Fort Collins Air Quality April 12-14, 2017

The warm weather probably brought a lot of people outside these last few days, but you may have also noticed that the foothills looked a bit hazy. Looking at the hourly time series of PM_2.5 concentrations, we do see higher concentrations compared to previous days.

Time series of PM_2.5 concentrations measured in Fort Collins, CO for 10 April - 15 April, 2017. Data courtesy of cdphe.gov.

So, what is causing these higher concentrations? Our guess would be smoke from prescribed fires. The CDPHE did not put out a specific warning for Northern Colorado, but there is the standard "Light to moderate smoke is possible near prescribed fires and small wildfires around the state."

The Hazard Mapping System also showed smoke plumes over northern Colorado/Wyoming on April 12-14. The plots show the plumes being transported different directions. While none of these show the plume directly over Fort Collins, the wind could have switched directions and blown the plume towards the southeast in between these times.

HMS Smoke Plumes and Fire Locations  in northern CO/southern WY for 12 April - 14 April, 2017. Data courtesy of http://www.ospo.noaa.gov.

Checking inciweb (https://inciweb.nwcg.gov/state/6/), there were a few prescribed fires around the state. Our guess would be on the Red Feathers Lake Prescribed Burn (https://inciweb.nwcg.gov/incident/5027/).

We also noticed however, that the coarse PM is high. This is often indicative of dust, which could have also been transported with the strong winds.

Time series of  coarse PM concentrations measured in Fort Collins, CO for 10 April - 15 April, 2017. Data courtesy of cdphe.gov.

What is a Prescribed Burn?
A prescribed burn is a controlled, purposefully ignited fire. These have been "prescribed" in order to reduce hazardous fuel loads. The goal is to burn up lots of ground fuel so that if a wildfire is ignited, it will not spread as quickly.