Road based transport system is the major source of poor health outcomes and the situation is more exacerbated in developing nations. Air pollution is the major cause of the most health problems Emissions and tyre burning is the major source of air pollution (Horner 1993; Hinkova et al,. 1995). Childhood asthma, (Guo et al., 1999) adult chronic obstructive pulmonary disease exacerbations, chronic bronchitis and increasing greenhouse gas emissions (Stott 2000; Patz et al., 2000) caused by air pollution.. In urban areas, accelerated hearing loss and sleep degradation are the outcomes of high-vehicle density with loud engines and horn use. (Singh & Rao 2001; Wong et al., 2002). High density of traffic can lead to increased stress levels, resulting in cardiovascular morbidity (Greenwood et al., 1996) and lost work productivity. 600 million people through out the world in urban areas were exposed to air pollutants generated by traffic. (Cacciola et al., 2002). Despite these associations, a little attention is paid by developing nations to monitor the negative impact of road transport system.
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In Pakistan lead, nitrous oxide, sulpher dioxide, carbon monoxide and 10-μm particulate matter are produced mainly by the vehicles. (Brandon 1995). Number of vehicles is increasing at a rate of 10% in Pakistan. In Pakistan during 1977 to 1997, carbon dioxide and sulpher dioxide emissions from transport were raised from 7 to 18 million tones and 52,000 to 105,000 tonnes respectively. In Lahore city, 96% of CO, 76% NO2 and 28% of suspended particulate matter are emitted by the vehicles. In comparison to average vehicle in USA, an average Pakistani vehicle emits 20 times as much hydrocarbon, 25 times as much carbon monoxide, and 3.6 times as much nitrous oxide in grams per kilometer (Brandon 1995). Levels of all air pollutants (ozone, sulphur dioxide and nitrogen compounds) are highest along the roadside in big cities of Pakistan. In 1991, mean blood lead level was 1.5-2.0 g and the highest in Asia, while according to World Health Organisation (WHO) guidelines, it is 15 μg/dl (Perakh et al., 2001).
In Pakistan, almost US $233 and 368 per year is consumed on health due to air pollution(morbidity, mortality and loss of intelligence quotient level) (Brandon 1995). Concerns of mounting air pollution in Pakistan comprise an inefficient diesel-based private transport system and an institutional failure to implement national environmental quality standards. In Pakistan there is evidence of hazardous level of emissions, there is a little attention on it and its impact on public health.
Air pollution of traffic is focused by epidemiologists and toxicologists. Vehicles in urban areas are run by natural gas, gasoline or diesel. The physical and chemical characteristics of various fuels are not the same in different regions in the world, like benzene content (Verma and Tombe, 2002),and for this reason it is difficult to generalize the findings on the whole. It is further complicated by different meteorological conditions, different percentage of heavy polluters (more motorcycles in the developing world), design of motor ways (graded or non-graded roads), driving habits, different maintenance as well as quality of and control measures for vehicles, and exposure profiles of people (Gwilliam, 2003).
Use of natural gas as an alternative fuel for the vehicles started in mid-1930 in Italy, principally after the energy crisis of the 1970s. Both developed and developing countries encouraged use CNG as a fuel for vehicles to reduce reliance on foreign oil. In Pakistan, there are more than 17,000 filling stations and 16 million vehicles are run by CNG according to International Association of Natural Gas vehicles (IANGV).
Compressed natural gas (CNG) has been promoted as a cleaner-burning fuel. CNG vehicles emit lower level of particulate matter, non methane organic gases, nitrogen oxides, carbon monoxide and air toxics as compared to diesel and gasoline vehicles. It is the basic reason to use CNG as an alternative fuel. CNG vehicles has lower cold-start emissions, evaporative emissions and running loss emissions (Goyal and Sidhartha, 2003; Nylund and Lawson, 2000). The abundant gas reserves is an additional use as fuel in place of gasoline to save foreign exchange. In fact, CNG-fueled vehicles produce less PM, but greater total hydrocarbons compared to diesel-fueled vehicles (McCormick et al., 2000). Characterization of the emissions from such vehicles has demonstrated that the emissions contain potentially toxic constitutents (Lapin et al., 2002). However, to date, few of the biological effects of these emissions have been examined.
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Environmental exposures in utero and during early life have effects on body’s structure, physiology and metabolism, and lead to diseases in adult life (Gluckman et al., 2004). Respiratory, cardiovascular and stroke related sickness and death is associated with air pollution (Banauch et al. 2006). Chronic inflammation of upper and lower respiratory tracts, alterations in circulating mediators and breakdown of the nasal epithelial barrier is evidenced in children living in polluted air ( Calderón-Garcidueñas, Franco-Lira et al. 2007). Air pollutants including PM increase plasma endothelin-1, a potent vasoconstrictor peptide that result in alterations in heart rhythm and fall in vagal responses (Calderón-Garcidueñas, Vincent et al. 2007).
Systemic inflammatory mediators and components of air pollution access to central Nervous System (CNS) by breaking the nasal respiratory and olfactory epithelium and the BBB. (Calderón-Garcidueñas et al. 2004). Progressive neuronal death was seen in neurodegenerative diseases such as Alzheimer,s due to chronic inflammatory processes in the CNS ( McGeer et al., 2006). Chronic inflammation of the respiratory tract results in systemic inflammatory response by producing inflammatory mediators that can reach the brain and consequently cause brain damage ( Calderón-Garcidueñas, Mora-Tiscareño et al. 2000). Olfactory neurons and cranial nerves such as the trigeminal and vagus should uptake ultrafine PM (UFPM), particulate-matter-associated lipopolysaccharides (PM-LPS), and metals. The systemic circulation, and macrophage-like cells loaded with PM from the lungs (Calderón-Garcidueñas et al.2004). Circulating cytokines and constitutively expressed cytokines receptors located in endothelial brain capillary cells activate the brain innate immune responses, followed by activation of cells involved in adaptive immunity (Simard and Rivest 2006). Headache is a major cause of morbidity in modern society. Among many other triggers of migraine like fatigue, stress etc, air pollution has also an impact on frequency and incidence of headache (Nattero & Enrico, 1996).