Ozone | South Carolina Department of Environmental Services

Ozone is a highly reactive, colorless gas pollutant that is not typically emitted directly into the air by any one source. Instead, ozone is considered a secondary pollutant, which means that it is formed through complex chemical reactions of molecules in the air. Specifically, ground-level ozone is formed when nitrogen oxides (NOx) and volatile organic compounds (VOCs) chemically react in the presence of sunlight. While ozone high up in the atmosphere protects us from harmful ultraviolet rays, exposure to high concentrations of ground-level ozone can be quite harmful to our health and environment. That is why we say ozone is “good up high, but bad nearby”.

High concentrations of ground-level ozone can create breathing problems, especially for children, people with asthma or other respiratory problems, and adults who work or exercise outdoors. According to the U.S. Environmental Protection Agency, ozone can also cause tree and crop damage. Mobile sources of air pollution such as cars, trucks, and lawn equipment, contribute to nearly half of the ozone formed in South Carolina.

High ozone concentrations generally occur on hot, sunny days in the spring and summer when the air is stagnant, and the sun’s rays shine more directly on the earth’s surface. Like the weather, ozone and its precursor pollutants can be transported from place to place by wind, resulting in significant changes in ozone concentrations from day to day and even hour to hour.

Ozone is a molecule made up of three oxygen atoms, often referenced as O3. Ozone is formed when heat and sunlight cause chemical reactions between oxides of nitrogen (NOX ) and Volatile Organic Compounds (VOC), which are also known as Hydrocarbons. This reaction can occur both near the ground and high in the atmosphere.

Just remember that ozone is "Good Up High, Bad Nearby."

Stratospheric ozone is good ozone. It forms about 10-30 miles above the Earth's surface and forms a protective layer, called the ozone layer, that shields us from too much of the sun's harmful ultraviolet radiation (UV).

Ground-level ozone is bad ozone. Ozone harms human health and the environment when it forms close to the ground. The most significant things that cause ground-level ozone to form are:

NOX and VOCs (from mobile source emissions and industrial processes), and
UV radiation (from sunlight).

We see higher ground-level ozone amounts most often in summer, due to increased amounts of UV radiation during the longer days, but ozone can still form in spring, fall, and even winter given the right conditions.

Even though the emission sources that contribute to ground-level ozone are typically found in urban areas, strong winds can also move it into rural areas, causing them to have high amounts of ground-level ozone.

People with respiratory conditions such as asthma, or those who are active outside on days when ozone amounts are high can feel shortness of breath, wheezing, and coughing. We can all take actions to help protect ourselves and reduce the damaging effects of this pollutant on our health and environment.

SCDES monitors ozone levels each year from March 1st through October 31st as mandated by the U.S. Environmental Protection Agency ozone regulations. The March through October monitoring ozone season that is chosen for South Carolina is based on when the atmosphere is more conducive to ozone formation, which is highly dependent on weather conditions. Monitors help us understand the actual amount of ozone occurring at a particular location as well as the distribution of ozone concentrations across the state.

SCDES meteorologists provide next-day ground-level ozone forecasts from March 31st to September 30th to allow the public to be proactive about protecting their health by reducing outdoor activities and by reducing their own contributions to emissions when ozone concentrations are expected to be high. If ozone levels are forecast to reach unhealthy levels (exceeding the ozone National Ambient Air Quality Standard), SCDES will declare an 'ozone action day' advising people to reduce their activity levels outdoors, especially for those with respiratory conditions, such as asthma. Historical monitoring data indicates that unhealthy ozone concentrations are extremely rare during fall and winter months due to beneficial weather conditions and the lower sun angle that typically keeps ozone concentrations lower than in spring and summer months. Since the vast majority of days in March and October exhibit “code green” ozone concentrations (i.e., low concentrations similar to other fall and winter months), forecasters currently do not issue daily ozone forecasts for these two ozone monitoring season months. Forecasters keep an eye on ozone observations and weather conditions each day during these two months and issue an 'ozone action day' in the rare event that is necessary. Additionally, historical monitoring data shows that ozone forecasts are not necessary in the Coastal Plain region of South Carolina outside of the Charleston area (shown by the “no forecast” white area on the ozone forecast map) due to lower emissions and more favorable weather conditions for cleaning the atmosphere of ozone precursor pollutants at locations closer to the coast.

Ways to get the South Carolina ozone forecast:

Visit SCDES's Air Quality Forecast page.
Sign up for daily forecast emails, texts, or tweets using EPA's free EnviroFlash service.

Other Ozone Forecasts

Don't live in South Carolina? Here are some useful links to find the ozone forecast in other areas:

Georgia,
North Carolina, and
Find your state and the national forecast at AirNow.

Drive Less

Driving a car is likely a person's single most polluting daily activity. Driving less reduces the number of vehicles on the road which helps to reduce air pollution from vehicle emissions.

Other ways to reduce the number of vehicles on the road include:

Using an Alternative Work Schedule (if possible). A flexible work schedule allows you to work a staggered schedule to avoid driving in peak rush hour traffic.
Telecommuting (if possible). This allows you to work from home and reduces the miles you drive to and from work.
Shopping by phone, mail, or the Internet.
Have a healthier commute by walking or biking to your destination.

Drive Smart

How we operate our vehicles can help reduce pollution. Here are some ideas:

Do not idle your vehicle. Turn off your engine if you expect to be stopped for long periods of time (except in traffic). Consider not using drive-through windows, instead park and walk inside.
Slowly increase your car's speed and use cruise control on the highway.
Trip-Chaining, which combines several errands into a single trip
Obey the speed limit. It saves gas and reduces greenhouse gas emissions.
Keep your vehicle tuned up and your tires properly inflated. Both help save gasoline and improve air quality, as well as make your car safer.
Don't top off the gas tank.
When shopping for that next car, consider more efficient, less-polluting models.

Use Air-Friendly Products

Many products in our homes, yards or offices are made of chemicals that escape into the air when used. To reduce this type of pollution:

Select water-based solvents or those with low volatile organic compound (VOC) content.
Use water-based paints or those labeled zero VOC.
Paint with a brush instead of a sprayer; paint overspray from a sprayer can disperse into the air
Store solvents like paint thinners in airtight containers so that they do not evaporate into the air you breathe.
Use a reel or electric lawn mower and other non-gas-powered equipment such as edgers.

Participate in Community Initiatives

Learn more about air pollution reduction strategies for your neighborhood:

Register for the SCDES Breathe Better (B2) Program and receive anti-idling signs for businesses and school campuses
EPA SmartWay Program helps companies reduce fuel use, lower costs, and decrease emissions through sustainable transportation practices.

There are safe ways to limit your exposure to ozone without reducing healthy physical activity.

Sign up for our ozone forecast so you can plan outdoor work or exercise during your day to avoid possible high levels of ozone.
Use these recommendations for schools and outdoor activities to modify plans for outdoor activities such as recess, lunch, and physical education class.
If you're involved in an activity that requires heavy exertion, you can reduce the time you spend on this activity or substitute another activity that requires more moderate exertion (e.g., go for a walk rather than a jog).
No matter how fit you are, cutting back on the level or duration of exertion when ozone levels are high will help protect you from ozone's harmful effects.
Plan outdoor activities when ozone levels are lower, usually in the morning or evening.

Due to the hazardous nature of high ozone concentrations, the State has implemented plans to comply with the National Ambient Air Quality Standards (NAAQS) as defined in the Clean Air Act. The Ozone State Implementation Plan (SIP) is the accumulated record of many documents that form a blueprint and timeline to assure compliance. This plan includes control plans, regulations, state emissions inventories, and transcripts of public involvement.