Name of research institute or organization:

Project description: C2-C5 alkanes, alkenes and alkynes are useful tracers of natural and anthropogenic emissions. With diverse emission sources and moderately short atmospheric lifetimes, non-methane hydrocarbons (NMHCs) exhibit significant latitudinal, seasonal and vertical gradients [1]. They primarily react with the hydroxyl (OH) radical in the atmosphere, although also with ozone, nitrate, chlorine and bromine. Unsaturated NMHCs (alkenes) react faster with OH compared to the saturated alkanes, and therefore, in remote atmospheres (e.g. marine boundary layer, or free troposphere), long-lived alkanes such as ethane and propane are generally the most abundant [1]. Observing the changing ratios in abundance particular hydrocarbons, e.g. branched to straight chain alkanes, alkanes to acetylene etc – can give an indirect measurement of the integrated radical concentration, and this property has been used to probe not only OH [2] but also NO3 [3], Cl and Br [4] in the atmosphere. These unique reaction rates provide information on transport and dilution of air-masses, but are needed also to understand the photochemical processes occurring in situ, as NMHCs, along with NOx, are the key chemical precursors of O3 [5]. In the free troposphere where O3 has an enhanced photochemical lifetime and a proportionally greater influence on climate [6], light hydrocarbon measurements are needed to calculate free tropospheric photochemical O3 production, and in determining their potential to act as sinks for OH.