Precipitation Chemistry Measurements Research Articles

Widespread impacts to precipitation of the East Palestine Ohio train accident

On 3 February 2023, a Norfolk Southern train derailment occurred in East Palestine, Ohio. The accident and subsequent fire resulted in the emissions of large amounts of hazardous compounds to the ambient atmosphere over many days. We used precipitation chemistry measurements routinely collected by the National Atmospheric Deposition Program (NADP) to estimate the spatial extent and chemical compounds deposited as a result of the accident. Our measurements revealed a large areal impact from the Midwest through the Northeast and likely Canada, and perhaps as far south as North Carolina (portions of 16 states, 1.4 million km2). Observations showed the expected high chloride concentrations, but also unexpectedly high pH (basic) and exceptionally elevated levels of base cations exceeding 99th percentiles versus the historic record. These results were consistent with the meteorological conditions and atmospheric trajectories, and were not due to highly-concentrated low volume precipitation samples or wildfires. The robust measurements of the NADP network clearly show that the impacts of the fire were larger in scale and scope than the initial predictions, and likely due to the uplift from the fire itself entraining pollutants into the atmosphere. A more detailed evaluation of the accident and resulting fire could further refine the full impact of the atmospheric concentrations, dry and wet deposition, and the more specific extent of the spatial impact.

Long-term increasing trends in the wet deposition of secondary inorganic constituents in SW Indian precipitation

Precipitation chemistry measurements are essential to estimate the deposition of ionic components that are beneficial or harmful to the ecosystems and quantify the wet scavenging of the atmospheric constituents. A long-term (2006 to 2016) database of the water-soluble inorganic components in the rainwater (RW) at Pune (an urban location) and Sinhagad (a high-altitude rural location) in southwest India was examined to understand the trends in measured anthropogenic components and the factors controlling the chemistry of RW in this region. We observed the long-term increasing trends in NH4+ at Pune and SO42−, NO3¯, and NH4+ at Sinhagad. About 10% of rain samples were acidic (below 5.6). Low pH values were generally measured at Pune (8%) and Sinhagad (9%) stations when the air mass back trajectories (AMBTs) originated from land. This study suggests that NO3¯ plays a vital role in acidifying the rain in both the sampling stations, though SO42− remains the dominant factor. The high concentrations of Ca2+ and NH4+ have played a significant role in neutralizing the acidity of RW. The cluster analysis of AMBTs showed that at Pune 74% and Sinahagd 65% of rain events were associated with oceanic air masses from the Arabian Sea.

Source Apportionment of Aerosol at a Coastal Site and Relationships with Precipitation Chemistry: A Case Study over the Southeast United States.

This study focuses on the long-term aerosol and precipitation chemistry measurements from colocated monitoring sites in Southern Florida between 2013 and 2018. A positive matrix factorization (PMF) model identified six potential emission sources impacting the study area. The PMF model solution yielded the following source concentration profiles: (i) combustion; (ii) fresh sea salt; (iii) aged sea salt; (iv) secondary sulfate; (v) shipping emissions; and (vi) dust. Based on these results, concentration-weighted trajectory maps were developed to identify sources contributing to the PMF factors. Monthly mean precipitation pH values ranged from 4.98 to 5.58, being positively related to crustal species and negatively related to SO42−. Sea salt dominated wet deposition volume-weighted concentrations year-round without much variability in its mass fraction in contrast to stronger seasonal changes in PM2.5 composition where fresh sea salt was far less influential. The highest mean annual deposition fluxes were attributed to Cl−, NO3−, SO42−, and Na+ between April and October. Nitrate is strongly correlated with dust constituents (unlike sea salt) in precipitation samples, indicative of efficient partitioning to dust. Interrelationships between precipitation chemistry and aerosol species based on long-term surface data provide insight into aerosol–cloud–precipitation interactions.

