Geographical variations of major and trace elements in East Antarctica

Surface snow samples have been analyzed for a total of 37 elements including Na, Mg, Al, K, Ca, Fe, Ba, Cd, Fe, Cd, Cr, Cu, Ga, Li, Mn, Pb, Se, Sr, V, Zn, As, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Th by inductively coupled plasma mass spectroscopy (ICP-MS). Rare earth elements in surface snow were evaluated after preconcentration of the samples in a class 1000 clean room. These samples were collected between 1991–1993 during the oversnow traverses along a 2200 km route in East Queen Maud Land, Antarctica. They include one at Dome Fuji Station (77°32′S, 24°08′E; 3810 m a.s.l.) built on the top of the second highest dome. In coastal area, fallout flux for Na, Mg, Sr and Cu or more weakly for Ca and Ba shows an apparent decrease according to the distance from the coast. On the other hand, fallout flux for Co, Ni and Cd shows an increase at 2500–3000 m or >3500 m above sea level. For Mn, Se, Zn and As, it shows a combined pattern of these two types. For Al, V and Pb, a constant profile with an intermittent peaks along this route was indicated. These geographical distributions of fallout flux for each element could reflect polar stratospheric precipitation or long-range tropospheric transport from the southern hemisphere. In the present study, concentrations of rare earth elements in Antarctic surface snow at sub-ppt level are first reported. A clear rare earth pattern is noticed in the Antarctic samples and rare earth ratios are also valuable to estimate anthropogenic emissions to the Antarctica.     

Total and methyl mercury patterns in Arctic snow during springtime at Resolute,Nunavut, Canada

Patterns of gaseous elemental mercury (GEM) were monitored at 20 and 150 cm above the snowpack near Resolute Bay, Cornwallis Island, Nunavut, Canada near the Upper Air Station of Environment Canada (74°42′N, 94°58′W) from 7 May (day 127) to 12 June (day 163) 2003. At this time of year there was 24 h daylight but still a strong diel change in solar radiation. Daily patterns of GEM-tracked solar radiation with a lag of about 2 h and the GEM gradient between these two heights showed the direction of flux. In addition to the previously established autocatalytic reactions involving halogens where reactive gaseous mercury and fine particulate mercury result in direct deposition to the snow, both diffusion to and volatilization from the snow occurred on a regular basis. Total mercury (THg) in the snowpack increased to near 30 ng L⁻¹ following 8 d of atmospheric mercury depletion then decreased to values near 1 ng L⁻¹. Losses from the snow could not be accounted for in melt water as stream runoff values were also low. In other words, most of the mercury associated with increased levels in snow was volatilized back to the atmosphere either directly from the snow or from the water surfaces. However, using accepted mass transport coefficients, the flux appeared low and other mechanisms are suggested. In contrast to THg, methyl mercury (MeHg) in the snow reached values near 140 pg L⁻¹ but also declined to less than detection limit (10 pg L⁻¹) with the onset of warmer temperatures. MeHg in stream runoff water was similar to maximal values seen in the snow. This observation is consistent with the view that MeHg came in the snowfall or was deposited to the snow pack rather than produced in the snow. In contrast, much of the THg associated with mercury depletion events was volatilized back to the atmosphere.     

Black carbon concentrations in precipitation and near surface air in and near Halifax,Nova Scotia

Black carbon (soot) concentrations have been measured in rain water, snow samples and near surface air at several locations in Nova Scotia, Canada. The average black carbon concentration in near surface air in summer was found to be 0.54 μg m^-3 compared to 1.74 μg m^-3 in the winter season. These values are comparable to black carbon concentrations found in other mid-size urban areas. The black carbon concentration in rain water and snow samples varied between an undetectable amount to about 20 μg kg^-1 of rain (or melt) water. The relatively low concentrations of black carbon in precipitation are attributed to extratropical cyclones that often develop off-shore to the east and south of Nova Scotia in relatively clean conditions of the marine boundary layer.     

