Is Pollution from Wood Smoke Going Down?
All Your Burning Questions Answered

By Kerry Kelly and Nancy Daher

Historically, burning wood has contributed 5 to 10% to our winter-time particle pollution problem.  A recent study from the University of Utah, the US EPA and the Utah Division of Air Quality (DAQ) has found that wood-burning’s contribution to fine particulate matter (PM2.5) levels has declined by a factor of 4 to 5 over the past 10 years (from approximately 2.5 µg/m3 in 2007 to 0.5 µg/m3 in 2017, see figure).  This decrease is evident even if we normalize for seasonal differences in our inversion patterns.  Our findings are important as the state seeks to meet National Ambient Air Quality Standards while continuing to meet the needs of its growing population and economy.

Smoke from burning wood creates PM2.5, a harmful air pollutant, that passes deep into the lungs and can trigger asthma, heart attacks, strokes, and premature death. The elderly, children, and individuals with compromised lungs are more susceptible to PM2.5 pollution.  Heating with wood generates significantly more pollution per unit energy than heating with natural gas.  For example, heating your home with an EPA-certified wood stove, which burns cleaner than other wood-burning heating devices, generates approximately 150 times more PM2.5 pollution than heating with natural gas. Fireplaces and uncertified wood stoves are even more polluting.

We have been studying the contributors to our winter-time PM2.5 levels for the past 8 years, and we’ve been partnering with Dr. Kotchenruther (EPA Region 10) and Dr. Jaramillo (University of Utah) to understand wood-burning’s contributions.  Our previous work in 2013 and 2016 suggested that wood-burning was a significant contributor to our PM2.5 problem.  In this study, we looked at the composition of PM2.5 on filters collected every 3 days at the Hawthorne monitoring station and every 6 days at the Lindon and Bountiful stations from 2007 to 2017.  We used statistical tools and the principle that particles from wood-burning have a different composition than particles that come from other sources, like diesel engines.  The analysis also considered the atmospheric conditions, such as whether there was an inversion that day, that can affect the presence of wood smoke.

Screen Readers: the following graphic is a timeline from 2008 to 2016+. These labels are included:

  • Pre-2008: Ban PM2.5=65
  • 2008: Ban PM2.5=35
  • 2012: Voluntary PM2.5=15
  • 2013: Ban PM2.5=25, voluntary PM2.5-12
  • 2015: SLC Ban PM2.5=12

An information bubble pointing to “pre 2008” reads: “1999 in SLC, parts of Davis and Utah Counties. 2005 in North Davis and Weber. This probably refers to the text that reads “Pre-2208: Ban PM2.5=65”.

An information bubble pointing to 2013 reads: “Proactive restrictions. Add Box Elder, Cache, Tooele, and parts of Utah County. Only EPA certified woodstoves sold. No wood-burning hydronic heaters sold.” This probably refers to the text that reads “2013: Ban PM2.5=25, voluntary PM2.5-12”.

An information bubble pointing to the beginning and ending end of “2015” reads: “Research shows wood burning a significant contributor to PM levels”.

an information bubble pointing to the beginning and ending of “2016+” reads “Changeouts: UCAIR 80+. State 2,000+”.

End of screen-reader description. Have a nice day.

PM2.5 timeline from pre-2008 until 2016+. An impressive and detailed screen-reader description is published above.

It is exciting that our earlier studies contributed to the discussion about woodburning and effective control strategies, which involved regulations, communication and incentives.  Regulatory efforts to control wood-burning began in 1999 with woodburning bans being called when PM2.5 levels reached 65 µg/m3 in Salt Lake, and parts of Davis and Utah counties.  Since that time, the state has taken a more proactive approach in restricting burning as highlighted in the figure below.  Since the mid-2010s, the Wasatch Front’s media outlets have done a great job publicizing solid-fuel burning restrictions, and organizations such as UCAIR, environmental advocates, health departments, and DAQ have been instrumental in communicating the adverse effects of burning wood in our constrained airshed.  In addition, the state legislature, UCAIR, and EPA have funded wood-stove conversions and exchanges.  Together these efforts are making a difference in our air quality.

This project was supported by funding from the Utah Division of Air Quality.

Our work also suggests that wood burning still occurs on no-burn days and that there may be some opportunities to reduce PM emissions from commercial wood-burning operations.  However, these would likely be more incremental improvements than those that we have seen since 2007.  However, as the population continues to grow, we’re going to have to continue to keep our eye on wood burning and significant contributors to our air quality challenges.
Nancy Daher
Nancy Daher

I am an air quality researcher and modeler at the Utah Division of Air Quality and an adjunct professor in Occupational and Environmental Health at the University of Utah. I received my doctorate degree in environmental engineering from the University of Southern California and have been actively engaged in air quality research for over 10 years. When not working, I enjoy spending time outdoors and with my family.

Kerry Kelly
Kerry Kelly

I am an Assistant Professor in Chemical Engineering and Associate Director of the Program for Air Quality, Health and Society at the University of Utah.