Characterizing and Quantifying African Dust Transport and Deposition to South America: Implications for the Phosphorus Budget in the Amazon Basin

AbstractSoils in the Amazon Basin are deficient in phosphorus, essential to soil fertility. Previous studies suggested that African mineral dust deposited to Amazonian soils served as an important source of phosphorus that enhances soil fertility. These studies lacked the quantitative measurements essential to validate estimates. Here we present daily measurements of mineral dust and PM10 carried in the trade winds at Cayenne, French Guiana, during 2002–2017. MERRA‐2 model dust concentrations showed excellent agreement with measurements over this period. Consequently, we used MERRA‐2 to estimate temporal and spatial deposition rates to Amazonia. Our annual deposition rate, 8–10 Tg dust, is substantially lower than previous estimates. Deposition rates are greatest over the northern and northeastern regions of South America. In contrast, rates are low in central Amazonia. Our results raise questions about the impact of African dust on soil fertility in Amazonia. However, African aerosol transport carries other aerosol species that could play a role in soil fertility, including biomass‐burning products known to contain substantial concentrations of phosphorus. Our study highlights the need for more measurements of aerosol and precipitation chemistry over wider expanses of South America in order to better characterize aerosol chemical and physical properties, to identify aerosol sources, and to constrain model estimates. We show that over 2002–2017 dust transport to South America was negatively correlated to rainfall over the Sahel in North Africa. Long‐term monitoring is needed to capture changes in transport from Africa that might occur as a result of climate change.

Aerosol and precipitation chemistry measurements in a remote site in Central Amazonia: the role of biogenic contribution

Abstract. In this analysis a 3.5 years data set of aerosol and precipitation chemistry, obtained in a remote site in Central Amazonia (Balbina, (1°55' S, 59°29' W, 174 m a.s.l.), about 200 km north of Manaus) is discussed. Aerosols were sampled using stacked filter units (SFU), which separate fine (d < 2.5 μm) and coarse mode (2.5 μm < d < 10.0 μm) aerosol particles. Filters were analyzed for particulate mass (PM), Equivalent Black Carbon (BCE) and elemental composition by Particle Induced X-Ray Emission (PIXE). Rainwater samples were collected using a wet-only sampler and samples were analyzed for pH and ionic composition, which was determined using ionic chromatography (IC). Natural sources dominated the aerosol mass during the wet season, when it was predominantly of natural biogenic origin mostly in the coarse mode, which comprised up to 81% of PM10. Biogenic aerosol from both primary emissions and secondary organic aerosol dominates the fine mode in the wet season, with very low concentrations (average 2.2 μg m-3). Soil dust was responsible for a minor fraction of the aerosol mass (less than 17%). Sudden increases in the concentration of elements as Al, Ti and Fe were also observed, both in fine and coarse mode (mostly during the April-may months), which we attribute to episodes of Saharan dust transport. During the dry periods, a significant contribution to the fine aerosols loading was observed, due to the large-scale transport of smoke from biomass burning in other portions of the Amazon basin. This contribution is associated with the enhancement of the concentration of S, K, Zn and BCE. Chlorine, which is commonly associated to sea salt and also to biomass burning emissions, presented higher concentration not only during the dry season but also for the April–June months, due to the establishment of more favorable meteorological conditions to the transport of Atlantic air masses to Central Amazonia. The chemical composition of rainwater was similar to those ones observed in other remote sites in tropical forests. The volume-weighted mean (VWM) pH was 4.90. The most important contribution to acidity was from weak organic acids. The organic acidity was predominantly associated with the presence of acetic acid instead of formic acid, which is more often observed in pristine tropical areas. Wet deposition rates for major species did not differ significantly between dry and wet season, except for NH4+, citrate and acetate, which had smaller deposition rates during dry season. While biomass burning emissions were clearly identified in the aerosol component, it did not present a clear signature in rainwater. The biogenic component and the long-range transport of sea salt were observed both in aerosols and rainwater composition. The results shown here indicate that in Central Amazonia it is still possible to observe quite pristine atmospheric conditions, relatively free of anthropogenic influences.

