Trace Gases and Radicals

Techniques for radical concentration measurements

The institute ICE-3 has many years of experience in the development and operation of highly sensitive instruments for measurements of trace gases in the ppb and pptv range. For OH radicals, atmospheric measurements have been achied as low as 0.01 pptv. The physical techniques that are being used are:

• Laser induce fluorescence (LIF)
  This method allows the direct laser detection of OH radicals. HO₂ and RO₂ radicals can be detected after chemical conversion to OH.

• Optical absorption spectroscopy

  • Differential Optical Absorption Spectroscopy (DOAS)
    for OH, SO₂, HCHO etc.
  • Cavity-Ringdown Spectroscopy (CRDS)
    for NO, NO₂, NO₃, N₂O₅, O₃, CO, CO₂, CH₄, H₂O
  • Cavity-Enhanced Absorption Spectroscopy (CEAS)
    for HONO and Glyoxal (under development)
  • Long-Path Absorption Photometry (LOPAP)
    for HONO
• Laser flash photolysis + LIF
  Measurement of atmospheric OH lifetimes, which depend on the concentrations of atmospheric OH reactants and their OH reaction rate coefficients.
• Chemiluminescence detection (CLD)
  for NO and NO₂
• Gas Chromatography
  for VOCs, CO, Peroxyacetylnitrate (PAN)
• Chemical-Ionisation Mass Spectrometry (CIMS)
  This technique can be applied for a variety of trace gases (e.g. VOCs and oxygenated VOCs), which can be ionised, for example, by H3O+, Br-, NO₃- ions. The measurement of HO₂ radicals by CIMS is under development. VOCs and oxygenated VOCs can be be measured by PTRMS or CIMS.

ICE-3 is also operating facilities that support calibrations and data assurance in international projects and measurement networks (e.g., ACTRIS, GAW).

• The atmosphere simulation chamber SAPHIR and the project EUROCHAMP allow instrumental tests and measurement comparisons under realistic tropospheric conditions.

• Within Global Atmospheric Watch (GAW), ICE-3 takes the role of a World Calibration Center for

  • airborne ozone sondes and humidity sensors
    (WCCOS und ESF)
  • measurements of NOx (WCC-NOx).