Ozone in the urban southeastern United States

Ozone measurements (daily maximum values) from the Aerometric Information Retrieval System database are analyzed for selected sites, during 1980 to 1988, in southeastern USA. Frequency distributions, for most sites during most years, show a typical bell-shaped curve with the higher frequency around the yearly daily maximum ozone mean of about 100 to about 110 microg m(-3) (50-55 ppbv). Abnormal years in ozone concentration may skew the distribution as the mean shifts. A correlation of daily maximum ozone concentrations above 140 microg m(-3) (70 ppbv) between sites shows a division between the sites in the northern protion of the region and those in the southern portion of the region. Variations in ozone levels are well correlated over distances of several hundred kilometers, suggesting that high values are associated with synoptic scale episodes. An ozone exposure analysis also shows higher ozone exposures (250-300 ppm days) in the northerly sites as compared to the southerly sites (150-170 ppm days).     

Effect of nickel on some aspects of protein metabolism in the gill and kidney of the freshwater fish, Cyprinus carpio L

Nickel has an adverse effect on some aspects of protein metabolism of the freshwater fish, Cyprinus carpio. The main changes observed were: (a) Decrease in soluble, structural and total proteins, AlAT and AAT activities with an increase in the levels of free amino acids, protease and GDH activities and ammonia in the gill and kidney at 1, 2, 3, and 4 days of exposure to a lethal concentration, 40 mg litre(-1) of nickel; (b) Increase in soluble, structural and total proteins, free amino acids and the activities of protease, AlAT, AAT and GDH with a decrease in ammonia and urea in these organs at 1, 5, 10 and 15 days of exposure to sublethal concentration, 8 mg litre(-1); (c) The magnitude in these changes increased over time with both concentrations of the metal, and was more marked in gill than in kidney.     

Variation of leaf gland volatile oil within a population of sweet gale (Myrica gale) (Myricaceae)

Summary The leaf gland volatile oils of ten sweet gale plants from a Scottish population were extracted in early summer. The results differed notably from reports of other populations in respect of the sesquiterpenes, -elemenone and germacrone, which were major components of the volatile oil. Three dihydrochalcones were also detected in the volatile oil. Variation within the population existed, particularly with respect to the relative importance of germacrone. Five plants were resampled in late summer and exhibited a marked reduction in -elemenone, a lesser reduction in germacrone and changes in the proportions of some monoterpenes.     

Modelling episodic acidification of surface waters: the state of science

Field studies of chemical changes in surface waters associated with rainfall and snowmelt events have provided evidence of episodic acidification of lakes and streams in Europe and North America. Modelling these chemical changes is particularly challenging because of the variability associated with hydrological transport and chemical transformation processes in catchments. This paper provides a review of mathematical models that have been applied to the problem of episodic acidification. Several empirical approaches, including regression models, mixing models and time series models, support a strong hydrological interpretation of episodic acidification. Regional application of several models has suggested that acidic episodes (in which the acid neutralizing capacity becomes negative) are relatively common in surface waters in several regions of the US that receive acid deposition. Results from physically based models have suggested a lack of understanding of hydrological flowpaths, hydraulic residence times and biogeochemical reactions, particularly those involving aluminum. The ability to better predict episodic chemical responses of surface waters is thus dependent upon elucidation of these and other physical and chemical processes.     

Comparison of episodic acidification in Canada, Europe and the United States

Episodic acidification is practically a ubiquitous process in streams and drainage lakes in Canada, Europe and the United States. Depressions of pH are often smaller in systems with low pre-episode pH levels. Studies on European surface waters have reported episodes most frequently with minimum pH levels below 4.5. In Canada and the United States, studies have also reported a number of systems that have had minimum pH levels below 4.5. In all areas, change in water flowpath during hydrological events is a major determinant of episode characteristics. Episodic acidification is also controlled by a combination of other natural and anthropogenic factors. Base cation decreases are an important contributor to episodes in circumneutral streams and lakes. Sulphate pulses are generally important contributors to episodic acidification in Europe and Canada. Nitrate pulses are generally more important to episodic acidification in the Northeast United States. Increases in organic acids contribute to episodes in some streams in all areas. The sea-salt effect is important in near-coastal streams and lakes. In Canada, Europe and the United States, acidic deposition has increased the severity (minimum pH reached) of episodes in some streams and lakes.     

