AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Chemical Characterization of Ice-Nucleating Bacteria by Aerosol Mass Spectrometry
ROBERT WOLF, Jay Slowik, Johannes Schneider, Caroline Oehm, Ottmar Möhler, Andre Prévôt, Urs Baltensperger, Paul Scherrer Institute
Abstract Number: 399 Working Group: Source Apportionment
Abstract Bacteria are omnipresent in the atmosphere. They have an impact on climate as efficient heterogeneous ice nuclei and they can pose a risk to human health. However, their contribution to ambient aerosol is still uncertain since quantitative online measurement techniques for the detection of airborne microorganisms are lacking. A better knowledge of the chemical composition of pure bacteria is necessary before they can be distinguished from other sources that contribute to total aerosol in ambient air. We present results of the analysis of selected ice-nucleation active bacteria by means of aerosol mass spectrometry. Different Pseudomonas species sampled from cloud and glacier-melt water were introduced into the AIDA chamber facility in Karlsruhe, Germany. An Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) equipped with a PM2.5 aerodynamic lens was used to determine the size and the chemical composition of the bacteria. The heater of the AMS was operated at 600°C and 730°C to investigate the influence of a delayed vaporization at the heater surface. At increased heater temperature the resulting size distributions show a bimodal structure in which the larger mode can be attributed to bacterial cells. The smaller mode at about 200-400 nm vacuum aerodynamic diameter can be assigned to both residual particles from the Agar nutrition medium and bacteria fragments. We demonstrate that the mass spectral signatures of the bacteria can be separated from those of the residual particles by principal component analysis. High-resolution mass spectra of the different Pseudomonas species and some nitrogen-containing marker peaks which could be used in the future to estimate the contribution of these bacteria to ambient aerosol will be presented.