Fog Deposition Research Articles

A pseudo-Lagrangian study of the sulfur budget in the remote Arctic marine boundary layer

The atmospheric sulfur cycle of the remote Arctic marine boundary layer is studied using trajectories and measurements of sulfur compounds from the International Arctic Ocean Expedition 1991, along with a pseudo-Lagrangian approach and an analytical model. The dimethyl sulfide [DMS(g)] turnover time was 59⁺¹⁸ ^-9h. Only 25⁺¹¹ _-9% of DMS(g) followed reaction paths to sulfur dioxide [SO₂(g)], sub-micrometre aerosol non-seasalt sulfate (nss-SO₄ ²⁻) or methane sulfonate (MSA). During the first 3 d of transport over the pack ice, fog deposition and drizzle resulted in short turnover times; 16⁺⁸ _-6 h for SO₂(g), 18⁺⁴ _-4h for MSA and 18⁺² ^-3 h for nss-SO₄ ²⁻. Therefore, DMS(g) will, owing to its origin along or south of the ice edge and longer turnover time, survive the original sub-micrometre sulfur aerosol mass and gradually replace it with new biogenic sulfur aerosol mass. The advection of DMS(g) along with heat and moisture will influence the clouds and fogs over the Arctic pack ice through the formation of cloud condensation nuclei (CCN). If the pack ice cover were to decrease owing to a climate change, the total Arctic Ocean DMS production would change, and potentially there could be an ice–DMS–cloud–albedo climate feedback effect, but it would be accompanied by changes in the fog aerosol sink.

Fog-water harvesting along the West Coast of South Africa: a feasibility study

Many parts of the West Coast of South Africa experience severe water shortages throughout the year. Despite the meager rainfall, however, the region is subject to a high incidence of fog which might provide water for water-poor communities. This paper investigates the fog water potential of the area. Since fog water collection rates are to some extent dependent upon the spatial and temporal characteristics of fog, these aspects were investigated. Pilot fog collectors were erected at six West Coast sites and the water collection rates measured over a three to four year period. It was found that the incidence of fog is mostly confined to the coastal zone below the 200 m contour line with fog frequency decreasing with latitude within this zone. The highest water collection rates were recorded at Cape Columbine where volumes in excess of 2.5 l/m2 of collecting surface can be expected to be collected per day. Of this, approximately 90% is due to fog deposition alone, while rainfall contributes to the remaining 10%. The quality of the water is good and fit for human consumption. WaterSA Vol.28(4) 2002: 349-360

A pseudo-Lagrangian study of the sulfur budget in the remote Arctic marine boundary layer

The atmospheric sulfur cycle of the remote Arctic marine boundary layer is studied using trajectories and measurements of sulfur compounds from the International Arctic Ocean Expedition 1991, along with a pseudo-Lagrangian approach and an analytical model. The dimethyl sulfide [DMS(g)] turnover time was 59+18-9h. Only 25+11-9% of DMS(g) followed reaction paths to sulfur dioxide [SO2(g)], sub-micrometre aerosol non-seasalt sulfate (nss-SO42−) or methane sulfonate (MSA). During the first 3 d of transport over the pack ice, fog deposition and drizzle resulted in short turnover times; 16+8-6 h for SO2(g), 18+4-4h for MSA and 18+2-3 h for nss-SO42−. Therefore, DMS(g) will, owing to its origin along or south of the ice edge and longer turnover time, survive the original sub-micrometre sulfur aerosol mass and gradually replace it with new biogenic sulfur aerosol mass. The advection of DMS(g) along with heat and moisture will influence the clouds and fogs over the Arctic pack ice through the formation of cloud condensation nuclei (CCN). If the pack ice cover were to decrease owing to a climate change, the total Arctic Ocean DMS production would change, and potentially there could be an ice–DMS–cloud–albedo climate feedback effect, but it would be accompanied by changes in the fog aerosol sink.

