Acid Deposition Long-Term Trends (1986) / Chapter Skim
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4. Patterns and Trends in Data for Atmospheric Sulfates and Visibility
4. Patterns and Trends in Data for Atmospheric Sulfates and Visibility
Pages 109-127
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From page 109... ...
In the eastern United States, sulfate particles are also the dominant contributors to visibility reduction (light extinction or light attenuation)
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From page 110... ...
DESCRIPTION OF DATA BASES Three types of nationwide data are examined in this chapter: visibility observations at a large number of airports, turbidity measurements at a few monitoring stations, and sulfate aerosol measurements at a few nonurban Environmental Protection Agency (EPA) sites.
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From page 111... ...
Because the results of these analyses are compared in Chapter 1 with other measures of overall acid deposition patterns in eastern North America, the data bases cited here pertain, whenever possible, to rural locations (as defined in World Aeronautical Charts, 1976)
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From page 112... ...
suggests that shifts in relative humidity and to some extent in temperature over the past 30 years may have affected visibility trends in the eastern United States substantially. Husar and co-workers, in providing the visibility data examined in this chapter, sought to minimize the influence of humidity by eliminating observations with fog or precipitation and normalizing for relative humidity.
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113 7~: it Q ~ ~ Go O — ~ .
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In this section, we shall look at the historical trends in that data base that were analyzed for 35 rural sites in the eastern United States, supplemented by visibility, turbidity, and sulfate data from a few other eastern locations. Figure 4.4(a)
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From page 116... ...
Figure 4.5 indicates that light-extinction levels decreased from the early 1940s to the early 1950s, then after a short level period increased from the late 1950s to about 1970, and finally fluctuated without any apparent trend between 1970 and the early 1980s. The overall increase in extinction from 1950 to the early 1980s is highly significant (t = 6.1)
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From page 117... ...
. than the percentage increase in light extinction.
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From page 119... ...
119 o ._ ~ ' ~ / jo ~ t I 1 ~ I m U]
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From page 120... ...
. Visibility data from the 35 airports were subdivided into the four regions of the eastern United States defined in Chapter 1 (Regions B
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Oct.-Dec. FIGURE 4.9 The seasonal patterns of fine-sulfate mass per unit volume, total fine-particle mass per unit volume, and light extinction for rural areas of the eastern United States.
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From page 124... ...
Another useful measure is the rich historical data base for atmospheric visibility, since sulfate particles are a major contributing factor to reduced visibility in the eastern United States. Although the atmospheric data bases for sulfates and visibility involve significant uncertainties, they can provide productive comparisons with data bases for emissions, precipitation, water quality, and other effects.
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From page 125... ...
1983. Comparison of visibility measurement techniques: eastern United States.
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From page 126... ...
1980. Ambient sulfate measurements on Allegheny Mountains and the question of atmospheric sulfate in the northeastern united States.
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From page 127... ...
1982. Source regions of summertime ozone and haze episodes in the eastern United States.
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