Dew Chemistry Research Articles

Seasonal contribution of dewfall to mercury deposition determined using a micrometeorological technique and dew chemistry

Deposition of mercury (Hg) to dew is thought to influence the diurnal dynamics of Hg species in the near‐surface air, yet this depositional pathway is not well characterized and is seldom accounted for in Hg budgets. This study quantifies Hg deposition to dew on a seasonal basis at a high‐elevation meadow in Shenandoah National Park, Virginia, and compares these rates with those for wet deposition and other forms of dry deposition. Dew samples were collected on a surrogate surface and analyzed for Hg concentrations (ng L−1), and dew depths (mm) were calculated using a micrometeorological approach based on the surface energy budget over 1 week period during each of the four seasons. Concentrations of Hg in dew (mean: 5.57 ng L−1) were lower than those observed in precipitation (mean weekly composite samples: 8.80 ng L−1). When dew deposition was scaled to the seasonal and annual levels, Hg deposition in dew was estimated to be 2–3 orders of magnitude smaller than wet deposition (estimated annual Hg deposition to dew/frost: ~120 ng m−2; 2008 annual precipitation deposition: ~12400 ng m−2). This disparity is attributed to the much lower dewfall amounts. Rates of Hg accumulation in dew were not related to gaseous elemental mercury (GEM) concentrations in the atmosphere nor were they related to measured GEM fluxes. They were, however, found to be similar to independently estimated rates of gaseous oxidized mercury (GOM) and particulate mercury (Hgp) deposition during the nighttime, suggesting that dew scavenges GOM and HgP from the atmosphere at the study site.

Dew chemistry and estimation of OH radical formation rates in forest area at Mt. Gokurakuji, Hiroshima, western Japan

Dew chemistry and estimation of OH radical formation rates in forest area at Mt. Gokurakuji, Hiroshima, western Japan

Chemical Composition of Dew Resulting from Radiative Cooling at a Semi-arid Site in Agra, India

Dew samples were collected between October 2007 and February 2008 from a suburban site in Agra. pH, conductivity, major inorganic ions (F−, Cl−, NO3−, SO42−, Na+, K+, Ca2+, Mg2+, and NH4+), and some trace metals (Cr, Sn, Zn, Pb, Cd, Ni, Mn, Fe, Si, Al, V, and Cu) were determined to study the chemistry of dew water. The mean pH was 7.3, and the samples exhibited high ionic concentrations. Dew chemistry suggested both natural and anthropogenic influences, with acidity being neutralized by atmospheric ammonia and soil constituents. Ion deposition flux varied from 0.25 to 3.0 neq m−2 s−1, with maximum values for Ca2+ followed by NH4+, Mg2+, SO42−, Cl−, NO3−, Na+, K+, and F−. Concentrations of trace metals varied from 0.13 to 48 μg l−1 with maximum concentrations of Si and minimum concentration of Cd. Correlation analysis suggested their contributions from both crustal and anthropogenic sources.

Modelling the dynamic chemical interactions of atmospheric ammonia with leaf surface wetness in a managed grassland canopy

Abstract. Ammonia exchange fluxes between grassland and the atmosphere were modelled on the basis of stomatal compensation points and leaf surface chemistry, and compared with measured fluxes during the GRAMINAE intensive measurement campaign in spring 2000 near Braunschweig, Germany. Leaf wetness and dew chemistry in grassland were measured together with ammonia fluxes and apoplastic NH4+ and H+ concentration, and the data were used to apply, validate and further develop an existing model of leaf surface chemistry and ammonia exchange. Foliar leaf wetness which is known to affect ammonia fluxes may be persistent after the end of rainfall, or sustained by recondensation of water vapour originating from the ground or leaf transpiration, so measured leaf wetness values were included in the model. pH and ammonium concentrations of dew samples collected from grass were compared to modelled values. The measurement period was divided into three phases: a relatively wet phase followed by a dry phase in the first week before the grass was cut, and a second drier week after the cut. While the first two phases were mainly characterised by ammonia deposition and occasional short emission events, regular events of strong ammonia emissions were observed during the post-cut period. A single-layer resistance model including dynamic cuticular and stomatal exchange could describe the fluxes well before the cut, but after the cut the stomatal compensation points needed to numerically match measured fluxes were much higher than the ones measured by bioassays, suggesting another source of ammonia fluxes. Considerably better agreement both in the direction and the size range of fluxes were obtained when a second layer was introduced into the model, to account for the large additional ammonia source inherent in the leaf litter at the bottom of the grass canopy. Therefore, this was found to be a useful extension of the mechanistic dynamic chemistry model by keeping the advantage of requiring relatively little site-specific information.

