Hydrocarbons vehicle emissions

Fig. 1. CO and hydrocarbon tailpipe emissions. Data from a test vehicle during a test cycle where the catalyst was mounted - 1.2 m from the exhaust part...

The Clean Air Act of 1990 establishes tighter pollution standards for emissions from automobiles and trucks. These standards will reduce tailpipe emissions of hydrocarbons, carbon monoxide, and nitrogen oxides on a phased-in basis beginning in model year 1994. Automobile manufacturers will also be required to reduce vehicle emissions resulting from the evaporation of gasoline during refueling. 

HYDROCARBONS Organic compounds that contain only hydrogen and carbon. The major sources of hydrocarbons in the atmosphere are vehicle emissions (unburned fuel) and gas leaks. Contributes to acid rain. 

The presence of polycyclic aromatic hydrocarbons in the environment is of obvious concern and, apart from specific occupational environments, human exposure to these compounds derives from combustion products released into the atmosphere. Estimates of the total annual benzo[aJpyrene emissions in the United States range from 900 tons (19) to about 1300 tons (20). These totals are derived from heat and power generation (37-38%), open-refuse burning (42-46%), coke production (15-19%) and motor vehicle emissions (1-1.5%) (19,20). Since the vast majority of these emissions are from stationary sources, local levels of air pollution obviously vary. Benzo[aJpyrene levels of less than 1 pg/1,000 m correspond to clean air (20). At this level, it can be estimated that the average person would inhale about 0.02 pg of benzo[aJpyrene per day, and this could increase to 1.5 pg/day in polluted air (21). 

Barrefors G, Petersson G. 1993. Assessment of ambient volatile hydrocarbons from tobacco smoke and from vehicle emissions. J Chromatogr 643 71-76. 

One of the considerations regarding the use of methanol as a fuel is that it emits higher amounts of formaldehyde, which is a contributor to ozone formation and a suspected carcinogen, compared to gasoline. Proponents of methanol dispute this, saying that one-third of the formaldehyde from vehicle emissions actually comes from the tailpipe, with the other two-thirds forming photochemically, once the emissions have escaped. They state that pure methanol vehicles produce only one tenth as much of the hydrocarbons that are photochemically converted to formaldehyde as do gasoline automobiles. 

A similar observation has been made in other countries where exhaust controls have been instituted. For example, vehicle emissions measurements made by remote sensing in Monterrey, Nuevo Leon, Mexico, showed that 1995 model years emitted 75% less CO, 70% less hydrocarbons, and 65% less NO compared to the pre-1991 vehicles without emission controls (Bishop et al., 1997). In Australia, emissions for pre-1986 vehicles were substantially larger than those from newer, catalyst-equipped cars, a factor of 4 for hydrocarbons, 2.5 for CO, and 2 for NO in addition, the reactivity (see Section 16.B) of the exhaust emissions... 

In Sweden, three-way catalysts have been required on all cars since 1989, and tax incentives were offered to purchase such vehicles in the 1987 and 1988 model years. Figure 16.34 shows the CO and hydrocarbon exhaust emissions as a function of model year of gasoline-powered cars, measured using a remote-sensing technique (Sjodin, 1994). There is a large decrease in the emissions from 1987 to 1988 and 1989, supporting the effectiveness of these motor vehicle exhaust controls. 

Inoue, O., Seiji, K., Kudo, S., Jin, C., Cai S.-X., Liu, S.-J., Watanabe, T., Nakatsuka, H. Ikeda, M. (1995) Urinary phenylglyoxylic acid excretion after exposure to ethylbenzene among solvent-exposed Chinese workers. Int. J. occup. environ. Health, 1, 1-8 Johnstone, R.A.W., Quan, P.M. Carmthers, W. (1962) Composition of cigarette smoke some low-boiling components. Nature, 195, 1267-1269 Jonsson, A., Persson, K.A. Grigoriadis, V (1985) Measurement of some low molecular-weight oxygenated aromatic and chlorinated hydrocarbons in ambient air and in vehicle emissions. Environ, int., 11, 383-392... 

Air pollution measures against gases from positive ignition engines of motor vehicles (emissions of CO and hydrocarbons)... 

Jonsson A, Persson KA, Grigoriadis V. 1985. Measurements of some low- molecular-weight oxygenated, aromatic, and chlorinated hydrocarbons in ambient air and in vehicle emissions. Environ Int 11 383-392. 

Garage and combustion appliances Vehicle emission, tobacco smoking, candles (aliphatic and aromatic hydrocarbons aldehydes, amines). 

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