The versatile size analyzing nuclei counter (vSANC)

Abstract

We present a new field-deployable expansion chamber condensation particle counter—the versatile size analyzing nuclei counter (vSANC). The measuring principle, which was adopted from the classical SANC, was optimized regarding ranges of operating temperatures (–20°C to +40°C), inlet gas pressures (0.2–.2 bar), inlet flow rates (1.6–9 l/min) and condensing liquids (alcohols, alcanes, water, etc.), all of which make vSANC applicable to a wide variety of environments. Precision determination of vapor supersaturation ratios allows estimating neutral cluster sizes without prior electrical-mobility based classification of the sample. Additionally, absolute number concentrations ranging from 102 to 107cm–3 can be measured without referring to external calibration standards. This enables size-resolved number concentration measurements of nanoparticles. Laboratory studies using n-propanol as condensing liquid demonstrated that charged (NH4)2SO4 and WOx particles as small as 1.5 nm can be counted with an efficiency of 10%. Furthermore, we observed an increase in counting efficiency of charged WOx particles by about 50% when lowering vSANC’s chamber and saturator temperatures from 23°C and 25°C to 13°C and 15°C, respectively. During spring 2014, the vSANC was operated at the SMEAR II station in Finland where the formation and growth of atmospheric clusters was investigated. Atmospheric new particle formation (NPF) was observed only when vSANC’s operating temperatures (13°C and 15°C) were close to the ambient air temperature (about 5°C–15°C). Diurnal concentration evolution measured with the vSANC was compared with data from a differential mobility particle sizer (DMPS) and a nano-condensation nucleus counter (nCNC, Airmodus A11). vSANC detected the NPF signal 2–3 h before the DMPS in agreement with the nCNC; however, a continuously present pool of highly concentrated neutral clusters in the sub- 3 nm diameter range could not be confirmed during these measurements.