The relationship between hydrogen and sulphate ions in precipitation-A numerical analysis of rain and snowfall chemistry

Acidic rain has been identified as potentially harmful to the aquatic and terrestrial components of the ecosystem. Sulphate measured in rain and snow has been used as a surrogate indicator of acidic deposition. If sulphur dioxide controls are the means to limit acidic deposition, then the association between sulphate and hydrogen ion concentrations in precipitation is an important factor in establishing such limits. Selected data on rain and snowfall chemistry from the National Atmospheric Deposition Program (NADP), the Electric Power Research Institute's SURE, the utility industries' UAPSP, and the Department of Energy's MAP3S were reviewed. Numerical analyses were performed to assess the relationship between hydrogen and sulphate ion concentrations. The strength of the association between hydrogen and sulphate ions varied from site to site. In the Midwestern and Eastern regions, the Pearson correlation coefficient was over 0.50 while in the Central and Upper Midwestern parts of the United States, the correlation coefficients were less than 0.25. Regardless of the strength of the association between hydrogen and sulphate ions, all but one of the NADP/NTN sites used in our analysis exhibited at least 30% of the anions (sulphate, nitrate, and chloride) associated with cations other than hydrogen. For sites where the strength of the association was weak, between 65% and 98% of the anions appeared to be associated with cations other than hydrogen. Because a large percentage of the anions (i.e. sulphate, nitrate, and chloride) appear to be associated with cations other than hydrogen even at those sites where the association between hydrogen and sulphate ions was strong, the complex chemistry controlling the acidity in precipitation may make it difficult to predict the impact of a reduction in sulphate concentration.     

Chemical composition of fresh snowfalls at Palmer Station,Antarctica

A first time investigation was performed to establish a chemical baseline for snowfall at Palmer Station Antarctica (64°46′S, 64°05′W) since there was no such record. A chemical baseline for snow could be use to validate climate change studies based on ice core analyses. The snow samples contained (from high to low mass concentration) total organic carbon, chloride, inorganic carbon, sodium, sulfate, magnesium, calcium, potassium, fluoride, ammonium, and nitrate, excluding hydrogen and hydroxide. The pH of these samples ranged between 4.0–6.2. The relatively low nitrate and relatively high sulfate concentrations found in our samples are consistent with the results of other studies for this region of Antarctica. The ions and pH do not appear to favor a particular wind direction during this period. The total deposition of sulfate and flouride via snowfall between 10 January and 10 February is conservatively estimated to be 4.78 and 1.3 kg km^-2, respectively.     

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.     

A winter study of air,cloud and precipitation chemistry in Ontario,Canada

During January and February 1984, a field project was conducted near North Bay, Ontario, Canada. The principal objective was to characterize the chemical and microphysical properties of the air masses, clouds and precipitation in this region of NE North America during the winter season. Two extensively instrumented aircraft with some newly designed cloudwater and snow collectors were used, as well as a surface station continuously monitoring pollutant concentrations and a precipitation event sampling network. Pollutant concentrations at the surface were found to vary with the airmass back trajectory with the highest concentrations observed for trajectories from the S and SW and the lowest from the N. Vertical profiles of aerosol particle (0.2−2 μm diameter) and NOx concentrations show similar trends with maxima of 1200 cm⁻³ and 7 ppb, respectively near ground level with air mass trajectories from the S, in comparison to values of 250 cm⁻³ and 1 ppb obtained with trajectories from the N. Cloudwater, aircraft precipitation and ground precipitation samples had a daily median pH of 3.6,4.6 and 4.2, respectively with the cloudwater having the highest sulphate and nitrate concentrations. The nitrate/sulphate equivalent concentration ratios in the cloudwater, aircraft precipitation and ground precipitation samples were 0.7,0.6 and 1.4, respectively. The data suggest that precipitation scavenging of nitric acid below cloud base is an important process during the winter season.     