Effects of clearfelling on stream and soil water aluminium chemistry in three UK forests

Data are presented demonstrating how clearfelling has changed soil and stream water aluminium chemistry. For soil waters, a strong empirical relationship was observed between inorganic aluminium (Al(inorg)) and total inorganic anion (TIA) concentrations. Before felling, chloride and sulphate accounted for the largest proportion of the TIA concentration. After felling, in soils where nitrification was active, nitrate became increasingly important. Where this led to an increase in TIA, Al(inorg) concentrations increased. Over five years, nitrate concentrations have fallen, along with TIA, resulting in a sympathetic decline in Al(inorg). Streams draining clearfelled areas initially became more acid, although chloride and sulphate concentrations decreased. Stream water nitrate concentrations increased soon after felling and remained higher than controls for up to four years. While nitrate concentrations were high, Al(inorg) remained unchanged. Subsequently, as nitrate and TIA decreased, Al(inorg) also declined to concentrations below those in the control stream. Clearfelling upland forests will not necessarily result in immediate improvements in water quality, although long-term benefits may be seen before canopy-closure of the next crop.     

Seasonal trend of fog water chemical composition in the Po Valley

Fog frequency in the Po Valley, Northern Italy, can be as high as 30% of the time in the fall-winter season. High pollutant concentrations have been measured in fog water samples collected in this area over the past few years. The combined effects of high fog occurrence and high pollutant loading of the fog droplets can determine, in this area, appreciable chemical deposition rates. An automated station for fog water collection was developed, and deployed at the field station of S. Pietro Capofiume, in the eastern part of the Po Valley for an extended period: from the beginning of November 1989 to the end of April 1990. Time-resolved sampling of fog droplets was carried out during all fog events occurring in this period, and chemical analyses were performed on the collected samples. Statistical information on fog occurrence and fog water chemical composition is reported in this paper, and a tentative seasonal deposition budget is calculated for H+, NH4+, NO3- and SO4(2-) ions. The problems connected with fog droplet sampling in sub-freezing conditions are also addressed in the paper.     

Observations of H2O2 and PAN in a rural atmosphere

Measurements of gaseous H2O2 and peroxyacetyl nitrate (PAN) concentrations in air are given for a site in rural southern England over an approximately 4-year period. In both cases the data show both diurnal and seasonal patterns. Temperature and wind direction had clear influences on the recorded concentrations of both species. There was an indication of increasing H2O2 concentrations with time. The use of a two-dimensional global model confirmed that this would be expected to occur alongside growth in ozone formation. It is suggested that, during photochemical episodes, the sequential build-up of ozone, PAN and H2O2 could be important in influencing the ability of vegetation to resist the effects of aggressive pollutants.     

An introduction to critical loads

The critical loads approach to emission controls of gaseous pollutants is a concept with a short but eventful history. Despite difficulties with definitions and agreed values, its acceptance within the UN-ECE Convention on Long Range Transboundary Air Pollution has provided the impetus for developing methods to put critical loads to a practical use-the revision of the UNECE emission protocols for sulphur and nitrogen. Methodologies first focus upon quantifying a pollutant threshold at which harmful effects occur on particular sensitive receptors (usually biological species). This threshold is known as the critical load for deposited pollutants, and as the critical level for gaseous pollutants acting on receptors. To calculate a critical load, biological effects are usually 'translated' to critical chemical values, e.g. harmful effects on fish 'translate' to alkalinity or aluminium concentrations in water; thus, critical load calculations may be based upon the chemistry of a system. Such calculations may be performed using simple, steady-state models, whilst the use of more complex, dynamic models provides an insight into the past and future trends. Maps of critical loads can be drawn using calculated values, and maps of pollutant deposition data will then show geographical areas where critical loads are exceeded. Spatial emission-deposition models can identify sources contributing to areas of excess loads and quantify necessary emission reductions. Optimization procedures applied to such models can derive abatement strategies related to economic costs and critical load effects. The critical load calculations may also be used to underpin the setting of target loads; these are pollutant loads, determined by political agreement, which take account of social, economic and political considerations.     

Deposition of ozone to a mature spruce forest: measurements and comparison to models

Removal of ozone at terrestrial surfaces provides a major sink for tropospheric ozone and, therefore, a constraint on the peak concentrations achieved during photochemical episodes. This study reports results from 5 years of almost continuous measurements of vertical profiles of ozone and related meteorological variables over a mature spruce forest in Bavaria. Deposition velocities calculated from flux/gradient and eddy correlation flux measurements have been compared with estimates based on a resistance model and yield satisfactory agreement during fine weather conditions. The results also suggest that biogenic emissions of reactive hydrocarbons from the forest influence the vertical profile of ozone.