Volume-weighted Average Concentrations Research Articles

On-farm NIR sensor for milk analysis: Exploitation of bias monitoring and bias correction

Long-term studies have shown a bias drift over time in the prediction performance of near-infrared spectroscopy measurement systems. This bias drift generally requires extra laboratory reference measurements to detect and correct for this bias. Since these reference measurements are expensive and time consuming, there is a need for advanced methodologies for bias drift monitoring and correction without the need for taking extra samples. In this study, we propose and validate a method to monitor the bias drift and two methods to tackle it. The first method requires no extra measurements and uses a modified version of Partial Least Squares Regression to estimate and correct the bias. This method is based on the assumption that the mean concentration of the predicted component remains constant over time. The second method uses regular bulk milk measurements as a reference for bias correction. This method compares the measured concentrations of the bulk milk to the volume-weighted average concentrations of individual milk samples predicted by the sensor. Any difference between the actual and calculated bulk milk composition is then used to perform a bias correction on the predictions by the sensor system. The effectiveness of these methods to improve the component prediction was evaluated on data originating from a custom-built sensor that automatically measures the NIR reflectance and transmittance spectra of raw milk on the farm. We evaluate the practical use case where models for predicting the milk composition are trained upon installation of the sensor at the farm, and later used to predict the composition of subsequent samples over a period of more than 6 months. The effectiveness of the fully unsupervised method was confirmed when the mean concentration of the milk samples remained constant, while the effectiveness reduced when this was not the case. The bulk milk correction method was effective when all relevant samples for the component were measured by the sensor and included in the analyzed bulk milk, but is less effective when samples included in the bulk which are not measured by the sensor system. When the necessary conditions are met, these methods can be used to extend the lifetime of deployed prediction models by significantly reducing the bias on the predicted values.

Source apportionment of rainwater chemical composition in wet precipitation at Kelaniya in Sri Lanka

Rainwater quality is of utmost importance as it can be used to predict atmospheric quality which of course governs, to some extent, the health of the ecosystem. In this regard, the research reported here was to study chemical characteristics of precipitation in Kelaniya, Gampaha District, one of the most populated and most urbanized districts in Sri Lanka. This study was conducted during the period from 2012 to 2014, and wet precipitation was analyzed for pH, conductivity, Na+, NH4+, K+, Mg2+, Ca2+, F−, Cl−, NO3−, SO42−, Pb, Cu, Mn, Al, Zn, and Fe for a total of seventy-eight (78) samples. Volume-weighted average concentrations of the major ionic species present in precipitation samples were in the order of Na+ > Ca2+ > Cl− > SO42− > NH4+ > Mg2+ > NO3− > K+ > F−. Neutralization of the acidic species would take place due to the presence of NH4+ and CaCO3. When considering marine contribution, SO42−/Na+, Ca2+/Na+, and Mg2+/Na+ ratios are higher than the reference value suggesting that contribution of sources be possible other than marine. Among metallic constituents, the concentration of Al is the highest while that of Mn is the lowest. Significant correlation is observed among certain ions and elements (Ca2+, SO42−, Mg2+, Al, Cu, Fe, Zn, and H+) which indicates their source of origin and chemical interaction. This study reveals that chemical composition of rain water depends on both anthropogenic activities and natural phenomena.

Long-term trends in aerosol and precipitation composition over the western North Atlantic Ocean at Bermuda

