Aircraft based four-channel thermal dissociation laser induced fluorescence instrument for simultaneous measurements of NO2, total peroxy nitrate, total alkyl nitrate, and HNO3

摘要

A four-channel thermal dissociation laser induced fluorescence (TD-LIF)instrument has been developed for simultaneous measurements of nitrogendioxide (NO), total peroxy nitrate (∑PNs), total alkyl nitrate(∑ANs) and nitric acid (HNO). NO is measured directly byLIF at 532 nm, whereas organic nitrates and nitric acid are thermallydissociated at distinct temperatures in the inlet to form NO, which isthen measured by LIF. The concentrations of each dissociated species arederived by the differences in measured NO relative to the referencecolder inlet channel. The TD-LIF was adapted to fly on board the UK Facilityfor Airborne Atmospheric Measurements (FAAM) BAe 146-301 atmosphericresearch aircraft in summer 2010, and to date has successfully flown in fivefield campaigns. This paper reports novel improvements in the TD-LIFinstrumentations, including (1) the use of a single wavelength laser, whichmakes the system compact and relatively cheap; (2) the use of a single beamlaser that allows easy alignment and optical stability against thevibrational aircraft environment; and (3) the optical assembly of fourdetection cells that allow simultaneous and fast (time resolution up to 0.1 s)measurements of NO, ∑PNs, ∑ANs and HNO.Laboratory-generated mixtures of PNs, ANs and HNO in zero air areconverted into NO and used to fix the dissociation temperatures ofeach heated inlet to test the selectivity of the instrument and potentialinterferences due to recombination reactions of the dissociated products.The effectiveness of the TD-LIF was demonstrated during the RONOCO aircraftcampaign (summer 2010). A chemiluminescence system that was measuringNO and a broadband cavity enhanced absorption spectrometer (BBCEAS)that was measuring one of the PNs (NO) were installed on thesame aircraft during the campaign. The in-flight intercomparison of the newTD-LIF with the chemiluminescence system for NO measurements and theintercomparison between ∑PNs measured by the TD-LIF and NOby the BBCEAS are used to assess the performance of the TD-LIF.