Article

A comparison of the precipitation chemistry measurements obtained by the CAPMoN and NADP/NTN networks

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Abstract

Precipitation chemistry measurementsobtained by the Canadian Air and PrecipitationMonitoring Network (CAPMoN) and the U.S. NationalAtmospheric Deposition Program/National Trends Network(NADP/NTN) have been examined using more than 7 yrof collocated data from two sites, namely, Sutton,Quebec, Canada and State College, Pennsylvania, U.S.A.In the case of the CAPMoN data, weeklyprecipitation-weighted mean concentrations, totalsample depths and total standard gauge depths werecomputed from daily data and compared to thecorresponding weekly sampling data of the NADP/NTNnetwork. Seasonal and annual precipitation-weightedmean concentrations and deposition values were alsocomputed for both networks and compared. Statisticallysignificant between-network biases were found to existin the weekly results for most of the measuredvariables, particularly standard gauge depth, sampledepth, pH, H+, NO3 -,NH4 +,Na+; the NADP/NTN values were consistently lowerthan those of CAPMoN with the exception of pH andNa+. The magnitude of the biases was less than35% of the median CAPMoN weekly value for the 7 yr. For most of the measured parameters, thevariability of the between-network differencesrepresented less than 20% of the median CAPMoN weeklyvalue. Both the between-network biases andvariabilities were functions of several physicalparameters, the most dominant being the sample depthand the ionic concentration. For seasonal and annualdeposition values, statistically significantbetween-network biases were found for H+,SO4 2-, NO3 -,Ca2+,NH4 + for both periods; for Mg2+ andK+ for seasonal data; and Cl- for yearlydata, with the NADP/NTN deposition values being lowerthan those of CAPMoN. The relative biases ranged from7 to 37%. Part of the between-network bias in thedeposition estimates was directly attributable to astrong bias in the standard gauge depths of the two networks.

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... Data from these two sites for 2001 were combined into a single annual record for this study. The CAN4 site is described by Sirois et al. (2000) as situated in open grassy areas surrounded by mixed forests on all sides. The CAN5-Frelighsburg site is located in rural, southern Quebec province; well removed from industrial and urban activity with some agricultural land use. ...
... CAN5 is located at 45 • 03 06 north latitude and 72 • 51 42 west longitude at an altitude of 195 m. The PA15 site, located at Pennsylvania State University, is described by Sirois et al. (2000) as situated in a broad valley between two mountain ridges in the Appalachian Mountains at 40 • 47 18 north latitude and 77 • 56 48 west longitude at an altitude of 393 m. The PA15 site is located in a 0.03 km 2 , mown grass area in otherwise forested land. ...
... Data from the CAN4 and PA15 colocated sites were compared by Sirois et al. (2000) for the period September 1986-December 1993 to evaluate the magnitude and bias of differences between network measurements on a weekly, seasonal, and annual basis. That work is referenced extensively herein. ...
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Precipitation chemistry and depth measurements obtained by the Canadian Air and Precipitation Monitoring Network (CAPMoN) and the US National Atmospheric Deposition Program/National Trends Network (NADP/NTN) were compared for the 10-year period 1995-2004. Colocated sets of CAPMoN and NADP instrumentation, consisting of precipitation collectors and rain gages, were operated simultaneously per standard protocols for each network at Sutton, Ontario and Frelighsburg, Ontario, Canada and at State College, PA, USA. CAPMoN samples were collected daily, and NADP samples were collected weekly, and samples were analyzed exclusively by each network's laboratory for pH, H(+), Ca(2+), Mg(2+), Na(+), K(+), NH4(+), Cl(-), NO3(-), and SO4(2-). Weekly and annual precipitation-weighted mean concentrations for each network were compared. This study is a follow-up to an earlier internetwork comparison for the period 1986-1993, published by Alain Sirois, Robert Vet, and Dennis Lamb in 2000. Median weekly internetwork differences for 1995-2004 data were the same to slightly lower than for data for the previous study period (1986-1993) for all analytes except NO3(-), SO4(2-), and sample depth. A 1994 NADP sampling protocol change and a 1998 change in the types of filters used to process NADP samples reversed the previously identified negative bias in NADP data for hydrogen-ion and sodium concentrations. Statistically significant biases (alpha = 0.10) for sodium and hydrogen-ion concentrations observed in the 1986-1993 data were not significant for 1995-2004. Weekly CAPMoN measurements generally are higher than weekly NADP measurements due to differences in sample filtration and field instrumentation, not sample evaporation, contamination, or analytical laboratory differences.
