Application of laser flash photolysis combined with time-resolved broadband UV absorption spectroscopy to measure the total OH radical reactivity Midhun George, Dr Lisa K. Whalley, Prof Dwayne E. Heard, Dr Mark A. Blitz, Dr Daniel Stone School of Chemistry, University of Leeds, UK The composition of the atmosphere is controlled by the emission rates and chemistry of trace species emitted into the atmosphere from a wide range of sources including industry, vehicle exhausts and plants. Emissions of nitrogen oxides and volatile organic compounds (VOCs) into the atmosphere lead to complex cascades of chemical reactions which are predominantly initiated by naturally occurring OH radicals. This chemistry results in the generation of secondary pollutants such as ozone (O 3 ) and secondary organic aerosol (SOA), which impact the climate and are harmful to human health. However, it is only possible to identify and measure the concentrations of a small fraction of the vast array of over 10,000 different atmospheric VOCs, which limits our ability to provide accurate assessments and predictions of air quality. Despite such challenges, it is possible to quantify the presence and impacts of unmeasured species in the atmosphere. Since most species emitted into the atmosphere react with OH radicals, measurements of the total loss rate of OH radicals in ambient air provides a means to quantify the presence of unmeasured species, and the extent to which they contribute to the production of O 3 and SOA. Such measurements of the total OH loss rate are used to define the OH reactivity (k OH ), which can be considered to represent the total loading of reactive pollutants in an air mass that oxidise to secondary pollutants. However, routine and long-term measurements of OH reactivity are hindered by a lack of suitable techniques. In this work, a novel field instrument based on laser flash photolysis coupled with time-resolved broadband UV absorption spectroscopy has been developed and characterised for long-term measurements of k OH . The poster will present the main results from the model and experimental studies conducted during the development and characterisation of the instrument. Preliminary results from field measurements will also be presented.
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