Air Quality Index - A way to measure the amount of the six major pollutants in the air. These pollutants are particulates, sulfur dioxide (SO2), carbon monoxide (CO), nitrogen dioxide (NO2), lead (Pb), and ozone (O3). A measurement of 0 to 100 is considered acceptable, but from 100 to 150 is unhealthy for old people, young children, and people with asthma. Above 150 is unhealthy for everyone.

Although any of the above mentioned pollutants can affect our weather, the most common in Kentuckiana are ozone and particulates. Particulates or particulate matter are fine particles of foreign matter that float around in the air we breathe. PM10 describes the fraction of airborne particulate matter that is less than 10 microns in size. Fine particles are of the greatest concern since they are capable of being easily transported over long distances on currents of air. Also, fine particles may be drawn into the respiratory airways where they may adversely affect health. Recently, the attention of scientists has been drawn towards studying the PM2.5 fraction and even smaller particles, which can penetrate the very deepest parts of the lung. PM10 and other particulate matter may vary considerably in chemical and physical composition. The principal sources of these particles are combustion processes, including traffic and industry.

Ground Level Ozone – Sometimes referred to as smog, ground level ozone is formed by a chemical reaction between volatile organic pollutants (VOCs) and oxides of nitrogen (NOx) in the presence of sunlight. Ozone concentrations can reach unhealthy levels when the weather is hot and sunny with little or no wind. Ozone at the ground level causes adverse effects on lung function and other unhealthy respiratory effects. Also known as tropospheric ozone, ground level ozone occurs near the earth's surface in the lowest layer of the atmosphere, also known as the troposphere. In the troposphere, ozone is a natural constituent of the air we breathe. However, at critical increased concentrations, it becomes a harmful pollutant. In natural (unpolluted) conditions, ozone is formed in the troposphere when UV radiation that reaches the Earth’s surface converts nitrogen dioxide to nitric oxide and an oxygen radical. The oxygen radical may subsequently react with diatomic oxygen, 02, to form ozone. Ozone is then broken down when it reacts with nitric oxide, forming diatomic oxygen and nitrogen dioxide.

Air Quality Alert - A message issued by the Department of Natural Resources (DNR) through the National Weather Service when the AQI is expected to reach above 100. This message encourages you to prevent air pollution by postponing the use of lawn mowing, motor vehicles, boats, as well as filling their vehicle gas tanks.

Jeremy Kappell
WHAS11 First Alert StormTeam Meteorologist

7/03/05