... Choices of prior hyperparameter values for our Bayesian analysis could not, of course, be based on the exploratory analysis of the analysis data set. Although Sirois et al. (2000) described the mean diierences between NADP and CAPMoN measurements, and the standard deviations of these diierences, they provided no prior information on the actual standard deviations of measurements by individual networks, the spatial distribution of deposition, or any aspects of the AIRMoN network. Therefore , we chose to specify diiuse but proper priors based on general considerations as follows. ...
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... ammonium from agriculture and calcium Table 1 for each site. Table 1 (Granat et al., 1996;Al-Momani et al., 1997;Sirois et al., 2000;Balasubramanian et al., 2001;Qin and Huang, 2001;Basak and Alagha, 2004;Likens, 2007). It is cautioned that the temporal range of measurements is varied for these studies, which can affect pH comparisons; for example, reductions in sulfur dioxide (SO 2 ) emissions in the Southwest over the last several years have resulted in reduced particulate sulfate levels (Matichuk et al., 2006;Sorooshian et al., 2011), which influences precipitation pH. ...
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Prior comparability studies of precipitation chemistry networks in eastern North America have reported that data derived from daily sampling are preferred over those obtained from weekly integrated sampling. However, the record of daily wet-only precipitation chemistry in the United States was interrupted for more than 3 years (from 5 January 1990 to 26 December 1993), precluding the generation of a single, continuous record since the start of operations in September 1976. A first attempt was made to reconstruct the record during the intervening (“gap”) years at a site in central Pennsylvania, where the Canadian Air and Precipitation Monitoring Network (CAPMoN) collocated daily sampling operations beginning in 1987. First, data from the original daily wet deposition monitoring program (the Multistate Atmospheric Power Production Pollution Study (MAP3S)) and from the most recent program (the Atmospheric Integrated Research Monitoring Network (AIRMoN)) were separately compared with the CAPMoN data. The internetwork biases so obtained were then merged and used to adjust the uninterrupted, overlapping CAPMoN data, thus enabling us to combine the different data sets and reconstruct the whole record for the major ions (SO42−, NO3−, NH4+, and H3O+). The between-network differences derived from the paired daily data (US datum–CAPMoN datum) show statistically significant negative biases (MAP3S, AIRMoN
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Detailed description of the distributions and seasonal trends of atmospheric nitrogen compounds is of considerable interest given their role in formation of acidic substances, tropospheric ozone and particulate matter and nutrient loading effects resulting from their deposition to sensitive ecosystems. While the oxidized nitrogen species have received considerable research and regulatory attention over the past several decades, little effort has been devoted toward quantifying the atmospheric budgets of reduced nitrogen compounds (NHx) associated with emissions of ammonia. The Regional Acid Deposition Model is enhanced to include detailed treatments of the physical and chemical processes regulating the fate of ammonia emissions and to model the interaction and chemical and thermodynamic coupling between atmospheric NOx-SOx-NHx species. To account for uncertainties in magnitude and seasonal variation of ammonia emissions, regional seasonal correction factors for ammonia emissions in the eastern United States are developed through successive model applications and comparison with measurements from regional networks of ambient concentrations and deposition amounts of various species. The resulting ammonia emissions show a distinct seasonal cycle with a maximum in summer followed by spring, fall, and winter. Our calculations suggest that the range between NH3 emissions during the cool and the warm season is a factor of 3-4. Correlations between model predicted ambient levels, gas/particle partitioning, and deposition amounts with measurements show good agreement on both an annual and seasonal basis with R2 in the 0.4-0.7 range for most species examined. Both model calculations and measurements indicate that during winter, large portions of the eastern U.S. are characterized by aerosols that are fully neutralized. Our model calculations for emission scenarios representative of the late 1980s-early 1990s period also indicate that reduced nitrogen species contribute 47(+/-8)% of the total nitrogen wet deposition in the eastern U.S.; this is in good agreement with 43(+/-9)% inferred from deposition measurements. These comparisons suggest that the model can capture the spatial and seasonal variability in distributions of various model species, the chemical interactions between reduced and oxidized nitrogen compounds in the troposphere, and the compositional characteristics of inorganic aerosol mass in the region.
Article
This is a manual for the Global Atmosphere Watch Precipitation Chemistry (GAW-PC) Programme. Where possible, it describes standard operating procedures and otherwise provides guidance on methods and procedures. The objectives of the GAW Precipitation Chemistry Programme are as follows: (1) to assure the harmonization of measurements conducted globally by various regional and national programmes; (2) to enable quantification of patterns and trends in the composition of atmospheric precipitation at global and regional scales; (3) to improve the understanding of biogeochemical cycles of major chemical species; (4) to facilitate global assessments of acid deposition and to investigate long-range transport from major source areas; and (5) to provide the data needed for evaluating the effects of acid deposition on major ecosystems, for example, coastal and sensitive areas, and for developing control measures. To address the first objective and to improve the quality of global data, the GAW-PC Programme has undertaken to revise its standard operating procedures, including all on-site, laboratory, data management and quality assurance aspects of the measurement system. The new procedures documented and presented in these chapters are for major ions in precipitation. The major ions and measurements covered in this manual are as follows: Sulfate, Chloride, Calcium, Conductivity, Nitrate, Sodium, Magnesium, Ammonium, Potassium, and pH. Other provisional measurements include Alkalinity and Organic Acids.
