Online measurement of PM from residential wood heaters in a dilution tunnel

ABSTRACT

The U.S. Environmental Protection Agency (US EPA) requires residential wood heaters (RWHs) to meet particulate matter (PM) emission limits in order to lower ambient concentrations and reduce public exposure. The current US EPA dilution tunnel PM measurement methods for RWHs were developed several decades ago and use manual filter samples to generate a single PM value for tests that can last more than 12 hours for stoves and 30 hours for central heating appliances. This approach results in averaging periods of high and low emissions together and provides limited data on emissions over the entire burn profile. Over the last decade, the U.S. ambient fine particulate monitoring network has transitioned to the routine use of online automated methods. However, stationary source measurement methods have not made this transition. There are no substantial technical issues in implementing real-time automated methods to measure PM for RWH emission certification purposes. The Thermo Scientific Tapered Element Oscillating Microbalance (TEOM™) has been widely used for ambient PM measurements. It is a true inertial mass measurement with high time resolution and sensitivity. This work compares measurements obtained using a Thermo 1400 or 1405 TEOM with ASTM E2515 manual filter samples, the current US EPA Federal Reference Method, for 172 test runs across a wide range of stoves and PM loading conditions. The TEOM measurements used the same filter media, similar filter face velocities, and filter temperatures as manual methods. PM measurements were well correlated (R² > 0.9), with TEOM values typically lower by 5% to 10%. TEOM data capture was high, with filter changes resulting in ~5 minutes of lost data, usually once or twice during a multi-hour test. We discuss differences between the two methods, such as post-sampling equilibration and measurement of PM on sample train surfaces (probe “catch”). We also provide examples of substantial non-water semi-volatile mass loss during sampling.

Implications: Measurement methods for continuous PM and our understanding of their performance has dramatically improved over the last thirty years. Highly time-resolved measurements of PM from residential wood heating appliances in an appliance certification testing context provide additional insight into both appliance performance and the suitability of the test method to assess that performance. This continuous measurement approach offers new opportunities to replace traditional US regulatory PM sampling integrated manual source methods like ASTM E2515 or EPA Method 5G testing. For measurement of combustion products that can have a wide range of physical and chemical characteristics, the TEOM’s actual mass measurement principle has advantages over the sensitivity of surrogate methods to different aerosols for use in a regulatory program. Although the TEOM is commonly used to measure ambient PM, it can readily be configured to meet the needs of continuous emission testing.

Acknowledgment

Funding for this project was provided by the New York State Energy Research and Development Authority (NYSERDA), Agreement #101132 and #123059, and the authors thank Dr. Ellen Burkhard, NYSERDA Project Manager, for helpful comments throughout the project. The opinions expressed in this report do not necessarily reflect those of NYSERDA or the State of New York. Additional funding for the HLS 2016 Vigilant species crib testing was provided by the US EPA. Mention of product manufacturer names or trademarks does not imply endorsement by NESCAUM or NYSERDA.

Data availability statement

The data that support the findings of this study are available from the corresponding author, [GA], upon reasonable request.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the New York State Energy Research and Development Authority [Agreement #101132 and #123059].

Notes on contributors

George Allen

George Allen is the Chief Scientist at Northeast States for Coordinated Air Use Management (NESCAUM) in Boston, MA.

Barbara Morin

Barbara Morin worked for the Rhode Island Department of Environmental Management and Department of Health and is currently an Environmental Analyst at Northeast States for Coordinated Air Use Management (NESCAUM) in Boston, MA.

Mahdi Ahmadi

Mahdi Ahmadi was an Environmental and Energy Analyst at Northeast States for Coordinated Air Use Management (NESCAUM) in Boston, MA. and is currently a consultant based in Austin, TX.

Lisa Rector

Lisa Rector is the Policy and Program Director at Northeast States for Coordinated Air Use Management (NESCAUM) in Boston, MA.