Application of linear discriminant analysis to the study of dew chemistry on the basis of samples collected in Poland (2004–2005)

AbstractThis paper presents the results of determination of selected characteristics (anions, cations, formaldehyde, hydrogen peroxide, phenols, TC, TIC, TOC and metals) in dew samples collected in six different sites in Poland. The influence of local parameters (e.g. wind speed, humidity) was investigated. Discriminant analysis was applied to the study of several dew samples collected from different sampling sites covering six agglomerations in Poland. Discriminant function analysis was used not only for classifying samples into different groups with a better than chance accuracy, but also for detecting the most important variables that discern between the groups of samples considered. In this way it was possible to identify which ions or other physicochemical features are responsible for the similarities or differences observed between different groups of dew samples. A good agreement with their origin and location was observed. It is interesting to note that the classification of all samples was dominated by pH, wind direction, pressure and temperature with a significant contribution of Na+ and Cl− ions.

Controlling Factors of Weak Acid and Base Concentrations in Urban Dewwater—Comparison of Dew Chemistry with Rain and Fog Chemistry—

Abstract Dewwater was collected from January 1993 to December 2000 in Yokohama, Japan, and analyzed for weak acid anions with other major chemical components. The volume-weighted average and medium pH of the dewwater were 4.88 and 6.08, respectively, at our sampling site. Weak acids (carbonate, nitrite, sulfite, formate, and acetate ions) were the major species in the dewwater and were several times higher than those in the rain- and fogwater. The concentrations of these species and ammonium ion can be estimated by the resistance model. The estimated values of N(III) correlate relatively well with the measured values, which shows the origin of N(III) in dewwater is nitrous acid in the ambient air. On the other hand, ammonium ion in the dewwater originated from not only gaseous ammonia but also aerosol ammonium ions. Hydrogensulfite ions in the dewwater which originated from sulfur dioxide are an important species as the precursor of the sulfate and they were stabilized by forming hydroxyalkanesulfonate (HASA). Formic acid and acetic acid in the dewwater originated mainly from gas, while the oxalic acid is from aerosol.

Effect of Acid Deposition on Urban Dew Chemistry in Yokohama, Japan

Abstract Dews or frosts formed on artificial collectors were collected during the early morning in Yokohama in 1993 and 1994 and analyzed for weak acids as well as major inorganic ions. In 1993 (n = 21) the dew pH ranged from 3.23 to 7.12 and averaged 4.60; in 1994 (n = 56) it ranged from 4.11 to 7.74 and averaged 5.41. Based on the average, NH4+ and Ca2+ were major cations (423 and 178 μequiv L−1 for NH4+ and Ca2+ in 1993, respectively, and 454 and 274 μequiv L−1 in 1994, respectively) and SO42− was the dominant anion (344 μequiv L−1 in 1993 and 271 μequiv L−1 in 1994) in dew water. The dew chemistry was characterized by relatively high concentrations of weak acid anions, particularly hydrogensulfite ion (HSO3−). Dew water sometimes had very high acidity (the minimum pH was 3.23 during the period of this research), which might have been due to the aqueous oxidation of S(IV). From a resistance model calculation, the S(IV) concentration in dew water was suggested to be influenced by the dissolution of HCHO from the atmosphere and the subsequent formation of HMSA.

