Effects of varying air trajectories on spatial and temporal precipitation chemistry patterns

This study was designed to determine if judicious use of synoptic data and an operational trajectory model could identify probable source regions of anthropogenic pollutants in northeastern United States precipitation and thus relate receptor measurements to emissions data without consideration of the complex intervening meteorological and chemical processes. The storm event of April 8 to 10, 1979, was selected for intensive study. Precipitation chemistry data were obtained from event samples at six MAP3S sampling sites and from hourly samples at Brookhaven National Laboratory. Concentrations of hydrogen, sulfate, nitrate and ammonium ions were used as receptor data. Some emissions data for SO_x and NO_x were obtained from the MAP3S emissions inventory. Surface and upper air meteorological data were analyzed. Backward trajectories ending at each of the sampling sites during the precipitation period were computed with the Heffter Interactive-Terminal Transport Model using selected transport layers. Results show that concentrations of pollutant species in event precipitation samples were much higher at stations at end points of trajectories passing through the Ohio River valley than at stations with other trajectories. Likewise, concentrations at Brookhaven were much higher during the end period of a trajectory through the same region than with more northerly and more southerly tracks. The model produced back trajectories consistent with synoptic flows. Concentrations of air pollutants in precipitation were roughly proportional to the number of major pollutant sources along the trajectory. These results suggest that a larger number of studies might identify more restricted source areas or even establish a quantitative relationship between source emissions along a trajectory and concentrations in precipitation at receptor sites.     

Modeling of pollutant transport and removal during a regional sulfate episode

As part of a multidisciplinary study performed for the National Commission on Air Quality, the phenomena of atmospheric transport and the removal of SO₂ and SO₄ ^? during a major regional sulfate episode (the period July 18–25, 1978 in the eastern U.S.) had been examined. The main objective of this study was the evaluation and the quantification of varying source/receptor relationships under atmospheric conditions conducive to long-range transport of fine particulate matter. In the case study presented here, air mass trajectories were obtained using the numerical NMC trajectory predictions and the results of the isobaric trajectory computations at the 850 mb level. The effects of alternative regional SO₂ emission reduction scenarios on the predicted ambient SO₂ and SO₄ ^? concentrations were also investigated using the new modeling methods that were specifically developed for this purpose.     

The Effect of Changes in European Anthropogenic Emissions on the Concentrations of Sulphur and Nitrogen Components in Air and Precipitation in Lithuania

Sulphur (S) and nitrogen (N) components are of great concern because acidification and eutrophication still remain an important environmental issue in many regions of the world. Continuous monitoring (1981–1999) of S and N components both in air and precipitation in Lithuania (LT) has allowed us to evaluate the regional and temporal variations in relation to the pollutant emission changes. Despite of inter-site variability in concentration of pollutants within the regional scale, data showed a marked decrease in S concentrations both in air and precipitation over the Lithuania as a whole. Non-seasalt sulphate (nssSO₄ ^2?) concentrations in precipitation and air decreased from 2.06 to 0.52 mgS/l and from 3.97 to 1.07 µgS/m³, respectively. The number of acidic (pH<5) precipitation did not exceed 50 % during 1995–1999. The observed trends for S species are consistent with those for sulphur dioxide (SO₂) emission in Europe and Lithuania. Although nitrogen dioxide (NO₂) concentration in air decreased by 17 %, significant changes in nitrate (NO₃ ^?) concentrations neither in precipitation nor in air have been observed. Three-day backward air isobaric trajectories were used for the identification of the source region of air pollutants     

Bridging the gap between air quality and precipitation chemistry

Data sets recently have become available providing simultaneous, regional scale observations of ambient air quality and precipitation chemistry. The data cover parts of the greater northeastern United States. With certain key assumptions, the observations of ambient SO_x and NO_x concentrations can be linked with precipitation concentrations through Junge's concept of rainout efficiency, assumed to be qualitatively equivalent to the washout ratio. A preliminary comparison between data taken from the Sulfate Regional Experiment (SURE) and the parallel precipitation studies using Junge's approach reveals certain useful consequences. Apparent dramatic differences in SO_x and NO_x scavenging are found. Ratios between sulfate in the aerosol and in precipitation compared with trace elements suggest the importance of particulate scavenging processes. Such results show promise for simplified analysis of these data as approaches to differentiating mechanisms involved in cloud-precipitation chemistry.     