Role of ammonia chemistry and coarse mode aerosols in global climatological inorganic aerosol distributions

We use an inorganic aerosol thermodynamic equilibrium model in a three-dimensional chemical transport model to understand the roles of ammonia chemistry and natural aerosols on the global distribution of aerosols. The thermodynamic equilibrium model partitions gas-phase precursors among modeled aerosol species self-consistently with ambient relative humidity and natural and anthropogenic aerosol emissions during the 1990s.Model simulations show that accounting for aerosol inorganic thermodynamic equilibrium, ammonia chemistry and dust and sea-salt aerosols improve agreement with observed SO₄, NO₃, and NH₄ aerosols especially at North American sites. This study shows that the presence of sea salt, dust aerosol and ammonia chemistry significantly increases sulfate over polluted continental regions. In all regions and seasons, representation of ammonia chemistry is required to obtain reasonable agreement between modeled and observed sulfate and nitrate concentrations. Observed and modeled correlations of sulfate and nitrate with ammonium confirm that the sulfate and nitrate are strongly coupled with ammonium. SO₄ concentrations over East China peak in winter, while North American SO₄ peaks in summer. Seasonal variations of NO₃ and SO₄ are the same in East China. In North America, the seasonal variation is much stronger for NO₃ than SO₄ and peaks in winter.Natural sea salt and dust aerosol significantly alter the regional distributions of other aerosols in three main ways. First, they increase sulfate formation by 10–70% in polluted areas. Second, they increase modeled nitrate over oceans and reduce nitrate over Northern hemisphere continents. Third, they reduce ammonium formation over oceans and increase ammonium over Northern Hemisphere continents. Comparisons of SO₄, NO₃ and NH₄ deposition between pre-industrial, present, and year 2100 scenarios show that the present NO₃ and NH₄ deposition are twice pre-industrial deposition and present SO₄ deposition is almost five times pre-industrial deposition.     

Winter arsenic pollution in 10 forest ecosystems in the mountainous border regions of the Czech Republic

Environmental Science and Pollution Research - Arsenic (As) concentrations and deposition fluxes were measured in snow and rime at 10 mountain-top sites near the borders between the Czech Republic...     

Simulation of aerosols and gas-phase species over Europe with the Polyphemus system. Part II: Model sensitivity analysis for 2001

This paper presents a multi-pollutant sensitivity study of an air quality model over Europe with a focus on aerosols. Following the evaluation presented in the companion paper, the aim here is to study the sensitivity of the model to input data, mathematical parameterizations and numerical approximations. To that end, 30 configurations are derived from a reference configuration of the model by changing one input data set, one parameterization or one numerical approximation at a time. Each of these configurations is compared to the same reference simulation over two time periods of the year 2001, one in summer and one in winter. The sensitivity of the model to the different configurations is evaluated through a statistical comparison between the simulation results and through comparisons to available measurements. The species studied are ozone (O₃), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), ammonia (NH₃), coarse and fine aerosol particles (PM_c and PM_2.5), sulfate, nitrate, ammonium, chloride and sodium.For all species, the modeled concentrations are very sensitive to the parameterization used for vertical turbulent diffusion and to the number of vertical levels. For the other configurations considered in this work, the sensitivity of the modeled concentration to configuration choice varies with the species and the period of the year. O₃ is impacted by options related to boundary conditions. PM_c is sensitive to sea-salt related options, to options influencing deposition and to options related to mass transfer between gas and particulate phases. PM_2.5 is sensitive to a larger number of options than PM_c: sea-salt, boundary conditions, heterogeneous reactions, aqueous chemistry and gas/particle mass transfer. NO₂ is strongly influenced by heterogeneous reactions. Nitrate shows the highest variability of all species studied. As with NO₂, nitrate is strongly sensitive to heterogeneous reactions but also to mass transfer, thermodynamic related options, aqueous chemistry and computation of the wet particle diameter. While SO₂ is mostly sensitive to aqueous chemistry, sulfate is also sensitive to boundary conditions and, to a lesser extent, to heterogeneous reactions. As with nitrate, ammonium is largely impacted by the different configuration choices, although the sensitivity is slightly lower than for nitrate. NH₃ is sensitive to aqueous chemistry, mass transfer and heterogeneous reactions. Chloride and sodium are impacted by sea-salt related options, by options influencing deposition and by options concerning the aqueous-phase module.     

