Read this article to learn about Air Pollutants:- 1. Classification of Air Pollutants 2. Adverse Effects of Air Pollutants.
Classification of Air Pollutants
The variety of matter emitted into the atmosphere by natural and anthropogenic sources is so diverse that it is difficult to classify air pollutants neatly.
However, they are classified in different ways as follows:
A. According to Origin:
1. Primary air pollutants are directly emitted from the sources into the atmosphere.
Typical air pollutants included under this category are:
(i) Inorganic gases such as SO2, NOX, H2S, CO, NH3, CO2, HF.
(ii) Particulate matter like ash, smoke, dust, fumes, mist, spray.
(iii) Olefinic and aromatic hydrocarbons.
(iv) Radioactive compounds.
2. Secondary Pollutants are those which are derived from the primary pollutants due to chemical or photochemical reactions in the atmosphere. Pollutants such as SO2, NO2, O3, sulphate and nitrate salts, aldehydes and peroxyaceiyl nitrate (PAN) are included in this category.
B. According to Sate of Matter:
1. Gaseous pollutants
2. Particulate pollutants
3. Aerosols
4. Metallic components
5. Radioactive pollutants
6. Pesticides
Gaseous Pollutants:
Nitrogen Oxides, NOX:
The oxides of nitrogen are N2O, NO, NO2, N2O3, N2O5. The atmospheric background concentrations are: N2O (0.25 ppm), NOx(0.1 to 2 ppm) and NOX (0.5 to 4 ppm). In air, NOX is converted into nitric acid by natural processes which is one of the constituents of acid rain.
Sulphur oxides, SOX:
Combustion of sulphur bearing materials produces SO2 and a little quantity of S03. Global emission of SO2 from natural sources like biological decay (H2S), sea spray and volcanic activity is 90, 40 and 5 million tonne per year while from anthropogenic sources such as coal, petroleum, smelting and sulphur production, it is 92, 26, 14 and 2 million tonne per year respectively.
Carbon monoxide, CO.:
CO, produced by incomplete combustion of fuel, is the major individual pollutant with a tonnage matching that of all other pollutants together. Global emission of CO from natural sources amounts to 3364 million tonne per year.
Anthropogenic sources of CO emission include: transportation (70 MT/year), fuel combustion (1.6 MT/year), industrial processes, (7.8 MT/year), solid waste disposal (7.8 MT/year), others (8.5 MT/year) amounting to 95.7 MT/year.
Particulate Pollutants:
Small solid particles and liquid droplets are termed particulates. Their number varies from several hundred per cm3 in clean air to more than 100,000 per cm3 in highly polluted air. Man made sources for particulate emission include flyash from power plants, smelters, fuel combustion, industrial operations, refuse burning etc. Every year natural sources discharge 800 to 2000 million tonne and man-made sources 200 to 500 million tonne of particulates.
Adverse Effects of Air Pollutants:
Effects of Air Pollutants on Human Health:
Acute exposure of NO2 in man causes bronchiolitis fibrosa obliterans, emphysema, lung cancer, pneumonia and silofilter’s disease. NO2 is also known to be transformed into methaemoglobin in blood. SO2, a severe allergenic agent, may cause watery nasal discharge, sneezing, dyspnoea, desqumation and bronchial spasms.
CO, when inhaled, passes through the lungs and diffuses directly into blood stream where it combines with haemoglobin to form carboxy haemoglobin. CO has affinity for haemoglobin, 210 times more than O2. Haemoglobin is thus unable to transport O2 to body tissues causing asphyxiation (lack of O2). Its long exposure may cause dizziness, unconsciousness and even death.
Particulates with SO2 cause silicosis, bronchitis and increased absenteeism among older workers.
Effects of Air Pollutants on Plants:
1. NO2 results in necrosis (dead areas on a leaf), chlorosis (reduction of chlorophyll), epinasty (downward curvature of leaf) and abscission (dropping of leaves).
2. SO2 causes bleached spots, chlorosis and affects photosynthesis along with ozone and PAN.
3. CO at higher levels (100 to 1000 ppm) causes leaf curling, leaf drop, reduced leaf size and interference with cellular respiration.
4. PAN results in silvering of lower surface of leaf, damage to sensitive leaves and suppressed growth.
Effects of Air Pollutants on Materials:
1. NO2 fades away dyes in clothes like cotton, rayon, causes cracks in rubber and produces photochemical smog with O3 and PAN.
2. CO2 damages fabric, leather, paint, paper and historic monuments. H2SO4 attacks marble causing stone leprosy. The CaSO4, so formed on the surface of masonry is twice as bulky as CaCO3 which looks leprous.
Hydrocarbons induce chemical alterations in textile, paper, rubber and polymers making them more brittle and fragile.
Effects of Air Pollutants on Animals:
Air-borne contaminants accumulate in forage and poison the animals when they graze it. Live-stocks near smelters suffer arsenic poisoning with symptoms like salivation, thirst and liver necrosis.