Dry Deposition of Atmospheric Aerosols: Approaches, Observations, and Mechanisms

Farmer, Delphine K.; Boedicker, Erin K.; DeBolt, Holly M

doi:10.1146/annurev-physchem-090519-034936

Cited by 57 publications

(42 citation statements)

References 139 publications

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“…(5) Csanady (1973) proposed this approach, and Venkatram and Pleim (1999) obtained essentially the same solution as we will find below. They commented, in 1999, "why not use a formulation that is consistent with the mass conservation equation."…”

Section: A Simple Model With Added Gravitational Settlingmentioning

confidence: 62%

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Constant flux layers with gravitational settling: links to aerosols, fog and deposition velocities

Taylor

2021

Atmos. Chem. Phys.

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Abstract. Turbulent boundary layer concepts of constant flux layers and surface roughness lengths are extended to include aerosols and the effects of gravitational settling. Interactions between aerosols and the Earth's surface are represented via a roughness length for aerosol which will generally be different from the roughness lengths for momentum, heat or water vapour. Gravitational settling will impact vertical profiles and the surface deposition of aerosols, including fog droplets. Simple profile solutions are possible in neutral and stably stratified atmospheric surface boundary layers. These profiles can be used to predict deposition velocities and to illustrate the dependence of deposition velocity on reference height, friction velocity and gravitational settling velocity.

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Section: A Simple Model With Added Gravitational Settlingmentioning

confidence: 62%

“…Note that if z 0m = z 0c , then R s = 0, and this may be controversial. Zhang et al (2001), Slinn (1982 and many others (see Saylor et al, 2019;Farmer et al, 2021) combine these resistances with a gravitational settling velocity through the relationship…”

Section: Some Profilesmentioning

confidence: 99%

Constant flux layers with gravitational settling: links to aerosols, fog and deposition velocities

Taylor

2021

Atmos. Chem. Phys.

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“…It has been known for many years that fog water can be deposited on vegetation and this has been incorporated into some boundary-layer fog models. It is also known that μm size aerosols can be removed from the atmosphere by turbulence at water, and other, surfaces (Farmer et al, 2021). It then seems surprising that, for marine fog, turbulence induced cloud/fog droplet deposition to water surfaces has not been recognised by most modellers as a significant potential addition to the deposition associated with gravitational settling.…”

Section: Discussionmentioning

confidence: 99%

“…If we broaden our view and consider aerosols in general, we find that significant work has been done in the same size range as fog droplets (1-50 μm). Recent reviews by Emerson et al (2020) and Farmer et al (2021) make it very clear that dry deposition (i.e. not rainfall related) of aerosol particles, solid or liquid, is a key process for their removal, that it is driven by turbulence and strongly dependent on particle size.…”

Section: Aerosol and Vegetationmentioning

confidence: 99%

Surface deposition of marine fog and its treatment in the WRF model

Taylor

Chen

et al. 2021

Preprint

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Abstract. There have been many studies of marine fog, some using WRF and other models. Several model studies report over-predictions of near surface liquid water content (Qc) leading to visibility estimates that are too low. This study has found the same. One possible cause of this overestimation could be the treatment of a surface deposition rate of fog droplets at the underlying water surface. Most models, including the Advanced Research Weather Research and Forecasting (WRF-ARW) Model, available from the National Center for Atmospheric Research (NCAR), take account of gravitational settling of cloud droplets throughout the domain and at the surface. However, there should be an additional deposition as turbulence causes fog droplets to collide and coalesce with the water surface. A water surface, or any wet surface, can then be an effective sink for fog water droplets. This process can be parameterized as an additional deposition velocity with a model that could be based on a roughness length for water droplets, z0c, that may be significantly larger than the roughness length for water vapour, z0q. This can be implemented in WRF either as a variant of the Katata scheme for deposition to vegetation, or via direct modifications in boundary-layer modules.

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“…Size-resolved fluxes, however, help to deepen understanding on particle sources and dynamics in the urban boundary layer. Additionally, the flux data is essential to parameterise dry deposition velocities and to validate urban air quality models (Saylor et al, 2019;Farmer et al, 2021). Size-resolved flux observations may point to situations of bidirectional particle fluxes, i.e.…”

Section: Introductionmentioning

confidence: 99%

Measurement report: Three years of size-resolved eddy-covariance particle number flux measurements in an urban environment

Straaten

Weber

2021

Preprint

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Abstract. Size-resolved particle number fluxes in the size range 10 nm < particle diameter (Dp) < 200 nm were measured over a 3-year period (April 2017–March 2020) using the eddy covariance technique at an urban site in Berlin, Germany. The observations indicated the site as a net source of particles with a median total particle number flux of FTNC = 0.86 × 108 m−2 s−1. The turbulent surface-atmosphere exchange of particles was clearly dominated by ultrafine particles (Dp < 100 nm) with a share of 96 % of total particle number flux (FUFP = 0.83 × 108 m−2 s−1). Annual estimates of median FTNC and FUFP slightly decreased by −9.6 % (−8.9 % for FUFP) from the first to the second observation year and a further −5.9 % (−6.1 % for FUFP) from the second to the third year. The annual variation might be due to different reasons such as variation of flux footprints in the individual years, a slight reduction of traffic intensity in the third year or a progressive transition of the vehicle fleet towards a higher share of low-emission standards or electric drive. Size-resolved measurements illustrated events of bidirectional fluxes, i.e. simultaneous emission and deposition fluxes within the size spectrum, which occurred more often in spring, late summer and autumn than in winter. Multi-year observations of size-resolved particle fluxes proved to be important for deeper understanding of particle exchange processes with the urban surface and the pronounced influence of traffic at this urban site.

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Dry Deposition of Atmospheric Aerosols: Approaches, Observations, and Mechanisms

Cited by 57 publications

References 139 publications

Constant flux layers with gravitational settling: links to aerosols, fog and deposition velocities

Constant flux layers with gravitational settling: links to aerosols, fog and deposition velocities

Surface deposition of marine fog and its treatment in the WRF model

Measurement report: Three years of size-resolved eddy-covariance particle number flux measurements in an urban environment

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