Article
In some studies of atmospheric pollution, deposition data may be available from several distinct monitoring networks. Systematic differences may exist between networks, and an effective statistical analysis of the data combined from all networks should account for this possibility. This article develops a Bayesian modeling approach for spatiotemporal data from two monitoring networks that accounts for possible network differences in measurement error biases and variances. Wet sulfate deposition data from two networks in the eastern United States, the National Acid Deposition Program/National Trends Network and the Clean Air Status and Trends Network, are combined and analyzed via our modeling approach. We examine whether the temporal trend in deposition from 1989-1997 varies regionally and whether the measurement error biases and variances differ between networks. We also demonstrate how prediction uncertainty is reduced using the combined data from levels obtained when basing prediction on data from only one of the networks.
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Data collected in the eastern US between 1990 and 2009 at 34 paired dry and wet monitoring sites are examined. A goal is to evaluate the air quality impacts occurring between 1990 and 2009 that are associated with concurrent legislatively-mandated changes in emissions. Four 5 year periods, 1990?1994 (P1), 1995?1999 (P2), 2000?2004 (P3), and 2005?2009 (P4) are considered, with a primary focus on P1-to-P4 changes. Results suggest that legislatively-mandated air pollution mitigation strategies have been successful in improving air quality and reducing atmospheric deposition in the eastern US. Respective P1-to-P4 reductions of estimated sulfur dioxide (SO2) and nitrogen oxides (NOx) emissions in the eastern US are 50 and 42%. Corresponding behavior of the following metrics associated with these emissions reductions are examined: monitored atmospheric concentrations of SO2, aerosol sulfate (SO4), and oxidized sulfur (S); dry, wet, and total deposition of S; monitored atmospheric concentrations of nitric acid (HNO3), aerosol nitrate (NO3), and their sum, oxidized nitrogen (OxN); dry, wet, and total deposition of OxN; monitored atmospheric concentration of aerosol ammonium (NH4); dry, wet, and total deposition of NH4; summed monitored atmospheric concentration of oxidized and reduced nitrogen (N); dry, wet, and total deposition of N; wet deposition of hydrogen ion (H?); monitored atmospheric concentration of ozone (O3); dry deposition of O3; and the summed monitored atmospheric concentration of aerosol NO3, SO4, and NH4 (CASTNET PM). Other metrics (e.g., ratios of dry to total deposition) are also considered. Selected period-to-period changes of air quality and deposition metrics at site, regional, and seasonal scales are discussed. As an example, despite P1-to-P3 reductions in estimated emissions of both SO2 and NOx, aerosol NO3 concentration increased in the east, with widespread wintertime numerical increases in both aerosol NO3 concentration and CASTNET PM. However, a reversal of this behavior is associated with continuing P3-to-P4 reductions of SO2 and NOx emissions. Thus, additional P3-to-P4 reductions of these emissions, especially NOx, appear to have made progress in altering the chemical regime of the wintertime eastern US atmosphere so that future emissions reductions and their resulting reductions in aerosol concentrations may no longer be accompanied by sub-linear changes (or actual increases) in CASTNET PM.
