Acid Deposition Atmospheric Processes in Eastern North America (1983) / Chapter Skim
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4. Empirical Observations and Source-Receptor Relationships
4. Empirical Observations and Source-Receptor Relationships
Pages 87-147
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From page 87... ...
Even so, sampling of ambient pollutants in the atmosphere and sampling of those in precipitation generally have not been simultaneous. There are no direct measurements of regional dry deposition for gases or particles.
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From page 88... ...
One of the greatest difficulties in establishing relationships between sources of pollution and conditions at receptors is accounting for the influences of atmospheric processes on the behavior of pollutants. The atmospheric processes involved include airflow, mixing, and chemical transformations.
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From page 89... ...
Since there are no direct measurements of dry deposition, regional patterns are estimated from ambient concentrations and deposition velocities (Appendix C)
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From page 90... ...
On a regional scale, the distribution of SO2 shows strong gradients near sources, but airborne sulfate shows relatively weak gradients. Concentrations of both SO2 and SOi are elevated over the industrialized or urbanized parts of the eastern United States (Figures 4.1 and 4.2)
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From page 91... ...
91 c~ o ;^ c c 04 ~: en c~ ct o .
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From page 92... ...
Dashed isopleth is based on limited quantities of SURE data for 1977-1978 and on data taken at Whiteface Mountain, New York, after 1978. Numbers in parentheses are calculated values of dry deposition rates in kilograms of sulfur per hectare per year assuming a uniform deposition velocity of 0.8 cm/s.
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From page 93... ...
This average is approximately equivalent to an annual average. Numbers in parentheses are calculated values of dry-deposition rates in kilograms of sulfur per hectare per year assuming a uniform deposition velocity of 0.2 cm/s.
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From page 94... ...
This result suggests that dry deposition of SO2 exceeds wet deposition in parts of the Ohio River Valley and the Ohio-Pennyslvania-western New York area but becomes progressively less important farther from the region of major emissions, to the northeast in New England and Canada. At large distances from sources, ambient concentrations of sulfur oxides are low; wet deposition will dominate dry deposition far from sources if precipitation is significant.
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From page 95... ...
The temporal behavior of sulfur oxides and nitrogen oxides is dominated by meteorological variability. For example, analysis of the SURE data indicates that the variability in ambient concentrations of SO2 was as much as an order of magnitude greater than the variability in SO2 emissions over the eastern United States (Mueller and Hidy 1983)
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From page 96... ...
_ _ _ + _ _ ~ 0 .4 I ~,) ,' t~o.5 ; $~ i\ 1 m mole/m2 ~ 0.01 kg/ha = 1 FIGURE 4.5 Spatial distribution of mean annual wet deposition of hydrogen ion weighted by the amount of precipitation in North America in 1980 (mmoles/m2 )
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From page 97... ...
. The slow-moving flow of southwesterly maritime air from the southern states entrains pollutants from sources in its path and eventually moves over the northeastern United States and eastern Canada.
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From page 98... ...
\ Cold air `~{ / I' ~< C~ Preci p. ~ l h , '\ i I, ~ , Warm air ,, a, ,' ~ Warm air ~7W Cold air _~: ~_ _ FIGURE 4.6 Idealized depiction of air masses and precipitation typically associated with warm fronts and low-pressure systems during autumn, winter, and spring in eastern North America.
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From page 99... ...
Air-mass stagnation under the high pressure area is referred to as cP2 conditions, while cPw refers to warm airflow from south to north on the west side of the anticyclone. Recent studies of fluctuations in SO2 and sulfate concentrations along with other evidence indicate that sulfate aerosol advec ted from distant origins makes a large contribution to the particulates in the New York City area only during the summer (Lioy and Morandi 1982, Tanner and Leaderer 1982)
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From page 100... ...
-of ~ -o-o 100 Y: _- ~ ~ ~ -- I if_17 1: - ~ 1 1 , ~ hi, , ~'10~ ~, , , i 1 1 of .
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From page 101... ...
101 C c o o ~ ~, ~ C ~ ~ 2 - ° ~ " ~ ~ IL IL a x E ~ o ° C C, ,' ~ o C ~ ~ C + a: u~ o o 8 - ° CD ~ ~ (ww)
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From page 102... ...
Another indication of the relative importance of meteorological processes in determining wet deposition can be found in European data. In eastern North America, the warmer months tend to be the period of greatest precipitation as well as of most rapid photochemistry.
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From page 103... ...
also point out that 56 percent of the total annual precipitation at Whiteface Mountain is carried by those air parcels and that the wet deposition of acid may be related more to this fact than to the higher concentrations in the precipitation originating upwind to the south and southwest. They also point out that the geographical gradient of acid deposition (normalized to the amount of rainfall)
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From page 104... ...
, which place most of the Adirondacks, a receptor region, in the same isopleth area as the Ohio River Valley, a source region. A similar trajectory study at Ithaca, New York (Henderson and Weingartner 1982)
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From page 105... ...
