Air pollution may be defined as the presence of one or more contaminants in the air in such quantities and for such durations which may be or tend to be injurious to human, animal or plant life, or property, or which unreasonably interferes with the comfortable usage of air.
Main cause of air pollution is Combustion During combustion, elements in the fuel get burned in air to form various air pollutants.
Types of Air Pollutants
- Primary pollutants: Pollutants which are being emitted into the air directly by point/area/line sources. Examples: CO, NOx, SO2, Pb, SPM, RSPM, VOCs
- Secondary pollutants: Pollutants which are getting formed from primary pollutants in the atmosphere. Some of the reactions are catalyzed by sun light. Examples: acid rains, smog, O3, H2O2, formaldehyde, peroxy acetyl nitrate (PAN)
Classification of Air Pollutants Air pollutants can be classified into three broad categories:
- Natural Contaminants: Natural fog, pollen grain, bacteria and products of volcanic eruption.
- Aerosols (Particulates): Dust, smoke, moist, fog.
- Gases and vapors:
- Sulfur compounds: SO2, SO3, H2S
- Nitrogen compounds: NO, NO2, NO3
- Oxygen compounds: O2, CO, CO2
- Halogen compounds: HF, HCl
- Organic compounds: Aldehydes. Hydrocarbons
- Radio active compounds: radioactive gases
Figure 2.1.1: Air pollution sources
AIR POLLUTION CONTROL
[A] Mobile Sources
- Vaporization of Gasoline should be reduced.
- Oxygen containing additives reduce air requirement
e.g., ethanol, MTBE (Hazardous).
– Methanol: (Less photochemically reactive VOC, but emits HCHO (eye irritant), difficult to start in winters: Can be overcome by M85 (85% methanol, 15% gasoline)
– Ethanol: GASOHOL (10% ethanol & 90% Gasoline),
– CNG: Low HC, NOx high, inconvenient refueling, leakage hazard.
– LPG: Propane, NOx high
Three-Way Catalytic Converter
A three-way catalytic converter has three simultaneous tasks:
- Reduction of nitrogen oxides to nitrogen and oxygen
- Oxidation of carbon monoxide to carbon dioxide
- Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water
[B] Stationary Sources
– Switching to less sulphur and nitrogen fuel
– Improving the combustion process
– New burners to reduce NOx
– New Fluidized bed boilers
– Integrated gasification combined cycle
– Particulate collection devices
– Flue gas desulphurization
MAJOR INITIATIVES TAKEN FOR AIR POLLUTION CONTROL IN INDIA (DURING LAST TWO DECADES)
- National ambient air quality standards based on health impact evolved (1982, 1994, 2009).
- Emission standards for air polluting industries developed for major industries
- Implementation of standards in 17 categories of highly polluting industries and other small/medium scale industries (stone crushers, brick kiln, re-rolling mills, etc.).
- Action plan implementation and pollution control in identified 24 problem areas.
- Coal beneficiation/clean coal technology –notification regarding use of beneficiated coal in thermal power plant.
- Improvement in vehicular technology (Euro-1, Euro-2, Euro-3, Euro-4, CNG vehicles, 4 stroke engines, etc.)
- Improvement in fuel quality -diesel with low sulfur content (0.25% in whole country and 0.05% in metro cities)
- Gasoline-lead phased-out throughout the country since 2000.
EMERGING NEW AREAS FOR AIR POLLUTION CONTROL IN INDIA
- Development of low cost ash removal technology from coal and promotion of clean coal technologies
- Technology for reduction of fluoride emission (primary & Secondary) from pot room of aluminum industries using Soderberg technology
- Development of NOx control standard for thermal power plants and refineries
- Prevention and control of fugitive emission in cement industry
- Use of high calorific value hazardous waste including petroleum coke in cement kiln
- Low cost flue gas desulphurization technology for thermal power plants ·
- Technology development of fugitive emission control from coke oven plants of iron & steel industry.
- Development of technology and standard to control emission of VOC, methyl chloride, P2O5, HCl, etc. from pesticide industry
- Development of odor control technology for paper & pulp industry and standardization the method of odor measurement
- Fluidized bed combustion technology for solid fuel containing higher ash
Development of improved design of Incinerators for Hazardous Waste.
- Control on emission of fine particulate matter (PM2.5) from engine using LPG, compressed natural gas (CNG), low sulphur diesel, low sulphur petrol, etc.
- Apportionment study for fine particulate matter (PM10, PM2.5) in major cities
- Technology for mercury emission control from thermal power plants.
- Noise and emission control system for small DG sets (<200 kW)
- Development of stack height guidelines for thermal power plants and industries using ventilation co-efficient of different regions in the country.