Methoden der Gruppe Crowley (nur Englisch)

Field 1. Cavity-Ring-Down Spectrometer (CRDS) for NO3 and N2O5

The CRDS is a field instrument which utilises the strong absorption feature of NO₃ at 662 nm to measure its optical extinction over a path length of more than 30 km, achieved by off-axis coupling of the light from a power modulated laser-diode into an optical cavity. N₂O₅ is measured indirectly following thermal dissociation to NO₃. The best detection limits (5 s averaging) achieved to date are ~ 1 ppt for NO₃ and ~ 3 pt for N₂O₅

Field 2. Chemical Ionisation Quadrupole Mass Spectrometer (CIMS-QMS)

The CIMS-QMS is a field instrument presently used for measurement of HNO₃ and SO₂ or PANS, depending on the primary chemi-ions used. Neutral trace-gases are sampled into a constant pressure ion-molecule reactor where secondary ions are generated prior to de-clustering (octopole) and mass selection (quadrupole). The CIMS-QMS is designed for operation both in aircraft and ground-based campaigns. Typical detection limits are 5-20 ppt (5 s) for e.g. PAN.

Field 3. Cavity-Ring-Down Spectrometer (CRDS) for NO2 , PANs and ANs

This CRDS measures the optical extinction of NO₂ at ~ 400 nm over a path length of more than 10 km. Two cavities are employed, one used for ambient NO₂, the second for measuring the NO₂ product of the thermal dissociation of PANs (at ~250 °C) or Alkyl Nitrates (ANs) at ~400 °C. The best detection limit so far is ~ 30 ppt for NO₂ (1 minute averaging).

Lab 1. Pulsed Photolysis 1 (PLP – LIF / RF)

Pulsed Laser Photolysis (PLP) radical generation is used to measure temperature and pressure dependent rate coefficients, product yields and photolysis quantum yields in the gas-phase. An exciplex laser is used to generate radicals (detected in real time using Laser Induced Fluorescence (LIF)) or atoms (detected using resonance fluorescence, RF). Reagent concentrations are monitored online by optical UV/Vis absorption spectroscopy.

Lab 2. Pulsed Photolysis 2 (PLP – LIF / TAS)

Chemistry is initiated by Pulsed Laser Photolysis (PLP) (Exciplex and Nd-YAG lasers) and followed in real time by monitoring reactants and products using Laser Induced Fluorescence (LIF) or Transient U/Vis Absorption Spectroscopy (TAS). Precursor concentrations are measured by FTIR and VUV absorption spectroscopy. Rate coefficients, quantum yields and reaction mechanisms can be obtained using this apparatus.

Lab 3. Quartz Reaction Chamber (QRC) with FTIR

The QRC is a cylindrical quartz reactor of volume 45 l equipped with internal multi-path optics to give an effective infra-red optical path–length of ~30 m. Photolysis is provided by appropriate lamps distributed around the cell. FTIR spectra (resolution of up to 0.02 cm^-1) are recording using a Bomem DA-008 spectrometer with MCT detector.

Lab 4. Aerosol Flow Tube (AFT)

The aerosol flow tube is an atmospheric pressure, laminar flow tube in which aerosol can interact with various trace gases at different relative humidities. Trace gases are monitored using Cavity-Ring-Down Spectroscopy or Chemical Ionisation Mass Spectrometry. Particles (size and number concentration) are measured using an aerodynamic particle sizer or electrostatic classifier with condensation particle counter. Variation of contact time and particle surface area allows us to derive kinetic data for heterogeneous reactions.

Lab 5. Ice Coated Flow Tube / Ice Reactor

An Ice Coated Flow Tube (ICFT) or a Ice Reactor (IR) is used to investigate the interactions of atmospheric trace gases with ice surfaces (~190-240 K) to derive physical constants such as adsorption isotherms or uptake coefficients or to investigate the efficiency of trapping during ice growth. The trace gases are detected using electron impact or chemical ionisation Mass Spectrometry

Lab 6. Wetted Wall Flow Tube / Knudsen Reactor

Either a Wetted Wall Flow Tube (WWFT) or an Ice Reactor (IR) are coupled to an electron impact Mass Spectrometer (MS) to investigate the interactions of atmospheric trace gases with various surfaces ranging from sea-salt solutions to mineral dust. Uptake and accommodation coefficients and products of gas-surface interactions are derived by analysis of trace gas concentrations.