Aerosol Scavenging Processes in Atmospheric Systems

Aerosol scavenging processes represent the ensemble of mechanisms by which particulate matter is removed from the atmosphere. These include in-cloud and below-cloud interactions with hydrometeors that lead to wet deposition, as well as processes that result in dry deposition onto surfaces. In-cloud scavenging occurs when particles act as cloud condensation or ice nuclei, becoming incorporated into cloud droplets or ice crystals and subsequently precipitating. Below-cloud scavenging, often termed impaction or washout, involves the capture of particles by falling raindrops or snowflakes as they descend through an aerosol-laden column of air. The efficiency of both pathways is governed by particle size, chemical composition, hygroscopicity and the intensity and type of precipitation. Scavenging coefficients are widely used to parameterise the removal rate in transport and climate models. Variability in meteorological conditions, cloud microphysics and aerosol properties leads to spatial and temporal heterogeneity in deposition patterns. Understanding these processes is critical for accurate simulation of aerosol lifetimes, radiative forcing and pollutant deposition to ecosystems and the built environment. Recent advances have improved representation of size-dependent collection efficiencies and have highlighted the interplay between aerosol composition and cloud dynamics, informing air quality management and climate projections.

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Aerosol Scavenging Processes in Atmospheric Systems publication trend

The graph below shows the total number of articles in aerosol scavenging processes in atmospheric systems across all publications each year (not limited to Nature Index journals).

Technical terms

Scavenging coefficient: A parameter expressing the rate at which aerosol particles are removed from air by precipitation per unit time.

Washout ratio: The concentration ratio between dissolved or suspended species in precipitation and in ambient air, used to assess below-cloud removal efficiency.

In-cloud scavenging: Incorporation of particles into cloud droplets or ice crystals via nucleation or impaction, leading to precipitation of those particles.

Below-cloud scavenging: Capture of aerosol particles by falling hydrometeors through processes of impaction, interception or Brownian diffusion.

Hygroscopicity: The ability of aerosol particles to take up water vapour, influencing their activation as cloud condensation nuclei.

Wet deposition: The removal of airborne particles or gases from the atmosphere by precipitation, including rain, snow or fog.

References

1. Intra-event evolution of elemental and ionic concentrations in wet deposition in an urban environment. Atmospheric Chemistry and Physics (2023).
2. An optimisation method to improve modelling of wet deposition in atmospheric transport models: applied to FLEXPART v10.4. Geoscientific Model Development (2023).
3. Development of a new semi-empirical parameterization for below-cloud scavenging of size-resolved aerosol particles by both rain and snow. Geoscientific Model Development (2014).