Effect of operating conditions and technology on residential wood stove emissions of criteria, greenhouse gas, and hazardous air pollutants

Residential wood heating (RWH) is a known source of particulate matter (PM), hazardous air pollutants (HAPs), and greenhouse gases (GHGs). However, the influence of operating conditions on emissions from certified cordwood stoves in the United States (U.S.) remains poorly understood. This study analyzes emissions data from different operational phases, including start-up, high heat, and low heat, to improve indicators of real-world stove performance. We tested five commercially available U.S. stoves through the four distinct operational conditions or phases of the novel Integrated Duty Cycle (IDC) testing protocol, which simulates typical residential wood-burning patterns by incorporating start-up, high heat, medium (or "maintain") heat, and low heat ("overnight" burn) phases. We determined emissions factors (EFs) by IDC phase for criteria, GHG, and HAP compounds, including volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs). We also developed a multiple linear regression model to assess the effect of dry burn rate (DBR) and IDC phase on each pollutant EF by stove technology type. IDC phase significantly influenced (p < 0.01) pollutant EFs from uncertified stoves and most emissions from catalytic/hybrid stoves, while DBR played a more substantial role in emissions from non-catalytic stoves. Current stove certification methods rely on a single nominal load under steady-state combustion, which does not reflect typical residential use. Additionally, we found DBR to be an inconsistent predictor of emissions in cordwood stoves. These findings underscore the importance of stove technology and operating conditions in determining RWH emissions, with implications for air quality science and regulatory policy.<i>Implications:</i> We report cordwood stove emissions factors by operating condition using the novel Integrated Duty Cycle (IDC) protocol on various U.S. technologies meeting 2020 New Source Performance Standards (NSPS) and one pre-NSPS, circa 1980 stove. We determined significant effects from IDC operating phase on uncertified and catalytic/hybrid stove emissions, but not noncatalytic stoves. This has important implications for use of emissions factors in air quality science, policy, and stove design, as different U.S. climate zones will influence the number of stove start-ups, fuel loading patterns, and frequencies of other "real world" operating conditions such as "high heat" and "overnight burn."