Denver’s air quality is expected to improve by the end of this week after the city has experienced several days of thick smoke and ranked worst air quality in the world on Saturday.

On Wednesday, Denver’s air quality index hovered at around 90, within the Environmental Protection Agency’s “moderate” category. The air quality is predicted to remain moderate on Thursday and then reach “good” Friday, Saturday, Sunday and Monday, according to IQAir.

This comes after Denver’s air quality was in the “unhealthy” range Saturday and Sunday, and the “unhealthy for sensitive groups” range Monday and Tuesday.

“Unhealthy” air quality between 151 and 200 means the air can cause adverse health effects for all people and serious effects for sensitive groups. A “good” air quality index is 0 to 50, “moderate” is 51 to 100 and “unhealthy for sensitive groups” is 101 to 150.

Denver weather: Smoke continues to create unhealthy breathing conditions

Meteorologists with the National Weather Service said the smoke is from an upper-level low pressure system moving from California and Canada, where large wildfires are burning, into Colorado’s Front Range.

However, weather patterns and pollution were already causing a tough summer for air quality in Denver before the smoke rolled in.

The state has declared nearly 50 Ozone Action Alert Days for Denver and the Front Range this season, including more than 30 consecutive days, according to the Department of Public Health and Environment. An average year has about 35 action days.

Even if the smoke clears after Friday, hazy and smoky conditions could become the new normal until the end of the fire season, some experts say.

Wildfire smoke exacerbates health conditions, contributes to more deaths, and it’s getting worse

Dan Welsch, an air quality meteorologist with the state health department, told The Denver Gazette last week that bad conditions will persist until the fires to the west become more contained.

“Current projections are unfortunately showing more of the same for at least the foreseeable future,” Welsh said.

When Denver’s air quality is in the “unhealthy” range, residents are urged to avoid outdoor exercise, keep windows closed and wear face masks when outdoors.