Vehicular Exhaust and Air Pollution

Introduction

Individual tailpipe emissions

Transport and fate in the environment

Measuring exposures

Prevention and control of exposure

Exposure Pathway

Risk assessment

Adverse effects


Harmful Effects

Dose Response

Absorption, Metabolism and Molecular Mechanisms of Action

Organ Sites of Toxicity

Biomarkers

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Transport and Fate of Vehicular Emissions in the Environment

Vehicular emissions are just one type of mobile sources causing air pollution today. Vehicular emissions contain carbon monoxide, nitrous oxides, hydrocarbons and particulate matter among many others. However, these four make up the major components of vehicular emissions in the environment. Historically, lead was also a major factor in air pollution caused my vehicular emissions.

Lead

Lead as an additive to gasoline began in the 1920’s. Leaded gasoline allowed for the development of more powerful engines, due to the decrease in “knocking”, a common problem with compression engines. This addition led to more than just powerful engines, it added to air pollution. During the combustion of gasoline, lead particles, among others, enter the atmosphere causing pollution. Lead additives in gasoline flourished until the Clean Air Act. The Clean Air Act Amendment of 1970 was the initial legislation that concerned mobile sources with air pollution. Standards were set for the emissions of hydrocarbons, carbon monoxide and nitrous oxides. However, legislation for lead additives in lead wasn’t passed until 1977. For the most part, this amendment was the one piece of legislation that accounted for the decrease and almost total elimination of lead emissions in the atmosphere. Currently, The only sources of leaded gasoline emissions are from non-road vehicles, such as farm machinery and airplanes.

Carbon Monoxide

Carbon monoxide is a colorless, odorless gas that is a byproduct from the incomplete combustion of fossil fuels. Over 90% of the concentration of carbon monoxide in metropolitan areas is from mobile sources.

Carbon Dioxide

Like carbon monoxide, carbon dioxide is a byproduct from the incomplete combustion of fossil fuels. It is also caused by the respiration of plant life throughout the world. Carbon dioxide is a major component to the greenhouse gas effect. Carbon dioxide and other gases absorb the radiation the earth releases back into the atmosphere. This absorption causes the planet to gradually warm, resulting in the phenomenon known as global warming.

Hydrocarbons

Hydrocarbons are also a byproduct from the incomplete combustion of fossil fuels. Hydrocarbons react with nitrogen oxides, also emitted from mobile sources, and in the presence of sunlight, form ozone. Ozone is the biggest component to photochemical smog.

Nitrogen Oxides

Nitrogen Oxides are also gases emitted during the burning of fuel in mobile sources. Like stated earlier, nitrogen oxides combine with hydrocarbons and other gases to form ozone, and therefore produce photochemical smog.

Particulate Matter

Particulate matter, or particles, is produced in various sizes from automobile emissions. The two of concern are PM10 and PM2.5. The numbers represent the size of the particles, measured in micrometers. The smaller a particle is, the further it can travel into the respiratory system. Particles reduce visibility and cause haziness.