, which tends to neutralize sulfuric acid; and (4) nitric acid, derived from NOX emissions that are partially due to vehicular traffic (about 44 percent of NOk emissions nationwide)
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From page 107... ...
sulfate ion concentration, and (d) nitrate ion concentration in precipitation as a function of the directional sector through which the air parcel passed to reach Whiteface Mountain, New York, in 1978.
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From page 108... ...
The evidence of the air-parcel trajectory studies at specific receptor sites in remote areas of the northeastern United States suggests that the industrialized region to the southwest is a major source of both nitric and sulfuric acids deposited at the sites. However, the high percentage of acid deposition in the Northeast associated with air parcels coming from the southwestern sector may be a result of the high percentage of total precipitation that is delivered by these parcels.
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From page 109... ...
Two such methods are regression on principal components, which eliminates problems with collinearity in explanatory variables, and empirical orthogonal function analysis (principalcomponent analysis) in which intersite covariations between end-product variables are examined.
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From page 110... ...
Evidently, variations in ambient SO2 levels in themselves have only a weak influence on variations in airborne sulfate concentrations in these cities, compared with the influences of variations in atmospheric processes or meteorological conditions. Rural data from the northeastern United States have Iso bean examined Gina these techniques (Henry et al.
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From page 111... ...
. This technique derives eigenvectors from the estimated covariances of sulfate concentrations between pairs of stations.
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From page 113... ...
In summer, for example, the pattern of the first empirical orthogonal function was identified with large-scale meteorological conditions leading to persistent mass transport of air around zones of high barometric pressure northeastward across the Ohio River Valley toward New England. These conditions were identified as being most likely for long-range pollution transport (Mueller and Hidy 1983)
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From page 114... ...
Rahn, University of Rhode Island, in an unpublished paper, 1982) that the elemental composition of particulate matter in aerosols might also be indicative of the origins of the aerosols after regional-scale transport and might help to resolve the question of the relative contributions of distant and local sources to acid deposition in eastern North America.
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From page 115... ...
The first problem arises because of the potential that the elements of interest as tracers may not be transported at the same rates and over the same distances as sulfates and nitrates, which are of primary concern in acid deposition. For example, manganese and vanadium have been proposed as characteristic tracers of emissions from Midwestern and eastern source regions, respectively.
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From page 116... ...
It seems likely that arrays of elements, rather than a single one, will have to be used as tracers of pollution of Midwestern origin. ANALYSIS OF HISTORICAL TRENDS In this and the next section we analyze the relationships between emissions and wet deposition using data obtained from monitoring networks.
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From page 117... ...
. The monitoring of precipitation chemistry at the Hubbard Brook Experimental Forest appears to provide the longest continuous record of deposition data at a receptor site in the northeastern United States.
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From page 118... ...
118 on o 1 ~ o In-'..
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From page 119... ...
A linear-regression analysis of the Hubbard Brook data against time indicates a decline in sulfate concentrations between 1965-1966 and 1979-1980 of about 33 + 18 percent (95 percent confidence limits)
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From page 120... ...
~ .' NO3 r -- ~ -- ~_, ~.~' 'it, ,,^~ A 90 85 80 ~/ 75 \/\ 65 60 _ 0 WA~> . / - ~ l 4.25 _ 4.20 _ I 4.15 _~ Q 4.10 _ 4.05 _ 4 00 _ ,,' 1 1 1 1 1 1 1 1 1 .1 1 1 1 _1 1969 1971 1973 Year 1975 1 977 1979 1981 FIGURE 4.14 Annual weighted concentrations of sulfate, nitrate, ammonium, and hydrogen ions and weighted pH of precipitation at Hubbard Brook Experimental Forest from 1964 to 1977.
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From page 121... ...
. The USGS network employed bulk samplers; single samples were collected on a monthly basis.
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From page 122... ...
122 21 20 19 18 17 16 10 9 7 _ 6 5 4 3 o 1960 1965 1970 so2 Regions IV la Year 1975 1978 aExcludes emissions from Vermont, which in 1980 amounted to about 7,500 tonnes of SO2 and 12,000 tonnes of NOX.
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From page 123... ...
. ~~ Regions la v __ IV _ __ I l I J 1960 1965 1970 1975 1978 Year FIGURE 4.15 Annual emission of SO2 and NOX in the eastern United States by EPA Region, 1960-1978 (million metric tonnes)
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From page 124... ...
124 ._ ._ Cal Cq ._ U
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From page 125... ...
- Q ~ x ~1 ~ ~ oo O ~t ~ `0 ~ O ~ ~ ~ _ ~ ~ O ~ 1- ~ ~ - ~1 u~ ~ oo tr)
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From page 126... ...
Both the USGS and New York State data are therefore of limited usefulness for assessing relationships between emissions and deposition influenced by long-range transport to rural areas. The most reliable data available in a continuous record are those from Hubbard Brook.
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From page 127... ...
, when the influence of gasphase chemistry is expected to be greatest. The annual average of the molar ratio of sulfate to nitrate in precipitation is relatively constant throughout the area of the northeastern United States and eastern Canada in regions in which the pH precipitation is low but increases in extreme northern Canada (Figure 4.17)
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From page 128... ...
and along coastal areas, possibly because of sea-salt sulfate. A lower ratio occurs near the Great Lakes, a region with a relatively low ratio of SO2 to NOx emissions.
