Acid Deposition Atmospheric Processes in Eastern North America (1983) / Chapter Skim
Currently Skimming:
1. Introduction
1. Introduction
Pages 12-28
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 12... ...
In this report we use the term acid deposition to encompass both wet and dry processes. DEPOSITION ACIDITY An acid is a chemical substance that, in water, provides an excess of hydrogen ions (H+)
|
From page 13... ...
There are no known natural causes that can account for either the distribution or the value of acidity in eastern North America. The region of highest acidity does, however, correspond to the regions of heavy industrialization and urbanization along the Ohio River Valley and the Eastern Seaboard, where anthropogenic emissions of sulfur dioxide (Figure 1.2)
|
From page 14... ...
SOURCE: U.S./Canada Work Group #2 (1982~. difficulties associated with comparing data obtained by means of different experimental methods of uncertain comparability at different sites at different times and because of difficulties in taking into account the influence of neutralizing substances on the data (Hanson and Hidy 1982, Stensland and Semonin 1982)
|
From page 15... ...
Pollution control equipment installed during this period also changed the chemical and physical characteristics of the emissions, substantially reducing direct emissions of sulfates and neutralizing substances in fly ash. Thus, while total emissions of SO2 in the United States increased between 1960 and 1970, urban concentrations of SO2 decreased (Altshuller 1980)
|
From page 16... ...
ENVIRONMENTAL EFFECTS Atmospheric deposition involves three components: emissions, deposition, and effects on receptors. Certain aspects of the effects of atmospheric deposition are of particular importance for the development of effective policies for emission control.
|
From page 17... ...
Secondary receptors are subject to wet and dry deposition indirectly and only after the pollutants have been in contact with other materials. Examples include the inner foliage of vegetative canopies, soil underneath vegetation, and subsurface layers of exposed soils.
|
From page 18... ...
Physical and Chemical States of Deposited Materials The effects of atmospheric deposition on primary receptors depend on the physical state (solid, liquid, or gaseous) and the chemical state (e.g., sulfur or nitrogen species)
|
From page 19... ...
Thus heavy rainfall exceeding surface evaporation -- even with low acid content -- can mobilize ions over time. This mobilization from the soil may be enhanced when acid-forming materials also are deposited from the atmosphere and washed away.
|
From page 20... ...
Effects are likely to be site-specific and dependent on the relative contributions of external and internal sources of acidity. Major factors determining effects of atmospheric pollutants on lakes and streams are (1)
|
From page 21... ...
Perhaps only in retrospect will we know with certainty that systems have changed, and the reversibility of these effects by natural processes might require far more time than the period initially required to cause the changes due to anthropogenic acidification. OTHER RELATED REGIONAL AIR POLLUTION PHENOMENA In addition to the atmospheric processes affecting acid deposition, there are other regional air pollution
|
From page 22... ...
The events are believed to be associated with increased concentrations of precursor gases, such as nitrogen oxides and hydrocarbons, that undergo reactions to form oxidants under conditions of largerscale atmospheric stagnation.
|
From page 23... ...
found an apparent association in the historical record of changes in visibility with changes in the combustion of fossil fuels. There seems little doubt that sulfate aerosols and other fine particles play a significant role in regional haze (NRC 1980)
|
From page 24... ...
Nevertheless, our goal required that we take account of both the theoretical understanding and observational evidence that are available today and make our best scientific judgment about their meaning. If national policy on acid deposition is to be made on the basis of the scientific information currently available, that policy could take several forms, including Other policies might incor in emissions, might be designed to achieve the maximum possible environmental benefit, or might be carefully engineered to bring risks, costs, and benefits into optimal balance.
|
From page 25... ...
ORGANI ZATION OF THE REPORT This report describes the state of knowledge as of the end of 1982 regarding the atmospheric processes relating emissions of precursor gases and acid deposition. It does not include a detailed examination of the effects of acidic or acidifying substances on ecosystems once deposited.
|
From page 26... ...
1980. Acid precipitation, plant nutrients and forest growth.
|
From page 27... ...
1981. The relative contribution of sulfuric and nitric acids in acid rain to the acidification of the ecosystem: implications for control strategies.
|
From page 28... ...
Pp. 88-99 in Proceedings of the Symposium on Effects of Air Pollutants on Mediterranean and Temperate Forest Ecosystems.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.