What Is Ground-Level Ozone?
Ozone is a gas composed of three oxygen atoms. While ozone can be found both in the Earth's upper atmosphere and at ground level, the location where it is found determines if ozone is considered beneficial or harmful to humans and the environment. When it is found in the upper atmosphere, ozone is beneficial by protecting us from the sun's ultraviolet rays. However, when this same gas occurs at ground-level, it is harmful and causes significant negative effects on human health and the environment.
Ground-level ozone is formed when volatile organic compounds (VOCs) and nitrogen oxides (NOx) react in the atmosphere with sunlight and heat. Ozone can be transported long distances by wind. For this reason, even rural areas can experience high ozone levels. Since ozone requires the combination of sunlight and heat to form, it is mainly of concern during "Ozone Season" from March through November.
Air Quality Index
Air quality is measured daily to determine how clean or polluted the local air is, and what associated health effects might be a concern. This measurement is called the Air Quality Index (AQI) and focuses on health effects experienced within a few hours or days after breathing polluted air.
The higher the AQI value, the greater the level of air pollution and the greater the health concern. AQI values below 100 are generally thought of as satisfactory. When AQI values are above 100, air quality is considered to be unhealthy, at first for certain sensitive groups, then for everyone as AQI values get higher.
Also visit EPA's AirCompare site to observe the air quality of various counties in the United States.
Updated: June 12, 2018