Development and Field Evaluation of a Multiple Slit Nozzle-Based High Volume PM2.5 Inertial Impactor Assembly (HVIA)

Abstract

This study presents the development and lab performance of a high volume (Q = 950 LPM), multiple slit nozzle-based PM2.5 (particle aerodynamic diameter < 2.5 µm) inertial impactor and the performance of the same was compared with an existing single stage low flow rate (Q = 15 LPM) PM2.5 impactor. Lab experiments were performed on various slit-based nozzle impactors using polydisperse dolomite powder as test aerosol. After carrying out rigorous parametric evaluation, the optimum slit nozzle-based impactor configuration selected had cutoff size of 2.51 µm (aerodynamic diameter) at an operating flow rate of 215 LPM (medium flow) with a pressure drop of 0.35 kPa across the impactor stage. The length of the slit of this optimum medium flow impactor was extrapolated to a flow rate of 950 LPM to obtain the high volume multiple slit nozzle-based PM2.5 inertial impactor assembly. This novel impactor assembly was fabricated from brass and chrome-plated and then retrofitted in a high volume dust sampler (Model AAS 217NL, Ecotech Instruments, India) downstream of the PM10 cyclone separator. High vacuum silicone grease was used as the impaction substrate. A field study was performed with co-located novel high volume impactor assembly (HVIA) and single stage low flow rate PM2.5 impactor, to not only compare the PM2.5 mass concentrations but elemental, anion and water soluble organic carbon (WSOC)/water soluble inorganic carbon (WSIC) concentrations as well in order to validate the HVIA developed in the present study.