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Aggregate Expenditures Schedule

A curve that traces out the relationship between expenditures--the sum of consumption, investment, government expenditures, and net exports--and the national income, at a fixed price level

Aggregate Supply Curve

A curve relating the total supply of the economy's goods and services at each price level, given the level of wages.

Agricultural drought

A period when the combination of deficient precipitation and/or excessive evapotranspiration results in inadequate water supplies for agricultural requirements. Typically defined as a period when soil moisture is inadequate to meet evapotranspirative demands so as to initiate and sustain crop growth. Could also include deficiencies of water for livestock or other farming needs.

Agricultural Pollution

Wastes, emissions, and discharges arising from farming activities. Causes include runoff and leaching of pesticides and fertilizers; pesticide drift and volatilization; erosion and dust from cultivation; and improper disposal of animal manure and carcasses. Some agricultural pollution is point source, e.g., large feedlots, which require permits under the Clean Water Act, but much is nonpoint source, meaning that it derives from dispersed origins, e.g., blowing dust or nutrients leaching from fields.

Agricultural zoning

A designation intended to protect farmland and farming activities from incompatible nonfarm uses. Agricultural zoning can specify many factors, such as the uses allowed, minimum farm size, the number of nonfarm dwellings allowed, or the size of a buffer separating farm and nonfarm properties.

Air carrier

An operator (e.g., airline) in the commercial system of air transportation consisting of aircraft that hold certificates of, Public Convenience and Necessity, issued by the Department of Transportation, to conduct scheduled or non-scheduled flights within the country or abroad.

Air mass

A large body of air having similar horizontal temperature and moisture characteristics.

Air pollutant

See air pollution.

Air pollution

One or more chemicals or substances in high enough concentrations in the air to harm humans, other animals, vegetation, or materials. Such chemicals or physical conditions (such as excess heat or noise) are called air pollutants.

Albedo

The fraction of the total solar radiation incident on a body that is reflected by it. Albedo can be expressed as either a percentage or a fraction of 1. Snow covered areas have a high albedo (up to about 0.9 or 90%) due to their white color, while vegetation has a low albedo (generally about 0.1 or 10%) due to the dark color and light absorbed for photosynthesis. Clouds have an intermediate albedo and are the most important contributor to the Earth's albedo. The Earth's aggregate albedo is approximately 0.3. See radiation, radiative forcing, photosynthesis.

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