A New Volatility Tandem Differential Mobility Analyzer to Measure the Volatile Sulfuric Acid Aerosol Fraction

Abstract

A volatility tandem differential mobility analyzer (VTDMA) was developed with the intention to measure the fraction of sulfuric acid in marine fine aerosols (Dp < 150 nm). This work focused on the design and calibration of an aerosol conditioner for the standard tandem differential mobility analyzer that heated a selected aerosol sample in a controlled manner while it minimized sample losses due to thermophoresis and diffusion. In designing an aerosol heater, the behavior of a monodisperse aerosol was modeled in a heated flow tube with a temperature-controlled wall under laminar flow conditions. This allowed for initial estimations of aerosol heating rates, heater dimensions, and aerosol deposition losses within the flow tube. The evaporation rate of sulfuric acid particles was also predicted and used to determine the minimum length of the aerosol heater needed to completely evaporate a sulfuric acid aerosol. Finally, the VTDMA was calibrated and tested for its ability to detect a sulfuric acid mass fraction in a monodisperse aerosol.