Abstract. Since the 1980s, emissions of SO2 and NOx (NO + NO2) from anthropogenic sources in the United States (US), Canada, and Europe have decreased significantly suggesting that the export of oxidized S and N compounds from surrounding continents to the atmosphere overlying the North Atlantic Ocean (NAO) has also decreased. The chemical compositions of aerosols and precipitation sampled daily on Bermuda (32.27° N, 64.87° W) from 1989 to 1997 and from 2006 to 2009 were evaluated to quantify the magnitudes, significance, and implications of associated tends in atmospheric composition. The chemical data were stratified based on FLEXPART (FLEXible PARTicle dispersion model) retroplumes into four discrete transport regimes: westerly flow from eastern North America (NEUS/SEUS); easterly trade-wind flow from northern Africa and the subtropical NAO (Africa); long, open-ocean, anticyclonic flow around the Bermuda High (Oceanic); and transitional flow from the relatively clean open ocean to the polluted eastern North America (North). Based on all data, annual average concentrations of non-sea-salt (nss) SO42– associated with aerosols and annual volume-weighted-average (VWA) concentrations in precipitation decreased significantly (by 22% and 49%, respectively) whereas annual VWA concentrations of NH4+ in precipitation increased significantly (by 70%). Corresponding trends in aerosol and precipitation NO3– and of aerosol NH4+ were insignificant. Nss SO42– in precipitation under NEUS/SEUS and Oceanic flow decreased significantly (61% each) whereas corresponding trends in particulate nss SO42– under both flow regimes were insignificant. Trends in precipitation composition were driven in part by decreasing emissions of SO2 over upwind continents and associated decreases in anthropogenic contributions to nss SO42– concentrations. Under NEUS/SEUS and Oceanic flow, the ratio of anthropogenic to biogenic contributions to nss SO42– in the column scavenged by precipitation were relatively greater than those in near surface aerosol, which implies that, for these flow regimes, precipitation is a better indicator of overall anthropogenic impacts on the lower troposphere. Particulate nss SO42– under African flow also decreased significantly (34%) whereas the corresponding decrease in nss SO42– associated with precipitation was insignificant. We infer that these trends were driven in part by reductions in the emissions and transport of oxidized S compounds from Europe. The lack of significant trends in NO3– associated with aerosols and precipitation under NEUS/SEUS flow is notable in light of the large decrease (37%) in NOx emissions in the US and Canada over the period of record. Rapid chemical processing of oxidized N in marine air contributed to this lack of correspondence. Decreasing ratios of nss SO42– to NH4+ and the significant decreasing trend in precipitation acidity (37%) indicate that the total amount of acidity in the multiphase gas–aerosol system in the western NAO troposphere decreased over the period of record. Decreasing aerosol acidities would have shifted the phase partitioning of total NH3 (NH3 + particulate NH4+ towards the gas phase thereby decreasing the atmospheric lifetime of total NH3 against wet plus dry deposition. The trend of increasing NH4+ in precipitation at Bermuda over the period of record suggests that NH3 emissions from surrounding continents also increased. Decreasing particulate nss SO42– in near-surface air under NEUS/SEUS flow over the period of record implies that the corresponding shortwave scattering and absorption by nss S and associated aerosols constituents also decreased. These changes in radiative transfer suggest a corresponding lower limit for net warming over the period in the range of 0.1–0.3 W m–2.

Wet deposition of particulate carbon to the Central North Atlantic Ocean

Elemental carbon (EC) and water-insoluble organic carbon (WIOC) concentrations were measured in wet-only precipitation samples collected on Terceira Island (Azores, Portugal) between December 2009 and October 2010, to investigate temporal variations, source regions and wet deposition fluxes. The global volume-weighted average (vwa) concentrations were 134±19μgCL−1 for WIOC and 15.0±1.6μgCL−1 for EC, which fall within the range of values that have been found in the European background atmosphere. The WIOC concentration exhibited a temporal variation over the study period with a minimum in winter (vwa 88±16μgCL−1) and a maximum in summer (vwa 477±86μgCL−1). This trend was due to the higher dilution effect of winter rains and possibly to an increase of biogenic particulate carbon incorporation during the growing season. A different temporal variation was observed for the EC concentration with a minimum in summer (vwa 4.2±3.3μgCL−1) and a maximum in spring (vwa 17.5±2.2μgCL−1). The observed trend was mainly related to changes in atmospheric circulation patterns over the Azores. A backward trajectory analysis was applied to identify possible source regions of particulate carbon. The highest WIOC and EC concentrations were associated with air masses that persisted for more than four days over the Central North Atlantic Ocean and with air masses arriving from Europe, respectively. Lower concentrations were observed in samples collected under the influence of back-trajectories from North America. Despite the lower abundance of particulate carbon, the wet deposition fluxes were higher for this group of samples, which reflects the higher amount of precipitation that is normally associated with air masses arriving in the Azores from the west and northwest sectors.