Fog deposition to Norway Spruce stands at high-elevation sites in the Eastern Erzgebirge (Germany)

Fog deposition was quantified by comparing the water budget of a small head-water catchment with direct measurements of evapotranspiration by the eddy-covariance-energy-budget-(ECEB)-method and with results of a resistance model. Results from the model showed a distinct altitudinal gradient in fog deposition mirroring different fog frequencies. For two water budget years the model amounted to 270 mm of occult precipitation, while the water budget comparison reached 215 mm. To characterize its contribution to element deposition fog was collected by active and passive samplers. Element fluxes were calculated by multiplying concentrations with modeled water fluxes stratified by wind directions in order to account for the influence of the Bohemian Industrial Basin. Element deposition through fog was in the case of SO 4 2−–S, NH 4 +–N and K + higher than wet deposition. Fog deposition is so an important path within bulk deposition for forested hill sites. The measured ion concentrations in fog water have declined considerably (60–90%) over the last 10 years at the same site. This trend confirms with other measurements of air pollution and atmospheric deposition in the Eastern Erzgebirge.

AEROSOL PARTICLE PROCESSING AND REMOVAL BY FOGS: OBSERVATIONS IN CHEMICALLY HETEROGENEOUS CENTRAL CALIFORNIA RADIATION FOGS

Fog composition and deposition fluxes of fog waterand fog solutes were measured in six radiation fogevents in San Joaquin Valley, California duringwinter 1998/1999. Measurements made at 2 hrintervals with 0.30 m2 and 0.06 m2 Teflondeposition plates yielded excellent reproducibility(relative standard deviations of 3.8–6.0%) forwater, nitrate, sulfate and ammonium. Water fluxesmeasured at 5 min intervals with a recordingbalance agreed well with the deposition platemeasurements before 8:00 AM. After 8:00 AMevaporation proved problematic. The averagedeposition velocity from the study for fog nitrate(3.8 cm s-1) was less than those for fogsulfate (5.1 cm s-1) and ammonium (6.7 cms-1). All three species generally exhibitedsmaller deposition velocities than fog water. Thespecies dependent trend in deposition velocitieswas consistent with preferential enrichment ofthese species in small fog drops (nitrate > sulfate> ammonium).

Throughfall and fog deposition of nitrogen and sulfur at an N-limited and N-saturated site in the San Bernardino Mountains, southern California

Inorganic nitrogen (N) and sulfur (S) deposition in bulk throughfall and fog were determined at two sites located at opposite ends (42 km apart) of a pollution gradient in the San Bernardino Mountains. Plot-level averages for total annual N and S deposition in throughfall in 1996 were 18.8 and 2.9 kg·ha-1, respectively, at Camp Paivika (CP) and 2.9 and 0.4 kg·ha-1, respectively, at Barton Flats (BF). Deposition of N in throughfall in the four transects at CP ranged from 12.1 to 31.7 kg·ha-1·year-1. Spatial variability was high because of heterogenous canopy cover and varying exposure to air pollution. Annual estimated stand-level deposition of N and S in fog were 10.9 and 1.9 kg·ha-1, respectively, at CP, and 0.6 and 0.2 kg·ha-1, respectively, at BF. We estimated that N deposition in fog contributed 35% of the total annual N deposition at CP and 13% at BF. Analogous values for S were 39% at CP and 26% at BF. Ammonium deposition in throughfall and fog at CP were 72 and 122% as high as NO3- deposition because of elevated NH3 emissions from dairy farms in the Chino-Norco area 34 km southwest of CP.

Isotopic assessment of the hydrologic importance of fog deposition on tall snow tussock grass on southern New Zealand uplands

The stable isotopic composition of rain, fog and groundwater was determined for three sites on the Otago upland snow tussocklands, southeastern South Island, New Zealand, for the snow-free period of November to June in 1996-1998. The rain and fog were collected concurrently, but the rain was consistently isotopically more depleted than the fog. The compositions of the rain form a line of the equation δD = 8.31δ 18 O + 13.6, which is similar to the line of δD = 8.11δ 18 O + 13.6 formed by the fog. The groundwater has compositions usually between those of the fog and rain, shows no isotopic evidence of evaporation, and is assumed to be a mixture of the two in sub-equal proportions. This pattern has been observed previously only in forested regions where the tree crowns act as collection mechanisms for fog water. On the Otago uplands, the only fog collection mechanism is interception gains through fog deposition on the relatively short (0.8-1.2 m) fine wispy foliage of the native tall snow tussock grasses (Chionochloa spp.). These results support earlier but debated claims that interception of fog by the foliage of the dominant tall snow tussock grasses makes a substantial contribution to the water yield from these uplands.

