Canadian Air And Precipitation Monitoring Network Research Articles

Contribution of emissions from the oil sands activities in Alberta, Canada to atmospheric concentration and deposition of nitrogen and sulfur species at a downwind site

Oil sands activities in the Athabasca Oil Sands Region in Alberta, Canada, are large sources of atmospheric NOx and SO2. This study investigated the impact of oil sands emissions on the atmospheric deposition of nitrogen and sulfur species at a downwind site, about 350 km from the oil sands facilities. Measurement data are from the Canadian Air and Precipitation Monitoring Network (CAPMoN) from 2015 to 2019, including ambient concentrations of HNO3, pNO3-, NO2, pNH4+, NH3, SO2, pSO42− and base cations, as well as concentrations of NO3−, SO42−, NH4+, and base cations in precipitation. Sector analysis of air mass back trajectories was conducted to distinguish measurements with different air mass origins. Median atmospheric concentrations and dry deposition fluxes of HNO3, pNO3-, NO2, pNH4+, pSO42−, and SO2 on days when the air masses came from the oil sands sector were significantly greater than those with the “Clean” sector by 34–67%, whereas the difference in NH3 concentration was not significant. Contributions of the oil sands emissions to dry deposition fluxes of these species ranged from 3.8 to 13.1%. The precipitation-weighted mean concentrations of NO3−, SO42−, and NH4+ in samples with the oil sands sector were 76 %, 65 % and 81 % greater than those with the “Clean” sector, respectively. Contributions of the oil sands emissions to wet deposition of NO3−, SO42−, and NH4+ were 12.5 ± 8.9 %, 8.7 ± 4.4 %, and 6.0 ± 3.3 %, respectively. The annual total deposition of nitrogen and sulfur were 1.9 kg-N ha−1 and 0.74 kg-S ha−1, respectively, of which 8.0 ± 3.5 % and 8.7 ± 3.6 % were from oil sands emissions. The total deposition of sulfur and nitrogen did not exceed the critical loads (CL) of acidity, but nitrogen deposition exceeded the CLs of nutrient nitrogen in the region.

Inter-comparison of measurements of inorganic chemical components in precipitation from NADP and CAPMoN at collocated sites in the USA and Canada during 1986–2019

Wet deposition monitoring is a critical part of the long-term monitoring of acid deposition, which aims to assess the ecological impact of anthropogenic emissions of SO2 and NOx. In North America, long-term wet deposition has been monitored through two national networks: the Canadian Air and Precipitation Monitoring Network (CAPMoN) and the US National Atmospheric Deposition Program (NADP), for Canada and the USA, respectively. In order to assess the comparability of measurements from the two networks, collocated measurements have been made at two sites, one in each country, since 1986 (Sirois et al., in Environmental Monitoring and Assessment, 62, 273–303, 2000; Wetherbee et al., in Environmental Monitoring and Assessment, 1995–2004, 2010). In this study, we compared the measurements from NADP and CAPMoN instrumentation at the collocated sites at the Pennsylvania State University (Penn State), USA, from 1989 to 2016, and Frelighsburg, Quebec, Canada, from 2002 to 2019. We also included in the study the collocated daily-vs-weekly measurements by the CAPMoN network during 1999–2001 and 2016–2017 in order to evaluate the differences in wet concentration of ions due to sampling frequency alone. The study serves as an extension to two previous CAPMoN-NADP inter-comparisons by Sirois et al. (Environmental Monitoring and Assessment, 62, 273–303, 2000) and Wetherbee et al., in (Environmental Monitoring and Assessment, 1995–2004, 2010). At the Penn State University site, for 1986–2019, CAPMoN was higher than NADP for all ions, in terms of weekly concentration, precipitation-weighted annual mean concentration, and annual wet deposition. The precipitation-weighted annual mean concentrations were higher for SO42− (2%), NO3− (12%), NH4+ (16%), H+ (6%), and base cations and Cl− (11–15%). For annual wet deposition, CAPMoN was higher for SO4−2, NO3−, NH4+ and H+ (5–17%), and base cations and Cl− (12–17%) during 1986–2019. At the Frelighsburg site, NADP changed the sample collector in October 2011. For 2002–2011, the relative differences at the Frelighsburg site were positive and similar in magnitude to those at the Penn State site. For 2012–2019, the precipitation-weighted annual mean concentrations were 5–27% lower than NADP, except for H+, which was 23% higher. The change in sample collector by NADP had the largest effect on between-network biases. The comparisons of daily-vs-weekly measurements conducted by the CAPMoN network during 1999–2001 and 2016–2017 show that the weekly measurements were higher than the daily measurements by 1–3% for SO42−, NO3−, and NH4+; 3–9% for Ca2+, Mg2+, Na+, and Cl−; 10–24% for K+; and lower for H+ by 8–30% in terms of precipitation-weighted mean concentration. Thus, differences in sampling frequencies did not contribute to the systematically higher CAPMoN measurements. Understanding the biases in the data for these networks is important for interpretation of continental scale deposition models and transboundary comparison of wet deposition trends.

