An Air Curtain Incinerator operates by forcefully projecting a high velocity of air across an open combustion chamber where clean woody debris is loaded. The “air curtain" traps unburned particles, or smoke, under it and the material burns again. An ACI is a preferred alternative to traditional open burning because it produces less smoke. People use ACIs for a variety of reasons, including wildfire cleanup and fire prevention efforts. Also, they can be used to slow the spread of forest pests and disease. However, ACIs do produce some air pollution and require air quality permits.
An emissions factor is a numerical value representing the quantity of pollutant emissions produced per unit for a specific activity, Emissions factor data is used to make informed permitting decisions. Previously, there was insufficient emissions factor data available for ACIs. Therefore in spring 2023, DEQ, along with the Oregon Department of Forestry
, Oregon Department of Agriculture
and Clean Water Services
, completed an ACI emissions test. The results will help make informed future policy and permitting decisions.
What are “emissions" and how do you test for them?
“Emissions" are essentially the amount of a pollutant, in a gaseous or particulate form, that is being put into the air from a specific source. Measurements or “factors" of emissions can be used to understand how one pollution source compares to another and to assess the performance of control strategies. DEQ uses emission factors to create air quality permits to control for air pollution and to protect public health.
How did the ACI Emissions Test help with Emerald Ash Borer response efforts?
The Emerald Ash Borer is an exotic beetle that infests ash trees. It was discovered in Oregon in June 2022 after a trained Oregon forest pest detector reported declining ash trees in Washington County. The Oregon Department of Forestry and Oregon Department of Agriculture responded and within weeks an EAB task force with more than 40 participating agencies, including DEQ, was created.
Under the task force, the Wood Waste & Wood Utilization subcommittee was convened to:
- Compile standards to prevent the spread of EAB out of Oregon quarantine areas.
- Identify locations, contractors and means of disposal of green wood waste.
- Explore alternative use practices to minimize wood waste.
There are several ways to treat infested materials to eliminate EAB's spread, including chipping to a specific size, kiln drying, etc. However, incineration through an ACI is considered one of the most effective ways to slow the spread of the beetle. Therefore, the subcommittee decided to combine DEQ's ACI emissions test with efforts to control EAB.
DEQ worked directly with partners from Oregon Department of Forestry and Clean Water Services to complete the ACI emission test. Testing occurred at Fernhill Wetlands, a CWS-owned property in Forest Grove. It used ash wood sourced from within the temporary emerald ash borer quarantine area
in Washington County.
To capture emissions from the ACI unit, a partial fume hood was designed and fabricated by Adventure Metal Machine Works
. The agencies worked with Montrose Environmental Services
, known for its air measurement practices and laboratory services, to design and conduct the ACI emissions testing and prepare the final report.
A second task force subcommittee, the Biomass Utilization Working Group, reviewed testing design, protocols and results. This group included representatives from TSS Consultants
, U.S. Biochar Initiative
, U.S. Forest Service
, Valley Environmental
and members of the public.
What are the next steps?
DEQ is committed to making data-informed decision that protect and enhance Oregon's environment. The agency is working with the U.S. Environmental Protection Agency
and the U.S Forest Service to explore options for additional emissions testing on slash pile burning and other types of air burners or carbonators. Additionally, DEQ is using information collected from these tests to inform how to protect public health, while removing barriers to the use of emissions reduction technologies.
How can I access the test results?
All test results are available at the following: