Get Adobe Acrobat Reader
Citizen Alert Button

Page Modified
3/15/12 11:05 AM

Air Quality Forcast

Why do we need to worry about air quality?

The quality of our local air affects the way we live and breathe. Millions of people live in areas where ground level ozone, very small particles, and toxic pollutants pose serious health concerns. Air pollution can impact our health over short periods of time or accumulate in our systems to pose chronic health concerns. When people have a short-term exposure to air pollutants above certain levels, they may experience temporary health concerns, such as eye irritation, throat irritation, and difficulty breathing. Exposure to air pollution may also trigger attacks of pre-existing lung conditions such as asthma. Long-term exposure to air pollution can cause or aggravate chronic health concerns, such as cancer and damage to the body's immune, neurological, reproductive, and respiratory systems.

Air pollution is not just a problem found in our cities. The air pollution that we create can cover large geographic areas and remain in the environment for long periods of time. These air pollutants can also be carried hundreds of miles by winds and can affect distant areas far from the source of the pollution.

Air Quality History

Clean Air Act

Air pollution has been a problem since the middle ages. In 1306 Edward I banned the burning of sea coal because of the noxious odors emitted. In the late 1800's the advancement of the Industrial Age in the United States dumped millions of tons of pollutants into the air and caused many health issues.

The first federal law passed in the United States that dealt with air pollution was the Air Pollution Control Act of 1955. It identified air pollution as a national problem and mandated federal research programs to investigate health and welfare effects of air pollution.

The Clean Air Act of 1963 was the next significant piece of legislation passed by the federal government to study and mitigate the effects of air pollution. Throughout the 1960's amendments were made to the Act to designate funding for research and control programs, set standards for auto emissions and industries, and began researching effects of transport from other countries such as Mexico and Canada.

In 1970, the Environmental Protection Agency (EPA) was formed along with the Clean Air Act of 1970. The formation of EPA marked a dramatic change in national policy regarding the control of air pollution. Whereas previous federal involvement had been mostly in an advisory and educational role, the new EPA emphasized stringent enforcement of air pollution laws. The passage of the Clean Air Act of 1970 marked the beginning of modern efforts to control air pollution.

The highlight of the 1970 amendments was the establishment of an air quality management approach based on the adoption on National Ambient Air Quality Standards (NAAQS). These standards limit the concentrations of pollutants that "endanger the public health or welfare." Initially, NAAQS were established for six pollutants, particulate matter, sulfur dioxide, carbon monoxide, nitrogen oxides, ozone and lead.

The Clean Air Act was amended again in November of 1990. The new legislation placed renewed emphasis on controlling emissions of hazardous air pollutants and introduced efforts aimed at controlling acid rain and ozone depletion in the atmosphere. The United States also participated in the Montreal Protocol, which established an international effort to phase out ozone-depleting substances. The 1990 amendments require the complete phaseout of CFCs and other ozone-depleting compounds by the year 2000.

Local History

Overall, there is a trend that air quality has been improving in Maryland. During the 1980's, Maryland averaged 20 days a summer when ground level ozone exceeded the federal health standard (Code Red conditions). Maryland averaged 10 Code Red days a summer during the 1990's. This improvement in air quality can be attributed to the fact that Maryland has adopted all mandated federal control measures, implemented numerous local control programs, and has gained some help from the local community in limiting pollution-forming activities on forecasted Code Red days.

Ground-level ozone is Maryland's most significant air pollution problem. MDE provides daily ozone forecasts for the Baltimore/Washington area over the period May to September.

What is ozone?


Ozone is an odorless, colorless gas which occurs naturally in the earth’s upper atmosphere, where it shields us from the sun’s harmful rays (‘good ozone"). At ground-level, ozone is a noxious pollutant created by a chemical reaction between oxides of nitrogen (NOx) and volatile organic compounds (VOCs) in the presence of sunlight ("bad ozone").

Ozone Cookbook

Atmospheric vs. Ground level

Whether ozone is good or bad depends on its location. Ozone occurs in two layers of the atmosphere. The stratospheric or "good ozone" layer extends from about ten miles above the earth’s surface upward to about 30 miles above the earth’s surface and protects life on earth from the sun’s UV-b rays. The layer surrounding the earth’s surface is the troposphere. The troposphere extends to a level about ten miles up, where it meets the stratosphere. Here, ground-level or "bad ozone" is an air pollutant that damages human health, vegetation, and many common materials. It is a key ingredient in urban smog.

The Ozone Layer

How is it formed?


Ground-level ozone is created when intense sunlight reacts with nitrogen oxides (NOx) and volatile organic compounds (VOCs). High concentrations of ground-level ozone occur during hot, sunny days, when the flow of air is limited or stagnant and a mixture of VOCs and NOx is present. The graphic below depicts where the different sources of NOx and VOC's.

Sources of NOx & VOC

Health affects

Ozone acts as a powerful respiratory irritant at the levels frequently found in most of the nation's urban areas during summer months. Symptoms include shortness of breath, chest pain when inhaling deeply, wheezing and coughing.

