Synonyms: 
Bromine oxide
Bromine monoxide

Multiple Axis Resonance Fluorescence Chemical Conversion Detector for ClO and BrO

Vacuum ultraviolet radiation produced in a low pressure plasma discharge lamp is used to induce resonance scattering in Cl and Br atoms within a flowing sample. ClO and BrO are converted to Cl and Br by the addition of NO such that the rapid bimolecular reaction ClO + NO → Cl + NO2 (BrO + NO → Br + NO2) yields one halogen atom for each halogen oxide radical present in the flowing sample. Three detection axes are used to diagnose the spatial (and thus temporal) dependence of the ClO (BrO) to Cl (Br) conversion and to detect any removal of Cl (Br) following its formation. A double duct system is used both to maintain laminar flow through the detection region and to step the flow velocity in the detection region down from free stream (200 m/sec) to 20 m/sec in order to optimize the kinetic diagnosis.

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Harvard Halogen Instrument

Many changes from the original Chlorine Nitrate instrument. NO2 instrument removed. New inlet with orifice for one halogen duct, addition of vacuum scroll pump, new RF oscillators and amplifiers, new RF frequency, new lamp housings and cooling for lamp modules. Flew in MACPEX without dissociation heaters, i.e., focus on BrO and ClO measurements and not measure ClONO2 or ClOOCl.

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mini-DOAS

mini-DOAS uses the Differential Optical Absorption Spectroscopy (DOAS) technique to identify and quantify trace gases using their narrow band absorptions.

This instrument studies:

1) the transport of short-lived halogenated species and their decay products to the stratosphere and the subsequent influence to the photochemistry and budget of Bromine (BrO) in the TTL.
2) the potential impact of halogen oxides to directly destroy UT/LS ozone.

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Chemical Ionization Mass Spectrometer

The CIMS instrument consists of a low pressure ion molecule reactor (IMR) coupled to a quadrupole mass filter by an actively pumped collisional dissociation chamber (CDC) and an octopole ion guide. The vacuum system is a 100 mm outer diameter stainless steel chamber evacuated with two small turbo pumps (70 l s-1). The mass filter is a set of 9.5 mm diameter quadrupole rods housed in the main vacuum chamber. The CDC is a short 80 mm diameter chamber that houses an octopole ion guide and is evacuated with a hybrid molecular drag pump. The IMR is evacuated with a scroll pump (300 l min-1) that also serves as the backing pump for the mass spectrometer.

Click here for the Collaborative Ground and Airborne Observations description page.

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DC-8 - AFRC, NSF G-V
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Chlorine Nitrate Instrument

The NO2-ClO-ClONO2-BrO instrument is composed of two separate instruments: A laser-induced fluorescence instrument for the detection of NO2 and a thermal dissociation/resonance fluorescence instrument for the detection of ClO, ClONO2 and BrO.

The NO2 detection system uses laser-induced resonance fluorescence (LIF) for the direct detection of NO2. Ambient air passes through a detection axis where the output of a narrow bandwidth (0.06 cm-1), tunable dye laser operating near 585 nm is used to excite a rovibronic transition in NO2. The excited NO2 molecules are either quenched by collision with air or fluorescence. The NO2 fluorescence is strongly red-shifted, with emission occurring over a broad range of wavelengths from 585 nm to the mid-infrared. The specificity of the technique is accomplished by tuning the laser frequency on and off resonance with a narrow spectral feature (0.04 cm-1) in the NO2 absorption spectrum. The difference between the fluorescence signal on and off resonance is related to the mixing ratio of NO2 through laboratory and in-flight calibrations. The observations are determined with an accuracy (1 sigma) of ±10% ±50 pptv, precision (1 sigma) of ±40 pptv, and a reporting interval of 10 seconds. Higher resolution (0.25 sec) data available on request.

The halogen detection system uses gas-phase thermal dissociation of ambient ClONO2 to produce ClO and NO2 radicals. The pyrolysis is accomplished by passing the air sampled in a 5-cm-square duct through a grid of resistively heated silicon strips at 10 to 20 m/sec, rapidly heating the air to 520 K. The ClO fragment from ClONO2 is converted to Cl atoms by reaction with added NO, and Cl atoms are detected using ultra-violet resonance fluorescence at 118.9 nm. A similar detection axis upstream of the heater provides simultaneous detection of ambient ClO. An identical twin sampling duct provides the capability for diagnostic checks. The flight instrument is calibrated in a laboratory setting with known addition of ClONO2 as a function of pressure, heater temperature and flow velocity. The concentration of ClONO2 is measured with an accuracy and detection limit of ±20% and 10 pptv, respectively, in 35 seconds (all error estimates are 1 sigma). The concentration of ClO is measured with an accuracy and detection limit of ±17% and 3 pptv, respectively, in 35 seconds.

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