Abstract
The relationship between dew and airborne particles is important in urban ecosystems, but the capability of dew to remove airborne particles remains unclear. During 2015 in Changchun, China, 74 dew and particle samples were collected simultaneously to investigate their chemical characteristics under normal, fog, and haze conditions. Analyses included measuring total dissolved solids, total suspended particulates, PM2.5 and PM10 concentrations, major cations (NH4+, Na+, K+, Ca2+, and Mg2+), major anions (F−, Cl−, SO42-, and NO3-), and organic and elemental carbon. Results showed that air quality deteriorated during haze but improved in fog. The particle size distributions, major cations, and carbonaceous species documented in the dew and airborne particles demonstrated consistent synchronous patterns with values descending in the order haze > normal > fog conditions. We found that dew is a good indicator of near-surface air quality. Specifically, its water-soluble ions and carbonaceous species could be used to distinguish emission sources and to identify the presence of secondary organic carbon. Dew is more effective at removing airborne particles in normal weather than in haze or fog conditions; PM2.5 removal rates were 21.5%, 15.2%, and 13.7% on normal, foggy, and hazy days, respectively. Dew condensation processes reduce concentrations of gaseous and particulate pollutants in the near-surface layer.
Highlights
Dew condensation is a common meteorological phenomenon
The particle size distributions changed little with proportions of PM2.5, PM10, and >PM10 established as 12.78%, 27.23%, and 59.99%, respectively
Because fog usually occurred after rainfall, air quality on such days was generally good
Summary
Dew condensation is a common meteorological phenomenon. Because of urban surface hardening and the heat island effect, is the frequency of dew occurrence in urban ecosystems high, and the condensation quantity is large [1, 2]. The dew condensation process represents effective natural atmospheric purification [3, 4]. Dew formation can help purify urban air [3], and dew is recognized as the sink of nighttime moisture and near-surface particulate matter (e.g., PM2.5 and PM10) [6]. The concentrations of both particulate matter and ions in dew are higher than in rain samples [1, 7]. The sedimentation of airborne particles is linked to both wet deposition (rain, snow, fog, and dew) and dry sedimentation processes (gravity settling), the former is the primary pathway via which pollutants are removed from the atmosphere [8]
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