Urban and rural observations of carboxylic acids in rainwater in Southwest of China: the impact of urbanization

Seven carboxylic acids in rainwater were simultaneously determined using ion chromatography for 13 months in two different sites, Guiyang and Shangzhong, southwest of China. Results showed formic, acetic and oxalic acids were the three predominant carboxylic acids. Their volume-weighted average concentrations were 14.24, 9.35, 2.79 μmol/L in Guiyang and 4.95, 1.35, 2.31 μmol/L in Shangzhong, respectively. A distinctive diurnal pattern in carboxylic acid concentrations (daytime>nighttime, t test, p < 0.05) was observed during the growing season in Guiyang. Shangzhong witnessed higher concentration of these acids during the growing season than that during the non-growing season. Direct emissions from growing vegetation or soils probably account for the main provenance of the acids in the rural area. However, the opposite trend were found in Guiyang and the anthropogenic sources during the non-growing season were the main reason. By comparison of our result with the previous data about 20 years ago, we calculated that at least 42% of acetic acids and 69% of formic acid originated from the anthropogenic sources in Guiyang. Furthermore, the ratio of formate/acetate in gas phase larger than 1 suggest the oxidation of unsaturated hydrocarbons from the human activity and/or natural sources were the main origin of carboxylic acids in Guiyang. While The F/A ratio in gas phase was less than 1 in Shangzhong which indicate the direct emissions from biogenic sources. Oxalic acid was in similar amounts in both sites, indicating the common source of the acid.

Speciation and Photochemistry of Mercury in Rainwater

Mercury speciation was determined in rainwater from 76 storms in southeastern North Carolina between September 1, 2003 and September 30, 2005. Volume-weighted average concentrations of total Hg (THg), total dissolved Hg (TDHg), particulate Hg (Hgpart) and dissolved monomethyl Hg (MMHg) were 45.5 pM, 34.8 pM, 12.0 pM and 1.1 pM respectively. TDHg accounted for 77% of THg in precipitation which is similar to Cu but significantly higher than Cr or Fe. Concentrations of the various Hg species were very similar during summer and winter indicating that there was not a dominant seasonal influence on Hg speciation in rainwater at this location. THg, TDHg, and MMHg concentrations were also not significantly impacted by storm origin suggesting that they are relatively well mixed regionally and that air mass back trajectory is not the dominant factor controlling their concentration at this location. Concentrations of TDHg and Hgpart were inversely correlated in rainwater samples subjected to irradiation with simulated sunlight, suggesting the distribution between dissolved and particulate Hg may be controlled by photochemical transformations. Unlike TDHg and Hgpart, no significant changes in MMHg were observed upon photolysis of rainwater indicating that its distribution is not significantly driven by sunlight-mediated reactions, in contrast to what has been observed in surface waters. Results presented in this study indicate that the speciation of Hg in rainwater is dynamic and is driven by a complex combination of natural and anthropogenic processes as well as interactions with sunlight.

Long-term fluctuation and regional variation of nutrient loads from the atmosphere to lakes

The atmospheric depositions were collected by ordinary bulk-samplers mounted with a glass or polyethylene funnel of 30 cm orifice. A long-term observation was carried out at a site (35 degrees 01'30"N, 135 degrees 58'07"E) in the urbanized area for 21 years since 1974. The annual volume-weighted average concentrations of total nitrogen (TN) and phosphorus (TP) were 1.02 +/- 0.30 and 0.031 +/- 0.015 mg(-1), respectively, and the loading rates were 14.5 +/- 2.8 and 0.43 +/- 0.16 kg ha(-1) yr(-1). The rates neither had a relationship with the precipitation (1,492 +/- 343 mm yr(-1)) nor showed any diachronic tendencies. In order to obtain the loading rate of TN and TP within 10% uncertainty under the significant level of 0.01, there is no way but to continue the observation for seven and eleven years or more, respectively. In order to clarify the regional variation of the loading amounts of the depositions, the samplers were set at 12 sites distributing throughout the Kinki District for two years. The distance from northernmost (2322 mm yr(-1)) to southernmost (1242 mm yr(-1)) is about 150 km. The average loading rates of the 12 sites were 16.2 +/- 2.5 kg ha(-1) yr(-1) of TN and 0.730 +/- 0.247 kg ha(-1) yr(-1) of TP. The depositions of NO3-N, NH4-N, and TN as well as TP showed tendencies with distances neither from a big city nor from Japan Sea.

