Air Pollution

By Jeffrey Masters, Ph.D. — Director of Meteorology, Weather Underground, Inc.
Effects of Air Pollution
A smoggy day in Seattle

Significant progress has been made in recent years cleaning up outdoor air pollution in the U.S. Between 1970 and 2004, total emissions of the six major air pollutants regulated by the Environmental Protection Agency (EPA) dropped by 54 percent. This is particularly impressive when noted that the gross domestic product increased 187 percent, energy consumption increased 47 percent, and U.S. population grew by 40 percent during the same time, proof that economic growth and environmental protection do go hand in hand. However, air pollution remains a serious threat to public health and the environment. Outdoor air pollution in the U.S. due to particulate pollution alone was estimated by the EPA in 1997 to cause at least 20,000 premature deaths each year. Other estimates place this number at 50,000 to 100,000 deaths per year. Globally, about 800,000 people per year die prematurely due to outdoor air pollution, according to a 2005 study (PDF File) published in the Journal of Toxicology and Environmental Health. This represents about 1.2 percent of total annual global deaths.

Deaths from urban air pollution

Figure 1. Deaths from urban air pollution in 2000, as estimated by the World Health Organization World Health Report, 2002.

While levels of many pollutants have been decreasing in recent years, progress cleaning up one serious pollutant, ground-level ozone, has been difficult. The American Lung Association estimates that over half of the nation's population lives in counties receiving a grade of "F" on their rating system for ozone pollution. The death toll due to air pollution only begins to touch the vast magnitude of human suffering caused by breathing our dirty air--for every 75 deaths per year due to air pollution in the U.S., health scientists have estimated that there are 505 hospital admissions for asthma and other respiratory diseases, 3,500 respiratory emergency doctor visits, 180,000 asthma attacks, 930,000 restricted activity days, and 2,000,000 acute respiratory symptom days.

The Clean Air Act requires the U.S. Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards for six pollutants, called "criteria pollutants", considered harmful to public health and the environment. The EPA maintains a database of air pollution forecasts generated for over 150 locations for these six pollutants by the local or state agencies responsible. These forecasts are sent to The Weather Underground as they are updated, and we post the forecasts for the affected areas. Many smaller cities and rural areas do not have air pollution forecasts available. A comprehensive web page indexing all the available air pollution forecasts and real-time air pollution observations is available at the EPA's AIRNOW site.

The National Ambient Air Quality Standards for the six criteria pollutants are listed below. Units of measurement are parts per million (ppm) by volume, milligrams per cubic meter of air (mg/m3), and micrograms per cubic meter of air (µg/m3). There are two types of national air quality standards. Primary standards set limits to protect public health, including the health of "sensitive" populations such as asthmatics, children, and the elderly. Secondary standards set limits to protect public welfare, including protection against decreased visibility, damage to animals, crops, vegetation, and buildings.

National Ambient Air Quality Standards
Pollutant Standard Value Standard Type
Carbon Monoxide (CO)
    8-hour Average 9 ppm (10 mg/m3) Primary
    1-hour Average 35 ppm (40 mg/m3) Primary
Nitrogen Dioxide (NO2)
    Annual Arithmetic Mean 0.053 ppm (100 µg/m3) Primary & Secondary
Ozone (O3)
    8-hour Average (2008) 0.075 ppm   Primary & Secondary
    8-hour Average (1997) 0.08 ppm   Primary & Secondary
    1-hour Average (limited areas) 0.12 ppm   Primary & Secondary
Lead (Pb)
    Quarterly Average 1.5 µg/m3   Primary & Secondary
Particulate (PM 10) {Particles with diameters of 10 micrometers or less)
    Annual Arithmetic Mean 50 µg/m3   Primary & Secondary
    24-hour Average 150 µg/m3   Primary & Secondary
Particulate (PM 2.5) (Particles with diameters of 2.5 micrometers or less)
    Annual Arithmetic Mean 15 µg/m3   Primary & Secondary
    24-hour Average 35 µg/m3   Primary & Secondary
Sulfur Dioxide (SO2)
    Annual Arithmetic Mean 0.03 ppm (80 µg/m3) Primary
    24-hour Average 0.14 ppm (365 µg/m3) Primary
    3-hour Average 0.50 ppm (1300 µg/m3) Secondary
What you can do about air pollution
Get educated! Weather Underground has compiled a Frequently Asked Questions about air pollution page, and list of links to more detailed air pollution information on the Internet:

1. Dockery, D.W., and C.A Pope III. Acute Respiratory Effects of Particulate Air Pollution. Annual Review Public Health, 1994, vol. 15,107-32.

2. Testimony of George Thurston, Hearing, Subcommittee on Health and Environment, Committee on Commerce, U.S. House of Representatives, Review of EPA's Proposed Ozone and Particulate Matter NAAQS Revisions, May 8, 1997.