Evaluation of a New Approach for Real Time Assessment of Wood Smoke PM Allen et al. Oct. 2004 Page -1- Evaluation of a New Approach for Real Time Assessment of Wood Smoke PM George A. Allen NESCAUM, 101 Merrimac St., Boston MA 02114 Peter Babich CT-DEP, Bureau of Air Management, 79 Elm Street, Hartford, CT 06106 Richard L. Poirot Vermont DEC - APCD, 103 South Main Street-Building 3 South, Waterbury, Vermont 05671 ABSTRACT Wood smoke from forest fires or anthropogenic activities can be a significant contributor to regional haze and PM2.5, but routine methods to quantify the extent of this source’s contribution to visibility impairment and ambient levels of PM2.5 have not been developed and evaluated. This paper evaluates an approach to semi-quantitatively measure the fraction of PM that is from wood smoke (WS PM) in real-time. A two-wavelength Aethalometer™ (Magee Scientific model AE42) was used to measure the optical absorption of PM-1 ambient aerosol at 880 nm (BC) and 370 nm (UV-C). Certain organic aerosol components of wood smoke PM have enhanced optical absorption at 370 relative to 880 nm (“Delta-C”). This enhanced absorption is shown to be a specific "indicator" of WS PM, but alone is not a quantitative mass measurement. Improved quantification of WS PM can be obtained when the two-channel Aethalometer is collocated with continuous PM2.5 and other measurements. A pilot study was performed to evaluate the potential for this approach in Rutland, VT between February and July, 2004. Aethalometer measurements were made at an existing VT-DEC monitoring site, collocated with continuous PM2.5, SO2, CO, and NOx measurements. Rutland is a valley city surrounded by elevated terrain and subject to strong winter morning inversions, and winter PM2.5 sample filters from this site often exhibit a distinct “wood smoke odor”. Local mobile sources also contribute to the observed PM and BC concentrations (but not Delta-C) at this site, primarily during weekday morning rush hour periods. Monitoring was performed during seasons with and without wood smoke to allow assessment of mobile source signatures without heating sources, since both have large BC components. The UNMIX model was used to apportion measured PM2.5 into several source categories; NOx and SO2 are used to distinguish PM contributions from WS, oil burning (primarily space heating), and mobile sources. WS PM was associated only with the Aethalometer Delta-C measurement even in the presence of substantial local mobile source and oil-burning aerosols. Paper #16, presented at the Air & Waste Management Association Visibility Specialty Conference on Regional and Global Perspectives on Haze: Causes, Consequences and Controversies. Asheville, NC, October 25-29, 2004.