Isotopic assessment of the hydrologic importance of fog deposition on tall snow tussock grass on southern New Zealand uplands

Isotopic assessment of the hydrologic importance of fog deposition on tall snow tussock grass on southern New Zealand uplands

Leaf Epidermal Hydathodes and the Ecophysiological Consequences of Foliar Water Uptake in Species of Crassula from the Namib Desert in Southern Africa

Abstract: Epidermal hydathodes were found on leaves of 46 of 48 species of Crassula collected from the Namib Desert in southern Africa. The possibility that these structures might allow the absorption of surface water was investigated in 27 species (including subspecies). The presence of hydathodes on leaf epidermi correlated, in most cases, with increases in leaf thickness and enhanced rates of nocturnal, and sometimes diurnal, CO2 uptake following wetting of the leaves during the night. The precise nature of these responses varied depending on the species. In addition, wetting only the older leaves on the lower portion of the shoot of C. tetragona ssp. acutifolia not only resulted in increased thickness of these leaves, but also effected an increase in leaf thickness and stimulation of CO2 uptake rates in the distal, younger portion of the shoot that was not wetted. Overall, foliar hydathodes were implicated in the absorption of surface water in many species of Crassula such that the ecophysiology of these desert succulents was positively affected. Although rainfall in the Namib Desert is infrequent, surface wetting of the leaves is a more common occurrence as a result of nighttime dew or fog deposition. Presumably, species with hydathodes benefit directly from this source of moisture. These findings have important implications in understanding a relatively unexplored adaptation of some xerophytes to an extremely arid environment.

Summertime fog chemistry at a mountainous site in central Europe

In this paper, 1997 atmospheric visibility data as an indicator for the presence and density of fog at our ecosystem research site in the Fichtelgebirge mountains, Central Europe, are presented. At this location (about 800 m a.s.l.), fog occurred on 50% of the days and added up to a total fog duration of 1158 h in 1997. Using the visibility as a determining parameter, an automatic system for the collection of fog water was developed, including an automatic sampler, and sampling on an event basis. The data from the summer 1997 season exhibit a large variability in the chemical composition of fog. Easterly winds were associated with fog with higher concentrations of the major ions (NH 4 +, NO 3 −, SO 4 2−) and metals than westerly winds. Although the H + concentrations are lower than concentrations measured between 1983 and 1988 in NE Bavaria, it is not clear from our data alone if the negative trend over time is significant. A simple parameterization of fog deposition shows that fog plays an important role in the water balance of our forests. However, more detailed studies are needed to quantify this input, and the input of pollutants and nutrients to the ecosystems through fog deposition.

Throughfall and fog deposition of nitrogen and sulfur at an N-limited and N-saturated site in the San Bernardino Mountains, southern California

Inorganic nitrogen (N) and sulfur (S) deposition in bulk throughfall and fog were determined at two sites located at opposite ends (42 km apart) of a pollution gradient in the San Bernardino Mountains. Plot-level averages for total annual N and S deposition in throughfall in 1996 were 18.8 and 2.9 kg·ha-1, respectively, at Camp Paivika (CP) and 2.9 and 0.4 kg·ha-1, respectively, at Barton Flats (BF). Deposition of N in throughfall in the four transects at CP ranged from 12.1 to 31.7 kg·ha-1·year-1. Spatial variability was high because of heterogenous canopy cover and varying exposure to air pollution. Annual estimated stand-level deposition of N and S in fog were 10.9 and 1.9 kg·ha-1, respectively, at CP, and 0.6 and 0.2 kg·ha-1, respectively, at BF. We estimated that N deposition in fog contributed 35% of the total annual N deposition at CP and 13% at BF. Analogous values for S were 39% at CP and 26% at BF. Ammonium deposition in throughfall and fog at CP were 72 and 122% as high as NO3- deposition because of elevated NH3 emissions from dairy farms in the Chino-Norco area 34 km southwest of CP.

A Proposed Fog Deposition Mechanism for the Formation of Salt Efflorescences in the Mpumalanga Highveld, Republic of South Africa

White efflorescences, representing evaporites that coat stubble grass vegetation, were observed in September 1991 on a farm in the Ermelo area, Mpumalanga highveld of the Republic of South Africa. Occurrences were in irregular patches. Investigation of the evaporites by means of X-ray diffraction, differential thermal analysis, scanning electron microscopy with EDX, and chemical analyses revealed the following minerals, presented in order of decreasing abundance: thenardite, bloedite, gypsum and kieserite. Accumulation of the salts, which are highly water soluble, probably occurred during the six dry winter months, suggesting a deposition rate of up to 11–15 g of thenardite m-2 yr-1. It is proposed that the efflorescences had formed by fog impaction on grass blades. They are, to the authors' knowledge, the first recorded evaporite deposits formed by atmospheric deposition.

