On the use of scavenging ratios for the inference of surface-level concentrations and subsequent dry deposition of Ca²⁺, Mg²⁺, Na⁺ and K⁺

Abstract

An inference technique is developed that allows estimation of the annual and monthly dry deposition of Ca²⁺, Mg²⁺, Na⁺, and K⁺. Conceptually, this technique is based on the premise that precipitation efficiently scavenges aerosols, resulting in a strong correlation between concentrations within precipitation and the surface-level air. Empirically, it is based on the linear relationship exhibited between the measured surface-level air and precipitation concentrations at 23 stations in Ontario, Canada, for the period 1983–1985. Correlations ranged from 0.513 for K⁺ to 0.946 for Mg²⁺. Because of the stochastic nature of such an approach, the assumptions inherent to the concept of scavenging ratios, and therefore this inference technique, must be carefully considered. Under such considerations, annual and monthly dry deposition of alkaline aerosols can be estimated at many locations across North America where precipitation concentrations are routinely measured.