Canadian wildfires sending smoke to the state triggered an air quality alert through Wednesday. The worst of the smoke is in northeastern Pennsylvania and parts of upstate New York.

PA’s Department of Environmental Protection said people with asthma or other breathing conditions should limit time outside. Smokey air can also have an effect on those who aren’t high risk.

“It’s the smaller particulates that are really bad,” said Dr. Neil Leary, director for the Center for Sustainability Education at Dickinson College. “They are responsible for killing an estimated 100,000 to maybe 250,000 people prematurely each year in the United States. So, episodes like this where you’re getting a boost in the amount of particulate matter that we’re breathing in due to wildfires adds to that health risk.”

Two years ago, more than 3,000 Canadian wildfires blanketed the eastern Untied States with smoke. The National Weather Service issued a code red for central Pennsylvania that summer, meaning the air quality posed a danger to the general population.

This time around, the department issued code orange alerts, meaning unhealthy for sensitive groups, in portions of the state. Most of Pennsylvania has at least moderate issues with air quality this week.