Relationship between chemistry of air, fresh snow and firn cores for aerosol species in coastal Antarctica

Aerosol and fresh snow concentrations have been determined at three coastal Antarctic stations, Dumont d'Urville, Halley, and Neumayer. Model estimates suggest that dry deposition, including that caused by wind pumping, is only a minor contributor (of order 1%) to chemical fluxes at these sites with relatively high snow accumulation. Larger dry deposition fluxes are possible for very large aerosol particles, including sea‐salt aerosol. Measurements of surface snow on successive days provide experimental data that constrain the contribution of dry deposition to probably less than 10% of annual fluxes for all ions, although very high episodic fluxes of giant sea‐salt aerosol cannot be ruled out. Spatial variability, and frequent snow, fog and drift events, make it difficult to improve this quantification. Both theory and measurement suggest that fog deposition is also a minor contributor to the annual flux (probably <1%). Sublimation of surface snow and of blowing snow may increase snow concentrations by a few percent, with a larger role in summer, but should not affect fluxes. Wet deposition in falling snow appears to be by far the major contributor. However, the relationship between concentrations in snow and in simultaneously sampled aerosol at ground level was poor for most species. Scavenging ratios derived from these data are higher than those from the limited data previously available, but have huge uncertainties associated with them. Particularly at sites with frequent drifting snow, groundlevel aerosol measurements may be inappropriate for deriving scavenging ratios. Despite this, there is a general seasonal coincidence of high aerosol concentrations and high snow concentrations. We are also able to trace the chemistry of fresh snowfall to an ice core collected up to 2 years later. Although some major snowfall events may be missing, it seems that, as expected, there is no significant postdepositional modification of chemistry for aerosol species in the top meter of firn.

Fog deposition in tall tussock grassland, South Island, New Zealand

Hill cloud microphysics was examined with a forward scattering spectrometer probe over tall tussock grassland at Swampy Summit near Dunedin, New Zealand. In a 4-month period, cloud water drop diameter spectra were obtained for 17 cloud–ground intersection events that varied from 1 to 61 h in duration. Rain fell in most events. Easterly conditions made up 60% of the events and had a median cloud drop diameter of 13.9 μm and 0.14 g m−3 liquid water content. For southwest winds, median drop diameter and liquid water content were significantly smaller at 9.8 μm and 0.05 g m−3.Aerodynamic conductance for momentum transfer, measured with a three-dimensional sonic anemometer, varied linearly with wind speed (R2=0.7) between 50 and 70 mm s−1 for wind speeds from 4 to 9 m s−1. Combining this relation with the cloud liquid water content measurements, cloud water deposition rates were estimated onto the 0.8-m-tall tussock canopy of one-sided leaf area index=3. These estimates were in the range 0.02–0.26 mm h−1 with a median of 0.05 mm h−1 which is the same as the median rate derived from the water balance of a large weighing lysimeter containing eight tussock plants. However, the water balance included a number of small quantities with determination of evaporation and rainfall being particularly difficult. Consequently, the lowest cloud water deposition rates for the water balance were sometimes negative. Nevertheless, even the maximum estimated rates incorporated into an annual calculation suggest cloud water deposition is unlikely to be a significant component of the water balance of a tall tussock grassland catchment. In the uplands of southern New Zealand, changing land use from tall tussock to pastoral agriculture with short vegetation is unlikely to alter streamflows via the cloud water deposition process.

Fog deposition on a coniferous forest in The Netherlands

Fog deposition in December 1992 and February 1993 (two periods of several days in which fog occurred) was monitored at the location Speulderbos in The Netherlands. Fog droplet deposition was measured with eddy correlation and samples of fog water were taken with a string collector. At the same time, throughfall deposition was measured and throughfall water was sampled. The occult (fog/cloud) deposition during these periods was 3.4 and 2.0 mg m −2s −1 respectively. Throughfall fluxes measured during these periods were a factor of three higher. The contribution of occult deposition to the total acid deposition to forests in The Netherlands is estimated to be about 5%. A clear relationship between the friction velocity u ∗ and turbulent deposition velocity v t of fog droplets could be derived. The measured turbulent deposition velocity for fog is half the deposition velocity for impulse v m.