Chemical composition of snowfall in the high Arctic: 1990–1994

From 1990 to 1994 at Alert, Nunavut, Canada, weekly snow samples were collected under low wind conditions to avoid contamination by blowing snow. They were analysed for major ions, Br⁻, and the organic ions methylsulphonate, formate, acetate and propionate. In the Arctic, where annual precipitation is low and blowing snow is common, these observations are unique. On an equivalent weight basis, acids and sea salt in snowfall are mixed approximately equally from December to January but from March to May acids dominate. The acidity of snowfall increases progressively throughout the winter to a May peak of ∼16 μeq l⁻¹. SO₄²⁻, Br⁻, and the organic acids acetate, and propionate peak in snowfall after polar sunrise indicate the influence of enhanced photochemical reactions. The greater enrichment of halides relative to sea salt Na⁺ in snow compared to aerosols indicates that gaseous uptake by snowflakes is important in the removal of these substances from the atmosphere and their deposition on to the Earth's surface. There is a marked difference between the seasonal variation of enrichment of Cl⁻ and Br⁻ in snow. The latter show a marked increase after polar sunrise while the former does not. These results provide valuable baseline information on the ionic content of fresh snowfall to be used in understanding the results of snowpack chemistry and post-depositional process studies conducted in the high Arctic.     

PM10 measurements at McMurdo Station,Antarctica

PM₁₀ aerosols at McMurdo Station, Antarctica were sampled continuously during the austral summers of 1995–1996 and 1996–1997. PM₁₀ (particles with aerodynamic diameters less than 10 μm) mass concentrations at Hut Point, located less than 1 km from downtown McMurdo, averaged 3.4 μg m⁻³, more than an order of magnitude lower than the USEPA annual average National Ambient Air Quality Standard (NAAQS) of 50 μg m⁻³. Concentrations of methanesulfonate and nitrate were similar to those measured at other Antarctic coastal sites. Non-sea-salt sulfate (NSS) concentrations on Ross Island were higher than those found at other coastal locations. The average elemental carbon concentration (129 ng m⁻³) downwind of the station was two orders of magnitude higher than those measured at remote coastal and inland Antarctic sites during summer. Average sulfur dioxide concentrations (746 ng m⁻³) were 3–44 times higher than those reported for coastal Antarctica. Concentrations of Pb and Zn were 17 and 46 times higher than those reported for the South Pole. A methanesulfonate to biogenic sulfate ratio (R) of 0.47 was derived that is consistent with the proposed temperature dependence of R.     

Seasonal patterns of heavy metal deposition to the snow on Lambert Glacier basin,East Antarctica

Al, V, Mn, Fe, Cu, As, Cd, Ba, Pb, Bi and U were determined in a continuous series of 46 snow samples from a 2.3-m snow pit, covering the time period from austral spring 1998 to summer 2002, at a site on the east side of the Lambert Glacier basin in East Antarctica. Concentrations are very low for all metals and differ by orders of magnitude from one metal to another, with the mean concentrations ranging from 0.028 pg g⁻¹ for Bi to 165 pg g⁻¹ for Al. It is estimated that anthropogenic contributions are dominant for Cu, Pb and probably As, in the snow in our study area while the natural contributions from rock and soil dust, sea-salt spray and volcanic emissions account for most of the measured concentrations of the other metals. Our snow profiles show pronounced seasonal variations for Mn, As, Ba, Pb and Bi throughout the year, but a very different situation is observed between different metals. These observations suggest that heavy metals determined in our samples are controlled by different transport and deposition mechanisms related to physical and chemical alterations in the properties and sources of aerosol.     