Article
Nitrogen and P leaching from agricultural land to ground water ping systems, and fertilizer applications influence soil poses a threat to water quality, but it may be possible to control nutrient concentrations and drainage rates, leading us dissolved nutrient leaching by choosing appropriate management practices. The objective of this study was to evaluate the effects of to believe that it may be possible to control NO3-N and agricultural practices on dissolved N and dissolved P leaching from dissolved reactive P leaching from agricultural soils by topsoil to subsurface soil after crop harvest. Intact soil cores and small choosing appropriate management practices. disturbed soil columns were collected from a factorial (tillage crop Tillage has a two-fold effect on nutrient leaching: first,
Article
This study is a comparison of the weekly aggregated MAP3S (1981–1989) and AIRMoN (1992–1995) daily precipitation chemistry record, to the NADP/NTN weekly data at four collocated sites in the eastern U.S.A. Data for conductivity, H+, NO-3, and SO2-4 all strongly support the hypothesis that the weekly and daily network concentrations of these ions are comparable for both time periods. Data for ammonium show a statistically significant bias for both time periods with the daily record having concentrations approximately 14% higher than the weekly values. This bias also has been observed in other studies of weekly and daily networks, and may be a function of residence time samples remain in the field and/or in storage before analysis. Significantly higher Cl- and K+ concentrations in the MAP3S data set from 1986 to 1989 suggest a contamination problem and use of these data is not recommended for this time period. Potassium concentrations during the other years of record compare poorly between the daily and weekly networks on a weekly basis. Annual data compare well. The other base cation weekly concentrations (Ca2+, Mg2+, Na+) also do not compare well, with average weekly differences ranging from 23 to 51%. However, both the daily and weekly networks show a very similar temporal decline in the sum of base cation concentrations of about 30% from the periods 1981–1985 to 1992–1995. Network Ca2+ and Mg2+ concentration trends also compare well for the entire period of record. Intranetwork variability, assessed in a separate study at several collocated NADP sites in the eastern U.S.A., could account for 1/5 to 1/2 of the internetwork bias for most ions. Intranetwork relative error may account for 1/4 to 2/3 of the internetwork relative error. This study supports the concept that the MAP3S and AIRMoN networks represent a continuous event/daily network data base of high quality for conductivity, H+, NO-3, and SO2-4 concentrations. Comparisons in trends of NH+4, Ca2+ and Mg2+ also suggest that these ions represent a quality long-term database. Daily network NH+4 (and possibly Na+) concentrations may be better estimates of actual precipitation concentrations than the weekly network data.
Article
The formation of sulfate and nitrate in eastern North America is chemically linked to the abundance of oxidants and therefore to the emissions of nitrogen oxides (NOx). Depending on conditions, NOx reacts under either of two distinct photochemical regimes, defined by the types and levels of radical production. In the low-NOx regime (typical of summer), nitrogen dioxide (NO2) is readily consumed during nitric acid formation, leaving an excess of radicals that recombine to form peroxides and a highly oxidizing state favorable to sulfate formation. On the other hand, under high-NOx conditions (as in winter), the oxidizing capacity of the atmosphere is reduced because the NO2 rapidly combines with and thereby depletes hydroxyl radicals, producing nitric acid, but few peroxides. The distinction between these two chemical regimes is crucial for interpreting atmospheric deposition data because it determines whether sulfate or nitrate is the dominant acidifying component. Evidence for these regimes is gained from seasonal observations of sulfate and nitrate in rain samples collected at several sites of the National Atmospheric Deposition Program (NADP). A simple modeling exercise elucidates the processes by which sulfate and nitrate are formed under the high- and low-NOx states.
Article
The long-term trends in atmospheric reactive nitrogen (Nr) species at 12 Canadian Air and Precipitation Monitoring Network (CAPMoN) stations (9 with air and precipitation observations) across Canada were evaluated during the period 1988–2007. The non-parametric Mann–Kendall test was used to determine monotonic trends in the annual average concentrations of gaseous nitric acid (HNO3), particulate nitrate (pNO3−), particulate ammonium (pNH4+), wet ammonium (NH4+) and wet nitrate (NO3−) in response to emission reductions primarily driven by the Canada–United States Air Quality Agreement. Annual air concentrations (1988–2007) of pNH4+ and HNO3 significantly decreased at all CAPMoN stations, while pNO3− concentrations increased at 6 of 9 stations. Precipitation NH4+ had no significant or consistent trend; in contrast precipitation NO3− concentrations significantly decreased at 9 of the 11 stations and increased at one (non-significant). Normalized temporal sequences showed consistent patterns across Canada for several Nr species. Annual average air concentrations of pNH4+ and HNO3 had synchronous time-series with consistently decreasing concentrations across all CAPMoN stations (1988–2007), in contrast, pNO3− had a complex temporal pattern, characterised by an initial period of no change (1988–1993), followed by a period of steep increase (1993–2002) and then a period of steep decrease (2002–2007). The period of steep decrease started around 2002 and was mirrored by all Nr species (except wet NH4+) at all CAPMoN stations. The steep decrease was consistent with the observed decrease in NOx emissions from power plants and on-road vehicles in the United States and Canada. Legislated emission reductions have resulted in significant decreases in Nr concentrations except for NH4+, as such uncontrolled ammonia emissions continue to be a significant source of Nr.
