Air Quality Standards

Apart from particulate matter the other major air pollutants are gaseous pollutants. In the general, Gaseous pollution is classified into two categories, normally inorganic and organic vapors. In the former class there are sulphur di oxide, nitrogen oxides, hydrogen sulphite, hydrogen chloride, hydrogen fluoride, carbon mono oxide and ammonia. In the latter are the hydrocarbons, mercaptans, keystones and esters. Clean air is considered to be a basic requirement of human health and well being. However, air pollution continues to pose a significant threat to health. Secondary standards are designed to protect public welfare from any known or anticipated adverse effects of a pollutant.

As per recent BIS standard the following limits have been recommended. The ambient air standards as propounded by EPA of USA and adopted by BIS are shown in the following table.

Air Pollution Control Devices

Air pollution control equipment is broadly classified into two categories- one controls particulate matter and the other controls gaseous emission. Various consideration are required to be made while selecting a control device for an industry. Mostly industries face problem with particulate matter collection and gaseous emission has to be controlled by proper pre treatment and maintaining certain design parameters such as dew point. For particulate matters, some of the major factors are collection efficiency of the device, initial cost operating and maintenance cost, space required arrangement, material of construction. Important factors considered in this connection are as follows.

• Particulate characteristics such as particle size range, shape, density and physical, chemical properties such as agglomeration tendencies, corrosiveness, hydroscopic tendencies, stickiness, inflammability, toxicity, electrical conductivity and others.
• Gas characteristics such as temperature, pressure, humidity density, dew points of condensable components viscosity, electrical conductivity etc.
• Process factors such as volumetric gas emission rate, particulate concentration, variability of  material flows rates, collection efficiency allowable pressure drop, product quality requirement etc.
• Operational factors such as floor space, pressure temperature, corrosion etc.
• the levels of air quality necessary with an adequate margin of safety, to protect the public healthy, vegetation and property.
• whenever and wherever two consecutives values exceeds the limit specified above for the respective category, it shall be considered adequate, reason to institute regular/continuous monitoring and further investigations.