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Acid Deposition Long-Term Trends (1986) / Chapter Skim
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5. Precipitation Chemistry
Pages 128-199

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From page 128...
... Whelpdale, and Gary Oehlert INTRODUCTION The Role of Precipitation Composition in This Study The chemical composition of wet deposition has been central to the question of the effects of acid deposition and the long-range transport of air pollution since the issue of "acid rain" rose to prominence in Europe two decades ago. Early evidence linked acidic substances in precipitation to harmful effects on surface waters and fisheries in Scandinavia, and as a consequence interest has since focused on precipitation acidity and acid deposition rather than on the more general case of deposition of air pollutants.
From page 129...
... Even historical air-concentration data, from which dry deposition might have been estimated, are sparse and incomplete. Out of necessity, therefore, we focus on wet deposition data.
From page 130...
... in the United TABLE 5.1 Median Ion Concentrations for 1979 for Three NADP Sites (~eq/L) GA MN NY Ion (42 Samples)
From page 131...
... have concluded, by applying multiple linear-regression analysis for a central Pennsylvania site, that on the average, sulfuric acid is the principal contributor to hydrogen-ion concentration in rain, but the acidity in snow is principally from nitric acid. Variability in Acid Deposition: The Role of Meteorology Any discussion of short- and long-term trends in acid deposition cannot ignore the role of meteorological and climatological variability.
From page 132...
... However, since local sources can affect bulk data through high levels of dry deposition, the only
From page 133...
... Several different evaluations are described in this chapter, with emphasis on evaluating those United States data sets quoted most frequently in trend studies. Comparing Three-Month Regional Bulk Data Concurrently with Wet-Only Data Most of the published comparisons between bulk and wet-only ion concentrations are for eastern sites.
From page 134...
... used for comparing concentrations of various ions in wet-only deposition with those in bulk samples. The arabic numbers indicate the number of bulk sampling sites within each area.
From page 135...
... C Since there were no NADP sites in area V, computer-generated contour maps (for weighted-average concentration) for all data available for the period 1978 - mid-1983 were used to estimate average NADP ion concentrations for this area.
From page 136...
... typical problem with bulk data, concentration effects owing to sample evaporation, was probably not a major factor given the close agreement of bulk ion concentrations with the wet-only concentrations. This finding suggests that the funnel and bottle design of the Hubbard Brook bulk sampler effectively prevented this problem for long-term averages at this site.
From page 137...
... and pH for All New York NADP Sites and for Two New York USGS Bulk Sites Time-Adjusted Weighted Average Weighted Average Mean and Standard Deviation for Mays Mays Ion Seven NADP Sitesa Hinckleyb Points Hinckley Point Ne 23 24 23 24 Ca2+ 8.4 + 2.0 30.2 74.2 26.3 71.6 Mg2+ 3.5 + 0.8 7.7 17.1 6.7 16.5 K+ 0.8 + 0.6 2.1 2.9 1.8 2.8 Na+ 6.2 + 3.5 5.4 10.4 4.7 10.0 NH4+ 16.5 + 5.5 31.2 22.7 37.3 27.5 Sumf 35.4 76.6 127.3 76.8 128.4 NO3 30.2 + 5.4 41.7 46.5 62.1 54.7 SO2- 64.8 + 13.4 72.5 82.2 65.9 76.4 C1- 5.8 + 3.3 8.9 15.2 8.9 15.2 pH 4.22 (4.15-4.33) g 3.99 3.99 3.90 3.86 H+ 60.4 + 10.3 102.3h 102.3h 126.4h 138.3h aVolume-weighted concentrations for 1978-1982.
From page 138...
... The table also presents weighted-average concentrations of data from Hinckley and May s Point, two of the USGS bulk sampling sites in New York; later in this chapter these two sites are listed with three others for consideration of regional time-trend analysis. The Hinckley and May s Point sites were chosen for inclusion in Table 5.4 because these sites tend to represent the extremes in concentrations found at the USGS stations, with the Hinckley site tending to have the lower concentrations and the May s Point site the higher concentrations (Barnes et al.