Spatial and seasonal variations of elemental composition in Mt. Everest (Qomolangma) snow/firn

In May 2005, a total of 14 surface snow (0–10 cm) samples were collected along the climbing route from the advanced base camp to the summit (6500–8844 m a.s.l.) on the northern slope of Mt. Everest (Qomolangma). A 108 m firn/ice core was retrieved from the col of the East Rongbuk Glacier (28.03°N, 86.96°E, 6518 m a.s.l.) on the north eastern saddle of Mt. Everest in September 2002. Surface snow and the upper 3.5 m firn samples from the core were analyzed for major and trace elements by inductively coupled plasma mass spectroscopy (ICP-MS). Measurements show that crustal elements dominated both surface snow and the firn core, suggesting that Everest snow chemistry is mainly influenced by crustal aerosols from local rock or prevalent spring dust storms over southern/central Asia.There are no clear trends for element variations with elevation due to local crustal aerosol inputs or redistribution of surface snow by strong winds during the spring. Seasonal variability in snow/firn elements show that high elemental concentrations occur during the non-monsoon season and low values during the monsoon season. Ca, Cr, Cs, and Sr display the most distinct seasonal variations. Elemental concentrations (especially for heavy metals) at Mt. Everest are comparable with polar sites, generally lower than in suburban areas, and far lower than in large cities. This indicates that anthropogenic activities and heavy metal pollution have little effect on the Mt. Everest atmospheric environment. Everest firn core REE concentrations are the first reported in the region and seem to be comparable with those measured in modern and Last Glacial Maximum snow/ice samples from Greenland and Antarctica, and with precipitation samples from Japan and the East China Sea. This suggests that REE concentrations measured at Everest are representative of the background atmospheric environment.     

Spatial and temporal variations in San Joaquin Valley fog chemistry

Fog was sampled at four locations in California’s San Joaquin Valley (SJV) during December 1995 and January 1996 as part of the 1995 Integrated Monitoring Study (IMS95). The fog sampling campaign was conducted in two phases. During the first phase, fog was sampled at three southern SJV surface locations, two urban (Fresno and Bakersfield) and one rural (near the Kern Wildlife Refuge). Both bulk samples (representative of the entire fog drop spectrum) and size-fractionated samples were collected. During the second phase, bulk fog samples were collected at three elevations on a 430 m television transmission tower in the northern SJV, representing some of the first observations of vertical variations in fog composition. SJV fog was observed to be consistently alkaline. The median pH measured in the southern SJV was 6.49, with a range from 4.97 to 7.43. Dominant species in the fog water were ammonium (median southern SJV concentration of 1008 microequivalents/l (μN)), nitrate (483 μN), sulfate (117 μN), acetate (117 μN), formate (63 μN), and formaldehyde (46 μM). Concentrations of the inorganic ions were similar in the urban and rural fogs, although occasionally much higher spikes of S(IV) and sulfate were observed in Bakersfield fog. Acetate, formaldehyde, and total organic carbon, by contrast, were observed to be present in greater concentration in the urban fogs. Bakersfield IMS95 fog concentrations of most species were similar to those measured there in the early 1980s, although concentrations of S(IV) and sulfate were much lower in IMS95 fogs. Significant differences were found between the composition of large and small fog drops, with pH differences at times exceeding one pH unit. The chemical heterogeneity present among SJV fog drop populations is likely to result in significant enhancement of aqueous sulfate production rates over those expected from average fog properties. Significant vertical variations were also observed in fog composition. Liquid water content was observed to increase strongly with elevation, while major ion aqueous concentrations in fog drops decreased with altitude. The total amount of solute contained within the fog (per unit volume of air) was observed to increase with altitude. These observations form a unique data set to be used for model evaluation and for further analysis of aerosol processing by fogs.     

Production and removal of aerosol in a polluted fog layer: model evaluation and fog effect on PM

