Investigation of reactive halogen species in a smog chamber and in the field

• Applicant: Professor Dr. Ulrich Platt
• Subject Area: Atmospheric Science ; Mineralogy, Petrology and Geochemistry
• Term: from 2008 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 24881704

• Final Report Year: 2016

Final Report Abstract

Besides the new developments in DOAS instruments described above, the newly gained knowledge by sub project Platt within the DFG project Haloproc 2 is listed in the following: The impact of NOx and VOCs on the chemistry of reactive halogen compounds. Measurements of NO2, BrO and IO at the Dead Sea showed a strong anti‐correlation between NO2 and reactive halogen species. Thus, the formation of halogenated nitrate compounds (HNCs) like BrONO2 and IONO2 are assumed to play an important role and act as a strong sink and reservoir gas for reactive bromine and iodine. An important conclusion is that the total amount of reactive halogen species (RHS) cannot solely be determined by the abundance of the species BrO and IO. Further, HNCs are likely to undergo heterogeneous reactions on sea salt aerosols. These heterogeneous reactions can lead to an exponential release of reactive halogen species from the aerosol surface. Elevated layers of reactive bromine as observed during the field measurements at the Dead Sea can be explained by the vertical transportation of RHS reservoir gases and heterogeneous release processes several hundred meters above the water surface. Importance of the formation of higher halogen oxides (OIO, OBrO) for tropospheric chemistry in the vicinity of salt lakes. During the measurement campaign at the Dead Sea no significant amounts of OBrO and OIO were detected while mixing ratios of BrO and IO clearly above the detection limit. Therefore it can be assumed that OBrO and OIO play a minor role in the halogen chemistry of the Earth’s atmosphere. The role of chlorine in atmospheric chemistry above salt lakes. By the direct observation of OClO during the field campaign at the Dead Sea, first evidence of reactive chlorine chemistry above salt lakes was found. Since OClO is most likely formed by the reaction of BrO and ClO, significant amounts of ClO are expected at the Dead Sea. However, due to instrumental limitations, ClO could not yet be observed directly. Hot spots of halogen compounds at ground level? (strong evidence from provided smog chamber experiments). From our data there is evidence for elevated formation of reactive halogen species at ground level (above the water surface). Further evidence for an inorganic release of reactive halogen compounds from salt surfaces. The combination of MAX‐DOAS and LP‐DOAS at the Dead Sea revealed a strong vertical gradient of IO near the water surface. Further, the marked correlation of wind speed, water surface roughness and IO abundance strongly indicates an inorganic release of iodine from the water surface of the Dead Sea. What is the vertical distribution and what is the impact of transport processes on the local tropospheric chemistry and ozone budget? Strong vertical gradient of IO were found near the water surface. The measurements of vertical profiles of reactive halogen species showed that confined, elevated layers of BrO can be formed which implicates a vertical transport of reservoir gases or precursors. However, a strong impact of meteorology was observed. Further, it is assumed that the unique topography of the Dead Sea Valley supports the formation of elevated layers of BrO. Thus the observations at the Dead Sea may not be transferred to a global scale.

Publications

• Broadband Cavity Enhanced Differential Optical Absorption Spectroscopy (CE‐DOAS) ‐ Applicability and Corrections. Atmos.Measur.Tech. 2 (2009) 713–723
  Platt, U., J. Meinen, D. Pöhler and T. Leisner
  
• (2012), ’Bromine and Chlorine Explosion’ in a Simulated Atmosphere, Doctoral Thesis University of Heidelberg
  Buxmann, Joelle
  
• Halogenation processes of secondary organic aerosol and implications on halogen release mechanisms. Atmos.Chem.Phys. 12 (2012) 5787‐5806
  Ofner, J., N. Balzer, J. Buxmann, H. Grothe, P. Schmitt‐Kopplin, U. Platt and C. Zetzsch
  
• Observations of bromine explosions in smog chamber experiments above a model salt pan. Int.J.Chem.Kinetics 44 (2012) 312–326
  Buxmann, J., N. Balzer, S. Bleicher, U. Platt and C. Zetzsch
  
• An instrument for measurements of BrO with LED‐based Cavity‐Enhanced Differential Optical Absorption Spectroscopy, Atmos. Meas. Tech., 7, 199‐214
  Hoch, D. J., Buxmann, J., Sihler, H., Pöhler, D., Zetzsch, C., and Platt, U.
  
• Consumption of reactive halogen species from sea‐salt aerosol by secondary organic aerosol: slowing down the bromine explosion. Environ.Chem. 12 (2015) 476‐488
  Buxmann, J., S. Bleicher, U. Platt, R. von Glasow, R. Sommariva, A. Held, C. Zetzsch and J. Ofner
  
• Vertical distribution of BrO in the boundary layer at the Dead Sea. Environ.Chem. 12 (2015) 451‐460
  Holla, R., S. Schmitt, U. Friess, D. Pöhler, J. Zingler, U. Corsmeier and U. Platt
  
• (2016), The dynamics of reactive halogen species at the Dead Sea Valley. Doctoral Thesis University of Heidelberg
  Schmitt Stefan