Integrating nephelometer with a low truncation angle and an extended calibration scheme

A resurgence of interest has arisen lately in the use of reciprocal nephelometers in aerosol instrumentation that also measures other optical properties such as extinction by the cavity ringdown method and absorption by the photoacoustic method. This paper provides fresh insight into these nephelometers from perspectives of instrument component evaluation, intra-instrument comparison and basic calibration. In particular, a 4 degrees truncation angle reciprocal integrating nephelometer ( IN) is described and demonstrated. An experimental setup for the measurement of the IN sensor cosine response is developed and described. To calibrate the IN, the sampling volume can be filled with an aerosol with negligible light absorption ( e. g., ammonium sulfate), and scattering and extinction coefficients are monitored simultaneously. The performance of the IN is evaluated, at a wavelength of 532 nm, through extensive comparison with a 1 degrees truncation angle integrating sphere integrating nephelometer (ISIN) that operates at the same wavelength. The intercomparison included measurements of ambient aerosol, kerosene soot, ammonium sulfate aerosol, NaCl aerosol and CO2 gas. Results of a linear regression analysis indicate an agreement between the IN and the ISIN within +/- 8%. The main advantages of the IN over the ISIN are its fast time response, relatively large signal-to-noise (S/N) ratio and design simplicity.