Foliar and Soil Deposition of Pesticide Sprays in Peanuts and Their Washoff and Runoff under Simulated Worst-Case Rainfall Conditions

There are few studies that relate the timing and amounts of pesticide washoff from plant foliage during rainfall to runoff losses at the edge of the field. We hypothesized that foliar deposits, if washed onto the soil slowly during rainfall, may then undergo less leaching during the period of infiltration that occurs prior to soil saturation and runoff, thus exhibiting larger runoff losses than pesticides on/in the soil at the beginning of rain. We measured the runoff of ethalfluralin, metolachlor, chlorothalonil, and rhodamine WT dye using simulated rainfall on 450 m2 mesoplots planted in peanut. Ethalfluralin was applied preplant incorporated, and metolachlor was applied preemergence on bare soil. Chlorothalonil and rhodamine WT were applied to the peanut canopy at maturity. Rainfall was simulated 24 h after each chemical application (in May and July, 1998, and May and August, 1999) using raindrop sprinklers, applying 5.5 +/- 0.5 cm over a 2 h period to create reasonable worst-case conditions; between 3 and 9 mm of runoff was generated. Volume-weighted average concentrations of chemicals in runoff were 7, 104, 163, and 179 ug L(-1) for ethalfluralin, metolachlor, chlorothalonil, and rhodamine WT, respectively. The total amounts of chemicals lost in the runoff events were 0.04 +/- 0.01, 0.2 +/- 0.1, 0.6 +/- 0.5, and 0.2 +/- 0.1, as percents of amounts applied, respectively. Rhodamine WT formed a vivid red solution on wetting and provided visual clues to the dynamics of chemical washoff/runoff. The washoff from rain-exposed peanut foliage appeared to be complete within a few minutes of the beginning of rainfall, and disappearance of dye from rain-exposed soil surface occurred within the first 10 min of rainfall. However, dye was present in runoff water at near-constant concentrations throughout the 2 h runoff event, indicating that near-constant amounts of chemical remained in the soil extraction zone. These results confirm earlier studies showing that soil incorporation at application significantly reduces runoff losses and that a majority of foliar residues can be washable if rainfall occurs within a few days after application. Runoff losses of foliar-applied pesticides were small relative to washoff amounts but were sensitive to runoff timing relative to washoff.

Chromium speciation in rainwater: temporal variability and atmospheric deposition.

The concentrations of the various chromium species were determined in 89 rainwater samples collected in Wilmington, NC, from October 1, 1999, to December 31, 2001. Volume-weighted annual average concentrations of Cr(total), particulate Cr, Cr(III)(aq), and Cr(VI)(aq) were 4.6, 2.2, 0.8, and 1.2 nM, respectively. There was distinct seasonal and diurnal variability in the concentrations of the various chromium species. Chromium emissions to the global atmosphere by both natural and anthropogenic sources are estimated to be 2.2 x 10(9) mol/yr. Using our rainwater concentration data along with other published rainwater Cr concentrations and an estimate for total global annual rain, the total global flux of chromium removed from the atmosphere via wet deposition is 2.1 x 10(9) mol/yr. This represents complete removal of Cr and indicates that essentially all chromium released into the global atmosphere is removed via rain. About half this chromium is dissolved with roughly equal concentrations of toxic Cr(VI) and relatively harmless Cr(III) species.

Methods for measuring mercury in rainfall and aerosols in Florida

The sampling and analytical methods used for the Florida Atmospheric Mercury Study (FAMS) have been carefully tested for reliability, accuracy and precision. A simple, 48 h low-wattage UV oxidation utilizing ultrapure dilute aqua regia was developed to solubilize Hg prior to analysis by reductive purge and trap stripping and dual amalgamation CVAFS. We found no significant differences for total Hg in rainfall samples among Teflon FEP (117 and 2500 cm 2), polymethylpentane (716 cm 2) or polycarbonate (49, 80, 117, 181 cm 2) funnels. For samples deployed for as long as one month, we found no significant differences for total Hg concentrations between samples with no added HCl vs samples with 7.5 ml 6M Q-HCl added per liter prior to bottle deployment. However, we observed significant adsorption of dissolved Hg to the bottle walls, even for acidified samples. The adsorbed Hg was successfully resolubilized using the aqua regia/UV oxidation treatment. We found no significant differences for total Hg in rainfall samples deployed for integration periods ranging from 12 to 36 days compared to the volume-weighted average concentrations for 24 h integrated samples at the same sites. No significant differences were found between aerosol Hg samples collected at 40–60 ℓ per minute on 47 mm, 0.45 μm polypropylene filters for integration periods of 24 h vs 6 days.

