Why is ground-level ozone worse on a sunny weekday than on a sunny weekend?

Ground-level ozone levels are typically higher on sunny weekdays due to increased emissions from vehicles and industrial activities, which peak during workdays. Sunlight promotes the chemical reactions between pollutants like nitrogen oxides and volatile organic compounds, leading to ozone formation. On weekends, reduced traffic and lower industrial output result in fewer emissions, leading to lower ozone levels despite similar sunny conditions. Thus, the combination of higher emissions and sunlight on weekdays creates worse air quality.