The influence of manganese leached from plants on dew chemistry

Abstract High concentrations of manganese, which are believed to be catalytically active for the oxidation of sulfite, are found in dew water on grass. In order to describe this oxidation the reaction was studied in a fog chamber. In the concentration and pH range normally found in dew on grass, the formation of sulfate is linearly dependent on the concentration of manganese and on the square root of the concentration of sulfite. The results indicate that the manganese‐catalyzed sulfite oxidation is an important reaction in dew on grass.

Dew Chemistry and Acid Deposition in Glendora, California, During the 1986 Carbonaceous Species Methods Comparison Study

Dew was collected and analyzed during the Carbonaceous Species Methods Comparison Study in the Los Angeles basin (Glendora, CA) in August 1986. Formate, acetate, and other carboxylate anions were consistently observed, with formate generally being the most abundant anion in the dew. These carboxylate anions appear to be attributable to deposition of carboxylic acids from the ambient air. Free acid (H+) was only about one-fifth of the total dew acidity; carboxylic acids could have accounted for half of the remainder. The H+ concentrations were far lower than in dew in the northeast United States (respective pH averages 4.7 and 4.0). Whereas dew in the Northeast was essentially a dilute HNO3/ H2SO4 mixture, that in Glendora contained substantial amounts of many other inorganic species. S(IV) in the dew in Glendora was stable against oxidation, even by H2O2, probably signifying formation of the bisulfite adduct with formaldehyde (considerable amounts of formaldehyde and acetaldehyde were present), in contras...

The chemistry of dews and frosts in indianapolis, Indiana

Dews and frosts forming on chemically clean Teflon surfaces were sampled for pH and ion concentrations during a 13-month period in urban Indianapolis, Indiana. We predicted that dews forming in this polluted atmosphere would be acidic due to absorption of SO 2, NO 2 and CO 2, but that frost pH would be neutral due to the lack of gas absorption. However, measured pH ranged from 6.0 to 7.2, and dew and frost pH were not significantly different. Anion and cation concentrations did not differ between dews and frosts, implying similar mechanisms and rates for scavenging of atmospheric chemicals. Sulfite and nitrite were present in many samples, indicating SO 2 and NO 2 absorption by both dews and frosts. The presence of ions (K +, Ca 2+, Mg 2+, Na +) lacking gaseous sources suggested that sedimentation of aerosols, primarily carbonates and salts, from surrounding agricultural lands occurred into dews and frosts as they formed. Carbonate deposition may have been responsible for near-neutral dew and frost pH. Dews sampled from sugar maple leaves were depleted of ammonium and enriched in other ions, but did not differ substantially in pH, compared to dews simultaneously sampled from Teflon. Temporal (overnight) sampling of dews on Teflon showed that dew chemistry changed substantially during the course of the night.

Dry deposition and dew chemistry in Claremont, California, during the 1985 nitrogen species methods comparison study

Dry deposition of HNO 3 and aerosol nitrate in Claremont, California, during the September 1985 Nitrogen Species Methods Comparison Study was evaluated by means of nylon and Teflon surrogate-surface collectors. Dew chemistry and deposition to dew were also investigated. The nitrate dry deposition was governed largely by HNO 3; most of the dry deposition of inorganic nitrate (defined here as HNO 3(g) plus aerosol nitrate) onto the surrogate collectors occurred in the daytime, reflecting chiefly a greater-than-10-fold diurnal variation in ambient HNO 3 (g) concentration. In the absence of dew, deposition velocities were ~1.3cms −3 for HNO 3(g), ~0.2cms −1 for aerosol nitrate, and 0.5cms −1 for nitrate without distinction between the two species. Night-time nitrate deposition velocities appeared to be lower when there was dew. The total titratable acidity of the dew, though considerable (~ 50 μM), was not present chiefly as free acidity (H +); the average pH was only ~ 5. Preliminary evidence suggests that some of the titratable dew acidity was derived from organic acids. These results are compared to dry deposition and dew chemistry in other areas.