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Ammonium concentration data in precipitation have been compiled to derive a concentration and deposition field for ammonium in Europe. Measurements referring to a total number of 218 measuring sites have been considered. Because of changes in the ammonium concentrations due to the use of improper sampling procedures, a correction procedure is proposed. This makes allowance for the type of sampler used, the length of the sampling period, and whether or not light-protected sample bottles are used. Dependent on the specific sampling procedure used correction factors range from 0.75 to 1.20. According to our calculations, the total wet deposition flux of ammonium in Europe in the early 1980s amounts to 2.4 Mt NH4 +y-1. However, for some parts of Europe the flux cannot be estimated very reliably because of the low number or even the absence of measuring sites. Compared to earlier estimates for around 1960, the ammonium wet deposition flux has increased by approximately 25% during the period 1960–1980.
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We examine the chemical differences between event and weekly samples of precipitation collected in northeastern Illinois from April 1980 to March 1982. Analyses were conducted for H+, Ca2+, Mg2+, NH4+, SO42− and NO3− concentrations as well as for pH and conductivity. In addition, the 1980–1981 samples, were titrated to determine the total, strong and weak acid concentrations. Although seasonal and annual precipitation amounts were different for the two years, the general pattern of event and weekly sample ion concentrations were similar. Weekly samples had significantly less [NH4+] and higher laboratory pH in all seasons and more [SO42−] in every season but summer. Weekly samples had significantly more [Ca2−] and [Mg2+] during seasons with little precipitation. Event and weekly [NO3−] were never significantly different. The weekly samples had more total acidity in the spring but less in the summer. The observed differences may be attributed to chemical degradation of the weekly samples while waiting collection and during shipment between the field and the laboratory.
Article
Measurements were made at the Turkey Lakes Watershed from 1981 to 1984. Results unexpected from the theory of the measurement methods appeared in the comparison: 1) one of the bulk deposition measurements produced lower deposition of acid-related ions than the two wet-only measurements, and 2) the monthly wet-only measurements produced higher deposition of sulphate than the two bulk deposition data sets (by 6 and 19%). Several results were consistent with the theory of the measurements: 1) the daily wet-only measurements produced deposition values lower than the weekly bulk deposition measurements and 2) the wet-plus-dry deposition measurements produced higher estimates of sulphate and nitrate deposition than the two bulk data sets (15-35% higher). -from Authors
Article
The National Atmospheric Deposition Program (NADP) was established in 1978 as a national monitoring network to investigate acid deposition. The National Trends Network (NTN) was established in 1982 to expand the NADP effort into areas not previously sampled. Most sites in the NADP were incorporated into the NTN operation. Data collected as part of the NADP/NTN programs are used to monitor spatial and temporal trends in the chemical composition of natural wet deposition and to provide accurate data to individual scientists or agencies involved in research on the effects of acid deposition. The report describes the results of the external quality-assurance programs operated by the U.S. Geological Survey during 1988. These programs: (1) Assess the precision and accuracy of onsite determinations of pH and specific conductance; (2) evaluate the effects of onsite and laboratory protocols on the bias and precision of NADP/NTN analyte determinations; (3) determine the comparability, bias, and precision of analytical results obtained by separate laboratories when portions of a common sample were analyzed; and (4) estimate the precision of the entire sampling system.
Article
Rain chemistry data taken in the United States have been examined for the consistency of sampling and chemical analysis methods used, and in relation to earlier European work. Attempts were made to quantify uncertainties, biases or equivalence associated with (a) sampling, analytical and calculational methods to deduce precipitation acidity; (b) use of data from different times and conditions; (c) failure to collect brief or light rainfall; (d) failure to collect initial precipitation in an event; (e) failure to analyze for magnesium in certain samples and (f) failure of previous investigators to consider all available data. These assessments were analyzed in conjunction with interpretation of spatial and temporal changes showing apparent trends in increased precipitation acidity over the eastern United States. The results show that the historical data are of insufficient quality and quantity to support any long-term trends in precipitation acidity change in the eastern United States. However, the observations do show that precipitation is definitely acidic over this region, and is probably more acidic than expected from natural baseline conditions. There is support for defining an area of relatively high acidity extending from Ohio to New England which depends upon the total mix of cations and anions present in precipitation. Although observations in the southeast are very limited, they suggest a region of elevated acidity (pH < 5.0) in rainfall from Alabama eastward through Florida. This was not present in data taken there in the mid 1950s. The reasons for this apparent change are not evident from analysis to date of either natural changes or industrialization, though the southeast has experienced a substantial increase in population, urbanization, electrical generation, and industrial growth over the past 25 years.
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This paper presents a framework for data quality assessment of annual and seasonal precipitation chemistry data summaries. Consideration has been to (i) using data from regional or national networks with established quality assurance/quality control programs and well documented network operation protocols, (ii) assessing regional representativeness of each sites, (iii) determining quantitative measures to define data completeness levels, and (iv) documenting the calculation procedures used to compute precipitation-weighted mean concentrations and wet deposition amount. The procedures described here are applied to data collected from 1980 to 1986 by five major acid deposition monitoring networks in North America and examples of annual sulfate deposition summaries are reported. It is recommended that the concepts of site representativeness, data completeness and overall data quality levels be adopted by the user community and routinely be reported along with a data summary. Further work on assesing accuracy and precision to accompany the data quality levels is recommended.