A radiation fog physics, gas- and aqueous-phase chemistry model is evaluated against measurements in three sites in the San Joaquin Valley of California (SJV) during the winter of 1995. The measurements include for the first time vertically resolved fog chemical composition measurements. Overall the model is successful in reproducing the fog dynamics as well as the temporal and spatial variability of the fog composition (pH, sulfate, nitrate, and ammonium concentrations) in the area. Sulfate production in the fog layer is relatively slow (1–4 μg m⁻³ per fog episode) compared to the episodes in the early 1980s because of the low SO₂ concentrations in the area and the lack of oxidants inside the fog layer. Sulfate production inside the fog layer is limited by the availability of oxidants in the urban areas of the valley and by SO₂ in the more remote areas. Nitrate is produced in the rural areas of the valley by the heterogeneous reaction of N₂O₅ on fog droplets, but this reaction is of secondary importance for the more polluted urban areas. The gas-phase production of HNO₃ during the daytime is sufficient to balance the nitrate removed during the nighttime fog episodes. Entrainment of air from the layer above the fog provides another source of reactants for the fog layer. Wet removal is one of most important processes inside the fog layer in SJV. We estimate based on the three episodes investigated during IMS95 that a typical fog episode removes 500–2000 μg m⁻² of sulfate, 2500–6500 μg m⁻² of nitrate, and 2000–3500 μg m⁻² of ammonium. For the winter SJV valley the net fog effect corresponds to reductions in ground ambient concentrations of 0.05–0.2 μg m⁻³ for sulfate, 3–6 μg m⁻³ for total nitrate, and 1–3 μg m⁻³ for total ammonium.     

Time-integrated sampling of glyphosate in natural waters

Environmental monitoring of pesticide residues in surface water is often done with time-integrated sampling where a specified volume is sampled each hour during, e.g., a week, thus avoiding at momentary high or low extreme concentrations. However, sampling over an extended period of time can result in losses of easily degradable analytes, why the stability of the target analytes over the timespan of the sampling must be checked. Glyphosate is one of the most widely used herbicides. Because of its chemical complexity, glyphosate binds differently to metals and colloids at different pH, and the degradation may also be affected. Recovery of glyphosate from spiked natural waters after 1 and 3 weeks of storage was higher when the samples were acidified to approximately pH 2 rather than at their natural pH. Keeping the samples refrigerated to 4 °C in darkness also enhanced recovery, while glyphosate losses were substantial from samples kept at their natural pH at 20 °C. Total loss of glyphosate was observed in some samples kept at natural pH, 20 °C, and daylight; a loss partly due to binding to metals or colloids that could only partially be reversed by acidification. For 1-week time-integrated sampling a small amount of hydrochloric acid in a piece of heat-sealed hydrophobic micro-porous tubing is added to the sampling bottles before deployment, a procedure that acidifies the samples during collection keeping them below pH 2 until analysis, thus minimising losses of glyphosate. The method also allows determination of the primary degradation product aminomethylphosphonic acid (AMPA).     

Characteristics of the major chemical constituents of PM2.5 and smog events in Seoul,Korea in 2003 and 2004

One hundred ninety-five chemically speciated samples were collected from March 2003 to February 2005 in the Seoul Metropolitan area to investigate the characteristics of the major components in PM_2.5 and to characterize the chemical variations between smog and non-smog events. The annual average PM_2.5 concentration was 43 μg m⁻³ that is almost three times higher than the US NAAQS annual PM_2.5 standard of 15 μg m⁻³. During this sampling period, smog and yellow sand events were observed on 27 and 10 days, respectively. The PM_2.5 concentrations and its constituents during smog events were about two–three times higher than those during non-smog and yellow sand events. In particular, the mass fractions of secondary aerosols such as sulfate, nitrate, and ammonium during the smog events were higher than those of the other constituents. The mean concentration and mass fraction of secondary organic carbon (SOC) were highest during the winter smog events. Sulfate, nitrate and SOC that can have long residence times were important species during the smog events suggesting that regional scale sources rather than local sources were important. Five-day backward air trajectory analysis showed that the air parcels during smog events passed through the major industrial areas in China more often than those during non-smog events.     