Seasonal and spatial trends in south Greenland snow chemistry

The spatial, temporal, source and physical controls on chloride, nitrate, sulfate and sodium in south Greenland snow are presented in this paper based on chemical data from snowpit and fresh snow samples. The snowpit samples cover the period June 1982–June 1984 and the fresh surface snow samples represent one storm event sampled over a 38-km traverse from Dye 3 to the southwest. Oxygen isotope dated records of chloride, sodium, excess sulfate and nitrate are discussed with respect to input timing and source. Notably the anthropogenic influx of excess sulfate is apparent in addition to an influx of excess sulfate that coincides with and is attributed to the arrival of the El Chichon cloud in S Greenland. The El Chichon event is also marked by highs in chloride and nitrate. Examination of fresh surface snow reveals geographic, temperature and moisture controls on deposition. Some excess sulfate close to Dye 3 can be attributed to local pollution.     

Trends in snowpack chemistry and comparison to National Atmospheric Deposition Program results for the Rocky Mountains, US, 1993–2004

Seasonal snowpack chemistry data from the Rocky Mountain region of the US was examined to identify long-term trends in concentration and chemical deposition in snow and in snow-water equivalent. For the period 1993–2004, comparisons of trends were made between 54 Rocky Mountain Snowpack sites and 16 National Atmospheric Deposition Program wetfall sites located nearby in the region. The region was divided into three subregions: Northern, Central, and Southern. A non-parametric correlation method known as the Regional Kendall Test was used. This technique collectively computed the slope, direction, and probability of trend for several sites at once in each of the Northern, Central, and Southern Rockies subregions. Seasonal Kendall tests were used to evaluate trends at individual sites.Significant trends occurred during the period in wetfall and snowpack concentrations and deposition, and in precipitation. For the comparison, trends in concentrations of ammonium, nitrate, and sulfate for the two networks were in fair agreement. In several cases, increases in ammonium and nitrate concentrations, and decreases in sulfate concentrations for both wetfall and snowpack were consistent in the three subregions. However, deposition patterns between wetfall and snowpack more often were opposite, particularly for ammonium and nitrate. Decreases in ammonium and nitrate deposition in wetfall in the central and southern rockies subregions mostly were moderately significant (p<0.11) in constrast to highly significant increases in snowpack (p<0.02). These opposite trends likely are explained by different rates of declining precipitation during the recent drought (1999–2004) and increasing concentration. Furthermore, dry deposition was an important factor in total deposition of nitrogen in the region. Sulfate deposition decreased with moderate to high significance in all three subregions in both wetfall and snowpack. Precipitation trends consistently were downward and significant for wetfall, snowpack, and snow-telemetry data for the central and southern rockies subregions (p<0.03), while no trends were noted for the Northern Rockies subregion.     

The record of anthropogenic pollution in snow and ice in Svalbard,Norway

From the examination of the spatial distribution of pollutants and of the record from ice cores, it is demonstrated that Svalbard is strongly affected by anthropogenic pollution. This pollution has caused an increase of approximately 90% in the acidity of the snow deposited in the Archipelago since the beginning of the Industrial Revolution. High concentrations of H⁺, frequently greater than 10 μeq l⁻¹ (i.e. with pHs lower than 5.0), associated with high concentrations of sulphates, indicate that Svalbard is experiencing the phenomenon of acid deposition. The first part of this work reviews the existing knowledge of atmospheric, snow, and ice pollution in Svalbard. This is followed by an examination of the acidity time series, supported by excess-sulphate measurements, performed on an ice core from central-eastern Spitsbergen that provide a historical record of acid deposition over a 54 year period. An ice core recovered from Austfonna, Nordaustlandet provided baseline values and also a record of acidity in precipitation before and during the entire industrial period, thereby allowing the evolution of acid deposition in the Archipelago to be traced. The records of these two Svalbard cores also reflect the overall regional trends.     