Article
The U.S. Geological Survey used four programs in 1990 to provide external quality assurance for the National Atmospheric Deposition Program/National Trends Network (NADP/NTN). An intersite-comparison program was used to evaluate onsite pH and specific-conductance determinations. The effects of routine sample handling, processing, and shipping of wet-deposition samples on analyte determinations and an estimated precision of analyte values and concentrations were evaluated in the blind-audit program. Differences between analytical results and an estimate of the analytical precision of three laboratories routinely measuring wet deposition were determined by an interlaboratory-comparison program. Overall precision estimates for the precipitation-monitoring system were determined for selected sites by a collocated-sampler program.
Article
A comparison between weekly and event samples has been undertaken to assess the differences introduced by different sampling periods.The data analyzed cover the period 18 March 1981-28 June 1983.The weekly samples yielded lower concentrations and deposition values for all ions analyzed. The differences were significant at the 99.9 per cent confidence level.
Article
The study compares data obtained using the equipment and protocols of the U.S.-based National Atmospheric Deposition Program/National Trends Network (NADP/NTN) with data from the Canadian Air and Precipitation Monitoring Network (CAPMoN). This intercomparison focuses on the differences in sampling interval employed in each network (weekly in NADP/NTN; daily in CAPMoN), as well as on the comparability of the overall network operations. Given sufficient comparability and the relatively high spatial density of sites in each network, it may be possible to combine these two data sets and so be able to develop isopleth maps that span the U.S.-Canadian border without major discontinuities. After a description of the sampling sites and protocols used in the study, the authors consider the analytical methods used to process and intercompare the data. Actual results are presented and discussed.
Conference Paper
Precision estimates are presented for precipitation chemistry and depth measurements made by the Canadian Air and Precipitation Monitoring Network (CAPMoN). The estimates were made for daily measurements of ion concentration and precipitation depth as well as for weekly, 28-day, seasonal and annual precipitation-weighted mean concentrations and depths. The data on which the estimates are based were collected from collocated samplers at five CAPMoN sites during the period 1985 to 1993. The data pairs from the collocated samplers were used to calculate the between-instrument error defined as 1/√2 times the difference between the paired sample concentrations (or depths). For all of the ion concentrations and depths, the between-sampler errors were found not to be normally distributed, but the normality of the distributions improved with the length of the (volume-weighting) time period considered. A set of quantitative measures of overall network precision were derived in absolute (mg L-1) and relative (%) units. These included the Modified Median Absolute Deviation (M.MAD), the P90% probability values and the Coefficient of Variation (CoV). The latter, defined as the percent ratio of the M.MAD to the median concentration (or depth), represents the relative precision at the center of the error and concentration (and depth) distributions. Based on the CoV values, the relative precision of the CAPMoN measurements was very high (better than 4%) for SO 4 2- , NO 3 - , pH, H+, NH 4 + , sample depth and standard gauge depth, and not as high (between 10 and <35%) for Cl-, Na+, Ca2+, Mg2+, and K+. The ions with the lowest median concentrations had the poorest relative precision since so many of the concentrations were at or near the analytical detection limit. Except for the sample and standard gauge depths, both the absolute and relative precision improved with the length of the precipitation-weighting period. Detailed statistical testing established that the precision of the daily measurements is dependent on a number of factors, the most dominant being sample depth and concentration, i.e., the absolute precision improves with increasing sample depth and decreasing concentration. The strength of these relationships diminished with the length of the precipitation-weighting period being considered. Laboratory-related sources of imprecision were found to account for less than 4% of the overall daily measurement imprecision for most species, while field-related sources of imprecision accounted for the balance. Specialized plots are shown which allow data users to estimate the absolute and relative precision at any concentration and depth value.
Article
Uncertainties in the calculation of monthly, seasonal and annual precipitation-weighted-mean concentrations due to missing data are addressed. An algorithm is presented to estimate the effects of missing samples through the use of a simulation technique. Quantitative estimates of uncertainty due to missing data are given for monthly, seasonal and annual precipitation-weighted-mean sulphate and nitrate concentrations at six monitoring sites where daily precipitation samples were taken. It is found that the expected value of the precipitation-weighted-mean concentration estimator is biased if the percentage of missing samples (% MN), and the percentage (% MP) of the precipitation amount associated with the missing samples, are different. The absolute value of the bias becomes larger as the difference increases. The standard deviation of the estimator increases with increasing values of % MP. For a given value of % MP, its a minimum when % MN is equal to % MP, and increases with increasing differences between % MN and % MP. These results indicate that % MN of about 10%, which is not uncommon in precipitation networks data, gives an uncertainty of about 10, 5 and 2 % for monthly, seasonal and annual averaging periods, respectively. Procedures to estimate confidence intervals for the true values from observed precipitation-weighted-mean concentrations are presented.
