Measurement of sub-3 nm flame-generated particles using butanol CPCs in boosted conditions

WashU affiliated authors: Girish Sharma, Pratim Biswas (Dept. of Energy, Environmental and Chemical Engineering)

Abstract: While condensation particle counters (CPCs) are routinely used to measure particle number concentrations in the size range from 3 to 1000 nm, the detection efficiency for sub-3 nm particles remains relatively poor. In this study, the performance of an ultrafine butanol based CPC for the measurement of alkyl ammonium halide ions, flame-generated particles of titanium dioxide (TiO2) and soot is evaluated. Homogenous nucleation of butanol vapors, and detection efficiency of THAB ions are systematically evaluated for a range of saturator temperatures (39–45 °C) and capillary flow rates (30–70 sccm). The optimal operating conditions with minimal background interferences was found to be a saturator temperature of 45 °C and capillary flow rate of 70 sccm. Flame generated particles of TiO2 and soot were activated more readily than the alkyl ammonium halide salts of similar mobility diameters, especially in the below 1.6 nm mobility size range, whereas above 1.6 nm the detection efficiency is independent of particle material, but depends on particle size. The negative charge on the particles is found to promote activation with butanol vapors leading to higher activation efficiencies than positively charged particles. Finally, the importance of butanol as a working fluid, and its calibration for precise measurement of sub-3 nm particles is discussed. This will enable researchers to perform experiments using a ‘conventional’ CPC with boosted conditions for the understanding of early stages of particle formation and growth in different aerosol reactors.