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Health Department

Explanation of the Middle Tennessee Air Quality Forecast

This air quality forecast covers the Middle Tennessee counties of Davidson, Cheatham, Dickson, Robertson, Rutherford, Sumner, Williamson and Wilson. It includes a forecast category and corresponding color code for the expected maximum PM2.5 (fine particulate matter) and 8-hour average ozone concentration for the next two days. The PM2.5 forecast will be issued on a daily basis for the entire year. The ozone forecast will be issued from March 1 until October 31 which is the typical ozone season for the Middle Tennessee area. The forecasts will be issued daily by approximately 3:00 p.m. In addition to this website, a daily recorded update of the Air Quality Forecast can be obtained by calling 615-340-0488.

The forecast provides information to the public about PM2.5 and ozone air pollution and their associated health effects. Pollutant specific health effects statements and cautionary statements are provided along with the forecasts. The forecasts also use the following descriptive words and colors to characterize daily air quality.

Air Quality Index Levels of Health Concern Numerical Value Meaning
Good 0-50 Air quality is considered satisfactory, and air pollution poses little or no risk.
Moderate 51-100 Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution.
Unhealthy for Sensitive Groups 101-150 Members of sensitive groups may experience health effects. The general public is not likely to be affected.
Unhealthy 151-200 Everyone may begin to experience health effects; members of sensitive groups may experience more serious health effects.
Very Unhealthy 201-300 Health alert: everyone may experience more serious health effects.
Hazardous > 300 Health warnings of emergency conditions. The entire population is more likely to be affected.

Download the "Air Quality Index Levels" chart

The forecasts are made by using historical air quality and meteorological data (to determine trends) combined with current monitored air quality data and the expected meteorology for the forecast period. This data is then analyzed by computer models to predict the maximum PM2.5 and 8-hour average ozone concentration in the eight county area comprising the Nashville Metropolitan Statistical Area (MSA).

The forecast is being made to alert those in our area that may be sensitive to elevated levels of ozone so that they can make decisions related to their daily activities. However, the air quality forecast is exactly what it says—it is a forecast. Just as our television meteorologists sometimes miss whether it will be cloudy or sunny in our area, sometimes we will miss the actual PM2.5 and ozone category or color code for the day. If there is any question as to how a day will be forecast, we will make every effort to err on the side of over predicting the expected maximum concentration as the intent of this forecasting process is to protect the health of the citizens of Middle Tennessee.

The Middle Tennessee Air Quality Forecast is a cooperative effort between the Metropolitan Public Health Department Pollution Control Division, Tennessee Department of Environment and Conservation Air Pollution Control Division, the Environmental Protection Agency and the Tennessee Valley Authority.

Related Links

AIRNOW - Near real time animated maps of air quality concentrations across the United States as well as other useful air quality information.

Smog City - Interactive tool for understanding ozone formation.