The metro Denver area saw clear skies Monday for the first time in a while, with 2020 being the worst year for air quality in a decade.

In metro Denver, 2020 has had far more dangerous air quality alerts than any full year in the last 10 years, according to the Colorado Department of Public Health and Environment.

Air quality alerts measure fine particulate matter in the air that is smaller than 2.5 microns, PM 2.5. The matter’s small size allows it to get deep into people’s lungs and, when levels are high in the air, it can damage one’s health to just be outside.

So far in 2020, there have been over 30 PM 2.5 alerts in the metro Denver area. In 2019, alerts didn’t even reach 15.

Yearly PM 2.5 alerts haven’t passed 30 in any other year this decade, remaining under 10 in eight years between 2010 and 2020.

Experts say though PM 2.5 rates have actually improved in Denver in recent years, this year’s record-breaking wildfire season has hidden all progress and drastically decreased the city’s air quality.

Two of Colorado’s top three largest-ever wildfires, Pine Gulch and Cameron Peak, are currently burning.