Pollutants & health

What you should know about the air you breathe


Sulfur Dioxide (SO2)

SO2Sulfur dioxide is a colorless gas produced by fossil fuel-burning motor vehicles, refineries and power plants. Fossil fuels such as coal and oil vary in sulfur concentrations and, therefore, in the amount of sulfur dioxide they produce when burned. A high level of sulfur dioxide in exhaust gas can interfere with emission control mechanisms for other pollutants. It reduces respiratory volume and increases breathing resistance in those exposed, especially asthmatics. Studies have also shown that daily mortality rates are consistently associated with sulfur dioxide and ozone levels.

Particulate Matter (PM)

PMParticulate matter (PM) consists of soot and dust particles smaller than the diameter of a human hair. These have two classifications:

  • PM10, or coarse size particles, have a diameter of less than 10 microns.
  • PM2.5, or fine size particles, have a diameter of 2.5 microns or less. This is less than 1/8th the diameter of a human hair. 

The size of these particles enables them to penetrate deeply into our lungs and become captured by lung tissue. The finer the particles, the deeper the penetration and therefore the more danger posed. Even a small increase in PM2.5 can significantly increase mortality. In fact, The American Lung Association believes that PM2.5 represents the most serious threat to our health. 

Exposure to PM pollution has been associated with respiratory and cardiac problems, infections, asthma attacks, lung cancer and decreased life expectancy—with 500,000 annual premature deaths estimated by the World Health Organization. Those most susceptible to this pollution include children, athletes, senior citizens, and people with pre-existing respiratory problems.

Sources of PM include diesel exhaust, soil dust, tire wear, and soot. Exhaust from diesel vehicles produces 79% of the particulate emissions from mobile sources; PM from this source is especially dangerous because of the hundreds of different chemicals that are adsorbed to the particle.

Ozone (O3)

OzoneOzone forms when hydrocarbons combine with nitrogen oxides and chemically react in sunlight. Hydrocarbons and nitrogen oxides are produced primarily by motor vehicles and various industrial practices. Ozone is a highly reactive oxidizing agent that breaks down organic materials, and it is the primary component of smog, which is formed when a natural phenomenon called an "inversion layer" traps these gases and prevents them from dissipating into the atmosphere. As populations grow, ozone and smog are becoming problems for large cities throughout the country.

Symptoms of ozone exposure include coughing, shortness of breath, wheezing, fatigue, throat dryness, chest pain, headaches and nausea. It has been linked to inflammation of lung tissue, reduced lung capacity, development of asthma, increased lung cancer mortality rates, and accelerated lung aging. Ozone also reduces the respiratory system's ability to fight infection and remove foreign particles such as particulate matter. Lung damage from long-term exposure to ozone can be permanent, while short-term exposure appears to be reversible. Those who are most susceptible to ozone pollution include children, athletes, senior citizens, and people with pre-existing respiratory problems.

Nitrogen Oxides (NOx)

NOxNitrogen monoxide (NO) and nitrogen dioxide (NO2) are the two forms of nitrogen oxide (NOx) found in the atmosphere. Nitrogen oxides contribute to the formation of ozone, production of particulate matter pollution, and acid deposition. The presence of nitrogen oxides gives smog its brown appearance. It is produced by factories, motor vehicles and power plants that burn fossil fuels. Diesel engines produce a disproportionately large amount of NOx when compared to gasoline engines because of their high-temperature combustion process.

NO2 has been shown to irritate lung tissue, cause bronchitis and pneumonia, and reduce resistance to respiratory infections; its presence in the atmosphere can have synergistic effects with other forms of air pollution. The health effects of ozone are magnified in the presence of NO2. Frequent or long-term exposure to high levels of nitrogen oxides can increase the incidence of acute respiratory illness in children.


HydrocarbonsHydrocarbons are a class of reactive organic gases (ROG), which are formed solely of hydrogen and carbon. They are formed in the incomplete burning of any organic matter such as oil, wood or rubber; the primary sources are combustion engine exhaust, oil refineries, and oil-fueled power plants. Another source is evaporation from petroleum fuels, solvents, dry cleaning solutions, and paint.

The health risks of hydrocarbons primarily stem from their contribution to ozone and the resulting smog problem. High levels of hydrocarbons in the atmosphere can interfere with oxygen intake by reducing the amount of available oxygen through displacement. Carcinogenic forms of hydrocarbons are considered hazardous air pollutants, or air toxics.

Carbon Monoxide (CO)

COCarbon monoxide (CO) is a colorless, odorless gas produced by burning organic matter such as oil, natural gas, fuel, wood or charcoal. Motor vehicles produce 67% of the man-made CO that is released into the atmosphere. It displaces oxygen in red blood cells, reducing the amount of oxygen available to cells for respiration. Exposure to CO can result in fatigue, angina, reduced visual perception, reduced dexterity, and death. The elderly, young children, and people with pre-existing respiratory conditions are particularly sensitive to CO pollution. It is extremely deadly in an enclosed space, such as a garage or bedroom.

Air Toxics

Air_ToxicsAir toxics, also known as hazardous air pollutants, are pollutants that cause or are suspected of causing cancer in those exposed to them. The category is comprised of 188 toxic and potentially toxic compounds listed by the Federal Clean Air Act. They are generally organic chemicals, including some hydrocarbons that are highly evaporative in nature. Air toxics come from motor vehicles, chemical plants, paint, and any other operation that uses organic compounds. Benzene, formaldehyde, acetaldehyde, 1,3-butadiene, and acrolein are typical examples.

The nature of air toxics still poses many uncertainties about their true health effects. These chemical compounds have many different forms and metabolites as they are broken down, and little is known about how they interact with the body. Benzene has been shown to cause aplastic anemia and acute myelogenous leukemia in occupational studies of workers exposed to it. Known health concerns related to aldehydes include cancer, asthma, and respiratory tract irritation. It is also believed that these air toxics have impacts on the reproductive system by causing chromosomal aberrations or mutations.

The health effects of particulate matter from diesel exhaust are thought to be attributable to the many air toxics that are adsorbed to the particles. These small particles penetrate deeply into the lungs, and are the perfect vehicle for delivering air toxics into the body.






Be a part of the Coalition that works for all Californians' right to breathe clean air!

Get Involved

Stay updated on news, actions and events
We will not share your email address.

Air News