Butler County residents sensitive to air quality should remain inside Thursday, June 12, with the significant concentrations of ozone gases, according to the Pennsylvania Department of Environmental Protection.

The department issued a code orange for air quality in southwest Pennsylvania, including Allegheny, Armstrong, Beaver, Butler, Fayette, Washington and Westmoreland Counties.

Young children, the elderly and those with respiratory problems such as asthma, emphysema and bronchitis are especially vulnerable to the effects of air pollution.

Residents are encouraged to drive less, carpool or take public transportation, combine engines, limit engine idling, refuel after dusk and conserve electricity to reduce ozone gas concentrations.

The concentration of ozone gasses is caused by a combination of low-level smoke from Canadian wildfires and 90-degree temperatures with light southwest winds.

The concentration forms from nitrogen oxides and volatile organic compounds called precursors reacting to sunlight. High ozone levels are most common during the summer with long days of sunshine.

Ozone precursors often come from car exhaust and industrial air emissions and can be compounded by wildfires.

The U.S. Environmental Protection Agency’s Air Quality Index provides standardized color codes for forecasting and reporting daily air quality. Green signifies good air quality; yellow means moderate air quality; orange represents unhealthy pollution levels for sensitive groups of people; and red warns of unhealthy pollution levels for all. An “Air Quality Action Day” is declared when the index is expected to be Code Orange or higher.

Residents are encouraged to check airnow.gov for current conditions in their area.