Orographic enhancement of snowfall

Field studies have been conducted at a hill site in Scotland to measure the variation with altitude of wet deposition by snowfall. The results showed that, due to wind drift effects, snowflakes were captured very inefficiently by snow collectors. It was therefore not possible to measure an increase in precipitation with altitude. The average concentrations of principal ions dissolved in the snow water were calculated over a two-month period. The results showed that the concentrations increased by factors of between 1.4 and 1.9 with an altitude rise of 400 m. A model of the orographic enhancement of snowfall by the seeder-feeder effect showed that the orographic enhancements of precipitation and pollutant deposition were significantly greater for snowfall than for rainfall. The wind drift of snow crystals and the evaporation of precipitation in dry valley air were important in determining the patterns of deposition.     

Radiation-transfer modeling of snow-pack photochemical processes during ALERT 2000

The delta-Eddington radiation transfer model is used to calculate actinic fluxes and photolysis rates within the snow pack during the ALERT 2000 field campaign. Actinic fluxes are enhanced within the snow pack due to the high albedo of snow and conversion of direct light to diffuse light. The conversion of direct to diffuse light is highly dependent on the solar zenith angle, as demonstrated by model calculations. The optical properties of Alert snow are modeled as 100 μm radius ice spheres with impurity added to increase the absorption coefficient over that of pure water ice. Using these optical properties, the model achieves good agreement with observations of irradiance within the snow pack. The model is used to calculate the total actinic flux as a function of solar zenith angle and depth for either clear sky or cloudy conditions. The actinic flux is then used to calculate photochemical production of nitrogen oxides from nitrate photolysis assuming that nitrate in snow has the same absorption cross section and quantum yield in snow as in aqueous solution. Assuming all photo-produced nitrogen oxides are released to the gas phase, we derive a maximal flux of nitrogen oxides (NO_x+HONO and possibly other products) from the snow pack. The value of this maximal flux depends critically on the assumed quantum yield for production of NO₂, which is unknown in ice. Depending on the assumed quantum yield, the calculated maximal flux varies between values four times smaller than the observed NO_x+HONO flux to five times larger than the NO_x+HONO flux. Therefore, it appears that the calculated flux is in approximate agreement with the observations with a great need for improved understanding of nitrogen photochemistry in snow.     

Critical loads and their exceedances at intensive forest monitoring sites in Europe

Intensive forest monitoring by means of harmonised methods has been conducted in Europe for more than a decade. Risks of atmospheric nitrogen and sulphur deposition are assessed by means of calculations of critical loads and their exceedances. In the present study throughfall and bulk deposition of nitrate (N-NO(3)), ammonium (N-NH(4)) and sulphate (S-SO(4)) show marked spatial patterns and temporal trends. In the period of observation (1999-2004), sulphate deposition on intensive monitoring plots decreased by about one quarter. This is in line with the reduction of S deposition by 70% since 1981 in Europe as a result of successful air pollution control politics under the Convention on Long-range Transboundary Air Pollution (CLRTAP). However, sulphate and especially nitrate and ammonium deposition were found to still exceed critical loads at many forest sites, indicating a continued need for further implementation of air pollution abatement strategies.     

The contribution of ship emissions to air pollution in the North Sea regions

As a consequence of the global distribution of manufacturing sites and the increasing international division of labour, ship traffic is steadily increasing and is becoming more and more important as an origin of air pollution.This study investigates the impact of ship emissions in coastal areas of the North Sea under conditions of the year 2000 by means of a regional chemistry transport model which runs on a sufficiently high resolution to study air pollution in coastal regions. It was found that northern Germany and Denmark in summer suffer from more than 50% higher sulphate, nitrate and ammonium aerosol concentrations due to contributions from ships. The implementation of a sulphur emission control area (SECA) in the North Sea, as it was implemented at the end of 2007, directly results in reduced sulphur dioxide and sulphate aerosol concentrations while nitrate aerosol concentrations are slightly increased.     