Background pollution in the Arctic air mass and its relevance to North American acid rain studies

The Arctic air mass is a unique meteorological feature of the northern hemispheric atmosphere. Possessing well-defined meteorological characteristics, it occupies not only the polar region but also a large fraction of the Canadian and Eurasian land masses during the period November to April. Poor pollutant removal by precipitation and dry deposition within the air mass and a strong transport pathway between Eurasian mid-latitudinal sources and the north, result in elevated levels of acidic anthropogenic aerosols and gases in the air mass during winter. In summer, weak north/south transport and strong pollutant removal between the Arctic and mid-latitudes and within the Arctic, results in lower airborne concentrations of acidic pollutants. Due to the presence of the relatively polluted Arctic air mass, ‘background’ air concentrations of SO₄ ⁼, SO₂ and total NO₃ ^? are elevated in western Canada during winter. Typical mean monthly concentrations from December to March are 0.8 to 2.1, 1.0 to 2.4 and 0.1 ? 0.6 μg m^?3, respectively. In the absence of the neutralizing influence of alkaline soil dust, the acidity of snow forming in western Canada during winter is expected to range from 5 to 20 μeq l ^?1.     

Historical data of atmospheric sulfur in three monitoring periods for Europe

During the last 25 yr three major monitoring programs (EACN, OCED and EMEP) were conducted in Europe that furnished continental background air and precipitation quality data. Comparisons of these measured data show that SO₂ concentrations in air and sulfate ion concentrations in precipitation do not vary in parallel with changes in S emissions. This lack of correlation between emissions and ambient air and precipitation concentrations among the three networks is believed to be due mostly to differences in sampling and analytical procedures, as well as the shift in S emissions from low sources to high stacks.     

An analysis of wet deposition of sulfate using a trajectory model for East Asia

A long-range transport model for East Asia was developed to estimate the wet deposition of sulfate. The model is a trajectory type which is appropriate for long-term analysis. Trajectories of air masses are calculated by tracing the wind field which changes spatially and temporally. The processes of reactions, rainout removal, intake of sulfate in cloud water into rain water, and dry and wet depositions are considered. It is possible to calculate the concentration of sulfate in precipitation at a receptor by performing material balance in a grid box containing the receptor.The results obtained by the long-range transport model were evaluated through comparison with observation data of acidic deposition. The observation was conducted at 21 stations throughout Japan for one year. The calculated amount of wet deposition of sulfate in Japan was 0.22Tg/y in S equivalent, while the observed amount was 0.29Tg/y. The long-range transport model can predict almost 80% of observed wet deposition. The contributions of domestic anthropogenic sources and volcanic eruption to wet deposition of sulfate in Japan were estimated using the longrange transport model. The ratio of the deposition of sulfate due to Japanese anthropogenic sources to that due to the Asian continental sources was about 1 to 2. Since air stream from the direction of the Asian continent dominates during winter, the contribution of Japan to wet deposition in the region which faces the Sea of Japan amounted to less than 15%. The contribution of the sulfur oxides from volcanoes was about 20%.     

Impacts of Air Pollutants on Vegetation in Developing Countries

The predicted increases in emissions of primary pollutants in many rapidly industrializing countries may have severe consequences for the health and productivity of forest trees and agricultural crops. This paper presents a review of air pollution impacts on vegetation in developing countries by summarising information describing the direct impacts to vegetation caused by a number of air pollutants (sulphur dioxide (SO₂), nitrogen oxides (NOx), ozone (O₃) and Suspended Particulate Matter (SPM)). This information has been collected by experts from a number of rapidly industrializing countries in Asia, Latin America and Africa and includes observations of visible injury in the field and the use of transect studies and controlled experimental investigations to ascribe damage to different pollutant concentrations. The ability to synthesise this information to define exposure-response relationships and subsequent air quality guidelines similar to those established in North America and Europe is assessed. In addition, the use of regional and global models describing pollution concentrations is discussed with reference to assessing the extent of adverse impacts and identifying regions likely to be most at risk from air pollution, both for the present day and in the future. The evidence summarised in the paper clearly shows that current pollutant concentrations experienced in many developing countries, particularly Asia, can result in severe damage to vegetation and that without appropriate control measures such damage is likely to worsen in the future as pollutant emissions increase.     

