Automobile exhaust emissions, measure

Kley, D, H. Geiss and V. A. Mohnen (1994) Tropospheric ozone at elevated sites and precursor emissions in the United States and Europe. Atmospheric Environment 28, 149-158 Klingenberg, H. (1996) Automobile exhaust emission testing. Measurements of regulated and unregulateed exhaust gas components, exhaust emission tests. Springer-Verlag, Berlin,... 

Of the six heavy metals discussed in this chapter, Pb has been studied extensively with respect to the environmental effects. Clair Patterson, the father of environmental Pb studies, in one of his many major publications concerning the global Pb cycle (Patterson and Settle, 1987), noted that during pre-industrial times Pb in the troposphere originated from soil dusts and volcanic gases. In modern times (1950-1980) the proportion of natural Pb in the atmosphere is overwhelmed by the industrial sources of smelter emissions and automobile exhausts. Lead air pollution levels measured near our Nation s roadways decreased 97% between 1976 and 1995 due to the consequence of the Clean Air Act that eliminated leaded gasoline which interfered with the performance of catalytic converters. 

The absorption of infrared radiation (1 to 1,000 micrometers, or 0.0000394 to 0.0394 inches) causes bonds in molecules to vibrate. A bond in the molecule must undergo a change in the dipole moment when the infrared radiation is absorbed. The stiffer the bond, the more energy is required to cause the bond to stretch. Therefore the frequency required to cause C-N, C=N, and C N bonds to stretch increases from left to right. Often the infrared spectrum is considered to be a fingerprint of the molecule. Matching a sample s spectrum with a standard spectrum can positively identify the sample. This technique is used to measure emissions in automobile exhaust. 

Because we made two significant assumptions, this equation is a highly idealized model for the combustion of gasoline. The use of octane to represent all of the hydrocarbons in gasoline is mainly for simplicity. If we chose to, it would not be very difficult to write similar combustion equations for each hydrocarbon that is actually present. But the assumption of complete combustion is more drastic. You probably know that typical automobile exhaust contains a number of compounds besides carbon dioxide and water vapor. Most states require periodic emissions testing to measure the levels of carbon monoxide and hydrocarbons in a car s exhaust, and some states or local areas also require additional tests for other types of compounds. Because these compounds don t appear among the products in our equation above, their presence implies that our simple model does not show the full picture. What additional factors could we consider to get a more complete description of engine chemistry ... 

Figure 28.9 Principle for real-time, triggered automobile exhaust measurement with an open-path TDLAS set-up (right), here exemplified for the monitoring of NH3 emission (left). Courtesy of TDL Sensors Ltd (2003)...

The second important target of the anti-air pollution policies was the automobile. The general goal was the introduction of a car with reduced exhaust emissions. This was aimed through an intricate system of direct, fast acting fiscal benefits and regulations. The most important measures were ... 

Shape-selective reactions have been extensively studied since zeohtes were first used in catalytic crackers during 1967" and Mobil has introduced several octane-boosting processes since 1968. ° Gasoline composition and octane number were reviewed when the Clean Air Act was passed in 1970. This mandated the phased removal of tetraethyl lead from gasoline as catalytic converters (see Chapter 11) were introduced to treat automobile exhaust gas. Octane boosting was the first in a series of measures that led to reformulated gasoline and improved exhaust emissions standards. 

In addition to what appears to be a heterogeneous chemical source for HONO, it has also been shown to be emitted directly from combustion systems. For example, it has been measured in the exhaust of noncatalyst-equipped automobiles (Pitts et al., 1984b), from natural gas combustion in a kitchen stove, and in the emissions from kerosene and propane space heaters (e.g., Pitts et al., 1985, 1989 Brauer et al., 1990 Febo and Perrino, 1991,1995 Spicer et al., 1993 Vecera and Dasgupta, 1994). 

As indicated before, previous detailed studies of particulate formation and emission processes in automobile engines and exhaust systems have been done using probes which extracted a (hopefully) representative sample of the exhaust gas that was subsequently analyzed for various particulate properties (5). Similar techniques have been used in the most recently developed systems to measure the amounts of particles emitted from auto exhaust. Such sampling techniques, however, suflFer from inherent disadvantages in that they interfere with the hot flow particulate processes and have an unknown effect on the particulates as they flow through the system to an exterior point of analysis. This problem can also be compounded by several phenomena anisokinetic sampling, deposition of particulates in the sampling system, or condensation caused by temperature drops. 

Since the internal combustion engine is the primary source of localized pollutant carbon monoxide emissions, control measures have been concentrated on automobiles and have been very successful in reducing carbon monoxide emissions. Carbon monoxide emissions may be lowered by employing a leaner air-fuel mixture, that is, one in which the mass ratio of air to fuel is relatively high. At air-fuel (mass mass) ratios exceeding approximately 16 1, an internal combustion engine emits virtually no carbon monoxide. Modern automobiles use catalytic exhaust reactors and precise computerized control of engine operation to cut down on carbon monoxide emissions. 

In the United States, measures to control the levels of automobile emissions and therefore of photochemical smog have become sophisticated since the first federal Clean Air Act of 1967. Modifications to the ICE have been extensive and included various redesigns of the combustion chamber, variations in the air-to-fuel ratio, reformulations of the composition of gasoline, the addition of the positive crankcase ventilation (PCV) valve to recirculate exhaust and underoxidized fuel gases through the combustion chambers, and the addition of carbon canisters that temporarily collect and then recirculate evaporated fuel from the gas tank and the fuel system. Some of these modifications have not always worked out as well as envisioned. For example, the 1990 modification to the Clean Air Act called for the addition of oxygenated... 

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