Uncertainty assessment of current size-resolved parameterizations for below-cloud particle scavenging by rain

Abstract

Abstract. Current theoretical and empirical size-resolved parameterizations of the scavenging coefficient ( ), a parameter commonly used in aerosol transport models to describe below-cloud particle scavenging by rain, have been reviewed in detail and compared with available field and laboratory measurements. Use of different formulations for raindropparticle collection efficiency can cause uncertainties in sizeresolved values of one to two orders of magnitude for particles in the 0.01-3 µm diameter range. Use of different formulations of raindrop number size distribution can cause values to vary by a factor of 3 to 5 for all particle sizes. The uncertainty in caused by the use of different droplet terminal velocity formulations is generally small than a factor of 2. The combined uncertainty due to the use of different formulations of raindrop-particle collection efficiency, raindrop size spectrum, and raindrop terminal velocity in the current theoretical framework is not sufficient to explain the one to two order of magnitude under-prediction of for the theoretical calculations relative to the majority of field measurements. These large discrepancies are likely caused by additional known physical processes (i.e, turbulent transport and mixing, cloud and aerosol microphysics) that influence field data but that are not considered in current theoretical parameterizations. The predicted size-resolved particle concentrations using different theoretical parameterization can differ by up to a factor of 2 for particles smaller than 0.01 µm and by a factor of >10 for particles larger than 3 µm after 2-5 mm of rain. The predicted bulk mass and number concentrations (integrated over the particle size distribution) can differ by a factor of 2 between theoretical and empirical parameterizations after 2-5 mm of moderate intensity rainfall.

Laboratory studies of collection efficiency of sub-micrometer aerosol particles by cloud droplets on a single-droplet basis

“…Previous studies have theoretically determined the CE between droplets and aerosol particles (Slinn and Shen, 1970;Beard, 1974;Grover et al, 1977;Davenport and Peters, 1978;Wang et al, 1978;Park et al, 2005;Tinsley et al, 2000Tinsley et al, , 2006Chate, 2005;Andronache et al, 2006;Feng, 2007;Croft et al, 2009;Tinsley, 2010;Wang et al, 2010;Tinsley and Leddon, 2013). In order to understand our experimental data, we compare them to a theoretical treatment of CE.…”

“…According to Santachiara et al (2012), significant discrepancies between theoretical and experimental studies have been found for submicrometer particles in the "Greenfield gap", and the measured values can be 1 to 2 orders of magnitude higher than predicted. According to Wang et al (2010), this disagreement could be because some physical processes considered in theoretical models are neglected, difficult to represent or hard to control in experimental studies.…”

Estimates of Atmospheric Aerosols Adhered to the High Voltage Electric wire in the Yangtze River Delta Region of China

“…E E is a new term added in this study, representing the collection efficiency by electric force generated by wire on particles. According to Wang et al (2010), E E is parameterized as:…”

“…Here, the length of wire was chosen as 100 times of particle size in order to generate effective electric force between wire and any size particles. q can be calculated according to Wang et al (2010):…”

Dependence of Daily Aerosol Wet Deposition on Precipitation at Appalachian Mountains Site in the United States

“…Wet deposition is the removal of atmospheric particles by precipitation and is often divided in two main processes: in-cloud and below-cloud scavenging (Andronache, 2003(Andronache, , 2006Henzing et al, 2006;Sportisse, 2007;Feng, 2009;Wang et al, 2010). Specific conditions determine the relative importance of each process and, overall, during significant precipitation events, the in-cloud scavenging is dominant.…”