Study Provides New Insights Into Impacts of Wildland Fires on Ozone Monitoring Equipment in Kansas

– EPA Region 7 Feature –

New research from EPA shows wildland fire smoke may affect the accuracy of some regulatory monitoring instruments that measure ozone. The measurements from these instruments are needed by state, local, and tribal air quality agencies to determine if levels of the pollutant exceed the national standard.

image of Burning crew member KS burns story — **A prescribed burn crew member monitors a patch of burning rangeland. It is a slow, controlled burn. (Photo credit: U.S. EPA)**

Within EPA Region 7, improved emission factors are important in supporting better performing air pollution dispersion modeling that allows policymakers to better balance public health concerns with the agricultural viability of the Flint Hills.

States have observed unexplained increases in ozone from monitors near active wildfires or prescribed burns. Some types of ozone monitors give inaccurate readings in a high-load smoke environment.

To find out why this was occurring, EPA researchers investigated and evaluated a popular ozone monitoring method, called UV-photometric, which determine ozone concentrations by measuring the amount of ultraviolet (UV) light absorbed by ozone molecules. This method is widely used by state, local, and tribal agencies at national monitoring stations to measure ozone levels and implement the regulations for the pollutant.

This routine monitoring of ozone is conducted using regulatory grade instruments known as Federal Reference Methods (FRMs) or Federal Equivalent Methods (FEMs), which have met rigorous scientific review for performance. Until recently, researchers and air quality managers only had a limited understanding about the performance of these monitors under the unique conditions of significant wildland fire smoke. This research is trying to identify and correct those monitoring issues to ensure that accurate ambient ozone data is provided to the public, including during wildfire events.

image of Prescribed burn smoke anim KS burns story2 — *CLICK TO VIEW ANIMATION:* Satellite imagery shows the smoke plumes from prescribed burns in the Flint Hills. (Photo credit: Cooperative Institute for Research in the Atmosphere, supported by Colorado State University and the National Oceanic and Atmospheric Administration.)

To understand how the FRMs and different types of FEMs perform in wildland fire smoke conditions, EPA researchers measured newly emitted smoke emissions from prescribed grassland fires in Kansas and Oregon in 2017 using five commercial ozone monitors simultaneously. All measurements were made in fresh emission plumes, where ozone is not expected to be detected.

The study found that the new ozone NO-chemiluminescence method, designated as an FRM in 2015, did not have operational problems when used in the smoke plumes. This method is based on measuring the amount of light released when ozone molecules chemically react with nitric oxide (NO) molecules. However, the ozone UV-photometric method showed varying degrees of smoke interference and did not provide accurate results.

Following the Kansas and Oregon studies, EPA researchers traveled to the U.S. Forest Service’s Rocky Mountain Fire Sciences Laboratory in Missoula, Montana, to conduct additional studies. Their observations in the grassland burns were confirmed in the laboratory burns of Ponderosa Pine.

They discovered that smoke from fires caused severe operational interference in some of the UV-photometric models, while others were affected to a lesser degree. The instruments overestimated ozone concentrations, resulting in higher readings than occurred. In some cases, researchers discovered that operating UV-photometric instruments in heavy smoke events resulted in irreversible damage to instrument components.

**EPA research team with ozone monitoring instruments at the Nature Conservancy Sycan Marsh Preserve in Oregon. (Photo credit: U.S. EPA)**

Researchers hypothesize the smoke interference is associated with high concentrations of volatile organic compounds (VOCs) that are emitted during the burning of trees and other vegetation. In this research effort, they identified a method that reduced the magnitude of this VOC interference, which can give monitoring agencies more confidence in their ozone measurements.

VOCs are organic chemical compounds whose composition makes it possible for them to evaporate under normal indoor atmospheric conditions of temperature and pressure.

These findings were recently published in the article, “Comparison of ozone measurement methods in biomass burning smoke: an evaluation under field and laboratory conditions” in the March 4, 2021, issue of Atmospheric Measurement Techniques. The new insights improve the understanding of state, local, and tribal monitoring agencies regarding the ozone monitoring technology options during wildland fire smoke events and the interpretation of ozone data collected. The work is also anticipated to be used by instrument manufacturers to understand the impacts of wildfire smoke on their monitors.

“An accurate ozone monitoring method, free of any potential interferences, will enhance the ability of the states to accurately separate true ozone concentration from other measurements at sites impacted by wildland fire smoke,” said Russell Long, lead EPA researcher on this study.

Regulatory monitors that use FRMs and FEMs are continuously reviewed and evaluated by EPA researchers to ensure that they meet needed performance specifications and to provide states with the proper tools and information needed to address ozone National Ambient Air Quality Standards for attainment/non-attainment issues. A list of updated methods is published every six months and can be found on EPA's FRM/FEM Research page.