Chemical composition, sources, and deposition fluxes of water-soluble inorganic ions obtained from precipitation chemistry measurements collected at an urban site in northwest China

Precipitation samples were collected at an urban site in Xi'an, northwest China during March to November in 2009 and were then analyzed to determine the pH and concentrations of water-soluble inorganic ions (Na(+), NH(4)(+), K(+), Mg(2+), Ca(2+), SO(4)(2-), NO(3)(-), Cl(-), and F(-)) in precipitation. The pH of precipitation ranged from 4.1 to 7.6 for all of the samples with an annual volume-weighted mean of 6.4. While a large portion of the precipitation events were weakly acidic or alkaline, around 30% of the precipitation events in the autumn were strongly acidic. Precipitation events with air masses from the northeast and the southeast were weakly acidic while those with air masses from the northwest and the southwest were alkaline. SO(4)(2-), Ca(2+), NH(4)(+), and NO(3)(-) were dominant ions in the precipitation, accounting for 37%, 25%, 18%, and 9%, respectively, of the total analyzed ions. Ca(2+) and NH(4)(+) were found to be the major neutralizers of precipitation acidity; however, the contribution of Mg(2+), although much lower than those of Ca(2+) and NH(4)(+), was important, in many cases, in changing the precipitation from weakly acidic to weakly alkaline. Enrichment factor analysis confirmed that SO(4)(2-) and NO(3)(-) were produced from anthropogenic sources, Ca(2+), K(+), and 80% Mg(2+) were from crustal sources, and Na(+), Cl(-), and ∼20% of Mg(2+) were from marine sources. The annual wet depositions were estimated to be 3.5 t km(-2) per year for sulfur; 2.3 t km(-2) per year for nitrogen, of which 0.8 t km(-2) per year was oxidized nitrogen and 1.5 t km(-2) per year was reduced nitrogen; and 3.0 t km(-2) per year for Ca(2+).

Measurements of fog composition at a rural site

Studies that focus on fog chemistry in the United States have been limited to relatively few locations. Apart from measurements along the East and West coasts and extensive analysis of radiation fog in the Central Valley of California, fog composition has been characterized in only a handful of other locations. To complement and expand the existing fog chemistry data that are currently available, a new field campaign was established at a rural location in Central Pennsylvania to produce a unique, long term record of fog composition. From 2007 to 2010, 41 fog events were sampled with an automated Caltech Heated Rod Cloudwater Collector (CHRCC). The collected samples were analyzed primarily for pH and major inorganic ions. Dissolved organic carbon (DOC) and trace metals were analyzed in selected samples and N-nitrosodimethylamine (NDMA) was quantified in two samples. Sample composition varied widely during the study period. Sulfate concentrations ranged from 15 to 955 (median = 123) μN and pH varied between 3.08 and 7.41 (median = 5.77). In terms of volume weighted averages, ammonium was the most abundant ionic species followed by sulfate, calcium, and nitrate. For the subset of samples in which DOC was analyzed, concentrations ranged from 2.2 to 22.6 mgC l−1. Comparisons with regional precipitation chemistry measurements reveal the influence of local agricultural and soil sources on fog composition. The sum of sulfate, nitrate, and ammonium measured in the present study is considerably lower than the majority of radiation, precipitation, and coastal fogs collected in the United States although the ammonium/(nitrate + sulfate) ratio is similar to those found in the Central Valley of California.

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.

