Smog
According to the United States Environmental Protection Agency (EPA) which tracks and reports air quality in the US, breathing smoggy air can be hazardous to human health because of it content of Ozone, particularly when ozone is present in dangerously elevated levels in the air we breathe. Ozone is formed in the summer when sunlight, associated with hot temperatures and stale air interacts chemically with urban air pollution emitted by motor vehicles, chemical plants, refineries and power plants. Toxic air pollutants may exist as particulate matter or as gases.
Ozone is a gas that is colorless, odorless and harmful when found in the Earth's lower atmosphere, near ground level. This is in contrast to the ozone that occurs naturally in the Earth's upper atmosphere, approximately 10 to 30 miles above the Earth's surface. The EPA indicates that the upper atmosphere ozone forms a protective layer that shields us from the Sun's harmful ultraviolet rays.
The Air Quality Index (AQI) developed by the EPA is a scale of air quality and is used to report the levels of ozone and other common air pollutants. The standard AQI ramps from 0 to 500. The higher the AQI value for a particular pollutant the greater the danger to human and animal health. Air quality is measured all over the country by monitoring systems.
From:Smog, Who Does It Hurt?:
| Ozone
Concentration (ppm) (8-hour average, unless noted) |
Air
Quality Index Values |
Air
Quality Descriptor |
| 0.0 to 0.064 | 0 to 50 | Good |
| 0.065 to 0.084 | 51 to 100 | Moderate |
| 0.085 to 0.104 | 101 to 150 | Unhealthy
for Sensitive Groups |
| 0.105 to 0.124 | 151 to 200 | Unhealthy |
| 0.125 (8-hr.) to 0.404 (1-hr.) | 201 to 300 | Very Unhealthy |
The EPA, to make it easier for people to understand air quality has created ozone color maps that show ozone levels in many areas of the country. The map is updated throughout the day and shows ozone buildups during the summertime.
Los Angeles, because of its hot and dry climate, its large urban population and varied air pollution sources, has long been recognized to have higher ozone levels than the rest of the US.
Ozone health effects
Even healthy people will experience irritation of the respiratory system. Ozone causes constriction of the bronchial airways. ie: coughing, sore throat, earaches, wheezing, chest discomfort, uncomfortable breathing. People who exercise of work outdoors may experience diminished exercise capacity. Those individuals with heart and lung disease react more severely to air pollution. People with asthma have more asthma attacks when ozone levels are high. Ozone makes individuals become more sensitive to allergens and can also be involved in the development of asthma. Ozone weakens the immune system, and facilitates the development of lung infections. Thus ozone can inflame and damage the lung tissue. Some particulates may contain carcinogens ("cancer stimulating agents").
Children appear to be more sensitive to the adverse effects of air pollution. Epidemiologists have documented an increased general rate mortality in children; increased events of acute respiratory disease; longer duration of infectious episodes; aggravation of bronchial asthma, especially severe, when high levels of air pollution were present.
Besides ozone, other harmful pollutants that reach dangerously unhealthy levels are carbon monoxide, sulfur dioxide, nitrogen oxide, lead, and fine particles of 10 microns of less. In 1992, Carbon Monoxide levels exceeded the federal air quality standards in 20 US cities.
A significant report was published in "Occupational and Environmental Medicine" - 2000 Dec; 57:818-22. The study's objective was to determine the association between air pollution and the risk of cardiovascular diseases. In over 7000 office workers in London between 1991-93 the investigators discovered higher concentrations of fibrinogen in the blood during the warm season - April to September - on days when atmospheric Nitrogen Dioxide was much higher than normal. An excess of fibrinogen increases the coagulability of the blood, making it easier for blood to clot. The investigators concluded a possible association between increased fibrinogen levels and an increased risk of cardiovascular events.
Other investigators, Nicolosi GL, have reported the role of fibrinogen in cardiovascular risk. He reported that hypertensive individuals with plasma fibrinogen levels greater than 3.5 g/liter has a 12 fold higher cardiovascular risk than those with plasma fibrinogen levels less than 2.9g/liter. (Nicolise G.L. In. J. Cardiology 1998; 65 suppl 1: 375-8.)
Air pollution and Exercise
According to the American Lung Association, "exercise makes us more vulnerable to health damage from air pollutants. We breathe more air during exercise or strenuous work. We draw air more deeply into the lungs. And when we exercise heavily, we breath mostly through the mouth, bypassing the nose, the body's first line of defense against pollution".
Since congress passed the Clean Air Act, the EPA has established and enforces the Air Toxic Program, in an attempt to reduce the risks to the public health and the environment. Because of their efforts, the country's air quality has improved significantly in the last 20 years.