Influence of particle properties on measuring a low-particulate-mass concentration by light extinction method

Abstract

The influence of particle size variation on particle concentration measurement via light extinction is a major challenge in the field, particularly when particle shape and composition can alter the size effect. In this study, a white-cell extinction system was used to characterize the extinction properties of several mineral and ash aerosols to illustrate the size effect among particles with different optical properties. The extinction coefficients of the aerosols were derived from real-time data and compared with the Mie calculation and modeled optical properties of ensembles of aerosol particles (MOPSMAP) simulation. The experimentally derived extinction coefficients of irregularly shaped silica aerosols were larger than those of spherical silica aerosol with an equivalent size in the range 0.5–3 μm. The deviation increased with particle shape deformity, which was consistent with the MOPSMAP simulation. Variations in the mass extinction coefficient, caused by a fixed size variation, increased with particle shape deformity, thereby demonstrating that particle shape deformity intensifies the influence of size variation on particulate extinction. The sensitivity of particulate extinction to size variation varied slightly among the alumina and silica aerosols. However, this sensitivity was negligible compared with the sensitivity of silica aerosols with different morphologies. According to the experimental results for ash aerosols, particle shape deformity is likely to introduce a systematic error of 25%–100% to the extinction-calculated concentration through the alteration of the extinction coefficient, indicating that stringent limitations for the acceptable particle size variation of non-spherical particles should be considered to guarantee the reliability of the extinction-calculated concentration.