By Mike Finney

While the air quality has improved in Delaware, the Department of Natural Resources and Environmental Control advises that the state is still in the ozone season.

Residents should continue to be vigilant about poor air quality and its impacts on their health and safety every day, officials say.

Wildfires in Quebec emitted particulate matter into the atmosphere, making the air unhealthy — and at times hazardous — last week, triggering the department to issue back-to-back “code red” action days.

The air quality index reading Monday showed Delaware as “yellow” for particulate matter, signifying that the atmosphere remains a moderate concern and that environmental officials continue to monitor the air’s status.

With a change in meteorological conditions and dozens of wildfires still burning in Canada, the poor air quality for particulate matter could return, carried down the East Coast and into Delaware by prevailing winds.

“We are forcibly coming to terms with the many faces of climate change in Delaware,” said Secretary Shawn M. Garvin. “The code red action days for particulate matter is a telltale indication of it. The Canadian wildfires dispersed particulate matter in some of the highest amounts recorded.

“The smoke was carried by winds and affected air quality many hundreds of miles away. Which is why we, as a country and as global citizens, must continue to monitor, to prepare, to adapt but also take action to address the impacts of climate change for protecting the health of people in Delaware and the planet.”

With summer weather ahead and little rain in the forecast after almost a month of negligible precipitation, most of Delaware’s attention to air quality now reverts to the ozone season (May 1-Sept. 30).

“Bad ozone” can contribute to existing health conditions in sensitive groups, particularly children, older adults and people with respiratory or cardiovascular problems. Therefore, the Environmental Protection Agency’s mantra for ozone is “good up high, bad nearby” — “nearby” meaning the ground level ozone known as the troposphere.

It’s “bad ozone” to be aware of in Delaware, the country’s lowest-lying state, where the transportation sector is the largest single cause of air pollution. This kind of pollution is formed from a chemical reaction in the lower atmosphere on hot, still, sunny days.

The state’s Division of Air Quality has found ozone pollution levels — comprising the pollutants that contribute most to ozone formation, volatile organic compounds and nitrogen oxides — come from in-state sources and blows in from upwind cities and states.

But ozone pollution doesn’t discriminate on where it ends up, officials say, and Delaware must always be on the alert for this intrusion.

Monday’s air quality index for ozone showed levels in the 40s, meaning good air quality.

The public can continue to check air quality reports in the coming days by signing up to receive alerts at de.gov/aqi or visiting airnow.gov.