Chemical Compositions of Dew and Scavenging of Particles in Changchun, China

Abstract

Dew and rain water were collected during 2013 and 2014 in Changchun, China. The dew was analyzed and the following parameters were measured: pH, EC, TDS, major anions (F−, Cl−,SO42-, andNO3-), and major cations (NH4+, Na+, K+, Ca2+, and Mg2+). The mean pH, EC, and TDS values of dew were comparable with the values for rainwater. The pH values of dew and rain were 6.72 and 6.16, respectively. Both EC (308 μS/cm) and TDS (154 mg/L) of dew were higher than those in rain samples. The concentration of main ions in dew was 1.5–5.7 times higher than levels in rainwater. The near-neutral pH values in dew were caused by the neutralization of acidity and buffering by the alkaline elements of soil origin (Ca2+). This neutralization was confirmed by a strong correlation between the acidic ions (SO42-andNO3-) and the major cations (Ca2+and Mg2+). Natural dust made an important contribution to the ions present in dews, but the presence of sulfate concentrations that are notably higher than rain water (up to 1584.5 μeq/L) indicated a significant contribution of anthropogenic sources. Dew has the ability to capture particulates, and the purifying effect on the underlying surface was obvious.

Urban dew and rain in Paris, France: Occurrence and physico-chemical characteristics

“…3), Paris rain being slightly more acidic than dew. This corresponds to the results found in some other urban areas as well as at humid sites (Xu et al, 2015 Tables 2-3).…”

The role of dew as a night-time reservoir and morning source for atmospheric ammonia

“…The average pH of dew at RMNP was 5.19 (median = 5.34), which is on the lower range of what has been reported for dew. For instance, Yaalon and Ganor (1968) and Xu et al (2015) found median dew pH of 7.7 and 6.72 in Jerusalem and Changchun, China, respectively, whereas Pierson et al (1986) reported an average dew pH of 4.0 at a rural site in Pennsylvania in a region containing several coalfired power plants. Given the remoteness of RMNP and low ionic concentrations, CO 2 dissolution plays an important role in governing dew pH.…”

“…Over the last 5 decades, several dozen studies have characterized dew composition and have found that NH + 4 is a ubiquitous constituent of dew and, in some environments, can be the most abundant cation (e.g. Polkowska et al, 2008;Wagner et al, 1992;Yaalon and Ganor, 1968;Yadav and Kumar, 2014). Average [NH + 4 ] reported in dew ranges from 25 µM (Lekouch et al, 2010) to 1600 µM (Yadav and Kumar, 2014).…”

Surface Wetness as an Unexpected Control on Forest Exchange of Volatile Organic Acids

“…Under wet conditions, these acids tend to partition to wet ecosystem surfaces inducing a downward flux, while under dry conditions, water films or droplets dry out and release acids to the atmosphere, thereby causing an upward flux. While simple solubility suggests that these volatile acids would dominantly remain in the gas phase, dew is often more alkaline than natural water, or water equilibrated with ambient CO 2 (dew pH > pKa for these acids) (Lekouch et al, 2010; Muselli et al, 2002; Takeuchi et al, 2002; Xu et al, 2015). The subsequent acid‐base equilibria will enhance partitioning from the atmosphere to the aqueous phase, as will additional hydrolysis chemistry or reactions.…”