Atmospheric mercury concentrations: measurements and profiles near snow and ice surfaces in the Canadian Arctic during Alert 2000

Gaseous elemental mercury (GEM) concentration measurements were made during the Alert 2000 campaign in Alert, Nunavut, Canada, between February and May 2000. GEM exhibits dramatic mercury depletion events (MDE) concurrently with ozone in the troposphere during the Arctic springtime. Using a cold regions pyrolysis unit, it was confirmed that GEM is converted to more reactive mercury species during the MDEs. It was determined that on average 48% of this converted GEM was recovered through pyrolysis suggesting that the remaining converted GEM is deposited on the snow surfaces. Samples collected during this campaign showed an approximate 20 fold increase in mercury concentrations in the snow from the dark to light periods. Vertical gradient air profiling experiments were conducted. In the non-depletion periods GEM was found to be invariant in the air column between surface and 1–2 m heights. During a depletion period, GEM was found to be invariant in the air column except at the surface where a noticeable increase in the GEM concentration was observed. Concurrent ozone concentration profiles showed a small gradient in the air column but a sharp decrease in ozone concentration at the surface. Other profile studies showed a 41% average GEM concentration difference between the interstitial air in the snow pack and ∼2 m above the surface suggesting that GEM is emitted from the snow pack. Further profile studies showed that during MDEs surface level GEM exhibits spikes of mercury concentrations that were over double the ambient GEM concentrations. It is thought that the solar radiation may reduce reactive mercury that is deposited on the snow surface during a MDE back to its elemental form which is then increasingly released from the snow pack as the temperature increases during the day. This is observed when wind speeds are very low.     

Sources of acidity in lakes and streams of the United States

Acidic (acid neutralizing capacity [ANC] < or = 0) surface waters in the United States sampled in the National Surface Water Survey (NSWS) were classified into three groups according to their probable sources of acidity: (1) organic-dominated waters (organic anions > SO4*; (2) watershed sulphate-dominated waters (watershed sulphate sources > deposition sulphate sources); and (3) deposition-dominated waters (anion chemistry dominated by inputs of sulphate and nitrate derived from deposition). The classification approach is highly robust; therefore, it is a useful tool in segregating surface waters into chemical categories. An estimated 75% (881) of acidic lakes and 47% (2190) of acidic streams are dominated by acid anions from deposition and are probably acidic due to acidic deposition. In about a quarter of the acidic lakes and streams, organic acids were the dominant source of acidity. In the remaining 26% of the acidic streams, watershed sources of sulphate, mainly from acid mine drainage, were the dominant source of acidity.     

Regional variation in the chemical composition of winter snow pack and terricolous lichens in relation to sources of acid emissions in the Usa river basin,northeast European Russia

The chemical composition of snow and terricolous lichens was determined along transects through the Subarctic towns of Vorkuta (130 km west-east), Inta (240 km south-north) and Usinsk (140 km, southwest-northeast) in the Usa river basin, northeast European Russia. Evidence of pollution gradients was found on two spatial scales. First, on the Inta transect, northward decreases in concentrations of N in the lichen Cladonia stellaris (from 0.57 mmol N g(-1) at 90 km south to 0.43 mmol N g(-1) at 130 km north of Inta) and winter deposition of non-sea salt sulphate (from 29.3 to 12.8 mol ha(-1) at 90 km south and 110 km north of Inta, respectively) were attributed to long range transport of N and S from lower latitudes. Second, increased ionic content (SO42-, Ca2+, K+) and pH of snow, and modified N concentration and the concentration ratios K+:Mg2+ and K+: (Mg2++Ca2+) in lichens (Cladonia arbuscula and Flavocetraria cucullata) within ca. 25-40 km of Vorkuta and Inta were largely attributed to local deposition of alkaline coal ash. Total sulphate concentrations in snow varied from ca. 5 micromol l(-1) at remote sites to ca. 19 micromol l(-1) near Vorkuta. Nitrate concentration in snow (typically ca. 9 micromol l(-1)) did not vary with proximity to perceived pollution sources.     

