Clean Air and the New, More Protective Ozone Standard

Why Did EPA Change the Standard?

The federal Clean Air Act requires EPA to review the health standards for certain pollutants every five years. As part of this process, EPA convenes the Clean Air Scientific Advisory Committee (CASAC), a group of independent scientific experts. CASAC reviews health literature and studies and makes recommendations based on their findings.

CASAC advised EPA that the 75 parts per billion (ppb) standard is not "fully protective of public health" and recommended the adoption of a stricter standard between 60 and 70 ppb, leaving the policy decision of what standard provides an "adequate margin of safety" to EPA's Administrator, as required by the Clean Air Act.

On October 1, 2015, EPA tightened the ozone standard to 70 ppb. At the same time, EPA adjusted the Air Quality Index (AQI) breakpoints to reflect this new standard.


The Air Quality Index (AQI)

AQI Values 2015 Breakpoints
2008 Standard
2016 Breakpoints
2015 Standard
Good
(0-50)
0-59 0-54
Moderate
(51-100)
60-75 55-70
Unhealthy for
Sensitive Groups
(101-150)
76-95 71-85
Unhealthy
(151-200)
96-115 86-105
Very Unhealthy
(201-300)
116-374 106-200
Hazardous
(301-500)
375-600 201-600
 

How Does This Work?

The AQI is the primary tool used to advise people about air quality conditions. This tool uses a series of breakpoints in the monitored air quality data to translate to the color-coded AQI chart.

As an example, during the 2015 ozone season, an air quality reading of 55 ppb would have been interpreted as code green, Good Air Quality. This year, the same reading, 55 ppb, will be interpreted as code yellow, Moderate Air Quality. The chart to the left illustrates the breakpoints for the 2015 and 2016 ozone seasons and how they relate to the AQI.

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Ground Level Ozone

The air today is much different from the air of say 20 years ago. After many years of federal and state regulations on vehicles, consumer products, power plants and other point sources, Maryland's air quality has dramatically improved. Efforts to reduce volatile organic compounds (VOCs) and nitrogen oxide emissions (NOx), which are the pollutants that form ground-level ozone, have greatly reduced the amount of air pollution in the State.

By controlling emissions, we have effectively altered the composition of the atmosphere by reducing the concentrations of certain chemical species in ways that affect reactions governing the production of ozone. The spatial and temporal aspects of ozone precursor distribution have changed from the 1980s when NOx and VOC concentrations were much higher. Now smaller reductions in NOx emissions appear to cause greater ozone reductions.

Use the chart below to help reduce your exposure and protect your health.

To learn about Maryland's monitoring work, please visit our Air Monitoring Program page
For your local air quality forecast, visit www.airnow.gov.

View or print guide in PDF (2 pp., 67KB, about PDF)

The Air Quality Index (AQI)

Air Quality Index
(0-500)
Who Needs to be Concerned? What Should I Do?
Good
(0-50)
It’s a great day to be active outside.
Moderate
(51-100)
Some people who may be unusually sensitive to ozone. Unusually sensitive people: Consider reducing prolonged or heavy outdoor exertion. Watch for symptoms such as coughing or shortness of breath. These are signs to take it a little easier.

Everyone else: It’s a good day to be active outside.
Unhealthy for Sensitive Groups
(101-150)
Sensitive groups include people with lung disease such as asthma, older adults, children and teenagers, and people who are active outdoors. Sensitive groups: Reduce prolonged or heavy outdoor exertion. Take more breaks, do less intense activities. Watch for symptoms such as coughing or shortness of breath. Schedule outdoor activities in the morning when ozone is lower.

People with asthma should follow their asthma action plans and keep quick relief medicine handy.
Unhealthy
(151-200)
Everyone

Sensitive groups: Avoid prolonged or heavy outdoor exertion. Schedule outdoor activities in the morning when ozone is lower. Consider moving activities indoors.

People with asthma, keep quick-relief medicine handy.

Everyone else: Reduce prolonged or heavy outdoor exertion. Take more breaks, do less intense activities. Schedule outdoor activities in the morning when ozone is lower.

Very Unhealthy
(201-300)
Everyone

Sensitive groups: Avoid all physical activity outdoors. Move activities indoors or reschedule to a time when air quality is better.

People with asthma, keep quick-relief medicine handy.

Everyone else: Avoid prolonged or heavy outdoor exertion. Schedule outdoor activities in the morning when ozone is lower. Consider moving activities indoors.

Hazardous
(301-500)
Everyone Everyone: Avoid all physical activity outdoors.


Note: If you don't have an air conditioner, staying inside with the windows closed may be dangerous in extremely hot weather.
In these cases, seek alternative shelter.