Long-term declines in atmospheric nitrogen and sulfur deposition reduce critical loads exceedances at multiple Canadian rural sites, 2000–2018

Abstract. Daily air concentrations of inorganic nitrogen (N) species, including gaseous HNO3 and particulate-bound (p)NH4+ and pNO3-, and sulfur (S) species, including SO2 and pSO42-, and precipitation concentrations of NO3-, NH4+, and SO42-, have been routinely monitored by the Canadian Air and Precipitation Monitoring Network (CAPMoN) since 1983. Data at 15 rural sites from 2000–2018 were used to estimate dry and wet N and S deposition fluxes, which were then used to explore their spatiotemporal trends and assess ecosystem damage through a retrospective analysis of critical loads (CLs) exceedances. Total (dry + wet) N deposition ranged from 1.7–9.5 kgNha-1yr-1 among the 15 sites, though dry deposition of NH3 and some oxidized N species were not included due to lack of monitoring data. Based on additional N measurements in 2010 at one of the sites, annual total N deposition may be underestimated by up to 32 %. Total N deposition was dominated by wet NO3- and wet NH4+ deposition, which together comprised 71 %–95 %. Contributions to dry N deposition were 40 %–74 % by HNO3, 11 %–40 % by pNH4+, and 5 %–25 % by pNO3-. Total S deposition ranged from 1.3–8.5 kgSha-1yr-1 and was dominated by wet deposition of SO42- and dry deposition of SO2. Relative percentages of wet and dry S deposition were 45 %–89 % and 11 %–55 %, respectively. Acidic ion fluxes were greatest in southeastern Canada and were comparable among the west coast, prairie, remote, and eastern Canadian sites. Oxidized N (dry HNO3, dry pNO3-, wet NO3-) deposition was greater than that of reduced N (dry pNH4+, wet NH4+) in the early 2000s. In 2014–2018, reduced N deposition surpassed that of oxidized N in southeastern Canada. Total N and S deposition decreased significantly at a rate of −0.03 to −0.25 kgNha-1yr-1 (−1.1 % yr−1 to −3.3 % yr−1) and −0.08 to −0.66 kgSha-1yr-1 (−3.5 % yr−1 to −6.6 % yr−1), respectively, among the sites. The weak declining trend in total N deposition at the west coast site was consistent with the slower decline in NOx emissions in western Canada. Reductions in total N deposition were driven by its oxidized form as trends in reduced N were non-significant. As a result, reduced N contributions to total N deposition increased on average from 42 % in 2000–2004 to 53 % in 2014–2018. Anthropogenic NOx and SO2 emissions reductions in both eastern Canada and eastern US were highly effective in reducing total oxidized N and total S deposition, respectively, in eastern Canada. Acidic deposition exceeded terrestrial CL at 5 of the 14 sites and aquatic CL at 2 of the 5 sites in the early 2000s. However, exceedances have been trending downwards and acidic deposition fluxes were mostly near or below CL after 2012 for the subset of sites assessed, which support recovery from historical acidification. Further assessments of CL exceedances are required in other Canadian regions susceptible to acidification and affected by elevated or increasing N and S emissions.

