Wet deposition of airborne lead

Scavenging by precipitation is an efficient means of removing particulate pollutants from the atmosphere. There are two main processes involved rainout, which is the scavenging by water droplets within the cloud layer, and washout, the scrubbing of air by falling raindrops (or snow). Precipitation scavenging is most effective for pollutants having a substantial vertical dispersal in the atmosphere, and the influence of local sources upon wet deposition is unlikely to be 

It is only recently that samplers have been developed which discriminate dry and wet deposition. From these, it is known that at background sites, remote from major sources of emission, dry and wet deposition each account for about a half of the total deposition of lead. 

Lead deposition at background sites in Britain has been measured as 0.046-0.186 mg m day [6]. This may be compared with the values determined at sites in and around London [7], shown in Table 4.2. Also included in this table is a value of lead deposition determined in Newcastle-upon-Tyne, England, in 1933, presumably as a result primarily of the burning of coal. This highly elevated level may be contrasted with the natural rate of 0.0044 mg day estimated from the analysis of lake sediments [8]. 

Newcastle-upon-Tyne, 1933 Deposit gauge 2.49 cited in [71 

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