The Coefficient of Haze as a Measure of Particulate Elemental Carbon

The technique to measure the coefficient of haze (COH) was developed in 1953 and was widely employed as a surrogate technique to measure total suspended particulate matter (TSP) in the 1960s. Because of the physical design of the sampler (known as the AISI Tape Sampler) used to measure COH, it was postulated that COH was directly related to the mass of fine elemental carbon particles (EC) with diameters less than 2.5 μm. To test the hypothesis, simultaneous samples of COH and EC were collected and analyzed during the 1981 Summer Study in Detroit. Regression analysis indicates that the two quantities are linearly related over the concentration range observed. Additional analyses indicate that COH is not related to TSP, fine particle mass, or light-scattering aerosol. Calculation of specific light absorption coefficients for EC from the COH data support the hypothesis that the tape sampler responds only to fine EC. A brief examination of historical COH data from Detroit suggests that the EC concentration has declined since 1972. This should be regarded as a preliminary assessment, however, until further verification of the COH-EC connection can be made.