Inorganic chemical components in precipitation in the eastern U.S. and Eastern Canada during 1989–2016: Temporal and regional trends of wet concentration and wet deposition from the NADP and CAPMoN measurements

With the implementation of the Clean Air Act Amendments of 1990 in the U.S. and similar emission reduction measures in Canada, sulfur dioxide (SO2) and nitrogen oxides (NOx = NO + NO2) emissions in the eastern U.S. and Eastern Canada declined significantly during the period 1989–2016. Correspondingly, air quality over the region improved tremendously and sulfate, nitrate and acidity in precipitation decreased significantly. In this study, we analyzed measurement data in the eastern U.S. and Eastern Canada from the two national long-term wet deposition networks, the National Atmospheric Deposition Program/National Trends Network (NADP/NTN) in the U.S. and the Canadian Air and Precipitation Monitoring Network (CAPMoN) in Canada, to reveal the spatial-temporal trends of precipitation concentrations and wet deposition of sulfate, nitrate, ammonium and acid in the eastern part of North America (broken into 4 different regions) for the period of 1989–2016. Comparing 2014–2016 to 1989–1991, the results show that the acid, sulfate and nitrate wet deposition decreased by 78%, 69% and 46% for 1989–2016, and decreased annually at rates of −2.8~-3.6% yr−1, -2.5~-2.9% yr−1, and -1.6~-2.0% yr−1 over different regions, respectively. It also revealed that there were no statistically significant trends for the annual mean wet concentrations of ammonium (NH4+) in precipitation in the Midwest and the Mid-Atlantic of the U.S. (P>0.4 respectively). However, there were statistically significant increasing trends of annual wet deposition of NH4+ over these latter two regions (P = 0.01–0.13) with an annual rate of increase of 0.6% and 0.4%, respectively. The increasing trends of wet deposition of NH4+ in these regions were mostly due to increasing annual precipitation amounts, as indicated by positive correlation coefficients between them (R = 0.67–0.77), and a statistically significant increasing trend of the precipitation amount during the period. The annual mean wet concentration of chloride ion (Cl−) in precipitation in the above two regions had a clear decreasing trend of −1.5% annually (P < 0.001). In 20 years (2010–2014 vs. 1990–1994), the frequency of acidic rain with pH < 5 was reduced from 72% to 49% in the Northeast U.S. and Eastern Canada, 88% to 37% in the Midwest, 97% to 60% in the Mid-Atlantic and 79% to 49% in the Southeast. The imbalance between the measured cations and anions increased over the years from 2009 to 2016 with the anions dropping lower than the cations in all regions. This can be attributed to the increased dissociation of weak organic acids, i.e., the free H+ contributed from these weak acids increased as the acidity of the precipitation decreased, but the corresponding conjugate bases were not measured and not included in the calculation of total anions. This pH buffering effect needs to be taken into account in assessing the reductions in acid deposition following the implementation of the Clear Air Act Amendments (CAAA) of 1990 in the U.S. and measures to reduce the emissions of SO2 and NOx in Canada.

Air quality in the eastern United States and Eastern Canada for 1990–2015: 25 years of change in response to emission reductions of SO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and NO&amp;lt;sub&amp;gt;&amp;lt;i&amp;gt;x&amp;lt;/i&amp;gt;&amp;lt;/sub&amp;gt; in the region

