Development of an Aerosol Mass Spectrometer for Size and Composition Analysis of Submicron Particles

TLDR

Atmospheric aerosols influence climate, air quality, and health, creating a demand for real‑time, size‑resolved, mass‑ and composition‑sensitive instrumentation. The authors developed an aerosol mass spectrometer (AMS) to meet this need and to provide quantitative analysis of aerosol size and composition. The AMS couples an aerodynamic aerosol inlet and time‑of‑flight sizing with flash vaporization and mass spectrometry, enabling particle size determination and mass detection in a single instrument. Calibration and fluid‑dynamics studies confirm accurate aerodynamic velocity, collection efficiency, and size classification for pure NH4 NO3 aerosols, and the instrument demonstrates reliable laboratory and field‑portable performance.

Abstract

The importance of atmospheric aerosols in regulating the Earth's climate and their potential detrimental impact on air quality and human health has stimulated the need for instrumentation which can provide real-time analysis of size resolved aerosol, mass, and chemical composition. We describe here an aerosol mass spectrometer (AMS) which has been developed in response to these aerosol sampling needs and present results which demonstrate quantitative mea surement capability for a laboratory-generated pure component NH4 NO3 aerosol. The instrument combines standard vacuum and mass spectrometric technologies with recently developed aerosol sampling techniques. A unique aerodynamic aerosol inlet (developed at the University of Minnesota) focuses particles into a narrow beam and efficiently transports them into vacuum where aerodynamic particle size is determined via a particle time-of-flight (TOF) measurement. Time-resolved particle mass detection is performed mass spectrometrically following particle flash vaporization on a resistively heated surface. Calibration data are presented for aerodynamic particle velocity and particle collection efficiency measurements. The capability to measure aerosol size and mass distributions is compared to simultaneous measurements using a differential mobility analyzer (DMA) and condensation particle counter (CPC). Quantitative size classification is demonstrated for pure component NH4 NO3 aerosols having mass concentrations 0.25mu g m -3. Results of fluid dynamics calculations illustrating the performance of the aerodynamic lens are also presented and compared to the measured performance. The utility of this AMS as both a laboratory and field portable instrument is discussed.