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 PM_2.5 (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) PM_2.5 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 PM_2.5 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 PM_2.5 impactor, to not only compare the PM_2.5 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.