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Air Curtain Incinerator Emission Testing

ACIs operate by forcefully projecting a high velocity of air across an open combustion chamber in which clean woody debris is loaded. The “air curtain" that is created in this process traps unburned particles (smoke) under it where it is re-burned. ACIs are a preferred alternative to traditional open burning because they produce less harmful smoke. Oregon uses ACIs for a variety of reasons including wildfire cleanup and fire prevention efforts. ACIs can also be used to control for and slow the spread of forestry pests and disease. ACIs still produce air pollution and require air quality permits and monitoring. Emission factors are used to make informed permitting decisions. Currently there are insufficient emissions factors available for ACIs, so DEQ and other project contributors are completing an ACI emission test in spring of 2023.

What are emissions and how do you test for them?

Emissions are essentially the amount of a pollutants, in a gaseous or particulate form, that is being emitted into the air from a specific source. Measurements of emissions can be used to understand how one source compares to another and also to assess the performance of control strategies. DEQ uses emission measurements to create air quality permits in order to control for air pollution and to comply with national air quality standards.

The biggest challenge when testing an ACI is capturing the emissions from the open combustion chamber, which requires continuous loading of materials. Emissions must be captured while also accounting for interferences (compounding emissions, ambient air, etc.) and ensuring that the collection method does not interfere with the air curtain. Without comparable estimates of emissions from a source of this type, it is very difficult to determine the appropriate sampling time and volume to maximize the detection of compounds present in small amounts. After soliciting for information from experts across the country and consulting with manufacturers (AirBurners, Inc. and Tigercat), DEQ began working with various partners to design a testing unit and appropriate testing plan.

How is this emission test helping with emerald ash borer response efforts?

Emerald ash borer is an exotic beetle that infests ash trees. Following the devastation of the beetle in the Midwest, Oregon took proactive steps, including developing the statewide readiness and response plan in 2021. Emerald ash borer was discovered in June 2022 after a trained Oregon forest pest detector reported declining ash trees in Washington County. Oregon Department of Forestry and Oregon Department of Agriculture responded to these reports and immediately initiated the statewide plan. Within weeks a task force led by ODA with over 40 participating agencies (including DEQ) was created and subcommittees were formed. The Wood Waste & Wood Utilization subcommittee was convened to 1) compile standards to prevent the spread of EAB out of Oregon quarantine areas, 2) identify locations, contractors, and means of disposal of green wood waste, and 3) explore alternative wood utilization practices to minimize wood waste.  Although there are several ways to treat infested materials (chipping to a certain size, kiln drying to a certain temperature, etc.) incineration is thought to be one of the most sanitary ways to slow the spread of the beetle. After several subcommittee discussions the idea of combining the DEQ ACI emissions test with efforts to control the ash borer was formed.

Who are the project contributors and where will the testing occur?

DEQ is working directly with partners from Oregon Department of Forestry and Clean Water Services to complete the ACI emission test. Testing will occur at Fernhill Wetlands a CWS-owned property in Forest Grove. The test will use a mix of woody materials including ash wood sourced from within the temporary emerald ash borer quarantine area within Washington County.

To capture emissions from the ACI unit, a partial fume hood has been designed and fabricated by Adventure Metal Machine Works. DEQ is working with Montrose Environmental Services, an international environmental solutions company known for comprehensive air measurement and laboratory services, to design and implement the testing protocol, complete the testing, and prepare findings report.

The Biomass Utilization Working Group - ACI Subcommittee helped to review testing design, testing protocol and advise on the project.  The ACI Subcommittee includes representatives from Valley Environmental, U.S. Forest Service, TSS Consultants, U.S. Biochar Initiative, and several members of the public.

The Wood Waste & Wood Utilization subcommittee also provides support for this project. The subcommittee includes representatives from ODF, ODA, DEQ, CWS, Oregon Parks and Recreation Department, the U.S. Forest Service, Washington County, Metro, City of Hillsboro, Oregon State University, and others from the U.S. Department of Agriculture. 

Where can I find more information?

If you would like more information about the ACI Emissions Testing project, please refer to the FAQs: Emerald Ash Borer Infestation and Air Curtain Incinerator.  


For more information, please contact