraction was up to 60%, χ increased by up to 50 percentage points after cloud processing, reaching an almost completely internal mixture. In contrast, for a case with high aerosol emissions and activated fraction of less than 20%, the increase in χ was less than 20 percentage points, and χ remained below 80% after cloud processing. The change in aerosol mixing state caused by coagulation within the cloud parcel was negligible. These findings highlight the complex influence of cloud processing on particle properties. Plain Language Summary: Every cloud droplet contains at least one aerosol nucleus. The composition and mass of this nucleus can be changed during a cloud's lifetime by several chemical and physical processes. Once the cloud evaporates, a modified aerosol population is released into the atmosphere compared to the population that formed the cloud, which may also have different impacts on climate. In this work, we used a particle‐resolved process model to study the effects of cloud processing on aerosols within clouds. This modeling approach is suitable for this research because each particle is tracked individually, which allows us to quantify changes in particle composition without simplifying assumptions, such as averaging composition within predescribed size ranges. Because of the formation of ammonium sulfate and nitrate in the cloud, particles that formed cloud droplets grew larger and were more likely to form cloud droplets in future cloud cycles. Overall, cloud processing by aqueous‐phase chemistry produced aerosol populations where the particles look more similar to each other in composition. Key Points: Aqueous‐phase chemistry processes cause aerosol populations to be more internally mixedThe change of aerosol mixing state due to aqueous phase chemistry was related to the fraction of activated particlesCoagulation within clouds has a negligible impact on aerosol mixing state
- Subjects
CLOUD dynamics; CLOUDS &; the environment; ATMOSPHERIC aerosols; AEROSOLS &; the environment; AIR pollutants
- Publication
Journal of Geophysical Research. Atmospheres, 2021, Vol 126, Issue 24, p1
- ISSN
2169-897X
- Publication type
Article
- DOI
10.1029/2021JD034992