Application of a multivariate chemical balance method to milan aerosol, fog and wet deposition data

Application of a multivariate chemical balance method to milan aerosol, fog and wet deposition data

A Proposed Standard Fog Collector for Use in High-Elevation Regions

Abstract The collection of fog droplets by vegetation is an important wet deposition process. It can, in fact, dominate the chemical and hydrological input to certain high elevation watersheds. However, measurements of fog deposition are rarely made and, where they do exist, comparisons of deposition rates in different locations have been hampered by the use of innumerable types of collection devices. A simple, inexpensive, 1-m2 fog collector that can produce measurements of the deposition of fog water to a vertical surface is described here. The collector has been used successfully in five countries to investigate the variation of fog deposition in complex terrain and to estimate the deposition to trees and to much larger fog collectors. It is proposed that it be employed widely as a standard to quantify the importance of fog deposition to forested high elevation areas and to measure the potential collection rates in denuded or desert mountain ranges. The standard fog collector costs about the same as a ...

Fluxes of chemical species to the Greenland ice sheet at Summit by fog and dry deposition

Experiments were performed during June–July 1992 to determine the impact of dry deposition and fog deposition on surface snow chemical inventories. The fluxes of SO 2− 4, NO − 3, Cl −, MSA, Na, Ca, and Al were measured by collecting deposited fog on flat polyethylene plates. Dry deposition fluxes of SO 2− 4 were measured using aerodynamic surfaces. Real-time concentrations of atmospheric particles greater than 0.5 um and greater than 0.01 um were measured using continuous monitors. Filter samplers were used to determine daily average atmospheric SO 2− 4 and MSA concentrations. Also, daily surface snow samples were taken and analyzed for SO 2− 4, NO − 3, Cl −, Na +, Ca 2+, and NHJ + 4. The real-time concentration data indicate that aerosol particles greater than 0.5 urn are efficiently incorporated into fog droplets. Results also show that condensation nuclei (CN) are not as greatly affected by fog as the larger particles. Fog fluxes of SO 2− 4 and NO − 3 have similar values and are approximately 4 times greater than those of Cl −, an order of magnitude greater than those of MSA, Na, and Ca, and two orders of magnitude greater than those of Al. The fog deposition flux of SO 2− 4 appears to be much greater than the dry deposition flux, based on experimental data. This indicates that dry deposition has a negligible effect on surface snow SO 2− 4 concentrations on days when there is fog. Such a finding is consistent with significant increases in surface snow SO 2− 4, NO − 3, and NH + 4 inventories seen after fog events. Cl − surface snow inventories are affected by fog but not as greatly. Variation in surface snow chemical inventories makes it difficult to obtain quantitative estimates of daily chemical fluxes. Surface snow Ca 2+ and Na + are relatively unaffected by post snowfall processes due to low atmospheric concentrations relative to the amount of material in fresh snow. Model results suggest that the fog fluxes have been underestimated by the current sampling technique.

Studies of fog events at two cloud forests near Caracas, Venezuela-I. frequency and duration of fog

Fog incidence was examined at two Venezuelan cloud forests directly to the Caracas Valley (Altos de Pipe, 1750 m elevation, and El Avila National Park, 2150 m) during the wet and dry seasons of 1989–1990. Fog frequency was extremely high during the morning hours; fog was present up to 92% of the time at 0800 h. Fog also was found to be a very important hydrological input in these high altitude forests during both the wet dry seasons. Preliminary measurements show that fog deposition accounts for an estimated 35 and 71% of annual precipitation at Altos de Pipe and El Avila, respectively, with fog occuring up to 326 days a year.

Air and fog deposition residues of four organophosphate insecticides used on dormant orchards in the San Joaquin Valley, California

Sampling was conducted at a station near Parlier, CA, in the inter, 1989, to assess the airborne concentrations of organophosphorus (OP) insecticides used as dormant sprays on deciduous fruit and nut orchards in the general region. For 24-h air samples, concentrations ranged to above 100 ng/m 3 for parathion, chlorpyrifos, and diazinon, and somewhat less (minimum ca. 30 ng/m 3 ) for methidathion. Nighttime air residues were generally higher than daytime residues, perhaps reflecting a lowered inversion boundary layer and calmer wind conditions at night. Oxons of the four OPs tended to be in higher amounts relative to the parent thions in day vs night samples, suggesting photochemical oxidant involvement in their formation