Analysis of cloud and precipitation chemistry at Whiteface Mountain, NY

Federal and state programs over the past two decades have resulted in the reduction of emissions of precursors of acid rain. Concomitant with these changes, measured concentrations of acidity in precipitation and in watersheds have shown a downward trend or improvement. However, another pathway for these precursors is through cloud and fog events that often tend to occur at high-elevation regions affecting the fauna and flora as well. In this study we report on long-term measurements of cloud water and precipitation chemistry made from 1994 onwards at a high-elevation location, Whiteface Mountain NY, in the northeastern United States. Trends and inter-relationship between the ions were examined along with ambient SO 2 measurements and Adirondack lakes chemistry data.

Long term precipitation chemistry and wet deposition in a remote dry savanna site in Africa (Niger)

Abstract. Long-term precipitation chemistry have been recorded in the rural area of Banizoumbou (Niger), representative of a semi-arid savanna ecosystem. A total of 305 rainfall samples ~90% of the total annual rainfall) were collected from June 1994 to September 2005. From ionic chromatography, pH major inorganic and organic ions were detected. Rainwater chemistry is controlled by soil/dust emissions associated with terrigeneous elements represented by SO42−, Ca2+, Carbonates, K+ and Mg2+. It is found that calcium and carbonates represent ~40% of the total ionic charge. The second highest contribution is nitrogenous, with annual Volume Weighed Mean (VWM) for NO3− and NH4+ concentrations of 11.6 and 18.1 μeq.l−1, respectively. This is the signature of ammonia sources from animals and NOx emissions from savannas soil-particles rain-induced. The mean annual NH3 and NO2 air concentration are of 6 ppbv and 2.6 ppbv, respectively. The annual VWM precipitation concentration of sodium and chloride are both of 8.7 μeq.l−1 which reflects the marine signature of monsoonal and humid air masses. The median pH value is of 6.05. Acidity is neutralized by mineral dust, mainly carbonates, and/or dissolved gases such NH3. High level of organic acidity with 8μeq.l−1 and 5.2 μeq.l−1 of formate and acetate were also found. The analysis of monthly Black Carbon emissions and Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) values show that both biogenic emission from vegetation and biomass burning could explain the rainfall organic acidity content. The interannual variability of the VWM concentrations around the mean (1994–2005) is between ±5% and ±30% and mainly due to variations of sources strength and rainfall spatio-temporal distribution. From 1994 to 2005, the total mean wet deposition flux in the Sahelian region is of 60.1 mmol.m−2.yr−1 ±25%. Finally, Banizoumbou measurements are compared to other long-term measurements of precipitation chemistry in the wet savanna of Lamto (Côte d'Ivoire) and in the forested zone of Zoétélé (Cameroon). The total chemical loading presents a maximum in the dry savanna and a minimum in the forest (from 143.7, 100.2 to 86.6 μeq.l−1), associated with the gradient of terrigeneous sources. The wet deposition fluxes present an opposite trend, with 60.0 mmol.m−2.yr−1 in Banizoumbou, 108.6 mmol.m−2.yr−1 in Lamto and 162.9 mmol.m−2.yr−1 in Zoétélé, controlled by rainfall gradient along the ecosystems transect.

Temporal Trends of Non-sea Salt Sulfate and Nitrate in Wet Deposition in Japan

Temporal trends of non-sea salt (nss-) sulfate and nitrate were analyzed from nationwide precipitation chemistry measurements provided by the Ministry of the Environment (MOE) for the 1988–2002 fiscal years (April–March). The concentrations and deposition of nss-sulfate were found to be decreasing, and those of nitrate were stable or slightly increasing at most sites. These deposition trends were discussed from the viewpoint of emissions of SO2 and NOX during the period of interest. Because monitoring techniques have changed in the number of active sites, samplers, and analytical methods during the operation period, the median of all annual depositions measured in Japan in a specific year was selected as the annual representative. The contribution of specific emission sources was also calculated for 1990 on the basis of the nss-sulfate and nitrate deposition in Japan obtained with a model simulation in which the model did not include volcanic emissions from Mt. Oyama, Miyakejima Island, which began to erupt suddenly and violently in 2000. For nss-sulfate, the calculated deposition agrees well with the intensity and trends of the median up to 1999. After 2000, a higher deposition than calculated in the preceding years was evident, which is attributable to the volcanic SO2 from Mt. Oyama. For nitrate, both the calculated and observed depositions were slightly increasing; however, the calculation was found to exceed the observation.

