Physical factors influencing winter precipitation chemistry

Abstract

Two case studies of winter precipitation events highlight the roles of transport and snow crystal riming (the capture of supercooled cloud droplets by snow crystals) in determining precipitation chemistry. In one case, passage of a cold front leads to a change in the air mass producing precipitation over the monitoring site. A simultaneous decrease in precipitation ion concentrations is observed. Correlations of the ion concentrations with the pseudoequivalent potential temperature, which serves as an air mass identifier, suggest that the decrease in ion concentrations is caused by the air mass change, rather than by washout of aerosols and gases from the atmosphere. In the second case, evidence is presented indicating that an increase in precipitation ion concentrations results from significant capture of polluted cloudwater droplets by the snow crystals. Influences on precipitation chemistry from both processes, transport and riming, can be large. In order to study other processes influencing precipitation chemistry that occur on similar time scales (minutes to hours), such as aerosol and gas scavenging or aqueousphase oxidation, it is important to evaluate possible confounding effects of tranmort and riming.

A seasonal nitrogen deposition budget for Rocky Mountain National Park

“…These observations support the expectation that wet deposition fluxes depend on meteorological conditions that yield high nitrogen species concentrations in RMNP and also produce precipitation. The efficiency with which pollutants are scavenged and deposited by precipitation can also be strongly influenced by cloud microphysical processes such as the extent of ice crystal riming (e.g., Collett et al 1991b), an issue not investigated in the current study.…”

Influence of temperate mixed and deciduous tree covers on Hg concentrations and photoredox transformations in snow

“…Snow is highly efficient at scavenging pollutants during crystal growth or during washout from the atmosphere (Collett et al, 1991;Franz and Eisenreich, 1998). Both organic (Carrera et al, 2001) and inorganic (Barbante et al, 2003) compounds can be incorporated into snow and may contribute to the overall contamination of snowpacks in northern (Garbarino et al, 2002) as well as in temperate areas (Veysseyre et al, 2001a,b).…”

Rapid change in nitrate and sulfate concentrations observed in early stage of precipitation and their deposition processes

“…Detailed analysis of temporal changes in pH values and ion concentrations from the measurements during individual precipitations was not performed. Collett et al (1991) observed individual precipitations in winter to investigate the physical factors influencing the ion deposition processes of snow. The observation periods were not continuous and, thus, the average ion deposition characteristics could not be obtained.…”