HYDROCARBON MEASUREMENTS AND THEIR USE AS ATMOSPHERIC TRACERS

Non-methane hydrocarbons (NMHCs) have been measured in the boundary layer and free troposphere to investigate their behaviour under different atmospheric chemical regimes. Ambient air samples were collected using the Whole Air Sampling (WAS) system aboard the UK atmospheric research aircraft - FAAM BAe 146 - and analysed using a dual-channel gas chromatograph coupled with the flame ionization detectors (FID). Hydrocarbon ratios were used to determine the presence of nitrate radicals in the atmosphere during summer, winter and autumn phases of the ROle of Nightime chemistry in controlling the Oxidizing Capacity of the AtmOsphere (RONOCO) campaign. The extensive data set showed that the pentane n – iso isomer pair were particularly useful when diagnosing the presence of different oxidants during day, night, dusk and dawn. A hydrocarbon variability versus lifetime approach applied to the entire winter and summer datasets proved useful in determining the presence or absence of the nitrate radical. Free tropospheric NMHC measurements were made over the period January 2009 - January 2011 above the UK. These data provided a rare description of the seasonal variations in this region of the atmosphere. A comparison of this work with earlier UK free troposphere studies made twenty years ago, revealed a decline in the amplitude of the seasonal cycle by a factor of approximately two for acetylene, benzene and toluene. Airborne measurements of NMHCs have also been made in boreal forest fire plumes over Canada between 12th July 2010 and 2nd August 2010 as a part of the research project - Quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites (BORTAS). The fire emission ratios for 29 different organic species relative to emission of CO have been derived. The comparison between observationally derived emission ratios and the GEOS-Chem Chemical Transport Model highlighted the influence of biomass burning as a large contributor to benzene, toluene, ethene and propene levels in many global locations.