What Does
Ground Level Ozone Mean?
Ground level ozone (O3) is a secondary pollutant formed when ultraviolet (UV) light acts on nitrogen oxides (NOx) and volatile organic compounds (VOCs).
Exposure to ground level ozone can result in difficulty breathing, shortness of breath, and coughing. It can also lead to respiratory diseases like asthma and bronchitis.
Ground level ozone is also known as tropospheric ozone.
Safeopedia Explains Ground Level Ozone
Ozone is present throughout the environment, but its concentration is highest in the troposphere (0 to 15 km) and in the stratosphere (15 to 50 km).
Ground level ozone is not directly emitted into the air but is formed through chemical reactions when ultraviolet (UV) light from the sun interacts with nitrogen oxides and VOCs. Since these pollutants are emitted by industrial facilities, refineries, vehicles, and solvents, ground level ozone levels are higher in urban areas than rural areas.
Because sunlight is a catalyst, ground level ozone is more abundant and hazardous on sunny days.
Formation of Ground Level Ozone
Nitrogen oxides and VOCs originating from combustion processes react photochemically to produce ground level ozone. These reactions are not immediate, but can take hours or days. Because of this slow process, ozone levels in certain regions can be the result of emissions from elsewhere.
Anthropogenic emissions of NOx and VOCs, known as ozone precursors, can also cause substantial increase in ozone concentrations known as smog. This occurs when favorable weather conditions like warm and slow-moving air coincide with high concentrations of ozone precursors. This can give rise to toxic ozone concentrations, which are hazardous to humans and vegetation.
Monitoring Ozone to Improve Air Quality
Ozone in the upper atmosphere is beneficial to the earth, as it prevents harmful UV radiation from reaching the planet’s surface. However, closer to ground level, ozone can harm human health as it reacts with lung tissue and can injure it upon inhalation. Exposure to ozone can worsen heart disease, asthma, bronchitis, and emphysema. It can also cause reductions in crop yield by entering the plant’s stomata and chemically reacting with its cells.
Ground level ozone is regulated by the Environmental Protection Agency (EPA) and identified as one of six common pollutants by the Clean Air Act. The EPA has national and regional rules aimed at reducing the emissions that contribute to the formation of ground level ozone. It enables state and local governments to meet its national air quality standards, such as those for vehicles and transportation as well as rules for haze and visibility.
Ozone levels typically reach their peak from mid to late afternoon as rush hour exhaust fumes have had sufficient time to react with the sunlight. In some areas, air quality alerts are sent out when concentrations of ozone are high, urging people to remain indoors, especially if they have respiratory conditions.
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