Antarctic snow record of cadmium,copper, and zinc content during the twentieth century

A snowpit in Coats Land, Antarctica, has been sampled in order to obtain a record of Cd, Cu and Zn covering the period 1923–1986. The snowpit record gives an indication of southern hemisphere (SH) pollution reaching Antarctica. For Zn, concentrations (averaging 1.5 ng kg^-1) can be explained as arising from natural crustal dust (based on Zn/Al ratios). No increase is observed over the period of the record here, despite a large increase in emissions from smelting operations. The main emitters are near the equator, and this may explain the lack of response in the Antarctic record. For Cd, concentrations (averaging 0.1 ng kg^-1) cannot easily be explained in terms of natural emissions, unless the volcanic input is dominant. No significant increase is seen in the snow for this metal also. For Cu, the natural input can explain only a small part of the concentration (averaging 3.5 ng kg^-1) measured, and increased concentrations (factor 2) are seen in the 1970s and 1980s compared to earlier decades. This is consistent with increased emissions from Cu smelting activities, particularly in Chile, where emissions are relatively far south compared to the main part of SH landmasses. Cu thus joins Pb as a metal whose natural cycle has been significantly perturbed even in the Antarctic atmosphere.     

Partitioning of formaldehyde between air and ice at −35°C to −5°C

The equilibrium partitioning of formaldehyde (HCHO) between air and snow was studied in a series of laboratory experiments conducted at −5°C, −15°C, and −35°C, in order to understand how partitioning of HCHO between air and polar snow varies with temperature, and thus seasonally on the ice sheet. Measured partitioning coefficients were 56, 93, and 245 mol l⁻¹ atm⁻¹ for −5°C, −15°C and −35°C, respectively, showing a similar trend as the values previously estimated from field observations. Estimates of the pseudo-first-order rate coefficient for air–snow exchange for the same three temperatures were 4.1×10⁻⁴, 1.1×10⁻⁴, and 1.1×10⁻⁵ s⁻¹, respectively. This implies a time scale for air–snow equilibration of the order of hours to days for HCHO accumulated at or near the ice–air interface on snow grains. Comparing the current laboratory partitioning coefficients with those estimated from measurements of air and freshly fallen snow in Greenland during summer demonstrates that the snow is supersaturated and should degas HCHO to the surrounding air. During this degassing, polar snow should be a significant source of HCHO to the lower troposphere.     

Effect of copper(II) on biodegradation of benzo[a]pyrene by Stenotrophomonas maltophilia

Benzo[a]pyrene (BaP) biodegradation by Stenotrophomonas maltophilia was studied under the influence of co-existed Cu(II) ions. About 45% degradation was achieved within 3 d when dealing with 1 mg L^?1 BaP under initial natural pH at 30 °C; degradation reached 48% in 2 d at 35 °C. Efficacy of BaP biodegradation reached the highest point at pH 4. In the presence of 10 mg L^?1 Cu(II) ions, the BaP removal ratio was 45% on 7th day, and maintained stable from 7 to 14 d at 30 °C under natural pH. The favorable temperature and pH for BaP removal was 25 °C and 6.0 respectively, when Cu(II) ions coexisted in the solutions. Experiments on cometabolism indicated that S. maltophilia performed best when sucrose was used as an additional carbon source. GC–MS analysis revealed that the five rings of BaP opened, producing compounds with one or two rings which were more bioavailable.     

Drop size-dependent S(IV) oxidation in chemically heterogeneous radiation fogs

Six radiation fog episodes were sampled in the Central Valley of California during winter 1998/1999. Drop size-resolved fog samples were sampled using a size-fractionating Caltech active strand cloudwater collector (sf-CASCC). The sf-CASCC collects a large fog drop sample, comprised mainly of drops larger than 17 μm diameter, and a small fog drop sample, comprised mainly of drops with diameters between 4 and 17 μm. The fog pH was found to vary between approximately pH 5.3 and 6.8, with the pH of the large fog drop sample typically several tenths of a pH unit higher than the simultaneously collected small fog drop sample. At these high pH values, dissolved sulfur dioxide can be rapidly oxidized by a variety of chemical pathways and also can react quickly with dissolved formaldehyde to form hydroxymethanesulfonate. The amount of sulfate produced by aqueous-phase oxidation during each fog episode was determined by application of a tracer technique. The ratio of large : small drop S(IV) oxidation was compared with theoretically predicted ratios of large : small drop S(IV) oxidation rates. Although the higher pH of the large fog drops should promote more rapid S(IV) oxidation by ozone, finite rates of mass transport into the large drops and an increasing rate of complexation of S(IV) by formaldehyde at high pH combine to depress theoretically predicted rates of aqueous sulfate production in large fog drops below rates expected for small fog drops. This prediction is supported by the tracer results that indicate the concentration of sulfate resulting from aqueous-phase S(IV) oxidation in small drops generally exceeded the concentration formed in large drops. These findings stand in sharp contrast to observations in acidic clouds at Whiteface Mountain, New York, where hydrogen peroxide was determined to be the dominant S(IV) oxidant and the rate of S(IV) oxidation was found to be independent of drop size.     

