Filter Light Attenuation as a Surrogate for Elemental Carbon

• Published in: Journal of the Air & Waste Management Association (1995) 2010-11, Vol.60 (11), p.1365-1375
• Main Authors: Chow, Judith C., Watson, John G., Green, Mark C., Frank, Neil H.
• Format: Article
• Language: English
• Subjects: Air Pollutants, Occupational - analysis; Air pollution; Algorithms; Applied sciences; Atmospheric pollution; Computer software industry; Environmental Monitoring - instrumentation; Environmental Monitoring - methods; Exact sciences and technology; Filtration; Light; Membrane filters; Methods; National parks; Optical instruments; Optical properties; Outdoor air quality; Particulate Matter - analysis; Pollution; Regression analysis; Seasons; Soot - analysis; United States; Watson, John G; Wilderness areas
• ISSN: 1096-2247; 2162-2906
• DOI: 10.3155/1047-3289.60.11.1365

Light attenuation (b att ) measured from filter light transmission is compared with elemental carbon (EC) measurements for more than 180,000 collocated PM 2.5 (particulate matter [PM] ≤ 2.5 µm in aerodynamic diameter) and PM 10 (PM ≤ 10 µm in aerodynamic diameter) samples from nearly 200 U.S. locations during the past 2 decades. Although there are theoretical reasons for expecting highly variable relationships between b att and EC (such as the effects of "brown carbon" and iron oxides in PM 2.5 ), reasonable correlations are found. These correlations are not a strong function of season or location (e.g., rural vs. urban). Median EC concentrations can be predicted from filter transmittance measurements to within ±15-30%. Although EC predicted from b att shows larger uncertainties (30-60%), especially at concentrations less than 0.3 µg/m 3 , the consistent mass absorption efficiency (σ att ) derived from the regression analysis demonstrates the feasibility of using b att as a surrogate for EC. This study demonstrates that a constant factor of 0.1 g/m 2 (equivalent to the 10 m 2 /g σ att used in the Interagency Monitoring of Protected Visual Environments chemical extinction formula) can be used to estimate EC concentrations from b att through a Teflon-membrane filter sample. Greater accuracy is achieved with site-specific σ att derived from a period with collocated EC measurements.