10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Measurement of Continuous PM and Black Carbon in a Wood Stove Dilution Tunnel
GEORGE ALLEN, Lisa Rector, NESCAUM
Abstract Number: 1636 Working Group: Instrumentation
Abstract The US EPA 2015 New Source Performance Standard (NSPS) for residential wood heaters includes development of test method protocols that use cordwood in lieu of the traditional dimensional lumber fuel for PM emission performance certification. This move to new fuels focused the need to improve the operational component of the EPA M28R test protocol for wood stoves. Both the process of designing a new test fueling protocol as well as a better understanding of how stove design needs to be changed to reliably burn cordwood cleanly can benefit from highly time-resolved measurement of aerosol emissions to identify what fueling and operational conditions dominate the emission test results. As part of several ongoing projects to inform upcoming Step 2 cordwood test protocols for the 2015 NSPS, robust techniques to measure continuous PM in a dilution tunnel have been developed. The Thermo 1400AB and 1405 TEOM ambient PM monitors have been operationally modified to provide robust 15-second PM measurements for this application, and are capable of measuring in excess of 1/2 gram/m3 PM. TEOM filter changes are typically 30 to 120 minutes or more apart and result in a data gap of only 2 to 3 minutes; a typical test for a clean technology stove usually has only a single filter change. Comparison to Method 5G manual filter PM samples shows high correlation over a wide range of concentrations and good numerical agreement. No sample conditioning is used for TEOM measurements. The TEOM uses the same Emfab TX40 filter media as the Method 5G sample trains, is run at the same temperature (30C), and with a similar face velocity. While semi-volatile (water, SVOC) mass dynamics are present in the TEOM data, because filter conditions are the same, they are the same dynamics occurring on the Method 5G samples. The only functional difference between the methods is that the TEOM filters can not be equilibrated using the required Method 5G filter desiccation process. TEOM data often go negative when filter loading is high and the burn cleans up; for fresh woodsmoke this is more likely due to SVOC loss than water, and more research is planned to quantify the components of this mass loss. A Thermo pDR1500 forward scattering particle instrument is also used to provide supporting PM measurements as well as a qualitative indication of particle size from the ratio of TEOM to pDR concentrations, since the pDR response to PM varies widely across the range of burn conditions during a test cycle. For a subset of test runs, black carbon (BC) is also measured in the dilution tunnel using an operationally modified Magee Scientific AE22 Aethalometer. Using a manual tape advance approach, 5-second BC concentrations in excess of 20 milligrams/cubic meter can be measured, with a data gap of 5-seconds between tape advances. The "gap" method is used to estimate and correct for filter optical loading artifacts. Measurement of continuous PM and BC provides a real-time estimate of the organic carbon (OC) aerosol mass (by difference) and thus the BC to OC ratio, which can be indicators of combustion conditions. Future work includes plans to perform the required EPA method testing to allow the TEOM to be used as an alternative to the current manual measurements for PM emission performance certification of residential wood heaters, and to couple the TEOM with a commercial dilution system to provide an alternative to the current dilution tunnel emission measurement approach.