Thursday, November 2, 2017

May-October (wildfire season) summary for Fort Collins

The wildfire season has come to a close, so I thought I would just give a quick overview of the summer air quality as it pertains to PM2.5.

We had several days of smoke this season, with very little of it being from local fires.  The following is a map of the CONUS showing the number of days with HMS smoke plumes from May-October 2017.
Number of days with an HMS smoke plume for the period of May 1st - October 31st, 2017. Data from
We obviously did not experience as many smoke days as the Northwest, but Fort Collins still had a significant number of days where the HMS product noted smoke compared to previous years. According to the HMS product, there were 41 days when smoke was noted over Fort Collins (2016 had 30; 2015 had 23; 2014 had 21; 2013 had 34; and 2012 had 69 days).

The maximum hourly concentration at the Fort Collins site was 106 ug/m3 and the maximum daily concentration was 60 ug/m3. (as a note, all PM data I show on this sites is from the real-time reports and have not been corrected or validated, meaning that these values may change). Both of these occurred on Labor Day (4th of September). You can read the blog post on that event here. This was the only day where the 24-hr concentration was greater than the EPA's standard of 35 ug/m3. However, as this was due to transported wildfire smoke, it will likely be classified as an exceptional event (which means it will be excluded when determining attainment status). Below is the time series of the 24-hour average PM2.5 concentrations in Fort Collins.

Time series of PM2.5 concentrations in Fort Collins, CO from May through October 2017. Data from
You can see from the time series that our air quality (as it pertains to particulate matter) is generally pretty good here in Fort Collins. Most of the days with elevated PM2.5 concentrations had smoke present. Earlier in the season (May and June), we had a few high PM days which we can't specifically attribute to smoke because the satellites do not clearly show plumes over Fort Collins. However, there were lots of fires in Mexico, Arizona, Utah, and New Mexico that were producing large smoke plumes. It is feasible that we got a little of that smoke here but that the plumes were much more diluted by the time they reached us so as not to be as distinct in the satellite images. There's also the possibility that these were due to more local sources as other monitoring sites in Colorado did not see the same PM increases. One exception would be June 27th. The HMS plumes did not extend as far north as Fort Collins, but all of the sites around Colorado did show increases in PM2.5 concentrations, and the HMS product did show smoke from a fire in Utah transported over all of Colorado on the 28th (we weren't on top of our blogging game during that event).

Some side thoughts: Environmental regulations have really helped improve air quality overall in the US. We have seen decreases in anthropogenic (meaning from human activity) emissions that have led to better "average" air quality. However, at the same time, we've also had lots more large wildfires that have produced extremely poor air quality for much of the western US. Reducing wildfire emissions is obviously difficult as it means stopping large wildfires before they start (land management, prescribed burns, people being more responsible, etc.). Thus, wildfire smoke is becoming an increasing health concern as it could be offsetting some of the air quality benefits gained from reductions in other emission sources. Know how to protect your health during smoke events and stay aware of current  air quality conditions!

Wednesday, October 18, 2017

Smoke from prescribed fire on October 17, 2017

I have been testing AOD (aerosol optical depth, a measure of light extinction due to aerosols in the atmosphere) devices this week. As such, I've been comparing results with nearby AERONET sites ( I was looking at the NEON_CVALLA site and noticed this weird spike in AOD in the afternoon yesterday (October 17th). I checked the other sites and saw spikes at the NEON_RMNP site, Table Mountain site, and high values at the Digital Globe calibration site. These are all Level 1 products, so they may not pass quality checks, but I still thought it was strange and warranted further investigation.
Level 1 AOD from NEON_CVALLA site on 17th October 2017. Image from: 
I checked HMS, and I noticed some fires near Fort Collins, which I assumed were probably prescribed fires since they aren't there today. Zooming in, I more clearly saw that there was indeed some smoke produced from the fires.

HMS Smoke and Fire product for October 17th, 2017 over the whole western US (left) and zoomed in over northern Colorado (right). Data from:

I double-checked this against MODIS. There was no smoke noted from the Terra instrument (which has a morning overpass), but there was smoke visible from the Aqua instrument (which has an afternoon overpass).
MODIS True Color Images from Terra (left) and Aqua (right) for October 17th, 2017.

I checked if there was any impact on our surface air quality, and there was a slight increase in PM2.5. Coarse PM (2.5-10) also increased. The timing seems earlier than what was noted by the satellites, but the satellites may have not picked it up in the morning and the smoke may have not made it to the AERONET sites until later in the day. There is also a diurnal cycle to the PM time series where concentrations are higher in the morning and night, and low during the day. This could be from the boundary layer trapping concentrations near the surface. Then, as the boundary layer grew throughout the day, concentrations decreased. It's hard to untangle all of this and directly attribute both the PM changes in Fort Collins and the AOD spikes at AERONET sites further downwind to this smoke, but it seems to be at least a plausible source.
PM2.5 and Coarse PM concentrations measured in Fort Collins, CO for October 16-18th, 2017.

Another double-check that this was indeed a prescribed fire sent me to InciWeb (where all fire incidents are recorded), where I found that the smoke was likely from the Pingree Hill Prescribed Burn ( as its location generally matched the location from the satellite data. They burned 95 acres yesterday.