A climatology of wet deposition scavenging ratios for the United States

Abstract A decade of weekly measurements of precipitation chemistry obtained in the US National Atmospheric Deposition Program (NADP) are combined with air concentration measurements from the Atmospheric Integrated Research Monitoring Network (AIRMoN) to estimate scavenging ratios (of concentrations in rain to like concentrations in surface air) for the ions that dominate precipitation chemistry—sulfate, nitrate, and ammonium. The intention is to provide a climatology of these ratios, for use in evaluating models that are now simulating precipitation chemistry as well as air quality. The scavenging ratios that are computed are found to be distributed approximately log-normally, with a standard deviation corresponding to about a factor of two. That is, if scavenging ratios are used to predict precipitation chemistry and wet deposition, then geometric means should be considered and the error for any given weekly prediction should be expected to be described by a standard deviation of a factor of two. (It follows that for daily predictions, the factor increases to about five.) Scavenging ratios appear to be similar for nitrate and ammonium, with those for sulfate being somewhat larger and displaying a behavior indicative of the contribution of in-cloud conversion from gaseous sulfur dioxide. Seasonal cycles are similar for most locations. The limited data available for western US stations indicate, however, that these locations yield scavenging ratios that can be significantly different from those characterizing the east. The data are in accord with the conventional understanding regarding the cloud scavenging of sulfur dioxide. For summer, each sulfur dioxide molecule appears to pass through an average of 1.3 clouds before being scavenged as sulfate. For winter, the average is 4.8 clouds.

On the Kosa (Asian Dust) Event in November 2002: Aerosol Number Concentrations and Precipitation Chemistry in Toyama, Japan

The Kosa event was observed widely in Japan on 12 November 2002. Measurements of size-separated aerosol number concentrations and precipitation chemistry were performed in Toyama during the autumn and early winter of 2002. The number of aerosol particles larger than 3.0 μm in diameter dramatically increased during the Kosa event, whereas the number concentrations of finer particles hardly changed. The concentration of non-sea-salt calcium and pH were high in the precipitation sampled during the Kosa event.

Comparison of long-term precipitation chemistry measurements at the Hubbard Brook Experimental Forest, New Hampshire.

From 1978 through 1989, a wet-onlyprecipitation collector operated for the NationalAtmospheric Deposition Program, an independantwet-only collector, and a bulk precipitation collectorwere co-located at the Hubbard Brook ExperimentalForest (HBEF) in central New Hampshire. A secondbulk precipitation collector was maintained at anotherlocation within the HBEF. There were statisticallysignificant differences between the chemistry fromco-located wet-only collections for Ca2+,K+, NH4+, pH, and NO3-. Thedifferences for K+ and pH though statisticallysignificant were very small but consistant. Thedifferences for Ca2+ were related to earlycontamination problems, and differences inNH4+ and NO3- were related toepisotic events. Bulk precipitation was significantlyricher in K+ than wet-only precipitation. Therewere no differences for any ions between the bulkcollections at the two locations. While there wereminor differences, after 1981 when the contaminationproblems had been resolved, data from all collectorsat all locations adequately characterized theprecipitation chemistry of the site.

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.

