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Angular illumination and truncation of three different integrating nephelometers: Implications for empirical, size-based corrections

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Author: Muller, T. · Nowak, A. · Wiedensohler, A. · Sheridan, P. · Laborde, M. · Covert, D.S. · Marinoni, A. · Imre, K. · Henzing, B. · Roger, J.C. · Dos Santos, S.M. · Wilhelm, R. · Wang, Y.Q. · Leeuw, G. de
Type:article
Date:2009
Institution: TNO Bouw en Ondergrond
Source:Aerosol Science and Technology, 6, 43, 581-586
Identifier: 241584
doi: doi:10.1080/02786820902798484
Keywords: Environment · Aerosol size distributions · Angular range · Calibration accuracy · Correction factors · Intercomparison · Lambertian illumination · Non-idealities · Operational data · Performance tests · Air quality · Calibration · Light · Light sources · Nephelometers · carbon dioxide · air pollution · angular illumination · article · calibration · data analysis · diagnostic accuracy · drug stability · illumination · intermethod comparison · light scattering · nephelometry · nonhuman · priority journal · Lambertia · Urban Development · Built Environment

Abstract

Integrating nephelometers are widely used for monitoring and research applications related to air pollution and climate. Several commercial versions of the instrument are available and are in wide use in the community. This article reports on results from a calibration and intercomparison workshop where several units of the three most widely used nephelometer models were tested with respect to their CO2 calibration accuracy and stability and non-idealities of their angular illumination function. Correction factors that result from the non-ideal illumination due to truncation of the sensing volumes in the near-forward and near-backward angular ranges and for non-Lambertian illumination from the light sources are presented, in particular for two models that have not previously been tested in this respect. The correction factors ranged from 0.95 to 1.15 depending on the model of nephelometer and aerosol size distribution. Recommendations for operational data analysis in context of these and previous performance tests are presented.