The Control of SO2 Dry Deposition on to Natural Surfaces by NH3 and its Effects on Regional Deposition

Two years of continuous measurements of SO₂deposition fluxes to moorland vegetation are reported. The mean flux of 2.8 ng SO₂ m^-2 s^-1 is regulated predominantly by surface resistance (r _c) which, even for wet surfaces, was seldom smaller than 100 s m^-1. The control of surface resistance is shown to be regulated by the ratio of NH₃SO₂ concentrations with an excess of NH₃ generating the small surface resistances for SO₂. A dynamic surface chemistry model is used to simulate the effects of NH₃ on SO₂ deposition flux and is able to capture responses to short-term changes in ambient concentrations of SO₂, NH₃ and meteorological conditions. The coupling between surface resistance and NH₃/SO₂ concentration ratios shows that the deposition velocity for SO₂ is regulated by the regional pollution climate. Recent long-term SO₂ flux measurements in a transect over Europe demonstrate the close link between NH₃/SO₂ concentrations and rc (SO₂). The deposition velocity for SO₂ is predicted to have increased with time since the 1970s and imply a 40% increase in v _d at a site at which the annual mean ambient SO₂ concentrations declined from 47 to 3 g m^-3 between 1973 and 1998.     

A chronology of nitrogen deposition in the UK between 1900 and 2000

Measurements of the concentrations of nitrogen compounds in air and precipitation in the UK have been made since the mid-19th century, but no networks operating to common protocols and having traceable analytical procedures were established until the 1950s. From 1986 onwards, a high-quality network of sampling stations for precipitation chemistry was established across the UK. In the following decade, monitoring networks provided measurement of NO₂, NH₃, HNO₃ and a satisfactory understanding of the dry deposition process for these gases allowed dry deposition to be quantified. Maps of N deposition for oxidized and reduced compounds at a spatial scale of 5 km × 5 km are available from 1986 to 2000. Between 1950 and 1985, the more limited measurements, beginning with those of the European Air Chemistry Network (EACN) provide a reasonable basis to estimate wet deposition of NO^? ₃?N and NH⁺ ₄?N. For the first half of the century, estimates of deposition were scaled with emissions assuming a constant relationship between emission and deposition for each of the components of the wet and dry deposition budget at the country scale. Emissions of oxidized N, which dominated total nitrogen emissions throughout the century, increased from 312 kt N annually in 1900 to a peak of 787 kt for the decade 1980–1990 and then declined to 460 kt in 2000. Emissions of reduced N, largely from coal combustion were about 168 kt N in 1900, increasing to a peak of 263 kt N in 2000 and by now dominated by agricultural sources. Reduced N dominated the deposition budget at the country scale, increasing from 163 kt N in 1900 to 211 kt N in 2000, while deposition of oxidized N was 66 kt N in 1900 and 191 kt N in 2000. Over the century, 68 Mt (Tg) of fixed N was emitted within the UK, 78% as NO _x , while 29 Mt of nitrogen was deposited (43% of emissions), equivalent to 1.2 t N ha^?1, on average, with 60% in the reduced form. Deposition to semi-natural ecosystems is approximately 15 Tg N, equivalent to between 1 and 5 t N ha^?1, over the century and appears to be accumulating in soil. The N deposition over the century is similar in magnitude to the total soil N inventory in surface horizons.     

