Technical Note: Use of a beam width probe in an Aerosol Mass Spectrometer to monitor particle collection efficiency in the field D. Salcedo1,2, T. B. Onasch3, M. R. Canagaratna3, K. Dzepina2,4, J. A. Huffman2,4, J. T. Jayne3, D. R. Worsnop3, C. E. Kolb3, S. Weimer5,*, F. Drewnick6, J. D. Allan7, A. E. Delia8, and J. L. Jimenez2,4 1Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Cuernavaca, Morelos, México 2Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado at Boulder, CO, USA 3Center for Aerosol and Cloud Chemistry, Aerodyne Research Inc., Billerica, MA, USA 4Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, CO, USA 5Atmospheric Sciences Research Center, University at Albany, Albany, NY, USA 6Particle Chemistry Department, Max Planck Institute for Chemistry, Mainz, Germany 7Department of Physics, University of Manchester Institute of Science and Technology, Manchester, UK 8Program in Atmospheric and Oceanic Sciences, University of Colorado at Boulder, Boulder, CO, USA *now at: EMPA, Duebendorf, Switzerland and Paul Scherrer Institute, Villigen, Switzerland
Abstract. Two Aerodyne Aerosol Mass Spectrometers (Q-AMS) were deployed in Mexico
City, during the Mexico City Metropolitan Area field study (MCMA-2003) from
29 March–4 May 2003 to investigate particle concentrations, sources, and
processes. We report the use of a particle beam width probe (BWP) in the
field to quantify potential losses of particles due to beam broadening
inside the AMS caused by particle shape (nonsphericity) and particle size.
Data from this probe show that no significant mass of particles was lost due
to excessive beam broadening; i.e. the shape- and size-related collection
efficiency (Es) of the AMS during this campaign was approximately one.
Comparison of the BWP data from MCMA-2003 with other campaigns shows that
the same conclusion holds for several other urban, rural and remotes sites.
This means that the aerodynamic lens in the AMS is capable of efficiently
focusing ambient particles into a well defined beam and onto the AMS
vaporizer for particles sampled in a wide variety of environments. All the
species measured by the AMS during MCMA-2003 have similar attenuation
profiles which suggests that the particles that dominate the mass
concentration were internally mixed most of the time. Only for the smaller
particles (especially below 300 nm), organic and inorganic species show
different attenuation versus particle size which is likely due to partial
external mixing of these components. Changes observed in the focusing of the
particle beam in time can be attributed, in part, to changes in particle
shape (i.e. due to relative humidity) and size of the particles sampled.
However, the relationships between composition, atmospheric conditions, and
particle shape and size appear to be very complex and are not yet completely
Citation: Salcedo, D., Onasch, T. B., Canagaratna, M. R., Dzepina, K., Huffman, J. A., Jayne, J. T., Worsnop, D. R., Kolb, C. E., Weimer, S., Drewnick, F., Allan, J. D., Delia, A. E., and Jimenez, J. L.: Technical Note: Use of a beam width probe in an Aerosol Mass Spectrometer to monitor particle collection efficiency in the field, Atmos. Chem. Phys., 7, 549-556, doi:10.5194/acp-7-549-2007, 2007.