Measurement of Formaldehyde by Laser Induced Fluorescence Spectroscopy

Tuesday, 16 December 2014
Danny R Cryer1, Trevor Ingham1,2, Lisa K Whalley2,3 and Dwayne E Heard1,4, (1)University of Leeds, School of Chemistry, Leeds, United Kingdom, (2)National Centre for Atmospheric Science, Leeds, United Kingdom, (3)University of Leeds, School of Chemistry, Leeds, LS2, United Kingdom, (4)National Centre for Atmospheric Science, University of Leeds, Leeds, United Kingdom
Gas phase formaldehyde (HCHO) is a key species in the troposphere. It is formed as an intermediate product during the removal of almost all volatile organic compounds (VOCs) by the hydroxyl radical (OH) and is a tracer of overall oxidising capacity. A new instrument has been developed for the measurement of [HCHO] by laser induced fluorescence (LIF) spectroscopy and deployed in the field. Ultra-violet (UV) radiation from a tuneable fibre laser was used to excite HCHO in a low pressure cell (~130 Torr) at ca. 353 nm with fluorescence collected between 390 – 550 nm. The resulting fluorescence was detected by a photomultiplier tube (PMT) and processed by photon counting techniques. The instrument performance will be described in detail in addition to a novel calibration method where a known quantity of HCHO was produced through photolysis of methanol (CH3OH) vapour in the presence of oxygen. The instrument was first deployed in June 2014 at a suburban site in York (UK). Data from this campaign and interpretation will be presented in addition to observations from more recent field measurements.