The influence of atmospheric n deposition on nitrous oxide and nitric oxide fluxes and soil ammonium and nitrate concentrations

The deposition of atmospheric N to soils provides sources of available N to the nitrifying and denitrifying microbial community and subsequently influences the rate of NO and N₂O emissions from soil. We have investigated the influence of three different sources of enhanced N deposition on NO and N₂O emissions 1) elevated NH₃ deposition to woodlands downwind of poultry and pig farms, 2) increased wet cloud and occult N deposition to upland forest and moorland and 3) enhanced N deposition to trees as NO^? ₃ and NH⁺ ₄ aerosol. Flux measurements of NO and N₂O were made using static chambers in the field or intact and repacked soil cores in the laboratory and determination of N₂O by gas chromatography and of NO by chemiluminescence analysis. Rates of N deposition to our study sites were derived from modelled estimates of N deposition, NH₃ concentrations measured by passive diffusion and inference from measurements of the ²¹⁰Pb inventory of soils under tree canopies compared with open grassland. NO and N₂O emissions and KCl-extractable soil NH⁺ ₄ and NO^? ₃ concentrations all increased with increasing N deposition rate. The extent of increase did not appear to be influenced by the chemical form of the N deposited. Systems dominated by dry-deposited NH₃ downwind of intensive livestock farms or wet-deposited NH⁺ ₄and NO^? ₃ in the upland regions of Britain resulted in approximately the same linear response. Emissions of NO and N₂O from these soils increased with both N deposition and KCl extractable NH⁺ ₄, but the relationship between NH⁺ ₄ and N deposition (ln NH⁺ ₄ = 0.62 ln N_deposition+0.21, r ² = 0.33, n = 43) was more robust than the relationship between N deposition and soil NO and N₂O fluxes.     

Chemical and physical properties of dry flue gas desulfurization products

Beneficial and environmentally safe recycling of flue gas desulfurization (FGD) products requires detailed knowledge of their chemical and physical properties. We analyzed 59 dry FGD samples collected from 13 locations representing four major FGD scrubbing technologies. The chemistry of all samples was dominated by Ca, S, Al, Fe, and Si and strong preferential partitioning into the acid insoluble residue (i.e., coal ash residue) was observed for Al, Ba, Be, Cr, Fe, Li, K, Pb, Si, and V. Sulfur, Ca, and Mg occurred primarily in water- or acid-soluble forms associated with the sorbents or scrubber reaction products. Deionized water leachates (American Society for Testing and Materials [ASTM] method) and dilute acetic acid leachates (toxicity characteristic leaching procedure [TCLP] method) had mean pH values of >11.2 and high mean concentrations of S primarily as SO(2-)4 and Ca. Concentrations of Ag, As, Ba, Cd, Cr, Hg, Pb, and Se (except for ASTM Se in two samples) were below drinking water standards in both ASTM and TCLP leachates. Total toxicity equivalents (TEQ) of dioxins, for two FGD products used for mine reclamation, were 0.48 and 0.53 ng kg(-1). This was similar to the background level of the mine spoil (0.57 ng kg(-1)). The FGD materials were mostly uniform in particle size. Specific surface area (m2 g(-1)) was related to particle size and varied from 1.3 for bed ash to 9.5 for spray dryer material. Many of the chemical and physical properties of these FGD samples were associated with the quality of the coal rather than the combustion and SO2 scrubbing processes used.     

Long-Term observations on the moulting frequency of the shrimp Lysmata seticaudata

The effects of body-size and temperature on moulting frequency of the shrimp Lysmata seticaudata Risso were examined under controlled laboratory conditions. Shrimp ranging in weight from approximately 0.4 to 1.14 g and maintained at 17°C exhibited intermoult periods of similar duration (20 d). On the other hand, small individuals (0.23 g) held at the same temperature moulted on the average every 14.5 d. Over a temperature range from 8° to 20°C mean intermoult periods were inversely and linearly related to temperature; an increase of 1 C⁰ resulted in a decrease in the intermoult period of approximately 1.5 d. Although temperature acted to regulate the intermoult period of each shrimp in increments of whole days, it had little effect on the time of moulting within any 24 h period, since moulting occurred more than 93% of the time between 18.00 and 08.00 hrs. The night-time moulting pattern also tended to be most pronounced at lower temperatures (8° and 13°C) and in larger individuals. Possible factors controlling this phenomenon and its occurrence in other crustacean species are discussed.     

