During the summer of 1979, coefficients for light extinction in the atmosphere were calculated from measurements made with a telephotometer placed 251 m from a black target in Research Triangle Park, North Carolina. The results are well correlated (r = 0.92 to 0.96) with integrating nephelometer measurements of scattering coefficients and are highly correlated (r = 0.99) with daily averages of sums of scattering and absorption coefficients. The average sum of scattering and absorption coefficients accounts for about 90% of the average telephotometrically measured extinction coefficient; absorption by particles and nitrogen dioxide contributes 7% and 2%, respectively. From analysis of aerosol mass and composition, it is inferred that sulfate and its cations were the major cause of light extinction and haze at the measurement site.