Ground-Level Ozone
O3 · Measured in ppb
About O3
A highly reactive gas formed when pollutants from cars, power plants, and other sources react with sunlight. Good ozone in the stratosphere protects us; ground-level ozone is harmful. Worse on hot, sunny days.
Sources
Chemical reaction of NOx and VOCs in sunlight (not directly emitted)
Health Effects
Chest pain, coughing, throat irritation, airway inflammation, reduced lung function, aggravated asthma
EPA Standards
| Annual Standard | 70 ppb |
| 24-Hour (Daily) Standard | 70 ppb |
Frequently Asked Questions
What is Ground-Level Ozone?
A highly reactive gas formed when pollutants from cars, power plants, and other sources react with sunlight. Good ozone in the stratosphere protects us; ground-level ozone is harmful. Worse on hot, sunny days.
Where does O3 come from?
The main sources of Ground-Level Ozone include: Chemical reaction of NOx and VOCs in sunlight (not directly emitted).
What are the health effects of O3?
Exposure to Ground-Level Ozone can cause: Chest pain, coughing, throat irritation, airway inflammation, reduced lung function, aggravated asthma.
What is the EPA standard for O3?
The EPA has set an annual standard of 70 ppb and a 24-hour (daily) standard of 70 ppb for Ground-Level Ozone.