AQI Guide/Report Descriptions
What is the Air Quality Index?
The U.S. Environmental Protection Agency (U.S. EPA) developed the Air Quality Index (AQI) to provide accurate, timely and easily understandable information about daily levels of air pollution. The index provides a uniform system for measuring pollution levels of the major air pollutants regulated under the Clean Air Act.
Once these levels are measured, the AQI figures are reported in all metropolitan areas of the United States with populations exceeding 200,000. Index figures enable the public to determine whether air pollution levels in a particular location are good, moderate, unhealthy or very unhealthy.
U.S. EPA and local officials use the AQI as a public information tool to advise the public about the general health effects associated with different pollution levels, and to describe precautionary steps that may need to be taken if air pollution levels rise into the unhealthy range.
Air Quality Index Intervals and Potential Health Effects
U.S. EPA has established air quality standards protecting against health effects that can occur within short periods of time (a few hours or a day) for each of the major air pollutants regulated under the Clean Air Act.
The AQI converts the measured pollutant concentration in a community's air to a number on a scale of 0 to 500. The most important number on this scale is 100, since this number corresponds to the standard established under the Clean Air Act.
For example, the eight-hour standard for ground-level ozone — that is, the allowable concentration of this pollutant in a community's air — is 75 parts per billion (ppb). A 75 ppb eight-hour average for ozone would translate to an AQI level of 100. An AQI level higher than 100 means that a pollutant is in the unhealthy range; an AQI level at or below 100 means that a pollutant reading is in the satisfactory range. The intervals and the terms describing the AQI air quality levels are as follows:
From 0 to 50 .......................... Good
From 51 to 100 ....................... Moderate
From 101 to 200 ..................... Unhealthy for Sensitive Groups
From 151 to 200 ..................... Unhealthy
From 201 to 300 ..................... Very Unhealthy (Alert)
The intervals on the AQI scale relate to the potential health effects of the daily concentrations of each pollutant. Each value has built into it a margin of safety that, based on current knowledge, protects highly susceptible members of the public. For example, if U.S. EPA reports an AQI level of 90 for ozone for a given metropolitan area, residents of that area would know that the ozone level for the region is at the high end of the moderate range.
Before determining which stage is to be called, officials examine both current pollutant concentrations and prevailing and predicted meteorological conditions.
Levels higher than 100 may trigger preventive action by State or local officials, depending on the level of the pollution concentration. This could include health advisories for citizens or susceptible individuals to limit certain activities and potential restrictions on industrial activities.
The 200-level is likely to trigger an "Alert" stage. Activities that might be restricted by local governments, depending on the nature of the problem, include incinerator use and open burning of leaves or refuse.
A level of 300 on the AQI will probably trigger "Warning," which is likely to prohibit the use of incinerators, severely curtail power plant operations, cut back operations at specified manufacturing facilities, and require the public to limit driving by using car pools and public transportation.
An AQI level of 400 or above would constitute an "Emergency," and would require a cessation of most industrial and commercial activity, plus a prohibition of almost all private use of motor vehicles. If air pollution were to reach such extremely high levels, death could occur in some sick and elderly people, and even healthy people would likely necessitate restrictions on normal activity.
This report is a listing of the "Air Quality Index" value calculated for the appropriate averaging period for a given pollutant as well as the maximum ambient value for that pollutant, for every Ohio EPA and Local Air Agency monitoring station for yesterday. This report is updated every hour in the event any values are reviewed and updated. Because the Ozone 8-hour average is a forward-rolling-average, the value for the 11:00 PM hour for a given day is calculated using data from 11:00 PM through 6:59 AM the following day. As a result, this report will show the full, previous, calendar day by 8:30 AM on a given day. Prior to that, from 12:00 AM until 8:30 AM each day, this report will still reflect two calendar days ago. All times EST. EDT will be an hour shifted from the times reported here.
Note: Data in these reports are always referenced to Eastern Standard Time (EST). Air quality reports are updated several times during a day at regular intervals (generally 15 or 30 minutes past the hour or hourly from 8 a.m. - 10 p.m.).
Disclaimer: These reports present the data in "RAW" form, meaning that the data you see are exactly what was collected electronically from each monitor. It is important to remember that "RAW" data are never considered valid until verified by Ohio EPA and Local Air Agency personnel.
The data in these reports have neither been validated nor quality assured by state or local air monitoring agencies. These data may change and are not considered official until they have undergone a quality assurance/quality control (QA/QC) review.
Odd data may be invalid due to possible equipment trouble or telemetry problems.