Article
Precipitation is currently collected by several methods, including several different designs of collection apparatus. We are investigating these differing methods and designs to determine which gives the most representative sample of precipitation for the analysis of some 25 chemical parameters. The experimental site, located in Ithaca, New York, has 22 collectors of 10 different designs. The designs include bulk (wet and dry deposition collected together), wet only (only rain and snow) and wet/dry (collects wet and dry deposition separately). In every sampling period, which varies from 1 day to 1 mo, depending on the time variable being tested, the following chemical parameters are determined: conductivity, pH, Ca, Mg, Na, K, NH4, N03, Ntotal Si04, PO4, Ptotal, Cl, SO4, DOC, Zn, Cu, Mn, Fe, Al, Ni, Cd, Pb, Ag, DDT, DDE, Dieldrin and PCB's.The results of the investigation lead us to conclude that: (1) Precipitation samples must exclude dry deposition if accurate information on the chemical content of precipitation is required. (2) Substantial contamination results when glass and plastic collectors are used to sample precipitation for inorganic and organic components, respectively. (3) The inorganic components of precipitation samples of low pH (3.5 to 4.5), with the exception of P04 and Cl, exhibited no significant change in concentration when stored at 4\dgC for a period of 8 mo. We believe this is due to the stabilizing influence of a large concentration of H ions. (4) If quantitative information on the chemical composition is required, precipitation samples should be collected at no longer than weekly intervals if immediate collection is not possible.
Article
A collocated, wet-deposition sampler program has been operated since October 1988 by the U.S. Geological Survey to estimate the overall sampling precision of wet atmospheric deposition data collected at selected sites in the National Atmospheric Deposition Program and National Trends Network (NADP/NTN). A duplicate set of wet-deposition sampling instruments was installed adjacent to existing sampling instruments at four different NADP/NTN sites for each year of the study. Wet-deposition samples from collocated sites were collected and analysed using standard NADP/NTN procedures. Laboratory analyses included determinations of pH, specific conductance, and concentrations of major cations and anions. The estimates of precision included all variability in the data-collection system, from the point of sample collection through storage in the NADP, /NTN database. Sampling precision was determined from the absolute value of differences in the analytical results for the paired samples in terms of median relative and absolute difference.
Article
Precipitation chemistry data derived from more than six years of concurrent sampling under the MAP3S and NADP/NTN protocols at the Penn State site in rural Pennsylvania are compared. Preprocessing of the data (sample and gage depths, concentrations of H3O+, SO42−, NO3−, NH4+) included aggregating the event and daily MAP3S data into weekly averages that coincide with the weekly data of the NADP/NTN program. A simple statistical model was applied to the differences of the paired data to look for systematic biases between the networks. The most notable bias occurred for ammonium concentration (NADP/NTN low), a finding consistent with other studies. A minor, but statistically significant, bias was also found for sulfate coccentration (NADP/NTN high). Both the ammonium and sulfate biases may be related to the relatively long time that the NADP/NTN samples remain in the field, thus strengthening arguments in favor of daily sampling protocols. The hydronium and nitrate concentrations exhibited remarkably high levels of comparability between the daily and weekly protocols. Overall, the data from the MAP3S and NADP/NTN networks are comparable, with the possible exception of ammonium, for some applications. The field results from about two years of duplicate sampling under the MAP3S protocol demonstrate that measurement precisions of only a few percent are possible when the protocol is consistently followed and the equipment is well maintained.
Article
From June 1988 to May 1990, a Joint Canada-United States measurement program known as EMEFS made daily air and precipitation measurements across eastern North America. Surface data were collected by five participating networks at approximately 130 sites for use in assessing regional air pollutant and deposition model performance. This paper describes the measurement program and focuses on its associated quality assurance program. The concentration measurements were found to have overall uncertainties of ± 2.3% for SO42− and NO3− for precipitation and, for the air concentrations, ± 6.4% for SO2, ± 5.4% for SO42−, and ± 10.3% for NO3−. These uncertainty levels generally satisfied the program data quality objectives for use in model evaluation studies and represent the quality of contemporary air precipitation chemistry networks.
