Code Orange declared for Philly, suburbs due to poor air quality

What you need to know

• Vulnerable residents are encouraged to stay indoors and limit or avoid outdoor activities.
• Here’s how to understand your air quality index.
• More air quality events can be expected this summer thanks to climate change.

The Philadelphia region on Wednesday will be under Code Orange Air Quality Action Day for Ozone.

The alert, issued Tuesday by the state Department of Environmental Protection, includes Bucks, Chester, Delaware, and Montgomery counties.

Ozone, a gas that’s harmful when breathed in, forms from a combination of heat and different pollutants.

An 8-hour average of ozone concentrations in the Code Orange range is expected, state Department of Environmental Protection officials said, citing a sunny forecast with light west to southwest winds and temperatures in the low- to mid-90s.

Under a Code Orange, air pollution concentrations may be unhealthy for vulnerable groups such as children, people with asthma, people with heart or lung disease, and older adults.

Local conditions may fall above or below Code Orange range. Residents are encouraged to visit AirNow.gov to check local conditions.