Air Quality on the Wasatch Front


The air in Utah along the Wasatch front is notorious for being bad in the winter. Sometimes in the summer, but in the winter it can get really, really bad. How bad you say? The news likes to hoot and holler when it is among the worst in the nation. But that is hardly the norm. The media are sensationalists looking to make a buck — but that is another post.

On a bad day, the PM2.5 (particulate matter measuring less than 2.5 micrometers in a cubic meter) can get above 100. The EPA considers 12 or less to be ”OK“. I generally agree with this. The air looks nice and clear when we are below a 12 in the Salt Lake Valley.

What is the source of all the stuff in the air?


The PM2.5 in the air is a complex mixture. Recently, the University of Utah did a study attempting to determine the source contributions to the PM in the air.

The actual paper from the study is published in a journal behind a paywall. I found a peer review draft. I doubt the numbers changed much between the peer review and the final paper.

The paper is called “Receptor model source attributions for Utah’s Salt Lake City airshed and the impacts of wintertime secondary ammonium nitrate and ammonium chloride aerosol” by Kelly, Kotchenruther, Kuprov, and Silcox.

They divide the PM into two categories. Primary and secondary. The largest source of PM is attributed to Ammonium Nitrate at 50–75%. However, they state:

The reader should note that factors determined in a source-attribution analysis using factor analysis methods like PMF and Unmix are not necessarily mutually exclusive. For example, a factor identified as predominantly ammonium nitrate aerosol is likely from a combination of primary and secondary sources including gasoline engines, diesel engines, and industrial facilities, even though these sources may also have separately identified factors. Hence, caution should be used in interpreting factor classifications too literally or with exclusivity.

That is a lot of stuff. What is says to me is that they cannot definatively separate the soup that is our air. The percentages will not add up to be 100% when they are all done.

So where does that leave us? What causes all the pollution?

They draw a comparison between Bountiful and Lindon. For the Bountiful location they state:

During winter, when PM 2.5 exceeded 20 μg/m3, the contributions ranged from 6–40% of the primary portion of PM2.5 for fugitive dust, 2–20% for diesel, 0–51% for gasoline, and 20–70% for wood smoke.

Note that is only for the primary contributions. There are secondary contributions as well. They go on:

During winter when PM2.5 concentrations exceeded 20 μg/m3 the PMF and Unmix results showed that secondary PM was the largest contributor to PM2.5 (60–67% for Salt Lake City, 72–73% for Lindon, 64-80% for Bountiful)...

So what does all that mean? The way I read it is that most of the pollution is due to secondary PM which may or may not be a combination of other sources like gasoline, wood smoke, diesel, even though they have their own separate categories and percentages.

So what has been done and what can be done to make our air better?

Here is a chart I found that shows progress made in air quality since the 1970s


Looking at the chart, there have been many improvements and overall, the air is getting better. I am sure this is a combination of many things. Unleaded gasoline, Geneva Steel leaving, better cars, better emmission controls on factories, etc. So what is left to make better? A lot of people are crying about the wood smoke.

How much of that terrible, terrible, terrible, terrible, wood smoke is there?

The media would have you believe that wood smoke is of the devil. In hell they have campfires all the time and everyone coughs a lot and has asthma.

According to the paper...I couldn't figure out a precise number. As I mentioned above, they warn against trying to do so. The same people that published the paper published a slide show on the Department of Environmental Quality website (that has since been pulled) showing wood smoke as high as 38% when the inversion is more than 20 micrograms, but below they have a caveat that says "percentages are for illustration purposes only".


This astounded me when I read this. Why would you ever produce a chart that leads the reader to a conclusion and in fine print state that you made the numbers up? Suggests that they have an agenda and could not quite come up with the data to support it.

In any case, the actual research found 20–70% of the primary contributions were from wood smoke. But secondary contributions made up to 73% of the total PM2.5. So that leaves 27% and wood smoke makes up 20–70% of that and may or may not contribute to the other 73%. Hopelessly confusing. The only useful data they came up with is that their “inventory“ predicted 2–3 times less smoke than they found.

Ban wood burning they say

The conclusion I have come to is that they do not know how much of the total is from wood smoke. They also do not take into consideration smoke from cooking as pointed out here.

However, in the winter, cooking smoke is likely lower.

Final thoughts

Bottom line is that here is some pollution from wood smoke. It is an easy fix too. If you have a gas furnace, just don’t light a fire. Turn on your furnace. That is all there is to it. Easy win. Even if there is only 5% wood smoke contribution to the overall PM2.5 that seems like a no brainer. It is already illegal to burn on certain days. The letter linked here points out that people still burn on mandatory no-burn days. I think he is right. There are people out there that burn no matter what even if it is not their sole source of heat.

I like a nice fire. There is so much more to a fire than just heat. However, instead of waiting until the day is red or almost red to ban burning, people should stop burning the moment that a high pressure system moves in. We all know it is going to get bad. Let’s all do our part to minimize how bad it gets.

There is still a lot that the rest of us can do, but it is a complicated problem. People have to go to work. Construction workers have to construct. Do we ban driving? Ban heavy equipment on certain days? Ban the local BBQ place from smoking? Ban cigarettes? Why pick on wood burning? Because like I said before, for most people whose sole source of heat is not solid fuel all they have to do is turn on their furnace. It is a simple way to remove a portion of the filth.

The rest of us chumps that don’t have a wood stove or fireplace should do what we can to reduce overall emissions as well. No one is exempt.

An outright ban is overkill. There are, in fact, people who have legitamate health or other financial reason to have both solid fuel and natural gas heaters, and use both at the same time. Sure you will have those idiots who burn tires in their yard because it is their “right”. Don’t be one of those people. Be responsible. The reason we have most of our stupid laws is because people cannot behave themselves.

Additional reading:

Comparing Particle Emissions from Traffic, Cigarettes and Heating

Peer Review Copy of that paper I talked about

How to burn wood efficiently and responsibly

Photo credits