Wetfall Deposition and Precipitation Chemistry for a Central Appalachian Forest

Abstract

Although extensive research on acidic deposition has been directed toward spruce-fir forests, less research has been done on the impacts of air pollution on eastern montane hardwood forests. The purpose of this study was to describe precipitation chemistry for several Appalachian hardwood forest sites at or near the Fernow Experimental Forest (FEF) to assess the potential for problems associated with acidic deposition. Emphasis was placed on seasonal patterns of ionic concentrations (H+, Ca++, NH4+; NO3-, and SO4=) and spatial variability of ionic concentrations and deposition among sites. Seasonal patterns of most ions showed highest concentrations during the summer months and deposition of H+ was especially pronounced during this time. Deposition of all ions was generally greater (related to greater precipitation) at three montane forested sample sites compared to a nonforested riverbottom site. Precipitation chemistry at FEF was similar to other sites throughout the eastern United States and contrasted sharply with mid-western and western sites. Eastern sites, including means for FEF sites, were uniformly 3-4 times higher in H+ and SO4= concentration than the mid-western and western sites. Precipitation at FEF was chronically acidic, more so during the growing season, and highest at higher elevations where environmental stresses can be most severe. Furthermore, there were occasional large discrepancies between the low-elevation site and the higher-elevation forested sites for precipitation chemistry and acidic deposition. These results suggest that synoptic-scale (network) data may greatly underestimate the pollutant conditions to which highelevation forest trees are exposed, since network data rarely take elevation into account and typically are based on annual ionic concentration and deposition means that may be considerably lower than those of the growing season.     

Effect of selected organic and inorganic snow and cloud components on the photochemical generation of nitrite by nitrate irradiation

The effect of selected organic and inorganic compounds, present in snow and cloudwater was studied. Photolysis of solutions of nitrate to nitrite was carried out in the laboratory using a UVB light source. The photolysis and other reactions were then modelled. It is shown that formate, formaldehyde, methanesulphonate, and chloride to a lesser extent, can increase the initial formation rate of nitrite. The effect, particularly significant for formate and formaldehyde, is unlikely to be caused by scavenging of hydroxyl radicals. The experimental data obtained in this work suggest that possible causes are the reduction of nitrogen dioxide and nitrate by radical species formed on photooxidation of the organic compounds. Hydroxyl scavenging by organic and inorganic compounds would not affect the initial formation rate of nitrite, but would protect it from oxidation, therefore, increasing the concentration values reached at long irradiation times. The described processes can be relevant to cloudwater and the quasi-liquid layer on the surface of ice and snow, considering that in the polar regions irradiated snow layers are important sources of nitrous acid to the atmosphere. Formate and (at a lesser extent) formaldehyde are the compounds that play the major role in the described processes of nitrite/nitrous acid photoformation by initial rate enhancement and hydroxyl scavenging.     

A study of photochemical and physical processes affecting carbonyl compounds in the Arctic atmospheric boundary layer

Experiments were conducted during the ALERT 2000 field campaign aimed at understanding the role of air–snow interactions in carbonyl compound chemistry and the associated ozone depletion in the atmospheric boundary layer. Under sunlit conditions, we find that formaldehyde, acetaldehyde and acetone exhibit a significant diel cycle with average ambient air concentrations of 166, 53 and 385 ppt, respectively. A box model of Arctic surface layer chemistry was used to understand the diel behavior of carbonyl compound concentrations at Alert, Nunavut, Canada, with a focus on the chemical and physical processes that affect carbonyl compounds. Results of the study showed that the measured carbonyl compound concentrations can only be simulated when a radiation-dependent snowpack source term (possibly photochemistry) and a temperature-dependent sink (physical uptake on snow grains) of carbonyl compounds were added to the model. We are able to simulate the concentration and amplitude of the observed diel cycle, but not the phase of the cycle. These results help confirm the importance of snowpack chemistry and physical processes with respect to carbonyl compound concentrations in the Arctic surface boundary layer, and reveal weakness in the details of our understanding.