Partic. vol. 28 pp. 93-101 (October 2016)
doi: 10.1016/j.partic.2016.03.002

Determining the relationship between chemical composition and size, shape and effective density of airborne fine particles through concurrent use of inertial and optical based measurements

Anand Kumar^{a, b}, Tarun Gupta^{a, c, *}

tarun@iitk.ac.in

Abstract

This study presents the development of a medium flow, multiple slit based PM_2.5 (particle aerodynamic diameter <2.5 μm) inertial impactor. Its performance was compared with that of a light scattering based optical particle sizer in a field study and in controlled lab based experiments using polydisperse dolomite powder as test aerosol. The impactor's optimum nozzle configuration had a cutoff size of 2.51 μm (aerodynamic diameter) at an operating flow rate of 215 L/min with a pressure drop of 0.35 kPa across the impactor stage. Because the apparent particle density of an ambient aerosol depends on the physical properties and the chemical composition of the particles, the PM_2.5 mass concentration was measured with an optical particle sizer and an inertial impactor over a weekday and a weekend day in a field study during which the effective particle shape factor and density were in tandem modified in order to compare the results from the two sampling techniques. The correlation of the two instrument results tended towards 1:1 with increasing values of shape factor (irregular shaped) and effective particle density. This observation was supported through chemical investigations of the collected mass, which showed a higher percentage contribution from elements which are mostly of crustal nature (namely, Ca, Fe, and Mg).

Graphical abstract

Keywords

Impactor; PM_2.5; Optical particle counter; Effective particle density; Shape factor