Filter light attenuation as a surrogate for elemental carbon

Abstract

Light attenuation (batt) measured from filter light transmission is compared with elemental carbon (EC) measurements for more than 180,000 collocated PM2.5 (particulate matter [PM] ≤ 2.5 μm in aerodynamic diameter) and PM10 (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 batt and EC (such as the effects of "brown carbon" and iron oxides in PM2.5), 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 batt shows larger uncertainties (30-60%), especially at concentrations less than 0.3 μg/m3, the consistent mass absorption efficiency (σatt) derived from the regression analysis demonstrates the feasibility of using batt as a surrogate for EC. This study demonstrates that a constant factor of 0.1 g/m2 (equivalent to the 10 m2/g σatt used in the Interagency Monitoring of Protected Visual Environments chemical extinction formula) can be used to estimate EC concentrations from batt through a Teflon-membrane filter sample. Greater accuracy is achieved with site-specific σatt derived from a period with collocated EC measurements. Copyright 2010 Air & Waste Management Association.