Article
Organic anions were measured in 16 precipitation events sampled in central Virginia between 25 April and 1 October 1983. Formic and acetic acids contributed 16% of volume weighted free acidity. The decrease in free acidity in stored aliquots was directly proportional to the disappearance of dissociated HCOO− and CH3COO−. The loss of free acidity between pH measured at field sites and at central laboratories was used to estimate dissociated organic acidity in samples collected by the National Atmospheric Deposition Program (NADP) and the MAP3S Precipitation Chemistry Project. Based on the arithmetic means of the volume weighted averages for each site, we estimate that organic acids contributed 18–35% of free acidity in NADP samples and 16% of free acidity in MAP3S samples. The loss of free acidity in MAP3S samples was three times greater during the growing season than it was during the rest of the year. Because they are rapidly assimilated by microbes, organic acids are unimportant in the long-term acidification of the environment.
Article
Event and weekly precipitation sampled with three types of collectors was stored under five different conditions and analyzed throughout a six-week time period to monitor changes in ionic composition. Ca++, Mg++, Na+, K+, H+, NH4+, SO42−, NO3− and Cl− were the constituents under observation. Dramatic variations in the concentrations of some species are attributable to the sample particulate loading. Although cooling retarded changes in ionic composition, immediate filtering after wet-only collection was the most effective means of retaining sample integrity and preventing adsorption-desorption reactions.
The 1997 Canadian Acidifying Emissions Assessment Volume 2: Atmospheric Science Assessment Report
  • Environment
Canada-United States Air Quality Agreement
  • U S Canada
LRTAP Interlaboratory Study L-23 For MajorIons and Nutrients Outliers in Statistical Data The spatial distributions of precipitation acidity and major ion wet deposition in North America during Wet deposition of ammonium in Europe
  • N Arafat
  • K Aspila
  • Canada Environment
  • V Barnett
  • T And Lewis
  • L A Barrie
  • J M Hales
Arafat, N. and Aspila, K.: 1990, LRTAP Interlaboratory Study L-23 For MajorIons and Nutrients. National Water Research Institute Report, Environment Canada. Barnett, V. and Lewis, T.: 1984, Outliers in Statistical Data, Second Edition, John Wiley & Sons, New York, 464 pp. Barrie, L. A. and Hales, J. M.: 1984, The spatial distributions of precipitation acidity and major ion wet deposition in North America during 1980, Tellus 36B, 333. Buijsman, E. and Erisman, J.-W.: 1988, Wet deposition of ammonium in Europe. Journal of Atmospheric Chemistry 6, 265. Canada–U.
External Quality Assurance Res-ults for the National Atmospheric Deposition Program/National Trends Network During
  • M A Nilles
  • J D Gordon
  • L J Schroder
  • C E Paulin
Nilles, M. A., Gordon, J. D., Schroder, L. J. and Paulin, C. E.: 1995, External Quality Assurance Res-ults for the National Atmospheric Deposition Program/National Trends Network During 1991. United States Geological Survey Report 93-4208, Denver Federal Center, Denver, CO.
Review of questions regarding rain acidity data Illinois State Water Survey, 2204 Griffith Drive Organic acidity in precipitation of North America Comparability and precision of MAP3S and NADP/NTN precipit-ation chemistry data at an acidic site in eastern North America
  • D A Hansen
  • G M Hidy
  • K O W James
  • W C Keene
  • J N Galloway
  • D Lamb
  • L Comrie
Hansen, D. A. and Hidy, G. M.: 1982, Review of questions regarding rain acidity data. Atmospheric Environment 16, 2107. James, K. O. W.: 1995, 1993 Quality Assurance Report NADP/NTN Deposition Monitoring, Illinois State Water Survey, 2204 Griffith Drive, Champaign, Ill. Keene, W. C. and Galloway, J. N.: 1984, Organic acidity in precipitation of North America. Atmospheric Environment 18, 2491. Lamb, D. and Comrie, L.: 1993, Comparability and precision of MAP3S and NADP/NTN precipit-ation chemistry data at an acidic site in eastern North America. Atmospheric Environment 27A, 1993.
LRTAP Interlaboratory Study L-23 For MajorIons and Nutrients
  • N Arafat
  • K Aspila
The 1997 Canadian Acidifying Emissions Assessment
  • Environment Canada
Canadian Air and Precipitation Monitoring Network Operators Instruction Manual-Precipitation
  • Capmon
Precipitation collectors intercomparison study
  • R G Pena
  • J A Pena
  • V C Bowersox
Deposition Monitoring: Methods and Results
  • D L Sisterson
  • V C Bowersox
  • T P Meyers
  • A R Olsen
  • R J Vong
  • J C Simpson
  • V Mohnen
Instruction Manual NADP/NTN Site Operation
  • Nadp Ntn