Ecological effects of sulfur dioxide,fluorides, and minor air pollutants: recent trends and research needs

The regulation of the emissions of 'traditional' primary air pollutants (fluorides, sulfur dioxide) has changed the pattern of exposure of ecological systems, with greatly reduced exposure close to sources, but with a smaller effect in some remote areas. Measurements show that recovery is occurring at some sites, in fresh water chemistry (reduced acidity) and in sensitive biota (sustainable fish populations). However, the pattern of change in exposure has not always been simply related to emission reductions. An understanding of responses to recent changes will improve our predictions of the response to future emission changes, both locally and globally. As exposure to 'traditional' pollutants is reduced, the potential for other pollutants to have effects becomes more evident. In the aqueous phase, we need to understand the role of soluble and suspended organics, but this also means explicit recognition of the possibility of phase exchange, and the role of photolytic reactions on plant, soil, and water surfaces. Do highly reactive free radicals in the atmosphere, formed by the action of sunlight on volatile organic compounds, have direct effects on plants? Organic compounds and heavy metals may be bioactive as gases and particles, but for many potentially toxic compounds, the experimental evidence for biotic response is very limited. To evaluate the potential effects of pollutants, we need to understand the pathways by which airborne pollutants enter and react within ecosystems. For vegetation, we have to consider bidirectional fluxes, and distinguish among uptake through stomata, through leaf surfaces, or through roots. There are several challenges for the future. (1) Can we devise experiments that permit exposure of vegetation to gases, particles, and/or aqueous pollutants at 'realistic' concentrations? (2) Can we include the potential interactions with photolytically derived free radicals, and the dynamics of exchange? (3) How do we allow for responses to pollutant mixtures, or the simultaneous exposure to pollutants in gas, particle, and aqueous phases? The recognition of the importance of the dynamic exchange of pollutants between phases will be the key to the development of effective experimental approaches to evaluating cause-effect relationships between pollutant mixtures and ecosystem responses.     

The Influence of Atmospheric N Deposition on Nitrous Oxide and Nitric Oxide Fluxes and Soil Ammonium and Nitrate Concentrations

The deposition of atmospheric N to soils provides sources of available N to the nitrifying and denitrifying microbial community and subsequently influences the rate of NO and N₂O emissions from soil. We have investigated the influence of three different sources of enhanced N deposition on NO and N₂O emissions 1) elevated NH₃ deposition to woodlands downwind of poultry and pig farms, 2) increased wet cloud and occult N deposition to upland forest and moorland and 3) enhanced N deposition to trees as NO ₃ ^– and NH ₄ ⁺ aerosol. Flux measurements of NO and N₂O were made using static chambers in the field or intact and repacked soil cores in the laboratory and determination of N₂O by gas chromatography and of NO by chemiluminescence analysis. Rates of N deposition to our study sites were derived from modelled estimates of N deposition, NH₃ concentrations measured by passive diffusion and inference from measurements of the ²¹⁰Pb inventory of soils under tree canopies compared with open grassland. NO and N₂O emissions and KCl-extractable soil NH ₄ ⁺ and NO ₃ ^– concentrations all increased with increasing N deposition rate. The extent of increase did not appear to be influenced by the chemical form of the N deposited. Systems dominated by dry-deposited NH₃ downwind of intensive livestock farms or wet-deposited NH ₄ ⁺ and NO ₃ ^– in the upland regions of Britain resulted in approximately the same linear response. Emissions of NO and N₂O from these soils increased with both N deposition and KCl extractable NH ₄ ⁺ , but the relationship between NH ₄ ⁺ and N deposition (ln NH ₄ ⁺ = 0.62 ln N_deposition + 0.21, r ² = 0.33, n = 43) was more robust than the relationship between N deposition and soil NO and N₂O fluxes.     