From page 139...
... Therefore, we suggest that the environment may be less pristine at the Ithaca NADP site than at the MAP3S site, resulting in higher ion concentrations in samples at the former. Despite this, the pH values for the NADP and MAP3S sites are essentially the same for this 32-month period, indicating that pH comparisons should be done in conjunction with comparisons of the other major ions.
From page 140...
... TABLE 5.6 Median Concentrations (mg/L) in Precipitation for Two Sites Near State College, Pennsylvania NADP NADP .
From page 141...
... Thus one may have reasonable confidence in applying the bulk data for trend analysis at this site. The sampling procedure at Hubbard Brook eliminated the evaporation problem, and evidently siting has minimized dry deposition effects, probably because of the long distance of this site from major sources of SOX emissions.
From page 142...
... Figures 5.2 to 5.6 show the annual precipitation amount weighted averages for hydrogen-ion concentration, pH, and concentrations of sulfate, nitrate, and ammonium. Figures 5.2 and 5.3 show hydrogen-ion concentrations up to 60-80 umol/L (pH 4.2-4.1)
From page 143...
... Wet deposition of hydrogen ion reaches 80 mmol/m2, sulfate and nitrate 40 mmol/m2, and ammonium 30 mmol/m2 in the eastern portion of the continent. Barrie and Hales (1984)
From page 144...
... , _ OH I | ^~ ___ f r — — — — — —— — \~25 `` ~ l__l______ .'_ ~ ~ ~ 2 I All ; · 09 ~ I I `` r-' ~~ ~~ ~~ C-___ em ~ I r - - - ~N '; i I V-_. I I \ ~ ~ '_/ '~;~' \ ~ —_ 'it 20 FIGURE 5.2 Spatial distribution of the precipitationamount-weighted annual mean hydrogen-ion concentration (micromoles per liter)
From page 145...
... A.... , ~ ~~,s~ W.,,',<;./' ~ FIGURE 5.3 Spatial distribution of the precipitationamount-weighted annual mean hydrogen-ion concentration (expressed as pH)
From page 146...
... , 2 0 ~_~3\ \,(' <0~, '1 6. FIGURE 5.4 Spatial distribution of the precipitationamount-weighted annual mean sulfate-ion concentration (micromoles per liter)
From page 147...
... ~ ~ i_. , ~ .; , ~ ~ ~~ ,-<; ~ dI>10\ 'arks .x ~ ~ -' FIGURE 5.5 Spatial distribution of the precipitationamount-weighted annual mean nitrate-ion concentration (micromoles per liter)
From page 148...
... 148 / / ~^ ' l V~ . ~ -- ~2~ ;063 9 ~ Nos ·7020~¢ O I -- I - , , ; ~ ma 94; 1 it's 1'-'~;-;-_ ~ ~/~ ~ .~, FIGURE 5.6 Spatial distribution of the precipitationamount-weighted annual mean ammonium-ion concentration (micromoles per liter)
From page 149...
... 149 .,i A, , . 1 , , `, - .~L /~ With FIGURE 5.7 Precipitation amount in 1980 expressed as a percentage of the long-term mean amount of precipitation in North America.
From page 150...
... 05 .~. ~ two FIGURE 5.8 Spatial distribution of annual wet deposition of hydrogen ions (millimoles per square meter)
From page 151...
... _i, _.;___. aim\ \ 25 ,,""- ~10~/ ~_20 :;17 .~ 23~ ~~ ~2 · 1 ~ ~ ~ - 24 ' ~ FIGURE 5.9 Spatial distribution of annual wet deposition of sulfate ion (millimoles per square meter)
From page 152...
... , ~_' ·~9 '',( 19 ~ . ~ ~1\ ~ ~ '~ FIGURE 5.10 Spatial distribution of annual wet deposition of nitrate ion (millimoles per square meter)
From page 153...
