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| Air
Pollution And Human Health |
The popularity of the diesel engine in heavy duty applications in trucking, rail road, marine transport, DG sets and construction industry is due to both its fuel efficiency and long service life relative to the gasoline engine. Compared with gasoline engine, diesel emissions are lower in carbon monoxide (CO), hydrocarbon (HC) and carbon dioxide (CO2), but higher in oxides of nitrogen (NOx) and particulate matter (PM). Diesel exhaust is a complex mixture of both particulate and gaseous phase. Diesel exhaust has particulate with mass median diameter of 0.05 to 1.00 micrometer, a size rendering them easily respirable and capable of depositing in the airways and alveoli. The particles consist of a carbonaceous core with a large surface area to which various hydrocarbons are absorbed, including carcinogenic polycyclic aromatic hydrocarbons (PAHs) and Nitro-PAHs that have elicited the most concern with respect to human health. The gaseous phase contains various products of combustion and hydrocarbons including some of the PAHs present in the particle phase. Once emitted, components of diesel exhaust undergo atmospheric transformation in ways that may be relevant to human health. For example, nitro-PAHs, created by the reaction of directly emitted PAHs with hydroxyl radicals in the atmosphere can be more potent mutagens and carcinogens and more bioavailable than their precursors. A study undertaken by a Swedish Consultancy, Ecotraffic (Peter Ahlvik and Ake Branberg,1999) shows that the cancer potency of diesel vehicles is more than two times than that of petrol vehicles in India (Fig 12).
But if only the most harmful of the exhaust emissions, that is particulate emission is considered, the carcinogenic effect of one new diesel car is equivalent to 24 petrol cars and 84 new CNG cars on the road. The Honorable Supreme Court of India has restricted the use of commercial diesel driven vehicles in Delhi due to its harmful effects. Starting from 1 April 2001 it has been made mandatory to use only Compressed Natural Gas (CNG) in all transport buses in Delhi. However, due to shortage of CNG vehicles and filling stations, the implementation has been extended till September 2001.
Table 15 Health Effects of Diesel Exhaust
| Emission Component | Atmospheric Reaction Products | Biological Impact |
| VAPOUR PHASE EMISSIONS | ||
|
Carbon dioxide |
- |
Major contributor in global warning. |
| Carbon monoxide |
- |
Highly toxic to humans, blocks oxygen uptake. |
| Oxides of nitrogen | Nitric acid, ozone | Nitrogen dioxide is a respiratory tract irritant and major ozone precursor. Nitric acid contributes to acid rain. |
|
Sulphur dioxide |
Sulphuric acid |
Respiratory tract irritation. Contribution to acid rain. |
| Hydrocarbons | ||
| Alkanes (£ C18) |
Aldehydes, alkyl nitrates, ketones |
Respiratory tract irritation. Reaction products are ozone precursors (in the presence of NO2) |
| Formaldehyde |
Carbon monoxide, hydroperoxyl radicals. |
Formaldehyde is a probable human carcinogen and an ozone precursor ( in the presence of NO2). |
| Acrolein ( Higher Aldehydes) | Peroxyacyl nitrates | Respiratory tract and eye irritation, causes plant damage. |
|
Monocyclic aromatic hydrocarbons (e.g. benzene, toluene) | Hydroxylated and hydroxylated nitro derivatives. |
Benzene is toxic and carcinogenic in human. Some reaction products are mutagenic in bacteria (Ames assay) |
| PAHs (£ 4 rings) (e.g.phenanthrene, flouranthene) | Nitro PAHs (£ 4 rings) | Some of these PAHs and nitro PAHs are known mutagens and carcinogens. |
| Nitro PAHs (2 & 3 rings) (e.g. nitronapthalene) |
Quinones and hydroxylated nitro derivatives. |
Some reaction products are mutagenic in bacteria (Ames assay) |
| PARTICLE PHASE EMISSIONS | ||
|
Elemental Carbon |
- |
Nuclei adsorb organic compounds; size permits its transport deep into the lungs (alveoli). |
| Inorganic sulpahte |
- |
Respiratory tract irritation |
| Hydrocarbons (C14-C35) |
Little formation, possibly aldehydes, ketones and alkyl nitrates. | Unknown |
| PAHs (³ 4 rings) (e.g. pyrene, benzo(a )pyrene) | Nitro-PAHs (³ 4 rings), Nitro-PAH lactones | Larger PAHs are major contributors of carcinogens in combustion emissions. Many nitro-PAHs are potent mutagens and carcinogens. |
|
Nitro-PAHs (³ 3 rings) (e.g. nitropyrenes) |
Hydroxylated nitro derivatives |
Many nitro-PAH are potent mutagens and carcinogens. Some reaction products are mutagenic in bacteria (Ames assay) |
Source: Aaron Cohen and Kristen Nikula,1999
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