Formate and acetate levels compared in monsoon and winter rainwater at Dayalbagh, Agra (India)

A total of 59 rainwater samples were collected during the winter and monsoon (1991–92) at Dayalbagh, Agra. This site is relatively free from the influence of anthropogenic emissions and the volume-weighted average concentrations (VWA) of formate in the winter and monsoon were 22.5±6, 16.1±3 while acetate VWAs were 17.1±5 and 13.8±3 μmol l-1, respectively. Although the VWAs varied between seasons, it was not statistically different. Total deposition (in mmol m-2) varied between season (winter formate, 1.4; acetate, 1.1; monsoon formate, 7.4; acetate, 6.4). A difference in VWA values may have occurred as a result of the dilution factor; the total rain depth from collected samples in the monsoon was 46 cm while that in winter was 6.3 cm. Sources at this site may be anthropogenic and natural; scavenging from the vapour phase, washout of soil particles and emissions from vegetative sources are probably important sources for formate and acetate.

An acidification model (MAGIC) with organic acids evaluated using whole-catchment manipulations in Norway

The results from two whole-catchment manipulation experiments in Norway are used to evaluate MAGIC (Model of Acidification of Groundwater In Catchments), a model of ecosystem biogeochemical response to acid deposition. MAGIC is an aggregated catchment-scale model of acidification that has been widely used in assessment activities in Europe and North America. The experiments involved artificial decrease (Reversing Acidification In Norway, RAIN) and increases (Humid Lake Acidification Experiment, HUMEX) in acidic deposition. Runoff from both sites is influenced by moderate levels of organic acids. At each site the model was calibrated to the control catchment and then applied to the manipulated catchments with only minor adjustments. The major responses in runoff chemistry to the manipulations were closely simulated by the model. Differences between simulated and observed volume-weighted annual average concentrations of all major ions were less than ±6 μequiv 1 −1 for the entire 4–8 year period of prediction. Trends in response to the manipulations were correctly simulated. Most of the residual error resulted from an inability of the model to reproduce the year-to-year variability (noise) around the trends. Although such model evaluations cannot ‘prove’ the correctness of the model structure, good fits to experimental data increase confidence in model applications for assessment and management purposes. Evaluations of this sort can also identify aspects of the model that need further development. For MAGIC, these are primarily a need for improvement in the calibration of aluminium solubility and a better process basis for nitrogen dynamics.

Soil solution response to experimental addition of nitrogen to a forested catchment at Gårdsjön, Sweden

Nitrogen has been added to a forested 0.52 ha headwater catchment at Gårdsjön on the southwest coast of Sweden to study the ecosystem response to elevated nitrogen deposition. The catchment is dominated by naturally generated, mixed-age conifers, mainly Norway spruce, with Scots pine in dry areas. After a pre-treatment period of about 1 year, nitrogen was added to the whole catchment as ammonium nitrate by means of sprinklers at an intensity of 3 mm h −1 (average concentration 230 mmol N1 −1). Total nitrogen input as throughfall to the catchment increased from the ambient 12.5 kg N ha −1 year −1 in the pre-treatment year to a total of 47.3 kg N ha −1 year −1 in the treatment years. Soil solutions were collected using tension lysimeters at four locations covering a moisture gradient from the dry upper to the wet lower parts of the watershed. Results from these locations were compared with soil solution composition at two locations in a nearby control catchment. After 2 years of nitrogen addition, the volume-weighted average nitrate concentrations in the treated catchment were higher than the pretreatment values, especially in the upper soil. Concentrations showed a progressive increase over time. The lack of the same increasing trend in the control catchment precludes natural variations in climatic conditions as the main cause for this increase. Relative to inputs, nitrate concentrations in soil solution were low and showed large variations between the drier and wetter locations. Differences in nitrate concentrations between pre-treatment and treatment periods declined with soil depth, indicating that most of the added nitrogen was consumed in the upper soil. The results from soil solution do not indicate increased nitrogen leaching below the rooting zone in the treated catchment and thus based on these results alone there is as yet no indication of nitrogen saturation.