Size distributions and formation of dicarboxylic acids in atmospheric particles

The PM2.5 concentrations and the size distributions of dicarboxylic acids in Hong Kong were studied. Eleven sets of daily PM2.5 samples were obtained at a downtown sampling site during the period of 5–16 December 2000 using an R&P speciation PM2.5 sampler. About 6–12% of the total oxalic acid was found in the gas phase in some samples. A good correlation between succinate and sulfate (R²=0.88) and a moderate correlation between oxalate and sulfate (R²=0.74) were found. Sampling artifacts of oxalate, malonate and succinate were found to be negligible. A total of 18 sets of 48–96 h size distribution data on dicarboxylic acids, sulfate, nitrate and sodium at an urban site and a rural site from June 2000 to May 2001 were obtained using a Micro-Orifice Uniform Deposit Impactor. Data from both sites show similar size distribution characteristics of the dicarboxylic acids. The condensation mode of oxalate was usually observed at 0.177–0.32 μm. The location of the peak of the droplet mode of oxalate was associated with that of sulfate. When the peak of sulfate in the droplet mode appeared at 0.32–0.54 μm, the peak of oxalate sometimes appeared at 0.32–0.54 μm and sometimes shifted to 0.54–1.0 μm. When the peak of sulfate in the droplet mode appeared at 0.54–1.0 μm, the peak of oxalate sometimes appeared at 0.54–1.0 μm and sometimes shifted to 1.0–1.8 μm. Oxalate, succinate and sulfate found in the droplet mode were attributed to in-cloud formation. The slight shift of the oxalate peak from 0.32–0.54 to 0.54–1.0 μm or from 0.54–1.0 to 1.0–1.8 μm was ascribed to minor oxalate evaporation after in-cloud formation. The maximum peak of malonate sometimes appeared in the droplet mode and sometimes appeared at 3.1–6.2 μm. The formation of malonate is associated to the reactions between sea salt and malonic acid.     

Rainwater formaldehyde: concentration,deposition and photochemical formation

Formaldehyde (HCHO) concentrations were measured in 116 rain samples in Wilmington, NC from June 1996 to February 1998. Concentrations ranged from below the detection limit of 10 nM, to 13 μM, in the range of HCHO levels reported at other locations worldwide. The volume-weighted annual average rainwater formaldehyde concentration was 3.3±0.3 μM and comprised approximately 3% of the measured dissolved organic carbon. Using the volume weighted average HCHO concentration and annual precipitation of 1.4 m, an annual formaldehyde deposition of 4.6 mmol m⁻² yr⁻¹ was determined. Rainwater is a significant source of formaldehyde to surface waters and may contribute as much as 30 times the resident amount found in natural waters of southeastern North Carolina during the summer. Formaldehyde concentrations did not correlate with precipitation volume suggesting continuous supply during rain events. Evidence is presented which indicates part of this supply may be from direct photochemical production in the aqueous phase. Formaldehyde levels exhibited a distinct seasonal oscillation, with higher concentrations during the summer. This pattern is similar to that observed with other rainwater parameters at this site including pH, nitrate, and ammonium, and is most likely the result of increased photochemical production, as well as biogenic and anthropogenic emissions during summer months. The concentration of formaldehyde in both winter El Nino rains and summer tropical rains was less than half its concentration in non-El Nino or non-tropical events, suggesting significant terrestrial input. Formaldehyde was correlated with hydrogen peroxide and non-sea-salt sulfate deposition suggesting a relationship between HCHO, H₂O₂, S(VI) within the troposphere.     