Abstract. SO2 and NOx are precursors to form sulfate, nitrate, and ammonium particles in the air, which account for more than 50 % of PM2.5 mass in the eastern US (Bell et al., 2007) and are dominant components of PM2.5 during many smog events (Dabek-Zlotorzynska et al., 2011). H2SO4 and HNO3, formed from the oxidation of SO2 and NOx, respectively, are the main sources of acid deposition through wet and dry depositions. NOx is also a precursor to the formation of tropospheric O3, which is an important atmospheric oxidant and is also essential for the formation of other atmospheric oxidants, such as OH and H2O2. In the past 26 years from 1990 to 2015, emissions of SO2 and NOx in the US were significantly reduced from 23.1 and 25.2 million t yr−1 in 1990 to 3.7 and 11.5 million t yr−1 in 2015, respectively. In Canada, SO2 and NOx were reduced by 63 % and 33 % from 1990 to 2014. In response to the significant reductions of SO2 and NOx emissions, air quality in the eastern US and Eastern Canada improved tremendously during 1990–2015. In this study, we analyzed surface air concentrations of SO42-, NO3-, NH4+, HNO3, and SO2 measured weekly by the Clean Air Status and Trends Network (CASTNET) in the US and measured daily from the Canadian Air and Precipitation Monitoring Network (CAPMoN) in Canada to reveal the temporal and spatial changes in each species during the 25-year period. For the whole eastern US and Eastern Canada, the annual mean concentrations of SO42-, NO3-, NH4+, HNO3, SO2, and TNO3 (NO3- + HNO3, expressed as the mass of equivalent NO3-) were reduced by 73.3 %, 29.1 %, 67.4 %, 65.8 %, 87.6 %, and 52.6 %, respectively, from 1990 to 2015. In terms of percentage, the reductions of all species except NO3- were spatially uniform. The reductions of SO2 and HNO3 were similar in the warm season (May–October) and the cold season (November–April), and the reductions of SO42-, NO3-, and NH4+ were more significant in the warm season than in the cold season. The reductions of SO42- and SO2 mainly occurred in 1990–1995 and 2007–2015 during the warm season and in 1990–1995 and 2005–2015 during the cold season. The reduction of NO3- mainly occurred in the Midwest after 2000. Other than in the Midwest, NO3- exhibited very little change during the cold season for the period. The reduction of NH4+ generally followed the reduction trend of SO42-; especially after 2000, the temporal trend of NH4+ was almost identical to that of SO42-. The ratio of S in SO42- to total S in SO42- plus SO2, as well as the ratio of NO3- to TNO3 increased by more than 50 % during the period. This indicates that a notable change in regional chemistry took place from the beginning to the end of the period, with a higher percentage of SO2 being oxidized to SO42- and a higher percentage of HNO3 being neutralized to NH4NO3 near the end of the period.

Inter-comparison of elemental and organic carbon mass measurements from three North American national long-term monitoring networks at a co-located site

Abstract. Carbonaceous aerosol is a major contributor to the total aerosol load and being monitored by diverse measurement approaches. Here, 10 years (2005–2015) of continuous carbonaceous aerosol measurements collected at the Centre of Atmospheric Research Experiments (CARE) in Egbert, Ontario, Canada, on quartz-fiber filters by three independent networks (Interagency Monitoring of Protected Visual Environments, IMPROVE; Canadian Air and Precipitation Monitoring Network, CAPMoN; and Canadian Aerosol Baseline Measurement, CABM) were compared. Specifically, the study evaluated how differences in sample collection and analysis affected the concentrations of total carbon (TC), organic carbon (OC), and elemental carbon (EC). Results show that different carbonaceous fractions measured by various networks were consistent and comparable in general among the three networks over the 10-year period, even with different sampling systems/frequencies, analytical protocols, and artifact corrections. The CAPMoN TC, OC, and EC obtained from the DRI model 2001 thermal–optical carbon analyzer following the IMPROVE-TOR protocol (denoted as DRI-TOR) method were lower than those determined from the IMPROVE_A TOR method by 17 %, 14 %, and 18 %, respectively. When using transmittance for charring correction, the corresponding carbonaceous fractions obtained from the Sunset-TOT were lower by as much as 30 %, 15 %, and 75 %, respectively. In comparison, the CABM TC, OC, and EC obtained from a thermal method, EnCan-Total-900 (ECT9), were higher than the corresponding fractions from IMPROVE_A TOR by 20 %–30 %, 0 %–15 %, and 60 %–80 %, respectively. Ambient OC and EC concentrations were found to increase when ambient temperature exceeded 10 ∘C. These increased ambient concentrations of OC during summer were possibly attributed to secondary organic aerosol (SOA) formation and forest fire emissions, while elevated EC concentrations were potentially influenced by forest fire emissions and increased vehicle emissions. Results also show that the pyrolyzed organic carbon (POC) obtained from the ECT9 protocol could provide additional information on SOA although more research is still needed.

