What’s up with that brown haze across Colorado’s Front Range when it is not summer ozone season?
This week's visibility alert extends through 4 p.m. Friday and it is effective in Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas and Jefferson counties.
A brown haze settled over the Front Range this week, leading the state to issue bans on indoor fires and to advise people to avoid driving as much as possible.
Colorado public heath officials also issued a warning that said moderate air quality could cause breathing difficulty for people with lung and heart disease. They were advised to avoid heavy physical exertion outside.
But it’s not summer ozone season. So what’s causing the poor air quality?
It’s the time of year when temperatures drop and the air stagnates, said Scott Landes, lead air quality meteorologist at the Colorado Department of Public Health and Environment. The winter pollution season lasts from Oct. 31 to March 31.
“During the winter months, we see a build-up of pollutants near the Earth’s surface because it can’t escape into the atmosphere,” Landes said.
Those pollutants are mostly fine particulate matter, known as PM2.5. Fine particulate matter is caused by the same sources as summer ozone pollution — automobile traffic and industrial production, Landes said. In the summer, wildfire smoke also causes particulate matter to hang in the air.
To reduce the amount of pollution on winter days, the state health department issues Action Day for Visibility alerts through its Winter High Pollution Advisory Program that ask people to drive less and avoid indoor fires unless they have an Environmental Protection Agency-approved wood-burning stove. People who heat their homes solely by burning wood are exempted from the ban, Landes said.
This week’s visibility alert extends through 4 p.m. Friday and it is effective in Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas and Jefferson counties, according to the state’s air quality website. The alert could be extended if the weather does not change.
The National Weather Service forecast calls for warm weather through Saturday. A change is forecast for late Sunday with a possibility of rain and snow and much colder temperatures at the start of the week.
A steady snow would clear the air, Landes said.
“Snow does a really great job of scouring the air,” he said.
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