Skip to content

Review and uncertainty assessment of size-resolved scavenging coefficient formulations for below-cloud snow scavenging of atmospheric aerosols

by L. Zhang, X. Wang, M. D. Moran, J. Feng
Atmospheric Chemistry and Physics ()
Get full text at journal


Theoretical parameterizations for the size-resolved scavenging coefficient for atmospheric aerosol particles scavenged by snow (Λsnow) need assumptions regarding (i) snow particle-aerosol particle collection efficiency <i>E</i>, (ii) snow-particle size distribution <i>N(D</ i>p), (iii) snow-particle terminal velocity <i>V</ i><i>D</i>, and (iv) snow-particle cross-sectional area <i>A</i>. Existing formulas for these parameters are reviewed in the present study, and uncertainties in Λsnow caused by various combinations of these parameters are assessed. Different formulations of <i>E</i> can cause uncertainties in Λsnow of more than one order of magnitude for all aerosol sizes for typical snowfall intensities. <i>E</i> is the largest source of uncertainty among all the input parameters, similar to rain scavenging of atmospheric aerosols (Λrain) as was found in a previous study by Wang et al. (2010). However, other parameters can also cause significant uncertainties in Λsnow, and the uncertainties from these parameters are much larger than for Λrain. Specifically, different <i>N(D</i>p) formulations can cause one-order-of-magnitude uncertainties in Λsnow for all aerosol sizes, as is also the case for a combination of uncertainties from both <i>V</i><i>D</i> and <i>A</i>. Assumptions about dominant snow-particle shape (and thus different <i>V</i><i>D</i> and <i>A</i>) will cause an uncertainty of up to one order of magnitude in the calculated scavenging coefficient. In comparison, uncertainties in Λrain from <i>N(D</i>p) are smaller than a factor of 5, and those from <i>V</i><i>D</i> are smaller than a factor of 2. As expected, Λsnow estimated from empirical formulas generated from field measurements falls in the upper range of, or is higher than, the theoretically estimated values, which can be explained by additional processes/mechanisms that influence field-derived Λsnow but that are not considered in the theoretical Λsnow formulas. Predicted aerosol concentrations obtained by using upper range vs. lower range of Λsnow values (a difference of around two orders of magnitude in Λsnow) can differ by a factor of 2 for just a one-centimetre snowfall (liquid water equivalent of approximately 1 mm). Based on the median and upper range of theoretically generated Λsnow and Λsnow values, it is likely that, for typical rain and snow events, the removal of atmospheric aerosol particles by snow is more effective than removal by rain for equivalent precipitation amounts, although a firm conclusion requires much more evidence. © Author(s) 2013.

Cite this document (BETA)

Authors on Mendeley

Readership Statistics

8 Readers on Mendeley
by Discipline
38% Environmental Science
38% Earth and Planetary Sciences
13% Chemistry
by Academic Status
50% Researcher
25% Student > Master
13% Student > Bachelor

Sign up today - FREE

Mendeley saves you time finding and organizing research. Learn more

  • All your research in one place
  • Add and import papers easily
  • Access it anywhere, anytime

Start using Mendeley in seconds!

Sign up & Download

Already have an account? Sign in