Air Quality

Air Quality

Our Position

The Alliance supports policies to encourage new technology-based solutions, including higher vehicle gas mileage standards to reduce carbon dioxide and green house gases, and believes the region should be held harmless for airborne ground level ozone generated outside and transported into the region.

Current Status

Air quality in the metropolitan Washington region is improving dramatically. In fact, in 2015 the region recorded only one Code Red (unhealthy for all) rated days.

Compare this to the 1980s when the region averaged 17 Code Red days. During the first decade of this century, the average is less than 3. Again, in 2015 there was only 1.

This progress has occurred despite dramatic increases in population, registered vehicles and vehicle miles traveled, in large part due to technological advances in fuel and engines.

The region’s current fiscally Constrained Long Range Plan (2015-2040) or CLRP and shorter term Transportation Improvement Plan (FY 2015-2020) conform to the requirements of the Clean Air Act Amendments of 1990. In fact since 1990 mobile source Nitrogen Oxide emissions have declined by nearly two-thirds and mobile source Volatile Organic Compound (VOC) emissions have declined by nearly 80%, again despite massive increases in population, motorized vehicles, daily trips and vehicle miles travel. Even better, with higher mileage standards, cleaner and alternative fuel vehicles and the retirement of older vehicles from the fleet transportation emission levels are expected to improve even more between now and 2040.

This progress is very important, not only for the overall health of area residents, but because for decades transportation opponents have tried to promote the false notion that air quality is getting worse and therefore the region cannot be permitted to build new highways and river crossings or upgrade existing facilities.

History of EPA's Ozone Standards

In 1971 the Environmental Protection Agency (EPA) established a 1-hour ozone standard of .08 parts per million (ppm) for Code Red (unhealthy for all persons) air quality. In other words, if an ozone monitor in a particular area were to record ozone levels at .08 ppm or higher within a 1-hour time period, the entire region would be considered in violation.

In 1979, the EPA revised the 1-hour Code Red standard upwards to .12 ppm, making it easier for the region to stay in conformity. Despite this adjustment, the Washington Metropolitan region averaged 17 Code Red days per year in the 1980s.

In July 1997, the EPA replaced the 1-hour standard with an 8-hour standard set at .084 ppm. The 8-hour standard is more difficult to meet because any exceedence over an 8-hour period (as opposed to only one hour) is considered a violation. With the 8-hour standard came the introduction of the Code Orange (unhealthy for sensitive groups) designation, which was set at .085 to .104 ppm. While still a violation, the Code Orange designation is severe as Code Red. Introduction of the Code Orange category was an acknowledgement that the Code Red category had been too broad.

As the number of Code Red days declined due to technological advances, the environmental community and media began treating Code Orange days as Code Red days with the implication that air quality was getting worse for everyone, when in fact it was improving.

On March 12, 2008, the EPA strengthened its national ambient air quality standards by lowering the Code Red threshold to .096 ppm and lowering the Code Orange theshold to .076. As a result, the region is likely to achieve more Code Orange or worse air quaility days not because our air is increasingly unhealthy, but because the standards are more rigorous.

EPA’s Ozone Air Quality Index Breakdown

The AQI is an index for reporting daily air quality ranging from 0 to 500. The higher the AQI value, the greater the level of air pollution and the greater the health concern.

For more information, click here.

An AQI level of 100 generally corresponds to the national air quality standard, which is the level the EPA has set to protect public health. AQI levels below 100 are generally thought of as satisfactory, while levels above 100 are considered unhealthy for at risk groups, and then for everyone as the AQI rises.

Air Quality Index
AQI Value

Air quality is considered good, and air pollution poses little or no risk.

Air quality may pose a moderate health risk, especially for those who are unusually sensitive to air pollution.

Unhealthy for Sensitive Groups
Members of sensitive groups, children and adults with respiratory and heart ailments, may experience health effects and should limit time spent outside. The general public is not likely to be affected.

Everyone may experience health effects and should limit their outdoor activity; members of sensitive groups may experience more serious health effects.

Very Unhealthy
Everyone may experience more serious health effects and should avoid outdoor activities, especially individuals with heart and breathing ailments, children, and older adults.

Ground Level Ozone

Ground level ozone is a colorless gas formed through chemical reactions on hot days.  Washington’s hot, humid climate and location downwind from Midwestern power plants are major contributors to the region’s ozone situation.

Ozone Components

Ozone consists of Volatile Organic Compounds (VOC) and Nitrogen Oxides (NOx).
VOC:  Are formed by fossil fuel combustion and evaporation of gasoline, solvents, paints, etc.
NOx:  Are the result of fossil fuel combustion.  Tends to increase at higher and lower speeds.  Congested highways generate lots of NOx.

Air Quality Data