Snow-to-air exchanges of mercury in an Arctic seasonal snow pack in Ny-Ålesund,Svalbard

The study of mercury (Hg) cycle in Arctic regions is a major subject of concern due to the dramatic increases of Hg concentrations in ecosystem in the last few decades. The causes of such increases are still in debate, and an important way to improve our knowledge on the subject is to study the exchanges of Hg between atmosphere and snow during springtime. We organized an international study from 10 April to 10 May 2003 in Ny-Ålesund, Svalbard, in order to assess these fluxes through measurements and derived calculations.Snow-to-air emission fluxes of Hg were measured using the flux chamber technique between ∼0 and 50 ng m⁻² h⁻¹. A peak in Gaseous Elemental Mercury (GEM) emission flux from the snow to the atmosphere has been measured just few hours after an Atmospheric Mercury Depletion Event (AMDE) recorded on 22 April 2004. Surprisingly, this peak in GEM emitted after this AMDE did not correspond to any increase in Hg concentration in snow surface. A peak in GEM flux after an AMDE was observed only for this single event but not for the four other AMDEs recorded during this spring period.In the snow pack which is seasonal and about 40 cm depth above permafrost, Hg is involved in both production and incorporation processes. The incorporation was evaluated to ∼5–40 pg m² h. Outside of AMDE periods, Hg flux from the snow surface to the atmosphere was the consequence of GEM production in the air of snow and was about ∼15–50 ng m⁻² h⁻¹, with a contribution of deeper snow layers evaluated to ∼0.3–6.5 ng m⁻² h⁻¹. The major part of GEM production is then mainly a surface phenomenon. The internal production of GEM was largely increasing when snow temperatures were close to melting, indicating a chemical process occurring in the quasi-liquid layer at the surface of snow grains.     

Application of the nested grid STEM to an early summer acid rain in South Korea

The nested grid Sulfur Transport Eulerian Model (STEM) was developed and used to simulate the acid rain in Korea that occurred on 10 June 1996. The present nested grid system consists of three-grid systems. The coarsest grid system includes China, Korean Peninsula and Japan with the horizontal grid size of 80 km and the finest grid system includes only Korea with the horizontal grid size of 8.9 km. The calculated gas-phase SO₂ and O₃ concentrations agree relatively well with the field measurements. In addition, the model successfully reproduces the measured sulfate and nitrate concentrations in the rain water and futhermore identified the high concentration regions of liquid-phase sulfate and nitrate. In the present simulation conditions, most of the gas-phase of SO₂ and HNO₃ were washed out. A close relationship between wet deposition fluxes and precipitation rates were found for sulfate and nitrate. Finally, the model results also showed that a fine grid size is required to accurately calculate gas-phase concentrations as well as acid deposition fluxes.     

Measurements of JNO3− in snow by nitrate-based actinometry

Chemical actinometry was used to measure nitrate photolysis rate coefficients, J_NO3⁻, on and in snowpack at Summit, Greenland. Sealed glass tubes containing nitrate and a hydroxyl radical trapping system were buried in snow and exposed for between 2 and 24 h. Average J_NO3⁻ values for 2-h midday exposures in early June on surface snow were 10–14×10⁻⁷ s⁻¹. Averages over 24 h were 3.5–4.5×10⁻⁷ s⁻¹. These values reflect the integrated photon flux and also any variation of the nitrate photolysis rate with temperature. Attenuation of J_NO3⁻ within the firn was 0.03–0.04 cm⁻¹ for 24-h exposures and 0.08 cm⁻¹ for a 2-h exposure. Different attenuation coefficients may relate to differential light penetration due to changes in sun angle over the course of 24 h.