Feasibility of the detection of trace elements in particulate matter using online high-resolution aerosol mass spectrometry

Abstract

The feasibility of using an online thermal-desorption electron-ionization high-resolution aerosol mass spectrometer (HR-AMS) for the detection of particulate trace elements was investigated by analyzing data from Mexico City obtained during the MILAGRO 2006 field campaign. This potential application is of interest due to the real-time data provided by the AMS, its high sensitivity and time resolution, and the widespread availability and use of this instrument. High-resolution mass spectral analysis, isotopic ratios, and ratios of different ions containing the same elements are used to constrain the chemical identity of the measured ions. The detection of Cu, Zn, As, Se, Sn, and Sb is reported. There was no convincing evidence for the detection of other trace elements commonly reported in ambient particulate matter (PM). The elements detected tend to be those with lower melting and boiling points, as expected given the use of a vaporizer at 600C in this instrument. The detection limit (DL) is estimated at approximately 0.3ng m 3 for 5min of data averaging. Concentration time series obtained from the AMS data were compared to concentration records determined from offline analysis of particle samples from the same times and locations by inductively coupled plasma based techniques (ICP; PM 2.5) and proton-induced X-ray emission (PIXE; PM 1.1 and PM 0.3). The degree of correlation and agreement between the three instruments (AMS, ICP, and PIXE) varied depending on the element. The AMS shows promise for real-time detection of some trace elements, although additional work including laboratory calibrations with different chemical forms of these elements is needed to further develop this technique and to understand the differences with the ambient data from the other techniques. The trace elements peaked in the morning as expected for primary sources, and the many detected plumes suggest the presence of multiple point sources, probably industrial, in Mexico City, which are variable in time and space, in agreement with previous studies. Copyright 2012 American Association for Aerosol Research © 2012 Taylor and Francis Group, LLC.