DETERMINING AEROSOL RADIATIVE PROPERTIES USING THE TSI-3563 INTEGRATING NEPHELOMETER

Methods for reducing and quantifying the uncertainties in aerosol opti cal properties measured with the TSI 3563 integrating nephelometer are presented. For nearly all applications, the recommended calibration g ases are air and CO,. By routinely characterizing the instrumental res ponse to these gases, a diagnostic record of instrument performance ca n be created. This record can be used to improve measurement accuracy and quantify uncertainties due to instrumental noise and calibration d rift. When measuring scattering by particles, size segregation upstrea m of the nephelometer at about I Crm aerodynamic diameter greatly incr eases the information content of the data for two reasons: one stemmin g from the independence of coarse and fine particles in the atmosphere , and the second stemming from the size dependence of the nephelometer response. For many applications (e.g., extinction budget studies) it is important to correct nephelometer data for the effects of angular n onidealities. Correction factors appropriate to a broad range of sampl ing conditions are given herein and are shown to be constrained by the wavelength dependence of light scattering, as measured by the nephelo meter. Finally, the nephelometer measurement is nondestructive, such t hat the sampled aerosol can be further analyzed downstream. Data from two nephelometers operated in series are used to evaluate this procedu re. A small loss of super-mu m particles (5-10%) is found, while the s ub-mu m data demonstrates measurement reproducibility within +/- 1%. ( C) 1998 American Association for Aerosol Research.