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National Air Quality Forecast Capability FAQs

COMMENT/QUESTION:

I like the ozone map now available, but can't really use it. There is no "guidance" given on the explanatory page as to what is considered a high range and low range. Where can we get information on what are safe levels and what are not?

RESPONSE:

PROVIDED BY:
Chet Wayland, Director
Air Quality Assessment Division
EPA’s Office of Air Quality Planning and Standards

The ozone maps available as air quality forecasting guidance products represent concentrations of forecasted ground-level ozone. The guidance is used by state and local air quality forecasters to assist them in issuing Air Quality Index (AQI) forecasts. The AQI links air quality-- in this case, for ozone concentrations-- to health effects and cautionary language or interpretive guidance for individuals.

When ozone is the only pollutant affecting air quality, the risks to people’s health can be described from both short-term exposure to ozone (based on 1-hr averaged concentrations) and longer-term exposure to ozone (based on 8-hr average concentrations). EPA developed the following scale that relates shorter and longer-term exposure to the ambient ozone concentrations, in parts per billion (ppb), to health risk.

Air Quality Index for Ozone

(based on 8-hour average concentration)
Index Values (Concentration Range) Air Quality Descriptors
 
Who needs to be concerned What should I do?
0 - 50
(0 - 54 ppb)
Good
 
No need for concern It's a great day to be active outside.
51 - 100
(55 - 70 ppb)
Moderate
 
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 easier.

Everyone else: It's a good day to be active outside.

101 - 150
(71 - 85 ppb)

Unhealthy for Sensitive Groups
 

Sensitive groups include: people with lung disease such as asthma, older adults, children and teenagers, and people who are active out- doors.

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.

151- 200
(86 - 105 ppb)
Unhealthy
 
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.

201 - 300
(106 - 200 ppb)
Very Unhealthy
 
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.

301 - 500
( ≥ 201 ppb)
Hazardous
 
Everyone Everyone: Avoid all physical activity outdoors.
(This ozone AQI table was last updated May 10, 2016 and can be downloaded as an image file or as a pdf)
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COMMENT/QUESTION:

I found this service surfing around your website. Could someone please explain how the air quality in NYC could be so much better than the rest of the Northeast?

RESPONSE:

PROVIDED BY:
Ken Schere, Senior Science Advisor
Atmospheric Modeling and Analysis Division
EPA’s National Exposure Research Laboratory

By looking at ozone, it may seem as though the air quality is better in the middle of NYC than elsewhere around it. This is misleading though. Ozone is produced through a complex set of chemical reactions in the atmosphere. It needs the starting ingredients of nitrogen dioxide and hydrocarbons to make the reactions happen. These gases are emitted in copious amounts from urban areas, such as NYC. One usually finds higher ozone in a downwind direction from the urban area, since it takes a few hours for the chemical reactions to occur and form higher ozone concentrations. So the pollutant gases emitted within NYC may cause higher ozone to form a few hours downwind, such as in southern CT or Long Island . However, if the winds are calm, the ozone-forming reactions will occur closer to the urban source areas and cause ozone buildup in the urban cores.

A complicating factor is that one of the precursor gases emitted in urban areas, nitrogen oxide, also depletes ozone. The effect is most dramatic in the evening and overnight hours when there is little or no sunlight. The net effect of these chemical and transport processes often causes the ozone concentrations within the core of large urban areas to be lower than the surrounding areas. However the air is not "cleaner" here even if the ozone concentrations are lower. The urban core is bathed in the ozone precursor gases, which themselves can be irritating or in some cases, toxic. A host of other pollutants, including fine particles, are also released in the urban areas. And under conditions of light winds and stagnation, ozone too can build up within the urban cores.

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COMMENT/QUESTION:

I would like to acquire NOAA's historical air quality forecast guidance. How can I get archived forecast products?

RESPONSE:

PROVIDED BY:
Ivanka Stajner
Manager, National Air Quality Forecast Capability
Science and Technology Integration
National Weather Service

Operational air quality forecast guidance is archived by the National Climatic Data Center (NCDC) in Asheville, NC. The guidance is archived in a binary format called GRIB2. Archived air quality forecast guidance files for ozone, smoke and dust can be requested at the following link https://www.ncdc.noaa.gov/has/HAS.StationYearSelect?datasetname=9950_01&subqueryby=STATION&applname=&outdest=FILE&dtypesort=dtypeord&stationsort=id. As the request gets processed, an email is sent with the link to access the data.

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