Geographical and Temporal Variations of Chemical Constituents in Winter Precipitation Collected in the Areas along the Coast of the Sea of Japan

The geographical and temporal variations of chemical constituents in winter precipitation collected in the areas along the coast of the Sea of Japan (AASJ) were discussed by analyzing the data obtained in the 1st and 2nd National Acid Deposition Survey by Japan Environmental Laboratories Association. In western Tohoku (WT) and Hokuriku (HR) areas in AASJ, in spite of large amounts of precipitation in winter, concentrations of non sea salt (nss-)SO₄ ^2? are not as low as the other areas, and nss-Ca²⁺ in these areas is lower than the other areas. As a result, H⁺ concentrations of precipitation in these areas are somewhat higher than other areas. From the temporal analysis of daily sampled data and back trajectory analysis of air mass, it was found that the concentrations of nss-SO₄ ^2?, NO₃ ^?, NH₄ ⁺ and nss-Ca²⁺ are correlatively varied when air mass come from the Asian Continent, showing higher concentrations at the western sites in AASJ and depending on the meteorological conditions such as the direction of in flow air mass.     

Selected Whiteface Mountain cloud water concentrations summers 1981 and 1982

A statistical analysis was made of source trajectory air mass regions versus receptor [SO₄ ^?2] in cloud water at Whiteface Mountain, Wilmington, New York for the summers of 1981 and 1982. Also tested was the assumption that in 1982 sulfate concentrations should decrease in the cloud water when associated with a trajectory from the west northwest. This assumption was based on the fact that Canadian smelters were idle during August 1982 which resulted in a reduction of SO₂ emissions by approximately 75%. The trajectory analysis was done using the NOAA/ARL transport model and anion-cation analysis of cloud water was performed using ion chromatography. The Canadian emission data were provided by the Air Resources Branch, Ministry of the Environment. Student's Test was used to test the null hypothesis that no [SO₄ ^?2] differences existed in the cloud water collected during 1981 and 1982. The results were suggestive of the following conclusions:

1. There is so much inherent noise in the data due to meteorological variability that the hypothesized decrease in [SO₄ ^?2] from the smelting operation could not be detected.
2. The trajectory analysis is not precise enough, due to the frequency of soundings and station spacing, to indicate the correct source-receptor for Whiteface Mountain; and a careful analysis of cloud water samples associated with fast moving cold fronts from the Sudbury region might detect an effect on sulfate production.
3. The available meteorology does not seem sufficient to explain the variation seen at the Whiteface Mountain field station.

     

Long range transport of air pollutants in Europe and acid precipitation in Norway

Observations show that pollutants from large emission sources may cause significant air concentrations 500 to 1000 mi away. Very acid precipitation occurs in such periods. The scavenging is often intensified by the topography. Case studies will be presented with special emphasis on acid precipitation in Scandinavia. Large scale dispersion models have been developed recently in order to estimate the long range transport of air pollutants. The models take into account chemical transformations as well as deposition of pollutants. The calculations will be compared with observations from airplanes and surface stations. A simple model has been integrated over a long period of time in order to derive the best value for the decay rate of SO₂. This best value is based on a day-by-day comparison with surface observations.     

Occurrence and turnover of atmospheric mercury over the nordic countries

A seasonal variation of both particle and gaseous Hg concentrations in the atmosphere is present in south-western Sweden. An average gaseous Hg level of 3.7 ng m^?3 is found in winter, compared to 2.8 ng m^?3 in summer. A weak decreasing south-north gradient for gaseous Hg in air over the Nordic countries is also present, with yearly average values from 3.2 to 2.8 ng m^?3. A gradient for particulate Hg is less clear. An air parcel trajectory sector classification of gaseous Hg levels in air, and to some extent the particulate associated Hg, clearly demonstrates the increased concentrations in the southern sectors, especially in south-western Sweden where the gaseous Hg increase is about I ng m^?3. These observations are consistent with an influence from the European continent. The average concentrations of Hg in precipitation at the various stations show a pronounced decreasing south-north gradient. A major portion of the total Hg present in precipitation is associated with particles. For the southern stations, a strong correlation between Hg and sulfate, or pH, is present suggesting a connection between Hg in precipitation and anthropogenic activities.     

