Size-resolved online chemical analysis of nanoaerosol particles: A thermal desorption differential mobility analyzer coupled to a chemical ionization time-of-flight mass spectrometer

Abstract

A new method for size-resolved chemical analysis of nucleation mode aerosol particles (size range from ĝ1/4 10 to ĝ1/4 30-nm) is presented. The Thermal Desorption Differential Mobility Analyzer (TD-DMA) uses an online, discontinuous principle. The particles are charged, a specific size is selected by differential mobility analysis and they are collected on a filament by electrostatic precipitation. Subsequently, the sampled mass is evaporated in a clean carrier gas and analyzed by a chemical ionization mass spectrometer. Gas-phase measurements are performed with the same mass spectrometer during the sampling of particles. The characterization shows reproducible results, with a particle size resolution of 1.19 and the transmission efficiency for 15-nm particles being slightly above 50-%. The signal from the evaporation of a test substance can be detected starting from 0.01-ng and shows a linear response in the mass spectrometer. Instrument operation in the range of pg-m 3 is demonstrated by an example measurement of 15-nm particles produced by nucleation from dimethylamine, sulfuric acid and water.