Metalloids in wet deposition on Bermuda: Concentrations, sources, and fluxes

The concentrations of antimony, arsenic, and selenium were determined in wet deposition samples collected on a daily (event) basis from 1988 to 1990 on Bermuda as a part of the Atmosphere/Ocean Chemistry Experiment (AEROCE). Isentropic back trajectories were used to identity air masses that passed over North America (59% of the events), Europe or North Africa (8%), or were largely marine in origin (33% of the events). The North American trajectories had the highest volume‐weighted average (VWA) concentrations and crustal enrichment factors for the three metalloids; the As/Se ratio and good correlations with acidity suggest inputs from fossil fuel combustion. The Euro‐African trajectories had the lowest VWA concentrations and enrichment factors that approached crustal values, indicating mineral aerosol inputs; values for marine events fell between these two extremes. The atmospheric flux of metalloids to the western Atlantic Ocean represents a major source of these elements in surface waters (up to 100% for Sb and Se; up to 61 % for As) and a corresponding sink in their global atmospheric budgets.

Formate and acetate in monsoon rainwater of Agra, India

Formate and acetate concentrations were estimated using ion chromatography in 19 precipitation samples collected on an eventwise basis during the monsoon season (July through September), 1991, at Dayalbagh, Agra. Volume‐weighted average (VWA) concentrations for formate and acetate were 5.8 and 6.55 μmol L−1, respectively. The VWA hydrogen ion concentration was 0.084 μeq L−1 (pH 7.07) and the correlation coefficient between the two ions was 0.85. The average formate to acetate ratio was low (0.88), possibly due to an increase in acetate contribution from direct emissions associated with heavy vehicular traffic load and/or indirect acetate formation by alkaline hydrolysis of PAN. Widespread local use of biomass as a domestic fuel may also contribute acetate. In 4 of the 19 precipitation events studied, higher values of both species were recorded. Contributions from soil in addition to vegetation, were suspected in these samples. Inputs from soil and combustion activities were supported by correlations among formate, acetate and Ca2+ (terrigenous species), K+, SO42− and NO31−.

Atmospheric deposition and solute export in giant sequoia ? mixed conifer watersheds in the Sierra Nevada, California

Atmospheric depostion and stream discharge and solutes were measured for three years (September 1984 — August 1987) in two mixed conifer watersheds in Sequoia National Park, in the southern Sierra Nevada of California. The Log Creek watershed (50 ha, 2067–2397 m elev.) is drained by a perennial stream, while Tharp's Creek watershed (13 ha, 2067–2255 m elev.) contains an intermittent stream. Dominant trees in the area include Abies concolor (white fir), Sequoiadendron giganteum (giant sequoia), A. magnifica (red fir), and Pinus lambertiana (sugar pine). Bedrock is predominantly granite and granodiorite, and the soils are mostly Pachic Xerumbrepts. Over the three year period, sulfate (SO42−), nitrate (NO3−), and chloride (Cl−1) were the major anions in bulk precipitation with volume-weighted average concentrations of 12.6, 12.3 and 10.0 μeq/1, respectively. Annual inputs of NO3-N, NH4-N and SO4-S from wet deposition were about 60 to 75% of those reported from bulk deposition collectors. Discharge from the two watersheds occurs primarily during spring snowmelt. Solute exports from Log and Tharp's Creeks were dominated by HCO3−, Ca2+ and Na+, while H+, NO3−, NH4+ and PO43− outputs were relatively small. Solute concentrations were weakly correlated with instantaneous stream flow for all solutes (r2 <0.2) except HCO3− (Log Cr. r2 = 0.72; Tharp's Cr. r2 = 0.38), Na+ (Log Cr. r2 = 0.56; Tharp's Cr. r2 = 0.47), and silicate (Log Cr. r2 = 0.71; Tharp's Cr. r2 = 0.49). Mean annual atmospheric contributions of NO3-N (1.6 kg ha−1), NH4-N (1.7 kg ha−1), and SO4-S (1.8 kg ha−1), which are associated with acidic deposition, greatly exceed hydrologic losses. Annual watershed yields (expressed as eq ha−1) of HCO3− exceeded by factors of 2.5 to 37 the annual atmospheric deposition of H+.