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From page 129... ...
The deposition ratios, however, are relatively invariable with respect to distance from major source regions, particularly during the warm season (1.4
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From page 130... ...
SOURCE: B Heikes, National Center for Atmospheric Research, personal communication (1983)
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From page 131... ...
Hi' r / If 1 ~8 0.74 ~ I ~ _ 4) ~~0.49 -- in 1 05 1,'-87 ~-5' ~ ~ - 0.81 ~ 0.34 /J: ~ ~ ~ 0.92 rat -~ 0~72 ~ 1.24 <~1.21 if o A___ __ ^7 1 1.64 1 __-~ ~ _ FIGURE 4.18 Average molar ratio of sulfur to nitrogen oxides in emissions in eastern North America in 1980.
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From page 132... ...
. It is surprising to note in addition that the annually averaged molar ratios in precipitation at the MAP3S, NADP, and CANSAP sites in eastern North America resemble the molar ratios of SO2 to NOx emissions averaged on an annual basis by state or province (Figure 4.18)
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From page 133... ...
However, the general similarity of wetdeposition and emission ratios on an annual average basis suggests that the incorporation of sulfuric acid in rain is not retarded with respect to the conversion and incorporation of nitric acid in rain. A small body of data suggests that the historical trends in the molar deposition ratios of sulfate to nitrate correspond to the trend in molar SO KNOX emission ratios.
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From page 134... ...
\\ -j'' -~ ~ 1975 1 980 Year FIGURE 4.19 Molar ratio of SO2 to NOX in emissions in the eastern United States by EPA Region and molar ratio of sulfate to nitrate in deposition at Hubbard Brook, New Hampshire, 1960-1978. SOURCE: Adapted from Tables 4.4 and 4.5.
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From page 135... ...
The second conclusion, however, suggests that the oxidative capacity is not saturated in the northeast. Furthermore, the similarity of deposition ratios in eastern Canada both to those in the eastern United States and to emission ratios upwind also tend to support this implication.
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From page 136... ...
were changed by changing SO2 emissions while keeping NOx emissions constant, that change should be reflected in a similar change in the ratio of sulfate to nitrate in wet deposition, all other emissions and conditions remaining unchanged. If dry deposition is linearly proportional to emissions, as suggested in the section on principal-component analysis, then the annual average ratio in bulk deposition in the area should also respond to changes in the emission ratio.
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From page 137... ...
Conceivably the uniformity of the annual SO ANON ratio in precipitation in the northeastern United States could reflect some as yet unidentified stoichiometric linkage between the atmospheric chemistry of SO2 and NO2. For example, the reaction of HOSO2 radicals formed in reactions of HO with SO2 could lead to HOSO2O2 and HOSO2O radicals, which could ultimately react preferentially with NC2 to form a one-to-one, S to N compound such as HOST ONO2 (see Chapter 3 and Appendix A)
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From page 138... ...
Comparison of emission ratios and deposition ratios constitutes indirect evidence for the absence of a serious nonlinearity even though we lack an adequate understanding of the intermediate chemical and meteorological processes to predict, either qualitatively or quantitatively, the deposition ratios from the emission ratios. It is our opinion that the necessary data and theoretical understanding to model the effects of emissions from distant sources on the composition of precipitation reliably and accurately will not be available in the near future.
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From page 139... ...
Indirect evidence based on patterns of the ratio of SO4 to Ned in annual deposition do not support the hypothesis of a strongly nonlinear relationship between SO2 emissions and sulfate deposition in eastern North America. Differences in the relationship between emissions and deposition in Europe and eastern North America may be the consequence of differences in meteorology, latitude, or other factors, such as the spatial distribution of sources, between the two regions.
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From page 140... ...
The spatial distribution of the annual average molar ratios of pollutants in emissions and deposition suggest that atmospheric processes in eastern North America lead to a thorough mixing of pollutants over a wide geographic area, making it difficult to distinguish between the effects of distant and local sources. On the basis of currently available empirical data, we cannot in general determine the relative importance for the net deposition of acids in specific locations of long-range transport from distant sources or more direct influences of local sources.
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From page 141... ...
on ambient sulfate concentrations in general, with occasional long-range influence during ducting situations involving southwesterly flows of air. Similarly, warm frontal precipitation may involve cloud formation in air parcels adverted for hundreds of kilometers from a southwesterly direction.
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From page 142... ...
1981. Air particulate control strategy development: a new approach using chemical mass balance methods.
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From page 143... ...
1980. Assessing sources, dispersion, chemical transformation and deposition of atmospheric sulfur over eastern North America by advanced Multivariate data analysis.
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From page 144... ...
. Identification of atmospheric particulate sources in Washington, D.C., using chemical element balances.
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From page 145... ...
1982a. Variation in chemical wet deposition with meteorological conditions.
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From page 146... ...
1981. State Water Survey Division, Atmospheric Chemistry Section at the University of Illinois, SWS Contract Report, Vol.
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From page 147... ...
1981. On the sources of summertime haze in the eastern United States.
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