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  • Glossary
| Last Updated:28/11/2023



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Growing, living in, or frequenting waters.

Appropriate Technology

It depends on the assessment of the society in which the technology is used based on the following criteria affordability benefits in relation to cost and whether it can be implemented on fully used

Air Quality Standards

Levels of atmospheric contamination by specific pollutants or under laws or ordinances enforced by municipal or state government or regional agencies.

Age Class

Is a group of animals in a population with approximately the same age (i.e., fawn, yearling, adult).aerobic

Animal Community

Animals of various species living within a certain habitat, each occupying a specific position in that particular environment; directly parallel to plant communities.

Aeration Tank

An aeration tank is a place where a liquid is held in order to increase the amount of air within it. The most common uses of aeration tanks are in wastewater recovery, as the high oxygen levels will increase the speed at which the water is cleaned. There are two main methods of aerating liquid: forcing air through the liquid or forcing liquid through the air.

Arterial Street

It is a street primary meant for through traffic on a continuous route


An index of the reflecting power of a surface. It is usually used of short-wave radiation. Light-coloured surfaces such as ice have a high albedo.

Acute Exposure

Contact with a substance that occurs once or for only a short time (up to 14 days) [compare with intermediate duration exposure and chronic exposure].


The word implies pleasing and agreeable environment. Amenity includes attractive open spaces, landscape features, special and recreational provisions and features of scenic or nature beauty.

Activated Sludge

Activated sludge is a process in sewage treatment in which air or oxygen is forced into sewage liquor to develop a biological floc which reduces the organic content of the sewage. In all activated sludge plants, once the sewage has received sufficient treatment, excess mixed liquor is discharged into settling tanks and the supernatant is run off to undergo further treatment before discharge. Part of the settled material, the sludge, is returned to the head of the aeration system to re-seed the new sewage entering the tank. The remaining sludge is further treated prior to disposal.


Requiring oxygen [compare with anaerobic].

Aerodynamic resistance


(Also called drag or aerodynamic drag.) The component of force exerted by the air on a liquid or solid object (such as a raindrop or airplane) that is parallel and opposite to the direction of flow relative to the object.

Air quality criteria


Quantitative and qualitative indications of the relationships between exposure to pollutants and effects on human health, animals, plants, and materials.

These are descriptive effects of pollution as a function of concentration averaged over various time durations. A time-averaged concentration is used because exposure to a high concentration of pollutants during a short time might have an impact equivalent to an exposure to a lower concentration over a longer time. Compare air quality standards.




Air pollution control


The process of attempting to limit the amount of air pollution by regulating the emission of pollutants or their precursors.

Control strategies are alternative long-term policies that could reduce air pollution, as projected using air-quality modeling. For primary pollutants such as sulfur dioxide, control strategies include burning cleaner low-sulfur coal, scrubbing sulfur dioxide from the combustion products before releasing them into the atmosphere, or changing to alternative fuels or processes. For secondary pollutants such as ozone that are not emitted directly but are created in the lower atmosphere by a complex series of chemical and photochemical reactions involving [[NOx]] and volatile hydrocarbons, control is achieved by changing the emissions of one or both of the primary reactants.

Air pollutants


Substances that do not occur naturally in the atmosphere.



Air–sea interaction

The processes that occur as a consequence of the air being in contact with the sea surface, and that affect the dynamics and thermodynamics of the air and water boundary layers.

These include 1) the exchange of momentum, heat, mechanical energy (e.g., wave energy, turbulence), and mass (water vapor, gas species, particulates, sea spray, air bubbles, etc.); 2) the generation of surface waves; 3) the generation of turbulence; and 4) the resulting effects on the vertical profiles of wind and current.

Air–fuel ratio


The ratio of air in a fuel mixture relative to the exact amount required to convert all of a hydrocarbon fuel to water and carbon dioxide (known as a stoichiometric mixture).

If the air content is higher than stoichiometric, the mixture is said to be fuel-lean; if the air content is less, the mixture is fuel-rich.



Agricultural Meteorology


In general, meteorology and micrometeorology as applied to specific agricultural systems and of agriculture as applied to specific atmospheric conditions.

This discipline may emphasize atmospheric transport of insects, pathogens, etc., that impact agriculture as well as energy and mass exchange of plants and animals with the atmospheric environment. The effect of soils and vegetation on the ratio of sensible and latent energy exchange is representative of the impact of agriculture on meteorology.

Agricultural Climatology


In general, climatology as applied to the effect of climate on crops.

