Measurement of black carbon (BC) by an optical method and a thermal-optical method: Intercomparison for four sites

Comparison of black carbon (BC) measurements obtained by two methods was performed for aerosols samples collected on Whatman 41 (W-41) filters, using an optical method (Magee Scientific Optical Transmissometer Model OT-21) and a thermal-optical method (Sunset Laboratory Thermal-optical analyzer). Samples were collected from four sites: Albany (a small urban site, NY), Antalya (coastal site, Turkey), Whiteface Mountain (remote site, NY) and Mayville (rural site, NY). At Albany, comparison between the two methods showed excellent agreement; a least-squares regression line yielded a slope of 1.02, and r2 = 0.88. Similar comparisons at Antalya (slope of 1.02, r2 = 0.5) and Whiteface Mountain (slope of 0.92 and r2 = 0.58) also gave very good relationship. At Mayville, the relationship between the two methods yielded somewhat lower regression: a slope of 0.75, and r2 = 0.44. The data from the four locations, when plotted together, yielded an excellent agreement: a slope of 0.91, and r2 of 0.84. Based on our measurements, it appears that optical measurement using the OT-21 can be successfully applied to determination of BC in W-41 filters. However, because of the variability in the chemical composition of BC aerosol at different locations, it is suggested that the calibration of OT-21 when using W-41 filters should be performed with a statistically significant numbers of samples for specific sites.