... _.-~ -- '' '` ~ ' 5 1~-~1o '',,,~8.8~~, ~ \^ '%.] ~ 68 FIGURE 5.11 Spatial distribution of annual wet deposition of ammonium ion (millimoles per square meter)
From page 154...
... 154 TABLE 5.8 Annual Mean Precipitation Amount (P) and Concentration of Major Ions (~eq/L)
From page 155...
... ; Ithaca, New York (IT) ; State College, Pennsylvania (PS)
From page 156...
... Numbers signify the ratio of sulfate concentration in precipitation in eastern North America to sulfate concentration in precipitation in remote areas of the world. SOURCE: Galloway et al.
From page 157...
... analyzed NADP data for seasonal variations in sulfate, nitrate, and hydrogen-ion concentrations. The sampling sites were grouped into five regions in the eastern United States, each containing from two to seven sites.
From page 158...
... Figure 5.12 shows that hydrogen-ion concentrations at remote locations are significantly lower than those in eastern North America and that remote sulfate and nitrate concentrations are consistently lower by more than a factor of 5. To illustrate the enrichment of North American concentrations of sulfate over global background, Figure 5.13 (Galloway et al.
From page 159...
... (See the section below on trends for Hubbard Brook and USGS bulk data.) Figure 5.14 summarizes the types of information available on which an evaluation of trends must be made.
From page 160...
... FIGURE 5.14 Summary of available precipitation chemistry data bases. by the Public Health Service/National Center for Atmospheric Research (PHS/NCAR)
From page 161...
... (1984) , shows sulfate concentrations in New York and Connecticut derived from bulk samples for the period 1910 to 1954.
From page 162...
... in bulk precipitation samples for locations in the northeastern United States. The width of the bar designates the period of sampling.
From page 163...
... The major points of concern about using these data for trend analysis involve (1) the amount of uncertainty and bias introduced by differences in sampling, analytical, and calculational methods and (2)
From page 164...
... and the 1970s (WMO/NOAA/EPA) show generally higher ion concentrations than do current NADP data.
From page 165...
... . The computergenerated contours are for the NADP wet deposition data for 1978-1981 for sites with at least 20 valid samples.
From page 166...
... . The computergenerated contours are for the NADP wet deposition data for 1978-1981 for sites with at least 20 valid samples.
From page 167...
... from NADP sulfate concentrations. Trends for Hubbard Brook and USGS Bulk Data The Hubbard Brook Data In this section we describe a trend analysis undertaken on the Hubbard Brook weekly bulk-precipitation chemistry data (Oehlert 1984a)
From page 168...
... . The statistical methods for the trend analysis are those described in Oehlert (1984b)
From page 170...
... could result, for example, from a decrease in the input of calcium sulfate, either as dry deposition (sulfur dioxide plus calcium on the funnel surface) or as wet deposition (calcium sulfate in precipitation)
From page 171...
... A summary of the trends since 1964 follows: Hydrogen ion: Record is variable with no significant trend; slight tendency to lower concentrations for parts of the period. Sulfate: Significant decrease of approximately 2~/yr superimposed upon periods of drift; decrease in winter and spring is greater than for summer and fall.
From page 175...
... No large step changes of the type illustrated in Figure 5.20 are evident in the monthly data for sulfate concentration in precipitation at Hubbard Brook. Qualitatively, the Hubbard Brook sulfate data show short-term increases and decreases superimposed upon a linear decrease from 1964 through 1980.
From page 176...
... 176 \,: L il 1 1 1 o o o HV3A ~ ~d OS J0 SN01 _ oo _ oo O ~ ~ -C~ cs)
From page 177...
... Thus, allowing for some regional linear trend, any effect of the shape of the paper mill emissions curve is statistically estimated to be significantly negative. From this nonphysical result we conclude that the trend present in the Hubbard Brook sulfate data is essentially uninfluenced by the paper mill emissions.