Measurements of precipitation composition at UK EMEP sites 1987–1992 and comparison with the HARM model

Precipitation composition has been measured daily at five UK EMEP sites since 1987. Sulphur dioxide and sulphate aerosol concentrations are also measured daily at the sites. Back trajectories and wind sectors calculated by the Norwegian Meteorological Institute have been used to characterise the variation in wet deposition in terms of air mass source. Contributions to wet deposition from various source regions have been estimated for Eskdalemuir. Observations from the EMEP sites have been compared with output from the Hull Acid Rain Model (HARM). HARM is a Lagrangian model using simplified meteorology but straight-line trajectories. Results are compared on a site-by-site and sector-by-sector basis and the model reproduces the general features of pollutant concentration and wet deposition indicated by the measurements. The possible effects of future reductions in emissions of SO₂ and NOx on precipitation concentrations by wind sector are described.     

Sulphur and nitrogen deposition in Norway,status and trends

The total deposition of sulphur (S) and nitrogen (N) components in Norway during the period 1988–1992 has been estimated on the basis of measurement data of air- and precipitation chemistry from the national monitoring network. There are large regional variations in depositions with highest values in the southwestern part of Norway. Time series analysis of annual mean concentrations of sulphur dioxide (SO₂) and sulphate (SO₄ ^––) in air, non marine SO₄ ^––, nitrate (NO₃ ^–) and ammonium (NH₄ ⁺) in precipitation, shows a significant reduction in the S concentrations both in air and precipitation. In precipitation the concentrations are reduced by 30–45 percent in Southern Norway and 45–55 percent in Central and Northern Norway. Even larger reductions are observed in air concentrations with 50–65 percent reduction in Southern Norway and 65–88 percent reduction further north. For N components there are generally no significant trends in concentration levels nor in precipitation or air. The observed trends are comparable with reported trends in emission.     

Mercury in forest canopy throughfall water and its relation to atmospheric deposition

A seasonal variation of both particle and gaseous Hg concentrations in the atmosphere is present in south-western Sweden. An average gaseous Hg level of 3.7 ng m⁻³ is found in winter, compared to 2.8 ng m⁻³ in summer. A weak decreasing south-north gradient for gaseous Hg in air over the Nordic countries is also present, with yearly average values from 3.2 to 2.8 ng m⁻³. A gradient for particulate Hg is less clear. An air parcel trajectory sector classification of gaseous Hg levels in air, and to some extent the particulate associated Hg, clearly demonstrates the increased concentrations in the southern sectors, especially in south-western Sweden where the gaseous Hg increase is about I ng m⁻³. These observations are consistent with an influence from the European continent. The average concentrations of Hg in precipitation at the various stations show a pronounced decreasing south-north gradient. A major portion of the total Hg present in precipitation is associated with particles. For the southern stations, a strong correlation between Hg and sulfate, or pH, is present suggesting a connection between Hg in precipitation and anthropogenic activities.     

Critical Toxicity Level of Arsenic and Elemental Composition of Arsenic-Induced Chlorosis in Hydroponic Sorghum

In this study, NO₂ and SO₂ levels during a specific winter episode in the city of Istanbul were researched with regard to the respective impact of weather conditions. The city under study has the largest population and is one of the most polluted cities of Turkey. Furthermore, Istanbul is vulnerable to trans-boundary transport of air pollutants from Europe, because its location is on the eastern end of the Continent, where westerly winds prevail. However, there has neither been any comprehensive study nor any regulation to fix and solve the air quality problem in the city so far. A framework was prepared to model air quality using MM5 for meteorological modeling and CMAQ for transport and chemistry modeling. This study was supported by the tracer and the trajectory investigations over the area of interest. The model results underestimated the concentration of air pollutants over Istanbul as expected. But, in spite of the coarse emission inventory, the similarity of the time series between the model and observation values during the simulation period is very encouraging for future studies. That is to say, the tracer and the trajectory studies indicated that trans-boundary sources are responsible for the poor air quality of Istanbul under specific weather conditions. It must be pointed out, though, that a high-resolution national emission inventory is needed to get more accurate results.     

