Evaluation of the new capture vapourizer for aerosol mass spectrometers (AMS) through laboratory studies of inorganic species

• Main Authors: W. Hu, P. Campuzano-Jost, D. A. Day, P. Croteau, M. R. Canagaratna, J. T. Jayne, D. R. Worsnop, J. L. Jimenez
• Format: Article
• Language: English
• Published: Copernicus Publications 2017-08-01
• Series: Atmospheric Measurement Techniques
• Online Access: https://www.atmos-meas-tech.net/10/2897/2017/amt-10-2897-2017.pdf

Aerosol mass spectrometers (AMSs) and Aerosol Chemical Speciation Monitors (ACSMs) commercialized by Aerodyne are widely used to measure the non-refractory species in submicron particles. With the standard vapourizer (SV) that is installed in all commercial instruments to date, the quantification of ambient aerosol mass concentration requires the use of the collection efficiency (CE) to correct for the loss of particles due to bounce. A new capture vapourizer (CV) has been designed to reduce the need for a bounce-related CE correction. <br><br> Two high-resolution AMS instruments, one with a SV and one with a CV, were operated side by side in the laboratory. Four standard species, NH₄NO₃, NaNO₃, (NH₄)₂SO₄ and NH₄Cl, which typically constitute the majority of the mass of ambient submicron inorganic species, are studied. The effect of vapourizer temperature (<i>T</i>_v ∼ 200–800 °C) on the detected fragments, CE and size distributions are investigated. A <i>T</i>_v of 500–550 °C for the CV is recommended. In the CV, CE was identical (around unity) for more volatile species (e.g. NH₄NO₃) and comparable to or higher than the SV for less-volatile species (e.g. (NH₄)₂SO₄), demonstrating an improvement in CE for laboratory inorganic species in the CV. The detected relative intensities of fragments of NO₃ and SO₄ species observed with the CV are different from those observed with the SV, and are consistent with additional thermal decomposition arising from the increased residence time and multiple collisions. Increased residence times with the CV also lead to broader particle size distribution measurements than with the SV. A method for estimating whether pure species will be detected in AMS sizing mode is proposed. Production of CO₂(g) from sampled nitrate on the vapourizer surface, which has been reported for the SV, is negligible for the CV for NH₄NO₃ and comparable to the SV for NaNO_3.. We observe an extremely consistent fragmentation for ammonium compared to very large changes for the associated anions. Together with other evidence, this indicates that it is unlikely that a major fraction of inorganic species vapourizes as intact salts in the AMS.