Trends In Sulfate Concentrations Research Articles

Temporal trends in sulphate concentrations at European sites and relationships to sulphur dioxide

Temporal trends in sulphate data taken from UK networks from the period 2001–2008 have been examined, together with trends in relevant precursor gases. In general, trends in sulphate are small, and the data sets are not of sufficient length to determine the direction of trend with confidence. Since relatively short periods of high or low concentration near to the start or finish of the period have a disproportionate influence, the choice of period over which the trend is calculated is crucial to the outcome. All six sites showed a significant reducing trend in sulphur dioxide, while ammonia data appear to be affected by sampling problems and site relocations and clear trends are not apparent. Data relating annual mean airborne concentrations of sulphur dioxide and sulphate from several countries can be related through a relationship of the form: χ [SO 4 2− ] = a·χ [SO 2 ] b + c in which a, b and c are constants and χ represents concentrations. While constant b remains the same for different countries, a and c can change in ways that appear to relate to either the distance from major SO 2 sources, or the oxidising capacity of the atmosphere. Using the relationship between SO 4 2− and SO 2 derived from UK sites allows estimation of the reduction in sulphur dioxide emissions affecting UK sites needed to reduce sulphate concentrations by 1 μg m −3 . This is 55% and 49% for Harwell and North Kensington respectively. ► Trends in sulphate from 2001–2008 are small and variable between sites. ► Trends in sulphur dioxide are consistently downward. ► The SO 4 2− :SO 2 relationship is curvilinear. ► Around 50% reduction in SO 2 emissions will deliver 1 μg m −3 reduction in SO 4 2− in the southern UK.

Sulphate trends in Europe: are we able to model the recent observed decrease

Abundance of sulphate in Europe has decreased substantially during the last two decades. In this paper, we investigate these recent trends in sulphate concentrations by applying the Oslo CTM2 model using three different sets of SO2 emission inventories. We perform time slice model simulations with emissions for the years 1985, 1995 and 2000 and compare our results with observations to investigate if there is consistency between measured and modelled sulphate trends. Overall the model reproduces the levels of sulphur and the decreasing sulphate trends reasonably well, although some discrepancies exist. The model shows a strong reduction in the surface concentration of sulphate similar to the observations, although a slightly smaller decrease. Continental and Eastern Europe experience the largest decrease in sulphate from 1985 to 2000; observations give 65 and 63% decrease, respectively, while modelled decreases are from 42 to 58% depending on the inventory. We have also studied to what extent our model results are sensitive and robust. Based on our model simulations we find that the EMEP emissions of the three sets of emission inventories are best to reproduce the trends in sulphate observations.

Response of sulphur dynamics in European catchments to decreasing sulphate deposition

Abstract. Following the decline in sulphur deposition in Europe, sulphate dynamics of catchments and the reversibility of anthropogenic acidification of soils and freshwaters became of major interest. Long-term trends in sulphate concentrations and fluxes in precipitation/throughfall and freshwaters of 20 European catchments were analysed to evaluate catchment response to decreasing sulphate deposition. Sulphate deposition in the catchments studied declined by 38-82% during the last decade. Sulphate concentrations in all freshwaters decreased significantly, but acidification reversal was clearly delayed in the German streams. In Scandinavian streams and Czech/Slovakian lakes sulphate concentrations responded quickly to decreased input. Sulphate fluxes in run-off showed no clear trend in Germany and Italy but decreased in Scandinavia, the Czech Republic and Slovakia. The decrease, however, was less than the decline in input fluxes. While long-term sulphate output fluxes from catchments were generally correlated to input fluxes, most catchments started a net release of sulphate during the early 1990s. Release of stored sulphate leads to a delay of acidification reversal and can be caused by four major processes. Desorption and excess mineralisation were regarded as the most important for the catchments investigated, while oxidation and weathering were of lesser importance for the long-term release of sulphate. Input from weathering has to be considered for the Italian catchments. Sulphate fluxes in German catchments, with deeply weathered soils and high soil storage capacity, responded more slowly to decreased deposition than catchments in Scandinavia and the Czech Republic/Slovakia, which have thin soils and relatively small sulphate storage. For predictions of acidification reversal, soil characteristics, sulphur pools and their dynamics have to be evaluated in future research. Keywords: acidification reversal, sulphur, sulphate release, Europe, catchments, deposition, lake, stream

CAN SITE-SPECIFIC TRENDS BE EXTRAPOLATED TO A REGION? AN ACIDIFICATION EXAMPLE FOR THE NORTHEAST

In the absence of true regional data on changes in the acid/base status of lakes in the northeastern United States, we explore the possibility of using site-specific trends information from a judgment sample of lakes to assess the efficacy of the Clean Air Act Amendments. A meta-analytical technique is used to combine trends results from 44 Long-Term Monitoring (LTM) lakes in the Northeast for the period 1982–1994, with the goal of producing estimates of overall trends in the region. The lakes are subdivided into subpopulations (High ANC, Intermediate Till Drainage, Thin Till Drainage and Perched Seepage lakes) on the basis of their expected response to changes in acidic deposition, and they appear to represent the most acid-sensitive of these lake classes well. While the overall tendencies in the trends are as expected (e.g., most of the recovery is observed in the most sensitive subpopulations), there is significant trend heterogeneity among the lakes within most of the subpopulations; this heterogeneity prohibits the summarizing of trends at the regional level (i.e., for all of the Northeast). This heterogeneity is explained by differences in the responses of lakes in two subregions (Adirondacks vs. New England), and we present trends results separately for each subpopulation within these two subregions. All subpopulations in both subregions showed decreasing trends in sulfate concentrations, probably a reflection of decreasing trends in sulfur deposition in the region. Few trends in nitrate concentrations were observed. Recovery (as evidenced by increasing trends in acid-neutralizing capacity) was evident in Thin Till and Intermediate Till Drainage lakes in New England, but not in the Adirondacks. Most groups of lakes exhibited downward trends in base cations (Σ[Ca2+ + Mg2+ + Na+ + K+]); the magnitudes of these trends were always greater in Adirondack lakes than in similar New England lakes. This suggests that the depletion of soil cation pools in the Adirondacks may be responsible for some of the differences in recovery between Adirondack and New England lakes. While export of base cations may be the key difference producing different trends results in the two subregions, the site-specific nature of the trends, and their possible lack of regional representation, should be considered in interpreting the overall results.

Seasonal and episodic trends in sulfate concentrations (1963-1978) in the eastern United States

Ambient air quality data available through 1978 for sulfates and sulfur dioxide have been analyzed for seasonal trends and episodic characteristics. Five sites around the eastern U.S. were monitored. Discussed are: the potential for artifact formation of sulfate/ results of seasonal trends in sulfate concentrations/ elevated sulfate concentrations and regional sulfate episodes/ and the contributions of primary sources of sulfates and secondary processes of sulfate formation. (12 graphs, 50 references)