Research on the effects of prolonged exposures (6 ½ hours) to relatively low levels of ozone have found reductions in lung function, biological evidence of inflammation of the lung lining and respiratory discomfort.

In studies of animals, ozone exposure has been found to increase susceptibility to bacterial pneumonia infection.

Recently, attention has begun to focus on the effects of long-term, repeated exposures to high levels of ozone. A study of a sample of long-time residents of Los Angeles, which has the highest and most frequent ozone problem in the nation, found that the group had a higher than expected loss of lung function over time. Long-term exposures of animals to moderate ozone levels produce changes in the structure of the lung.

Who is at risk?

The U.S. Environmental Protection Agency (EPA) has identified three groups of people who are at particular risk from high ozone levels:

1. People With Pre-Existing Respiratory Disease

People with existing lung disease (e.g., chronic bronchitis, emphysema, asthma) already suffer from reduced lung function and therefore cannot tolerate an additional reduction in lung function due to ozone exposure.

2. A Sub-Group Of The General Public Referred To As "Responders"

Studies have found that a sub-group of the general healthy population responds to ozone exposure while exercising with significantly greater losses in lung function than the average response of the overall group under study. There is currently no way to identify these "responders" prior to ozone exposure, but the EPA estimates that this sub-group represents 5 to 20 percent of the total U.S. population.

3. Individuals Who Exercise Outdoors

Numerous laboratory and "real world" ozone exposure studies confirm that people who exercise, or otherwise participate in activities that increase their respiratory rate, respond much more severely to ozone exposure than people at rest.

The Air Quality Index (AQI) and Air Quality Forecasts

The AQI is an index for reporting daily air quality. It tells you how clean or polluted your air is, and what associated health effects might be a concern for you. The AQI focuses on health effects you may experience within a few hours or days after breathing polluted air.

Think of the AQI as a yardstick that runs from 0 to 300. The higher the AQI value, the greater the level of air pollution and the greater the health concern. For example, an AQI value of 50 represents good air quality with little potential to affect public health, while an AQI value over 300 represents hazardous air quality.

An AQI value of 100 generally corresponds to the national air quality standard for the pollutant, which is the level EPA has set to protect public health. AQI values below 100 are generally thought of as satisfactory. When AQI values are above 100, air quality is considered to be unhealthy-at first for certain sensitive groups of people, then for everyone as AQI values get higher.

To make it easier to understand, the AQI is divided into five categories:

Air Quality Index
(AQI) Values

Levels of Health Concern


Recommended Action

When the AQI
is in this range:

...air quality conditions are:

…as symbolized by this color:

… these actions can be taken:

0 to 50



- Carpool, use public transit, bike, or walk.

- Keep cars and boats tuned.

- Use environmentally friendly paints and cleaning products.

51 to 100



- Consolidate trips and errands.

- Limit car idling when possible.

- Conserve electricity and set air conditioners to 78 degrees.

101 to 150

Unhealthy for
Sensitive Groups


- Children, adults who experience difficulty breathing outside, & those with respiratory or heart ailments should limit prolonged outdoor activities.

- Limit driving and refuel cars after dusk.

- Avoid using aerosol products.

- Carpool, use public transit, or telework.

151 to 200



- Children & those with respiratory or heart ailments should reduce outdoor activities.

- Avoid mowing lawns with gas-powered mowers.

- Put off any painting until later.

- Other recommendations listed above.

201 to 300

Very Unhealthy


- Children, older adults, & those with respiratory or heart ailments should avoid outdoor physical activities.

- Everyone else should avoid prolonged or heavy exertion outdoors.

- Other recommendations listed above.

Each category corresponds to a different level of health concern. The five levels of health concern and what they mean are:

What is being done and what can I do?

Washington County, as part of an Early Action Compact entered into with the EPA, has partnered with Maryland Department of the Environment and their Air Quality Action Days Program and with Clean Air Partners.

Air Quality Action Days

The Ozone Action Days program is a voluntary initiative by government, environmental groups, and business leaders working with the general public to take extra action to prevent air pollution when high ozone levels are predicted. Because ground-level ozone forms under certain weather conditions, a regional team of meteorologists can predict days when ground-level ozone concentrations may exceed health standards. These are generally hot (90+ degrees), sunny days with little or no wind.

Clean Air Partners

Clean Air Partners is a public-private partnership chartered by the Metropolitan Washington Council of Governments (MWCOG) and the Baltimore Metropolitan Council (BMC) to build and broaden awareness of how individuals contribute to air pollution while informing them about the adverse effects of ground level ozone.

The primary focus of the partnership is to promote easy and effective voluntary actions that individuals and employers can take to reduce production of and exposure to air pollution.

General Public

There are many simple actions that people and businesses can take to help reduce air pollution on Ozone Action Days. The next time you hear that it is a CODE RED day, lend a hand to make our air cleaner. Here's what you can do on Ozone Action Days.


Listed below are several links to other agencies that provide technical and educational services regarding air quality.

United States Environmental Protection Agency -
Maryland Department of the Environment -
Air Quality Forecast from -
Clean Air Partners -
American Lung Association -
American Heart Association -

Error processing SSI file