Measuring Aerosol and Heavy Metal Deposition on Urban Woodland and Grass Using Inventories of 210Pb and Metal Concentrations in Soil

The deposition of aerosols to trees has proved very difficult to quantify, especially in complex landscapes. However, trees are widely quoted to be efficient scavengers of particles from the atmosphere, and a growing proportion of the pollutant burden in the atmosphere is present in the aerosol phase. In this study, the deposition of aerosols onto woodland and grass was quantified at a range of locations throughout the West Midlands of England. The sites included mature deciduous woodland in Edgbaston, and Moseley, and mixed woodland at sites within Sutton Park, a large area of semi-natural vegetation. Aerosol deposition to areas of grassland close to the woodland at each site was also measured. Detailed inventories of ²¹⁰Pb in soils within the woodland and in grassland soils, together with concentrations in the atmosphere and precipitation, provided the necessary data to calculate the long-term (about 40 years) annual deposition of sub-micron aerosols onto grassland and woodland. The soil inventories of ²¹⁰Pb under woodland exceeded those under grass, by between 22% and 60%, with dry deposition contributing 24% of the total input flux for grass and 47% for woodland. The aerosol dry deposition velocity to grassland averaged 3.3 mm s^-1 and 9 mm s^-1 for woodland. The large deposition rates of aerosols onto woodland relative to grass or other short vegetation (× 3), and accumulation of heavy metals within the surface horizons of organic soils, leads to large concentrations in soils of urban woodland. Concentrations in the top 10 cm of these woodland soils averaged 252 mg kg^-1 for Pb with peaks to 400 mg kg^-1. Concentrations of Cd averaged 1.4 mg kg^-1, Cu, 126 mg kg^-1, Ni 23 mg kg^-1 and Zn 173 mg kg^-1. The accumulated Pb in urban woodland soils is shown to be large relative to UK emissions.     

Effects of air filtration at small SO2 and NO2 concentrations on the yield of barley

Two cultivars of Igri and Gerbel winter barley Horteum vulgare L. were grown in open-top chambers in filtered and unfiltered air at a site with approximately 10 nl litre(-1) SO2 and 12 nl litre(-1) NO2 (seasonal mean). The experiment ran for three consecutive seasons 1982-1983, 1983-1984, 1984-1985, and significant effects of filtration were observed for each crop. In years 1982-1983 and 1984-1985, the crops in unfiltered air yielded larger grain dry matter, 9% in 1982-1983, and 8% in 1984-1985. For both crops, the differences were statistically significant at the 5% level. Differences were also observed for the remaining above-ground dry matter, and these were consistent in direction in each year but statistically significant only in 1984-1985. In both growing seasons (1982-1983 and 1984-1985), there were no major pest infestations and no long-term water stress or photochemical ozone episodes. In the remaining experiment (1983-1984) similar air concentrations of SO2 and NO2 produced effects of the opposite sign to those observed in 1982-1983 and 1984-1985. Significant reductions in grain yield (13%) were obtained in unfiltered air. The only major environmental difference for the 1983-1984 crop was a notable dry period in May and June 1984 with marked water stress in the crop, requiring irrigation. These results suggest that the relationship between yield and pollutant concentration may be confounded by additional stresses, many of which are a common component of the growing season for major crops.     

The determination of toxaphene in environmental samples by negative ion electron capture high resolution mass spectrometry

A method is described for the analysis of toxaphene in environmental samples by high resolution gas chromatography high resolution mass spectrometry in selected ion electron capture negative ion mode. Toxaphene is detected by monitoring [M-Cl]- fragments ions of chlorobornanes (Cl6-Cl10) and chlorobornenes (Cl6-Cl7) using formal ion ratio criteria. The method shows high sensitivity and excellent specificity for the detection of chlorobornanes with negligible interference from of a wide range of common environmental organochlorines including chlordanes, PCBs and PCB-oxygen adducts. The analytical scheme is applicable to sediment and biological tissue samples and typically provide sample detection limits of less than 0.2 ng/g technical toxaphene for a 10 g sample.