Long-term trends in atmospheric reactive nitrogen across Canada: 1988–2007

Abstract 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 ( pNO 3 − ) , particulate ammonium ( pNH 4 + ) , wet ammonium ( NH 4 + ) and wet nitrate ( NO 3 − ) in response to emission reductions primarily driven by the Canada–United States Air Quality Agreement. Annual air concentrations (1988–2007) of pNH 4 + and HNO3 significantly decreased at all CAPMoN stations, while pNO 3 − concentrations increased at 6 of 9 stations. Precipitation NH 4 + had no significant or consistent trend; in contrast precipitation NO 3 − 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 pNH 4 + and HNO3 had synchronous time-series with consistently decreasing concentrations across all CAPMoN stations (1988–2007), in contrast, pNO 3 − 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 NH 4 + ) 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 NH 4 + , as such uncontrolled ammonia emissions continue to be a significant source of Nr.

An intercomparison of the deposition models used in the CASTNET and CAPMoN networks

To assess long-term trends in atmospheric deposition, the U.S. operates the Clean Air Status and Trends Network (CASTNET) and Canada operates the Canadian Air and Precipitation Monitoring Network (CAPMoN). Both networks use modeled dry deposition velocities and measured atmospheric concentrations to compute estimates of dry deposition. While concentration measurements from the two networks are comparable, flux estimates can be significantly different due to differences in the model-estimated dry deposition velocities. This study intercompares the dry deposition velocity models used by the networks to identify those model inputs and model algorithms that are responsible for the differences in the dry deposition velocity predictions of the gaseous trace species ozone (O3), sulfur dioxide (SO2), and nitric acid (HNO3). The Big-Leaf Model (BLM) used for CAPMoN was inserted into the CASTNET modeling framework so that the on-site meteorological data obtained at the CASTNET sites could be used as input to both models. The models were run for four CASTNET sites that spanned different land use types and climatologies. The models were incrementally modified to assess the impacts of algorithmic differences on the predicted deposition velocities. While differences in aerodynamic resistance between the models contributed strongly to differences in predicted dry deposition velocities for HNO3, it is the non-stomatal (ground and cuticle) resistance parameterizations that cause the largest differences for other chemical species. The study points to the need for further consideration of these resistances. Additionally, comparisons of both models against recent independent flux data are needed to assess the accuracy of the models.

Comparison of precipitation chemistry measurements obtained by the Canadian Air and Precipitation Monitoring Network and National Atmospheric Deposition Program for the period 1995–2004

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.

Dry deposition of individual nitrogen species at eight Canadian rural sites

Three nitrogen species in air, HNO3, particle nitrate (pNO3−), and particle ammonium (pNH4+), have been routinely measured for estimating nitrogen dry deposition in the Canadian Air and Precipitation Monitoring Network (CAPMoN) and the U.S. Clean Air Status and Trends Network (CASNET) for several decades. To investigate the relative contributions of other nitrogen species to total nitrogen dry and dry + wet deposition, 14 short‐term field campaigns were conducted between 2001 and 2005 at eight selected rural sites across eastern Canada. Air concentrations were measured for the total oxidized nitrogen (NOy) and major species comprising NOy (NO, NO2, PAN, PPN, HNO3, pNO3−), and for the two reduced nitrogen species (NH3, pNH4+). Dry deposition fluxes of NOy and NHx (= NH3 + pNH4+) were then estimated by combining measured concentrations of individual nitrogen species with their respective dry deposition velocities estimated from big‐leaf models using on‐site meteorological measurements. Nitrogen dry deposition were estimated to be 0.8–4.0 kg N ha−1 a−1, depending on location, with 60–75% from NOy and 25–40% from NHx. HNO3 and NO2 dominated NOy dry deposition while NH3 and pNH4+ contributed equally to NHx dry deposition. The pNO3−, PAN, and unidentified NOy species also contributed appreciable amounts to NOy dry deposition. Nitrogen dry + wet deposition from NOy + NHx was estimated at 4.3–11 kg N ha−1 a−1, with dry deposition accounting for 10–50%. The routinely monitored species accounted for less than 50% of total N dry deposition; thus, total dry + wet deposition from the Canadian monitoring network had a lower bias by 5–25% at most of the sites.

