Ibrahim O

Publications (3)0 Total impact

• Article: Auto MAX-DOAS measurements around entire cities: quantification of NO_x emissions from the cities of Mannheim and Ludwigshafen (Germany)

  Ibrahim O, Shaiganfar R, Sinreich R, Stein T, Platt U, Wagner T
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  ABSTRACT: We present Auto Multi-Axis (MAX-) DOAS observations of tropospheric NO₂ carried out on circles around the cities of Mannheim and Ludwigshafen (Germany) on 24 August 2006. Together with information on wind speed and direction, the total emissions of the encircled source(s) can be quantified from these measurements. In contrast to recent similar studies based on of zenith scattered sun light (elevation angle of 90°), we use a MAX-DOAS instrument mounted on a car, which observes scattered sun light under different elevation angles (here 45°, and 90°). Compared to simple zenith sky observations, MAX-DOAS observations have higher sensitivity and avoid systematic offsets in the determination of the vertically integrated trace gas concentration. Auto MAX-DOAS observations are especially well suited for the determination of the total emission of extended emission sources (e.g. whole cities), for which typically no sharply defined plumes are formed. In such cases, the trace gas concentrations can be rather small and thus even small systematic offsets in the observed integrated tropospheric trace gas concentration can have a large effect on the determined total emissions. However, such measurements are still affected by several uncertainties which need to be further investigated and minimised. The largest error source is probably the variability and imperfect knowledge of the wind field. In addition – depending on the trace species observed – also chemical transformations between the emission sources and the measurement location have to be considered. In this study we use local observations within the encircled area to quantify and correct these errors. From our observations we derive a total NO_x emission from the Mannheim/Ludwigshafen area of (7.2±1.7)×10²⁴ molecules/s (or 17350±4100 t, calculated with the mass of NO₂), which is in surprisingly good agreement with existing emission estimates.
  Atmospheric Measurement Techniques Discussions. 01/2010;
• Source

  Available from: R. Shaiganfar

  Article: Mobile MAX-DOAS observations of tropospheric trace gases

  Wagner T, Ibrahim O, Shaiganfar R, Platt U
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  ABSTRACT: From Multi-Axis- (MAX-) DOAS observations information on tropospheric trace gases close to the surface and up to the free troposphere can be obtained. Usually MAX-DOAS observations are performed at fixed locations, which allows to retrieve the diurnal variation of tropospheric species at that location. Alternatively, MAX-DOAS observations can also be made on mobile platforms like cars, ships or aircrafts. Then, in addition to the vertical (and temporal) distribution, also the horizontal variation of tropospheric trace gases can be measured. Such information is important for the quantitative comparison with model simulations, study of transport processes, and for the validation of tropospheric trace gas products from satellite observations. However, for MAX-DOAS observations from mobile platforms, the standard analysis techniques for MAX-DOAS observations can usually not be applied, because the probed airmasses can change rapidly between successive measurements. In this study we introduce a new technique which overcomes these problems and allows the exploitation of the full information content of mobile MAX-DOAS observations. Our method can also be applied to MAX-DOAS observations made at fixed locations in order to improve the accuracy especially in cases of strong winds. We apply the new technique to MAX-DOAS observations made during an automobile trip from Brussels to Heidelberg.
  Atmospheric Measurement Techniques Discussions. 01/2009;
• Source

  Available from: archives-ouvertes.fr

  Article: Enhanced tropospheric BrO over Antarctic sea ice in mid winter observed by MAX-DOAS on board the research vessel Polarstern

  Wagner T, Ibrahim O, Sinreich R, Frieß U, R. von Glasow, Platt U
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  ABSTRACT: We present Multi AXis-Differential Optical Absorption Spectroscopy (MAX-DOAS) observations of tropospheric BrO carried out on board the German research vessel Polarstern during the Antarctic winter 2006. Polarstern entered the area of first year sea ice around Antarctica on 24 June 2006 and stayed within this area until 15 August 2006. For the period when the ship cruised inside the first year sea ice belt, enhanced BrO concentrations were almost continuously observed. Outside the first year sea ice belt, typically low BrO concentrations were found. Based on back trajectory calculations we find a positive correlation between the observed BrO differential slant column densities (ΔSCDs) and the duration for which the air masses had been in contact with the sea ice surface prior to the measurement. While we can not completely rule out that in several cases the highest BrO concentrations might be located close to the ground, our observations indicate that the maximum BrO concentrations might typically exist in a (possibly extended) layer around the upper edge of the boundary layer. Besides the effect of a decreasing pH of sea salt aerosol with altitude and therefore an increase of BrO with height, this finding might be also related to vertical mixing of air from the free troposphere with the boundary layer, probably caused by convection over the warm ocean surface at polynyas and cracks in the ice. Strong vertical gradients of BrO and O3 could also explain why we found enhanced BrO levels almost continuously for the observations within the sea ice. Based on our estimated BrO profiles we derive BrO mixing ratios of several ten ppt, which is slightly higher than many existing observations. Our observations indicate that enhanced BrO concentrations around Antarctica exist about one month earlier than observed by satellite instruments. From detailed radiative transfer simulations we find that MAX-DOAS observations are up to about one order of magnitude more sensitive to near-surface BrO than satellite observations. In contrast to satellite observations the MAX-DOAS sensitivity hardly decreases for large solar zenith angles and is almost independent from the ground albedo. Thus this technique is very well suited for observations in polar regions close to the solar terminator. For large periods of our measurements the solar elevation was very low or even below the horizon. For such conditions, most reactive Br-compounds might exist as Br2 molecules and ozone destruction and the removal of reactive bromine compounds might be substantially reduced.
  Atmospheric Chemistry and Physics. 01/2007;