Improved lower particle size limit for aerosol time-of-flight mass spectrometry

The lower detectable particle size limit for a transportable aerosol time-of-flight mass spectrometer (ATOFMS) has been improved to 0.08 mum. This is lower than previously reported and has been achieved through instrumental modifications described in this paper. The uncertainty in the size measurement of particles with aerodynamic diameters less than 0.18 mum does not allow for determination of an exact size for unknown particles, but particles with aerodynamic diameters as low as 0.08 mum can still be detected and chemically analyzed. A calibration curve covering the size range 0.18-2.1 mum is presented. Simultaneously acquired positive and negative ion mass spectra of an individual 0.08 mum polystyrene latex sphere and an ambient particle with an aerodynamic diameter of 0.18 mum or less obtained with a transportable ATOFMS instrument are shown. The ability to precisely size and chemically analyze particles from a polydisperse sample down to 0.18 mum makes ATOFMS unique from other single particle mass spectrometry instruments.