Analysis of precipitation chemistry at a rural site in Hiroshima Prefecture, Japan

Event basis measurements of precipitation chemistry at Shobara, the rural area of the northeastern part in Hiroshima Prefecture in Japan, during the period 1984–1988, were assessed for determining the sources of major ions, and for understanding the relation between ionic concentrations and synoptic meteorological situations. Seasonal patterns of the volume-weighted mean concentrations for major ions except H + could be characterized by winter maxima and summer minima. Principal component analysis was performed on monthly ionic deposition. Varimax rotated three principal components accounting for approximately 90% of the total variance in the data set, could be interpreted to be acid, seasalt and soil. From back-trajectories for an event using 850 hPa winds, it was found that the volume-weighted mean concentration of non-sea-salt (nss−) SO 2− 4 for the air-mass transported from the northern part of Asian Continent was highest, and that the majority of high nss-SO 2− 4 concentrations for an event were observed for the continental air-mass under the condition of light precipitation amount.

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.

Deposition of nitrogen and other major inorganic compounds in Norway, 1992–1996

Representative measurements of air and precipitation chemistry have been used to estimate atmospheric deposition for the period 1992–1996. In coastal areas of SW Norway, large precipitation amounts with high concentrations of nitrate and ammonium resulted in annual nitrogen (N) inputs of more than 2 g m −2year −1 (20 kg ha −1year −1). Dry deposition is relatively unimportant in the areas with high precipitation intensities, whereas in some areas with less precipitation, forested areas may receive up to 30–50% of the total deposition in the form of dry deposition. Inputs of dry deposition to non-forested areas are much smaller, particularly during the period of snow cover. Comparison with similar estimates for the periods 1983–1987 and 1988–1992 show that there has been a decrease in the deposition of reduced N, by 2% and 14%, and in the deposition of oxidized N, by 6% and by 23%, relative to the two periods. The trend for oxidized N is somewhat smaller than expected based on reported emission reductions in Northern Europe. Changes in the emission rates from off-shore activities in the North Sea may partly explain the observed discrepancies. For ammonium, the trend may be influenced by both reduced emissions and by the reductions of sulphur dioxide and nitrogen oxides, which may have reduced the rate of conversion from ammonia to ammonium aerosol, thereby decreasing the atmospheric residence time and the transport across the North Sea. Inter annual variations in the meteorological conditions may also have influenced the amounts of deposition.

Concentration and deposition of acidifying air pollutants over Sweden: Estimates for 1991 based on the match model and observations

The MATCH (Mesoscale Atmospheric Transport and CHemistry) model has been developed as a tool for air pollution assessment studies on different geographical scales. MATCH is an Eulerian atmospheric dispersion model, including physical and chemical processes governing sources, atmospheric transport and sinks of oxidized sulfur and oxidized and reduced nitrogen. Using a combination of air and precipitation chemistry measurements and the MATCH model, the national and long-range transport contributions to air pollution and deposition can be quantified in the model region. The calculations for the year 1991 show that the Swedish import was about 4.5 times larger than the export for sulfur and about six times larger for reduced nitrogen, while the Swedish import of oxidized nitrogen only exceeded the export by 10%. Using the MATCH system we estimate the long-range transport in an independent way compared to EMEP. Comparison between the EMEP and MATCH calculations for 1991 show that the total deposition of oxidized nitrogen over Sweden is similar, while the EMEP-values for total deposition of oxidized sulfur and reduced nitrogen are 25% respectively 40% smaller than what is obtained from MATCH.

Spatial and Temporal Variability of Precipitation and Chemistry: Case Studies from the Frontal Boundary Study

Sequential precipitation and precipitation chemistry measurements were conducted on a 37-site, 100 km×100 km array in central Ohio during four cyclonic storms during the fall of 1989. Spatial (network) averages and variances in rainfall rate and inorganic chemical concentrations were calculated for hourly and total-event time periods. The average fractional intersite differences in concentrations vary among the events, and range from about 0.1 to 1, with sulfate among the least variable species. This variability is at best weakly correlated with intersite distance over the range 10-90 km. Removal of the estimated effect of rainfall rate variations on chemistry reduces interevent and intersite distance variability. In these events, there appears to be a baseline subgrid-scale spatial variability (including measurement error) for sulfate of no more than about 20%