Air Pollution

Introduction

Air pollution is one of the most widespread environmental problems because it occurs at many scales: indoor, local and regional, and global. Regional and global air pollution are especially difficult to control because polluters are often very distant from those damaged by their emissions. Each year outdoor air pollution causes an estimated $16 billion in direct damge in the United States, including crop and livestock damage, cleaning costs to clothes, and weathering of statues and buildings. Many billions of dollars more are lost due to increase health care expenses. In 1990, the EPA reported that over half the US population still lived in cities polluted by too much smog and ozone despite major reductions since 1970. Indoor air pollution is an even greater hazard. Radon and especially cigarette smoke cost many billions of dollars more.

Air pollution is not a single entity; thousands of gaseous, liquid, and solid compounds contribute to the atmospheric mess. The nature of some of these substances is well known while others are only now being studied and their threat to human health assessed. The most common and widespread air pollutants include six that the federal goverment has designated criteria pollutants, requiring the EPA to gather scientific and medical information on their environmental and human health effects.

Criteria Air Pollutants

Criteria pollutants are those for which maximum ambient air levels are mandated. In other words National Ambient Air Quality Standards (NAAQS) have been set. The standards specify the maximum levels of concentration of these pollutants allowable in the outdoor air. Air pollutants can be separated into Primary and Secondary air pollutants. Primary pollutants are emitted directly into the air. The six criteria pollutants are:

1. Particulate Matter (PM10 and PM2.5) - It includes dust, ash, lint, smoke, pollen, and many other suspended materials. PM10 and PM2.5 refers to the particle size in micro-meters (µm). Particles that are 2.5µm or less are respirable and can get to the gas exchange area in the lung and reach the circulatory system.
2. Sulfur Dioxide (SO2) - It is a colorless corrosive gas produced by fuel combustion. It can directly damage plants and animals. It is a precursor of acid deposition (acid rain) since it can lead to sulfuric acid.
3. Carbon Monoxide (CO) - Produce by any type of incomplete combustion. It is extremely toxic, odorless and colorless.
4. Nitrogen Oxides (NOx) - Consisting primarily of nitric oxide (NO) and nitrogen dioxide (NO2). They are formed when combustion occurs at very high temperatures.
5. Ozone (O3) - It is a photochemical oxidant. It is a Secondary air pollutant since it is form by a complex series of chemical reactions in the atmosphere in the precense of sun light. The precursos of ozone are nitrogen dioxide and volatile organic compounds (VOCs) or reactive hydrocarbons.
6. Lead (Pb) - It is a metabolic poison and neurotoxin that binds to essential enzymes and cellular components and inactivates them. The major source of lead used to be leaded gasoline.

Click here to go to the EPA web site on ozone.

Click here and get more information about ozone formation.

Clean Air Act

EPA: Air Now

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