How clean is the air in your metropolitan area or county? Use this map to find out.
The U. S. Environmental Protection Agency (EPA) has provided a scale called the Air Quality Index (AQI) for rating air quality. The AQI scale is based on the National Ambient Air Quality Standards (NAAQS) and is described in the Code of Federal Regulations, Part 58, Appendix G. This map is based on the EPA AQI scale.
The latest AQI image available is for January 6, 2009 as of 8:15 pm EST (Eastern Standard Time). If the image below is not current, force your browser to reload the correct image. Click on any of the boxes on the image for a detailed listing of all the AQI pollutants monitored in that area. Click anywhere on the image outside the boxes for the Air Quality Index (AQI) Report for the entire state.
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PLEASE NOTE: Data in this image is collected from IDEM air monitoring sites, local agencies, and private monitoring networks. This data has not been verified by the IDEM or the responsible entity and may change. While this is the most current data, it is not official until it has been certified by the appropriate technical staff. This image is updated hourly.
The image above shows the Air Quality Index (AQI) ratings for each of the NAAQS pollutants that are measured real-time and the critical pollutant that is driving the AQI rating in each metropolitan area or county where pollutant levels are monitored by the IDEM. The critical pollutant is the pollutant with the highest AQI rating measured in the area. The image is updated each hour and covers the period from midnight through the indicated ending time.
There are four pollutants in Indiana that go into the Air Quality Index: ozone, carbon monoxide, sulfur dioxide, and particulate matter. In the image above, each metropolitan area or county is represented by a small box which is color coded to match the AQI rating for the day (see How Do I Interpret the AQI Rating?). Inside the box, the pollutant that is driving the AQI rating is identified by its abbreviation (see the table below). At the bottom of each box is a small legend that indicates which pollutants are actively measured in that area. Please note that not all pollutants are measured in all areas. The table below briefly describes each pollutant that goes into the AQI.
| Pollutant | Abbreviation | Description |
|---|---|---|
| Ozone | O3 | Ozone is a form of oxygen with three atoms instead of the usual two atoms. It is a photochemical oxidant and, at ground level, is the main component of smog. Unlike other gaseous pollutants, ozone is not emitted directly into the atmosphere. Instead, it is created in the atmosphere by the action of sunlight on volatile organic compounds and nitrogen oxides.
In general, higher levels of ozone usually occur on sunny days with light winds, primarily from March through October. An ozone exceedance day is counted if the measured eight-hour average ozone concentration exceeds the standards. |
| Carbon Monoxide | CO | Carbon monoxide is a colorless, odorless, very toxic gas produced by the incomplete combustion of carbon-containing fuels, most notably by gasoline powered engines, power plants, and wood fires. The eight-hour standard can be exceeded during winter months when very stable atmospheric conditions exist. |
| Sulfur Dioxide | SO2 | Sulfur dioxide is produced by burning sulfur-containing fuels (such as coal), smelting metallic ores containing sulfur, and removing sulfur from fuels. There are three sulfur dioxide standards which include a 24-hour average, an annual average, and a three-hour average. |
| Particulate Matter | PM2.5 PM10 | Particulate matter is anything that is suspended in the air. It can be caused by natural phenomena or come from man-made sources. In high enough concentrations, particulates can aggravate existing respiratory problems or even trigger new ones. Particulate matter is broken down by the size of the suspended particles. The IDEM measures or plans to measure particulate matter in the range of 10 microns and smaller (known as PM-10) and 2.5 microns and smaller (known as PM-2.5). A micron is one-millionth of a meter or one 25-thousandth of an inch - by comparison, a human hair is about 50 microns in diameter. The IDEM uses an instrument known as a Tapered Element Oscillating Microbalance (TEOM) to determine mass concentrations of suspended particulates. The microbalance oscillates with a specific period; as more particles are deposited on the microbalance, the oscillation period changes. The amount of change correlates directly to the concentration of particles. This instrument provides a continuous readout of concentrations. The only difference between a PM-10 instrument and a PM-2.5 instrument is the inlet filter. Other instruments use different methods to determine PM (such as radiation attenuation). Coarse particulates (PM-10) come from sources such as windblown dust from the desert or agricultural fields (sand storms) and dust kicked up on unpaved roads by vehicle traffic. PM-10 data is the near real-time measurement of particulate matter 10 microns or less in size from the surrounding air. This measurement is made at standard conditions, meaning it is corrected for local temperature and pressure. Fine particulates (PM-2.5) are generally emitted from activities such as industrial and residential combustion and from vehicle exhaust. Fine particles are also formed in the atmosphere when gases such as sulfur dioxide, nitrogen oxides, and volatile organic compounds, emitted by combustion activities, are transformed by chemical reactions in the air. Large-scale agricultural burning or sand storms can produce huge volumes of fine particulates. PM-2.5 data is the near real-time measurement of particulate matter 2.5 microns or less in size from the surrounding air. This measurement is made at local conditions, and is not corrected for temperature or pressure. |
Each NAAQS pollutant has a separate AQI scale, with an AQI rating of 100 corresponding to the concentration where health effects for each pollutant begin to affect the general public. AQI ratings below 100 indicate no appreciable health risk.
Additional information about the AQI and how it can be used is available from the EPA.
The AQI scale is divided into the following categories:
| Air Quality | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Good | Moderate | Unhealthy (for sensitive groups) | Unhealthy | Very Unhealthy | Hazardous | |||||||||||||
| 0 | 51 | 101 | 151 | 201 | 301+ | |||||||||||||
| The AQI Air Quality Scale | ||||||||||||||||||
The AQI for ozone is based on either the peak eight-hour running average since midnight OR the peak one-hour measurement since midnight. The AQI's for sulfur dioxide, PM-10, and PM-2.5 are based on a 24-hour average sampled from midnight to midnight, and the AQI for carbon monoxide is based on the peak eight-hour running average since midnight. On most days the critical pollutant is ozone. Ozone one-hour average concentrations of 125 ppb or higher exceed the old NAAQS (AQI rating of 100 or higher). The new NAAQS for ozone is based on eight-hour averages.
