What do you understand by air quality standards ? Give Indian air quality standards for residential, industrial and sensitive areas.
Air Quality Standards are legal limits placed on levels of air pollutants in the ambient air during a given period of time. They characterize the allowable level of a pollutant or a class of pollutants in the atmosphere and thus define the amount of exposure permitted to the population and/or to ecological system.
A. Ambient air quality standards. These are a legal limits placed on the concentration of air pollutants in community where people and things are exposed. Ambient air quality standards need to be distinguished from Threshold Limit Value (TLV) for work-room atmosphere. The TLV are the permissible exposure levels for healthy adult worker for eight hours per day, five days per week. In contrast air quality standards are permissible exposures of all living and non living things for 24hrs/day, 7 days per week.
B. Other Air Quality Standards
1. Quasi-emission standard called ‘point of impingement standard’ which are the limit on specific pollutants of the ambient air at ground level required by national, state or local regulations
2 Soiling index which is the measurement of transmitted or reflected light through or from a spot of particulate matter collected on a filter for a prescribed period of time.
3. Odour standards
4. Visibility standard
5. Standards for particulate matter deposited
National Ambient Air Quality Standards (Explained In Hindi) NAAQS |Environmental Science | NET|UPSC|
Write short note on emission standard.
Emission standards establish permitted emission levels for specific groups of emitters and require that all the members of these groups emit no more than these permitted emission levels. These standards can be applicable to any selected group of emitters and can be national, regional or local in application. They can be based on AQS or can be entirely independent of any such AQS. Serving as an entirely separate and different type of strategy from air quality management.
Emission standards from mobile sources include aircraft, ships, railroad locomotive, motor vehicles. Motor vehicles include automobiles, trucks, buses and motorcycles. Emission standards prescribe limits of contaminants discharged into the atmosphere so that when standards are met adverse effects from air pollution will be minimized.
Emission standard from stationary sources include stationary site process, stack chimney, or vent intended to help achieve the desired air quality. They include standards for buffer zones, stack height, equipment design and fuel composition and those that directly limit the amount or concentration of a pollutant emitted from a source. Standards may be derived from process and equipment consideration, air quality consideration or both.
What are the objectives of sampling the atmosphere? Explain in-situ sampling and remote sensing methods for air pollutants.
Objectives of sampling the atmosphere: sonoroolorglobalgolevia
1. To identify specific industrial and other sources of pollution and
2. To determine the degree of air pollution control required for existing industries
3. To identify and control pollution from vehicular emission
4. To assess health hazards and potential damage to property
5. To determine the back ground pollution levels for application in industrial zoning, town planning or location of sites for certain types of industries requiring stringent air quality criteria.
6. To collect data for formulating and testing air pollution models
7. For purely scientific investigations sampling methods are classified into two categories
1. In-situ sampling
a. Intermittent sampling
b. Continuous sampling
2. Remote sensing
Intermittent sampling is less expensive and easy to operate. But it requires frequent personal attention and therefore more manpower and ancillary facilities. On other hand continuous methods are more expensive and are used only when long term investigations are undertaken. The remote sensing method of sampling is a recent development. It is possible to detect and measure the concentrations of several atmospheric pollutants by this technique. The main advantage of this is that physical access to the location where the measurement is to be made is not needed. Another advantage is the instantaneous space averages of the constituent concentration may be obtained. Method is costly and requires sophisticated equipments.
Write short note on dust falljar.
Dust fall jar is used to determine the particle fallout or dust fall in community atmosphere and is based on sedimentation principle and is adopted for particles size more than 10 microns. The collector is made of polyethylene, glass or stainless steel. The container is more than twice as high as its diameter at the base. This inhibits the re entrainment of dust due to drafts and heavy rain. The typical dust fall jar is constructed of plastic and is 20-32cm high and is 10-15 cm in diameter at the base with a slight inward taper of the walls from top to bottom.
Occasionally water containing algicide (1 mg of CuSO4 per litre of water) is added up to 500 ml to facilitate retention of particles, where error from loss of particles may occur as a result of gusty winds. After a month the soluble and insoluble matter is determined and the total solids collected are expressed in terms of weight per unit area per 30 days. In communities one dust fall container for every 2600 hectares is used. The method is simple inexpensive and requires no electrical power or moving parts. The disadvantage include lack of precision and inability to distinguish episodes of peak dust fall due to integration of the total sample weight over the entire sampling period (30 days).
Write short note on High volume sampler.
High Volume Sampler is used for collection of suspended particulate matter and is based on Stoke’s law. In HVS a motor is used to draw a sample through a filter area. The filter is 20cm*25cm mat which allows collection of an air sample at a rate from 18,900-28,350 cc/s over a nominal sampling period of 4-6 hrs and a normal sampling period of 24 hrs. These conditions permit the sampling from 1260-2100 сum of ambient air, with consequent extraction of about 0.5gms of suspended particulate (aerosols). This provides a substantial weight of sample for subsequent chemical and physical analysis. The sampler consists of
1. The face plate and gasket
2. The filter adapter assembly
3. Motor or blower unit
It is installed inside a casing which is provided with a roof so that the filter is protected from precipitation. An airflow measuring device such as a rotameter is en used to record the volume of sample air passing through the filter for calculating the mass of particulate per static volume of air(micro gram/cum of sample air)
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