Processes controlling the concentrations of SO&lt;sup&gt;=&lt;/sup&gt;&lt;sub&gt;4&lt;/sub&gt;, NO&lt;sup&gt;-&lt;/sup&gt;&lt;sub&gt;3&lt;/sub&gt;, NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;, H&lt;sub&gt;+&lt;/sub&gt;, HCOO&lt;sub&gt;T&lt;/sub&gt; and CH&lt;sub&gt;3&lt;/sub&gt;COO&lt;sub&gt;T&lt;/sub&gt; in precipitation on Bermuda

The composition of precipitation on Bermuda can be characterized as a slightly acidic, dilute seawater solution. The acidity of the solution is controlled by H 2 SO 4 , HNO 3 , HCOOH and CH 3 COOH in a 67:20:8:3 mixture, respectively. CaCO 3 and NH 3 have reduced the potential acidity of the solution by 24% and 13%, respectively. The concentrations of non-sea-salt (nss) SO= 4 and NO - 3 in precipitation on Bermuda are about a factor of three greater than those in remote marine areas of the world. These differences are attributed in part to anthropogenic activities. NH + 4 , HCOO T and CH 3 COO T concentrations in Bermuda precipitation more closely resemble remote areas, although there are distinct events where transport from North America is evident. Precipitation associated with air masses from the central Atlantic Ocean is enriched relative to remote marine areas by about a factor of two in nss SO= 4 . This appears to be caused by anthropogenic emissions in North America, Europe and Africa. There are higher volume-weighted average concentrations of nss SO= 4 and NO - 3 in storms on Bermuda associated with the NW airflow sector (from North America) compared to the SE airflow sector. These higher concentration are in part due to the influence of North America and in part due to lower amount of precipitation in the NW storms. An analysis of deposition differences between the two sectors confirms that there is at least a factor of two impact of North American anthropogenic activities on nss SO= 4 and NO - 3 in precipitation on Bermuda. DOI: 10.1111/j.1600-0889.1989.tb00319.x

Chemical composition of precipitation at Long Island, NY

Chemical analyses were performed on 387 sequential precipitation samples, both rain and snow, collected at Brookhaven National Laboratory, Long Island, New York, on 96 different days during the period from October 1983 to June 1985. The collection time for each individual sample was typically 30 min. The chemical species determined and the volume-weighted average and maximum concentrations (in parentheses) in units of μM were: H202:7(120), H2CO:6(60), H+:51(500), N03 −:30(350), S04 2−:25(270), NH4 +:18(250), Ca2+:3(48), Na+:32(400), and Cl−:37(380). A strong seasonal dependence was observed for H202 concentration, the maximum concentration in summer (120 μM) being 6 times greater than in winter. In addition, H202 concentration also exhibited a strong diurnal variation, with a maximum peaking in the afternoon and a minimum after midnight. These observations suggest that the production of H202 may be governed by photochemical activity. Nitrate concentration also displayed a strong diurnal variation, having a maximum around noon, but did not show a seasonal dependence. Relationships between various species and their possible sources are briefly discussed.

Study of acid deposition in Switzerland: Temporal variation in the ionic composition of wet precipitation at rural sites during 1983–1984

A study of the chemical characteristics of wet precipitation was carried out in central Switzerland. Wet-only samples were collected weekly at three sites during 1983 and 1984. The results were examined for spatial and temporal variations in the concentrations of major cations and anions and also compared with similar results from two other Swiss stations, one in the eastern part of the country and one at an alpine location. At the sites not under the direct influence of urban emissions, concentrations of sulphate, nitrate and chloride were very similar at altitudes of 515 and 950 m above sea level. Volume-weighted average concentrations observed were lower than at most other European sites used for comparison. Between 950 and 3500 m above sea level, concentrations decreased, but much less in the case of sulphate than in the case of nitrate. At sites surrounded by agriculture, most nitrate and sulphate was associated with ammonium, and not with hydrogen, ions. Anion acids were enriched in precipitation collected downwind of urban areas. The temporal variation in the concentration of sulphate and nitrate did not depend on location. It was determined by precipitation volume and seasonal factors; for instance, the increase in air temperature in spring, which was associated with an increase in sulphate. The most acidic events occurred during spring and summer months. They were characterised by an increase in the nitric acid content. Possible relationships between the variation in precipitation acidity and meteorological conditions are discussed.