Aerosol and precipitation chemistry relationships at big bend national park

Aerosol chemistry, precipitation and visibility parameters are currently being measured at Big Bend National Park in Texas. This is part of a large-scale air resource evaluation program which the National Park Service is sponsoring in several southwestern national parks and monuments to determine the potential impact of local and distant pollutant sources on the environmental quality within these areas. Analysis of aerosol samples collected at six sites in the Southwest indicates that soil-derived components, organic materials and the acid-base ions of sulfate, nitrate, and ammonium are the major constituents of suspended airborne particulate matter in the remote areas of the arid region. Comparison of particulate matter chemistry and precipitation chemistry data at Big Bend National Park shows consistent features which indicate that the airborne alkaline soil material and NH₃ largely neutralize the atmospheric acidic species of H₂SO₄ and HNO₃. Given the similarity of the particulate matter composition and loading at the other monitoring sites, it is suggested that the trace chemical composition of precipitation will be similar in many remote regions of the Southwest.     

The influence of basic aerosols on throughfall fluxes of sulfate,ammonium and nitrate in three oak stands along a distance gradient from a lime quarry

Three oak stands (Quercus petraea and Quercus robur) in the Weinviertel, Lower Austria, located along a distance gradient from a lime quarry, were studied to determine the effects of basic aerosols on the deposition of ammonium, nitrate and sulfate. Higher concentrations of limestone aerosols in the vicinity of the quarry are suggested by higher Ca²⁺ fluxes and pH in throughfall and precipitation. The ammonium/nitrate ratio in throughfall decreases with distance from the quarry, though monitoring of NH₃ and NO₂ concentrations in the air with passive samplers shows the opposite trend. These findings support the theory of discrimination against NH₃ in dry deposition due to the presence of Ca ²⁺ particles on leaf surfaces resulting from limestone aerosols. Higher sulfate deposition near the quarry is consistent with higher atmospheric SO₂ concentrations and co-deposition between calcium and sulfate.     

Wet deposition of mercury and ambient mercury concentrations at a site in the Lake Champlain basin

The “Great Waters” program, established in the 1990 Clean Air Act Amendments, mandated that atmospheric deposition of hazardous air pollutants to Lake Champlain (including Hg) be assessed. An assessment of the magnitude and seasonal variation of atmospheric Hg deposition in the Lake Champlain basin was initiated in December 1992 with one year of event precipitation collection, as well as collection of vapor and particle phase Hg in ambient air. Samples were collected at the Vermont Monitoring Cooperative air monitoring site at the Proctor Maple Research Center in Underhill Center, VT. The average volume-weighted concentration for Hg in precipitation was 8.3 ng/L for the sampling year and the average amount of Hg deposited with each precipitation event was 0.069 μg/m². The total amount of Hg deposited through precipitation during 1993 was 9.26 μg/m²/yr. A seasonal pattern for Hg in precipitation was evident, with increased concentrations and deposition during spring and summer months. Meteorological analysis indicated the highest levels of Hg in precipitation were associated with regional transport from the south regardless of season, and with transport from the west, southwest and northwest during spring and summer months. Concentrations of ambient vapor phase Hg were typical of rural locations and consistent across seasons. Ambient particulate Hg concentrations averaged 11 pg/m³ with highest concentrations during the winter months.     

Acid deposition at the summit of Mt. Fuji: Observations of gases,aerosols and precipitation in summer,1993 and 1994

Intensive observations of chemical species in aerosols, gases and other samples at the summit of Mt. Fuji and at Tarobo (at 1300m on the mountain'ts southern slope) was performed from July 28 to Aug. 3, 1993 and from July 25 to 30,1994. The most interesting observation was the abrupt increase in the sulfate concentration in aerosol collected in July, 1993 just after the typhoon (number 9306) passed the Japanese archipelago and the wind direction shifted from south to west. Chemical analysis indicated this aerosol was acidic. In contrast, the summit aerosol observed in 1994 was not acidic following a less dramatic rise in sulfate content. Back trajectory analyses were used to extrapolate from these measurement to an inventory of polluted air over the Asian Continent. The concentrations of gaseous SO₂ and HCl remained low during both observation periods, with some higher concentrations of NH₃.