HR: 1340h
AN: A33B-0895    [Abstracts]
TI: Evaluation of the Aethalometer and the Coefficient of Haze Sampler for Measuring Black Carbon Concentration
AU: * Kirchstetter, T
EM: twkirchstetter@lbl.gov
AF: Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley, CA 94720 United States
AU: Novakov, T
EM: tnovakov@lbl.gov
AF: Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley, CA 94720 United States
AU: Haesloop, O
EM: olivia.haesloop@yale.edu
AF: Yale University, PO Box 202330, New Haven, CT 06520 United States
AU: Boone, A
EM: aaboone2@ncsu.edu
AF: North Carolina State University, 1921 Wolftech Ln, Apt 201, Raleigh, NC 27603 United States
AU: Aguiar, J
EM: j_aguiar@pacific.edu
AF: University of the Pacific, 3601 Pacific Avenue, Stockton, CA 95211 United States
AB: Black carbon (BC) is an important indicator of air quality. BC imposes a positive radiative forcing of climate and is an indicator of diesel soot, a toxic air pollutant. Over the past two decades, the aethalometer, a filter-based light transmission instrument, has become widely used for monitoring atmospheric BC concentrations. Previously, BC was not routinely measured. In this presentation, we evaluate aethalometer and the potential for using the archived record of coefficient of haze (COH) measurements as a proxy for BC. Like the aethalometer, the COH sampler employs a light transmission method, but the collection substrate is a paper membrane rather than a quartz fiber filter. Our analysis consists of laboratory experiments and evaluation of air quality data sets. In the laboratory, we exposed both instruments to particles composed entirely of BC generated with a diffusion flame. In addition, the BC was collected on quartz filters and, using a spectrometer, light attenuation (ATN) was measured. The ATN measured by the aethalometer and COH instruments, as well as with the spectrometer, increased in less than constant proportion (i.e., nonlinearly) to increased BC mass loadings. Consequently, the instruments reported decreasing concentrations of BC and COH as their filters collected BC, even when exposed to constant concentrations of BC. These experiments indicate that the simple relationship BC = ATN/sigma, where sigma is the attenuation cross-section, does not accurately predict BC concentration if sigma is assumed to be constant in value, which it is in the aethalometer. Interestingly, COH and BC were linearly correlated, indicating that the two instruments have the same nonlinear response to particle loading. Given the different types of filters in each instrument, this suggests that the nonlinear response to particle loading has more to do with particle physics (e.g., particle shadowing) than with the filter (e.g., internal scattering). Regression analysis of monthly average BC and COH measured in California indicated a linear correlation - the slope of the regression is the same as that determined in our laboratory experiments. This indicates that COH may be used as a proxy for BC.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0365 Troposphere: composition and chemistry
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005