From page 178...
... (1982) analyzed the USGS data for time trends at all nine sites with monthly bulk data since 1965.
From page 179...
... . The data in Table 5.12 suggest that quantitative time-trend results from the USGS bulk data are subject to imprecision.
From page 180...
... Median sulfate concentrations showed an overall downward trend, while median nitrate concentrations increased in the 1960s and fluctuated thereafter. Median ammonium concentrations appear to have increased after 1975, and median pH showed a weak downward trend.
From page 181...
... The fact that the trends are similar to that at Hubbard Brook gives some confidence to proposing a regional trend in precipitation sulfate concentration. The World Meteorological Organization/ Background Air Pollution Monitoring Network Data In the early 1970s the United States and Canada established, respectively, ten and eight stations as part of the WMO Background Air Pollution Monitoring Network (BAPMoN)
From page 182...
... WATER YEAR BEGINNING · ~ · +. · ~ FIGURE 5.21 Box plots for precipitation chemistry at the Hinckley, New York, USGS site.
From page 184...
... The 1979-1982 CANSAP-APN and NADP Data As the importance of deposition monitoring became evident, several longer-term networks began operating in the late 1970s (Figure 5.14)
From page 185...
... ,,>7; ~ ~ | ~~~ ~) .it'' ~''.-.~4,1`,,,' /, , fee_ _ ' ,, _ ,7: ~ ~ ~ - W— so ~~ H + · 'a FIGURE 5.22 Comparison of the annual precipitationweighted-mean concentrations of sulfate, hydrogen, nitrate, calcium, and precipitation amount (designated P in top panels in (a)
From page 187...
... , and 5.22(c) show these features for the ions sulfate, nitrate, hydrogen, and calcium during the years 1980, 1981, and 1982, respectively; precipitation amount (P)
From page 188...
... NH 02 \ 1 1 ~ :] t: FIGURE 5.23 Locations of twelve NADP sites referred to in Figures 5.24 and 5.25.
From page 189...
... The median annual concentrations for major ions and combinations of ions are shown in Figure 5.24 for three of the sites (ILll, NY20, and NC41) , and volume-weighted
From page 191...
... a z 0 00 S~ o C~ o ~, a o 00 ~r UJ 0O o ~ oo z LLJ J C~ 00 o 00 a' S .~1 3 a)
From page 192...
... For site ILll the anions and hydrogen ion have similar median and weighted concentration patterns, although hydrogen ion is lowest in 1979 for the weighted concentration and in 1982 for the median concentration. For ammonium and the base cation sum (the sum of calcium, magnesium, potassium, sodium, and ammonium)
From page 193...
... · Spatial distributions of annual (precipitationweighted-mean) concentrations and wet deposition for the major ionic species in precipitation are adequately known on the regional to continental scale in North America to afford comparison with spatial patterns of emissions and other possible indicators of acid deposition, such as visibility and the quality of surface waters.
From page 194...
... . On the basis of preliminary analyses of CANSAPAPN and NADP data for the eastern half of the continent, changes in anthropogenic emissions during the period 1979-1982 are not readily apparent; concentration changes from year to year occur concurrently in both anthropogenic and natural constituents and are thought to be more strongly affected by meteorological rather than emissions changes during this period.
From page 195...
... Discourage bulk sampling except in specific circumstances in which it can be demonstrated that bulk and wet-only samples are providing comparable data. · Use other major ionic species (in addition to hydrogen and sulfate)
From page 196...
... 1984. The spatial distributions of precipitation acidity and major ion wet deposition in North America during 1980.
From page 197...
... 1984. Long-term trends in precipitation chemistry at Hubbard Brook, New Hampshire.
From page 198...
... 1984a. A statistical analysis of the trends in the Hubbard Brook bulk precipitation chemistry data base.
From page 199...
... 1982. An overview of acid rain monitoring activities in North America.


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