It includes especially the length of the growing season, the relation of growth rate and crop yields to the various climatic factors and hence the optimal and limiting climates for any given crop, the value of irrigation, and the effect of climatic and weather conditions on the development and spread of crop diseases. This discipline is primarily concerned with the space occupied by crops, namely, the soil and the layer of air up to the tops of the plants, in which conditions are governed largely by the microclimate.



Aggressive water


Soft, acidic water that is corrosive to metals (e.g., pipes).



Air pollution meteorology


The subdiscipline of meteorology devoted to the study of air pollution.

Topics include sources of pollutants, emission rates, plume rise, fallout, dry and wet deposition, chemistry, precipitation scavenging, dispersion (molecular diffusion and turbulent transport), short- and long-range transport (advection), trapping, venting by cumulus clouds, complex terrain and mesoscale circulations, receptors, impact on society, alerts and episodes, policy and regulation, modeling, prediction, control, and climate change.

Adhesive water


Water retained by soil constituents as a result of the molecular attraction between the water and the soil.



Acid snow

The accumulation of an acidic chemical from the atmosphere to the surface of the earth, or to plants and structures at the surface.

Acids have high concentrations of hydrogen ions when dissolved in water, indicated by a pH less than 7. Acids can corrode metals, dissolve some types of rocks such as limestone, injure plants, and exacerbate some conditions in humans and animals. Acid deposition can occur in two forms: 1) wet deposition including acid rain, acid snow, acid hail, acid dew, acid frost, and acid fog; and 2) dry deposition including fallout of heavy particles, gravitational settling of lighter particles, and interception by and reaction with plant surfaces. Sometimes all forms of acid deposition are loosely called acid rain, although literally acid rain refers only to the liquid form. Ambient carbon dioxide, always present in the air, dissolves in cloud drops and raindrops creating carbonic acid with pH ≈ 5.6. Because this is a normal occurrence in the atmosphere, rain is defined to be acid rain only when it has pH < 5.6. However, even in remote areas, there are sufficient sulfate, nitrate, ammonia, or soil cations (calcium or magnesium that are typically associated with carbonates) to cause "clean" atmospheric water to have pH in the range of 4.5–5.5. Polluted regions typically have pH in the range of 3–4, with values as low as 2–3. The chemicals that cause the greatest acid-deposition problems are oxides of sulfur (abbreviated as [[SOx]]) and oxides of nitrogen ([[NOx]]), which can react in the presence of atmospheric oxidants and water (e.g., clouds, fog and precipitation) to become sulfuric acid and nitric acid, respectively. These strong acids have an affinity for water, allowing droplets to grow hygroscopically in the atmosphere to produce haze or smog, even at relative humidities as low as 60% to 70%.

Acid pollution


Chemicals not occurring naturally in the atmosphere that either are acidic, or that easily react or dissolve in water to become acidic.

Air quality standards


Maximum legal concentration limits of air pollutants averaged over specified time periods.

These are prescriptive. If the actual measured concentration averaged over time exceeds the legal threshold, then the event is called an exceedence. Regulations often allow a limited number of exceedences each year, with fines or penalties imposed for too many exceedences. Regions with too many exceedences are required to develop plans to improve the air quality, for example, by changing automobile fuels and gas-station equipment or increasing the use of mass transportation.

In the United States, the standards are called National Ambient Air Quality Standards (NAAQS). Primary standards are designed to protect human health. Secondary standards are designed to protect crops, animals, structures, and commerce.

In Canada, these legal thresholds are called National Air-Quality Objectives. Three levels of standards exist within these objectives. In ascending order of concentration limit they are Maximum Desirable Level, Maximum Acceptable Level, and Maximum Tolerable Level.

Air pollution episode


1. An extended period of a high concentration of pollutants in the atmosphere.
2.A public alert or notification of unhealthful air quality.



Air pollution

The presence of substances in the atmosphere, particularly those that do not occur naturally.

These substances are generally contaminants that substantially alter or degrade the quality of the atmosphere. The term is often used to identify undesirable substances produced by human activity, that is, anthropogenic air pollution. Air pollution usually designates the collection of substances that adversely affects human health, animals, and plants; deteriorates structures; interferes with commerce; or interferes with the enjoyment of life.

Ambient water quality standards

.The maximum allowable amount of a substance in rivers, lakes or groundwater, given as a concentration. Ambient water quality standards can also refer to other properties of the water, such as temperature or pH. Standards are set to protect against anticipated adverse effects on human health or welfare, wildlife or the functioning of ecosystems