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| Air
Pollution And Human Health |
Oxides of nitrogen are released in all the types of combustion as they are formed by the oxidation of atmospheric nitrogen at high temperature. Nitric oxide usually emitted from the automobile exhaust is oxidised to nitrogen dioxide (NO2) by reaction with oxidants (prominently ozone) present in the ambient air. Nitrogen dioxide is a reddish brown gas with a characteristic pungent odour. It is corrosive and a strong oxidising agent. Nitrogen dioxide is the predecessor of gaseous nitric acid and nitrate aerosols, which has the biggest health impact. The major sources of NO2 are combustion-associated processes, such as motor vehicles, power plants as well as any high temperature combustion process used in industrial work. Oxides of nitrogen particularly nitrogen dioxide are toxic gases. The uptake of these gases in human body occur during breathing. Large percentage of inhaled NO2 is removed in the respiratory tract, which depend on mode of breathing, ventilation rate, increased penetration of NO2 to lower respiratory tract. Some of the major health effects of NO2 exposure are as follows
Table 5 Average Concentration Levels of Air Pollutants on Exposure Assessment
| Pollutant |
Personal Exposure |
Occupational Exposure |
Residential Exposure |
Ambient Air Quality |
NAAQS |
|
PM (µg/m3) |
330± 175 (RPM5) |
358± 187 (RPM5) |
308± 225 (RPM5) |
140± 102 (PM10) |
100 (PM10) |
| NOx (ppb) |
2.4 | 3.4 |
2.0 | BDL |
3.2 |
|
CO(ppm) | 2.4 |
3.4 | 2.0 |
BDL | 3.2 |
| Pb (µg/m3) |
2.32± 1.28 | 2.6± 2.5 | 2.47± 2.16 |
0.34± 0.25 | 1.0 |
| K (µg/m3) |
7.7± 6.9 | 7.9± 10.71 | 6.32± 2.74 |
0.54± .042 | - |
| Mn(µg/m3) |
0.33± 0.41 | 0.55± 0.64 | 0.12± 0.13 |
0.15± 0.18 | - |
| Cd (µg/m3) | 0.15± 0.16 | 0.27± 0.39 |
0.06± 0.35 | 0.017± 0.027 | - |
| PAH (ng/m3) |
23.83 | 42.36 |
5.2 | 21.2 |
- |
|
B(a)P(µg/m3) |
2.69 | 4.89 |
0.48 | 1.4 |
- |
Source: CPCB Report PROBES/77/200-01
Airway Reactivity and Pulmonary Effects
Nitrogen dioxide exposure can cause decrement in lung function (i.e. increased airway resistance), increased airway responsiveness to broncho-constrictions in healthy subjects at concentration exceeding 1 ppm. Below 1 ppm level, there are evidences of change in lung volume, flow volume, characteristics of lung or airway resistance in healthy persons. It has been established that continuous exposure with as little as 0.1 ppm NO2 over a period of one to three years, increases incidence of bronchitis, emphysema and have adverse effect on lung performance.
Respiratory Morbidity in Childern
The dysfunction of host defence, increased susceptibility to infections are generally caused due to affects on muco-ciliary clearance, functional and bio-chemical activity of alveolar macrophages and immunological competence. Exposure to excessive NO2, affect the defence mechanism leaving the host susceptible to respiratory illness.
Chronic Lung Disease
Nitrogen dioxide exposure may lead to chronic lung disease and variety of structural/morphological changes in lung epithelium conducting airways and air -gas exchange region. Exposure to high levels (>1.0 ppm) of NO2 cause estuation of bronchiolar and alveolar epithelium, inflammation of epithelium and definite emphysema.
Effects on Immune System and Host Defence
Nitrogen dioxide in large doses can result in dysfunction of host defences by causing structural alteration in ciliated cells of mucociliary escalator, in alveolar macrophages, decrease in phagocytosis, morphological and metabolic changes. The respiratory tract provide first time protective barrier against inhaled, viable and non-viable airborne agent. Breaches in defence system might increase the risk of diseases.
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