AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Development of a Novel Particle Mass Spectrometer for Online Measurements of Refractory Sulfate Aerosols
YUYA KOBAYASHI, Yu Ide, Nobuyuki Takegawa, Tokyo Metropolitan University
Abstract Number: 858 Working Group: Instrumentation and Methods
Abstract Sulfate aerosols are ubiquitous in the atmosphere. Ammonium sulfate (AS) is generally the dominant form of sulfate aerosols in urban air, whereas sodium sulfate (SS) and potassium sulfate (PS) may have large contributions in remote areas. Currently available methods for online measurements of sulfate aerosols, which are based on ion chromatography (IC) or thermal desorption aerosol mass spectrometry, cannot separately quantify nonrefractory and refractory sulfate compounds. We have developed a new particle mass spectrometer to measure nonrefractory and refractory sulfate compounds. Aerosol particles are introduced into a vacuum chamber via an aerodynamic lens unit and are collected on a thin graphite plate. To reduce loss of particles due to bounce on the plate, aerosol particles are coated by condensation of oleic acid vapor prior to the sample inlet. A focused CO2 laser coupled with the graphite plate enables high desorption temperature (black-body equivalent temperature of ~1000 K) for detecting AS, SS, and PS aerosols. The gas molecules evolved from these compounds are detected using a quadrupole mass spectrometer. The key parameters of the condensation growth tube for oleic acid coating (e.g., temperature, tube length) were optimized in the laboratory. The response of the instrument to monodisperse AS, SS, and PS particles was also tested in the laboratory. While a good linearity was found for these compounds, the sensitivity for PS exhibited smaller values compared to the other compounds. Possible thermal decomposition processes of AS, SS, and PS are discussed based on the fragment ratios of these compounds. We propose a method to separately quantify AS, SS, and PS mass concentrations from mixed particles containing these compounds.