Symmetric Inclined Grid Mobility Analyzer for the Measurement of Charged Clusters and Fine Nanoparticles in Atmospheric Air

摘要

The Symmetric Inclined Grid Mobility Analyzer (SIGMA) was developed for applications in atmospheric aerosol nucleation research with special attention to long-term routine measurements in natural atmospheric conditions. The new instrument was elaborated using the experience of the preceding scanning mobility analyzers Inclined Grid Mobility Analyzer (IGMA) and Balanced Scanning Mobility Analyzer (BSMA). The range of electric mobility is 0.032−3.2 cm2V−1s−1. The particle diameter distribution in the range of 0.4−7.5 nm is resolved considering the size-mobility correlation at air temperature and pressure measured with built-in sensors. The scanning technique ensures that possible peculiarities in the recorded size or mobility distribution are not caused by the technical troubles of individual mobility channels. High rate of air flow and isopotential principle suppress the disturbing effect of external electric fields and assure the representative sampling of air ions. The sheath air is coming from the atmosphere together with the sample air and is deionized by means of electrostatic filters. The residence time of the air in the instrument is 0.16 s and the temperature change does not exceed 0.5 K. Different of the previous instruments the positive and negative air ions are sampled from the same inlet air flow and measured exactly simultaneously. The sensitivity of the instrument is increased and allows measuring the mobility fraction concentrations of charged fine nanometer particles in atmospheric air at a standard 5-min time resolution with random errors of about 1 cm−3. The time resolution of 20 s is available at random errors of about 5 cm−3.