Network comparability and the reconstruction of a precipitation chemistry record at a monitoring site in the eastern United States

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<CAPMoN) of about 0.5 mm for rain gage depth and 4–5 μeq l−1 for the concentrations of SO42− and NO3−. The relative precision obtained for [SO42−] and [NO3−] ranged from 9% to 13%, which is similar to the findings of previous weekly based intercomparison studies. The reconstructed record (1988–2000) reveals the highest daily concentrations for all major ions for 1991, followed by a consistent decrease over the following 6 years.

Assessment of Wet Sulfate Concentration Changes at CAPMoN Sites, Canada

This paper describes a statistical analysis of wet sulfate deposition data sampled by the Canadian Air and Precipitation Monitoring Network (CAPMoN) since 1988 till 1997. The goal of the investigation is to detect presence of prevailing significant changes in the probability distribution of annual samples collected by the network at each site. The considerations are based on a first order autoregression model with second order polynomial trend and methods used for analysis of variance and multiple comparison. Unlike studies suggesting existence of long term trends in the data, methods applied here indicate absence of any systematic changes in the observed annual concentration patterns at most of the sites.

A statistical assessment of changes in precipitation chemistry at CAPMoN sites, Canada. Canadian Air and Precipitation Monitoring Network.

The objective of this study is to decide if chemical concentrations measured during 1988-1997 in precipitation by the Canadian Air and Precipitation Monitoring Network (CAPMoN) indicate changes in the annual patterns. The inference is based on SO4, NO3, Cl, NH4, Na, Ca and K concentrations monitored daily with the rain water acidity pH. By pattern is understood the probability distribution of the annual sample at a particular location. Most of the annual data can be well described by means of a linear regression model with second order polynomial trend and autocorrelated noise. Statistical analysis based on the model shows luck of systematic significant year to year increases or declines of the concentrations.

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

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+,SO42-, 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.

The Precision of Precipitation Chemistry Measurements in the Canadian Air and Precipitation Monitoring Network (CAPMoN)

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 SO42-, NO3-, pH, H+, NH4+, 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.

Evaluation of the capabilities of deposition networks to resolve regional trends and spatial patterns

Sulfur emission control programs are being implemented in North America at the same time as budgetary pressures are leading to reduced numbers of stations in acid deposition monitoring networks. In order to assess the effectiveness of emission control programs, it is essential that deposition monitoring networks continue to fulfill their principal goals of detecting and quantifying temporal changes in deposition, and of describing changes in spatial deposition patterns. A set of statistical techniques has been developed and applied to assess the capabilities of the Canadian Air and Precipitation Monitoring Network (CAPMoN) in southeastern Canada according to two performance criteria: (1) the ability of CAPMoN to detect and quantify projected regional trends in precipitation sulfate in a timely fashion, and (2) the ability of CAPMoN to delineate both present and projected future spatial patterns of wet sulfate deposition. In the area of southern Canada now receiving in excess of 20 kg ha −1 yr −1 wet sulfate deposition, the seven CAPMoN stations alone would be able to detect and quantify projected regional trends within one year of the 41 stations now operating in the area. However, in the regions now receiving less than 20 kg ha −1 yr −1 wet sulfate deposition, CAPMoN would require 4–8 yr longer than the larger set of currently available stations to detect projected reductions. The current configuration of CAPMoN is adequate to monitor some areas with sulfate deposition exceeding 20 kg ha −1 yr − until deposition goes below this value, but not those areas situated in extreme southwestern and southeastern Ontario, southern Quebec, and the Bay of Fundy region. In comparison to using all currently operating monitoring stations, using only CAPMoN stations underestimates the area in which wet sulfate deposition exceeds 20 kg ha −1 yr −1.

Step-wise analysis of precipitation and river chemistry trends in Atlantic Canada

Monotonic trends in hydrogen (H + ), sulfate (SO 4 -2 )and nitrate (NO 3 - ) were calculated using non-parametric techniques at four Canadian Air and Precipitation Monitoring Network (CAPMoN) sites and six nearby river systems in Atlantic Canada for the period 1983-1991. Over the whole interval, there were increasing nitrate concentrations and deposition trends at three of the four monitoring sites and no trends in SO 4 -2 or H + concentrations and deposition. We found that SO 4 -2 concentrations increased at three of our six river sites, NO 3 - increased at one site and H + decreased at one site. River exports showed no trends in the entire study interval. The series were also analyzed in five year time windows, incremented by six months, to see if changes in trend presence or direction would occur, compared to trend analysis over the entire interval. We show that while trends in river chemistry do not contradict deposition patterns, the changes that occurred were not necessarily in step. We also found that the trends which we measured were the result of short-term changes as opposed to long-term continuous monotonic trends. The time lag between precipitation and chemistry trend changes seemed longer in basins dominated by softwoods than by hardwoods.

