Multi-angle Absorption Photometer

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Contents

Measurement principle

Multi-Angle Absorption Photometry The Multi-Angle Absorption Photometer (MAAP; type 5012, Thermo Scientific Inc.) measures the amount of light (wavelength 637 nm) that is transmitted through and scattered back from a particle laden glass fibre filter (Petzold and Schönlinner, 2004). With a twostream-approximation radiative transfer model the absorption coefficients of the deposited particles can be derived with high accuracy.

Alternatively, the MAAP yields a mass concentration of light absorbing carbon (LAC) which requires the knowledge of the absorption efficiency. During instrumental comparisons against a thermal reference method, the originators of the MAAP derived an absorption efficiency of 6.6 m2 g-1 for rural and urban aerosol, which is generally used for the conversion of the light absorption into a “soot” mass concentration. The wavelength of the MAAP (637 nm) corresponds to the region of the solar spectrum where black carbon (BC) is the prime absorber, thus minimizing interferences with “brown carbon” and mineral dust.

The MAAP has a high time resolution (ca. 1 min) which allows to characterize diurnal cycles, and fast changes in ambient concentrations, for example at near-traffic observation sites. A central comparison of the six MAAP instruments deployed within GUAN yielded a reproducibility of the measurement, with a maximum deviation between the readings of 7 %, and R2 of all cross correlations being > 0.99.

Raman analysis of MAAP filters in GUAN

During the GUAN project, tapes of GF10 filter (Whatman) were employed for particle collection, with all filter spots being stored on the tape for eventual Raman analysis (Nordmann et al., 2009). We programmed the progression of the filter tape so that it advances at least once every day (00:00). Additional filter advancements take place when a threshold transmission is underpassed, i.e. at high ambient particle concentrations.

Operating software

Unzip the file MAAP_Operating_Software in a folder of a PC/notebook, which is connceted with the MAAP. After that, unzip the file MAAP_configuration_file and put the folder MAAPCONFIG directy on your hard disk and not in a subfolder of C:\. Do not place the folder on your desktop. This will not work, due to the spaces in the pathname of the desktop. Open the file maap_RH.xml in the folder C:\MAAPCONFIG and change the serial port number if necessary, and modify the storage path of the *.MAAP files. If a RH sensor is placed between MAAP and aerosol inlet and the connecting cable is plugged with an external electronic unit, set the respective value to 1 (true), otherwise set the value to 0 (false). Close the xml-file and open the MAAP_RH_DAY.exe in the MAAP_Operating_Software folder. The record of data starts after a short lag of time (1 minute). A time series of the measured black carbon concentration is visualized in the program.

References

  • Nordmann, S., W. Birmili, K. Weinhold, K. Müller, G. Spindler, and A. Wiedensohler: Measurements of the mass absorption cross section of atmospheric soot particles using Raman spectroscopy. J. Geophys. Res. Atmos., 118, 12075–12085, doi:10.1002/2013JD020021, 2013.
  • Nordmann, S., W. Birmili, K. Weinhold, A. Wiedensohler, S. Mertes, K. Müller, T. Gnauk, H. Herrmann, M. Pitz, J. Cyrys, H. Flentje, L. Ries, K. Wirtz: Atmospheric aerosol measurements in the German Ultrafine Aerosol Network (GUAN) - Part 2: Comparison of measurements techniques for graphitic, light-absorbing, and elemental carbon, and the non-volatile particle volume under field conditions. Gefahrst. Reinh. Luft, 69(11/12): 469-474, 2009. Download PDF courtesy of SPRINGER-VDI-VERLAG
  • Müller, T., B. Henzing, G. de Leeuw, A. Wiedensohler, A. Alastuey, H. Angelov, M. Bizjak, M. Collaud Coen, J. E. Engström, C. Gruening, R. Hillamo, A. Hoffer, K. Imre, P. Ivanow, G. Jennings, J. Y. Sun, N. Kalivitis, H. Karlsson, M. Komppula, P. Laj, S.-M. Li, C. Lunder, A. Marinoni, S. Martins dos Santos, M. Moerman, A. Nowak, J. A. Ogren, A. Petzold, J. M. Pichon, S. Rodriquez, S. Sharma, P. J. Sheridan, K. Teinilä, T. M. Tuch, M. Viana, A. Virkkula, E. Weingartner, R. Wilhelm, Y. Q. Wang (2011). Characterization and Intercomparison of Aerosol Absorption Photometers: Result of two Intercomparison Workshops. Atmos. Meas. Tech., 4, 245–268. Download from AMT
  • Petzold, A. and M. Schönlinner, 2004: Multi-angle absorption photometry – a new method for the measurement of aerosol light absorption and atmospheric black carbon, J. Aerosol Sci., 35, 421-441.

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