Source types in Canadian precipitation chemistry

Precipitation data generated by Canadian Air and Precipitation Monitoring Network (CAPMoN) have been analysed by an iterative multiple linear regression method, revealing five source types or components, each with distinctive seasonal and geographic variations. Each source types has its characteristics chemical profile. The profiles suggest that two of the source types are rural (apparently derived from fertilizer and soil), two are urban/industrial (apparently derived from SO2 and NOx emissions), and one is sea salt. The NOx-derived component is highly acidic, the SO2-derived component is also very acidic, the fertilizer component is slightly alkaline, and the soil component is more alkaline. Charge balance calculations show a fairly consistent deficit in anions, a deficit which is especially important for the NOx-derived component. The anion deficit results suggest that more complete chemical analyses are required. The chemical profiles from CAPMoN data have been used to determine the component contributions to precipitation data collected in Manitoba by the provincial Ministry of the Environment. Back trajectories for the Manitoba data show distinct geographic and seasonal effects, including: (i) seasalt input to Manitoba is derived mainly from Hudson Bay and the Arctic, especially in fall and winter; (ii) the SO2 component has ubiquitous sources, including polar sources: (iii) the fertilizer component arrives mainly form the U.S. rural Midwest, especially in spring and fall; (iv) the soil component has northern sources, with perhaps transpolar and trans-Pacific origins, in spring and summer; and (v) the NOx component appears to be derived from northern sources at polar sunrise in spring.

Wet deposition monitoring and modelling in New Brunswick — An area dominated by wet deposition due to long-range transport

Abstract Two wet deposition monitoring networks, the Coleson Cove Precipitation Monitoring Network (CCPMN) (12 stations) located in the Coleson Cove-Saint John area of south New Brunswick, and the Expanded New Brunswick Precipitation Monitoring Network (ENBPMN) (6 stations) covering the remainder of the province, were established in May 1988. The monitoring networks and a complementary modelling study were implemented to assess the relative contributions of local and distant sources to wet deposition in New Brunswick. Quality assurance/quality control activities for the networks included independent external audits, collocated samplers at one site and comparisons of weekly measurements at the ENBPMN sampler and the Canadian Air and Precipitation Monitoring Network (CAPMoN) sampler which makes daily measurements. The intercomparisons provided reassurance that the networks provided high quality data. Analysis of 2 years (June 1988–May 1990) data from the networks included routine statistical analyses for acid rain chemistry as well as analysis of 1 year of daily back trajectory data from Harcourt, New Brunswick. Three-day back trajectories determined at 12-h intervals from Harcourt on days with precipitatio showed that air masses originate mainly from regions in Quebec, Ontario and northeast U.S.A. which are known to have high sulphur oxide emissions. Some 18 trajectories were associated with 50% of the wet sulphate deposition and over 200 trajectories with 75% of the deposition in the 1-year period ending 31 May 1989. The MESOPUFF model, applied to an 800 km by 800 km domain that included the entire province of New Brunswick, was used to make predictions of wet sulphate and nitrate deposition at each of the wet deposition monitoring stations for a 2-year period, 1 June 1988-31 May 1990. Model predictions averaged over all receptors due to all sources in the model domain accounted for 7–25% of the measured seasonal average wet sulphate deposition and less than 3% of the measured wet nitrate deposition at all monitoring stations. Wet deposition in New Brunswick is thus dominated by distant sources through long-range transport. The model estimated that the oil-fired Coleson Cove thermal generating station contributed between 7% and 16% to the seasonal wet sulphur deposition and less than 3% of the seasonal wet nitrogen deposition at monitoring stations in the Coleson Cove-Saint John area. The estimates for wet nitrogen deposition are limited by the NO χ emissions information which is considered less reliable than SO 2 emissions information.