title: Development of a low-cost system for measuring conditional time-averaged gradients of SO2 and NH3.
abstract: A conditional time-averaged gradient (COTAG) system has been developed to provide direct long-term (weekly to monthly) average flux gradient measurements for a range of trace gases, between land and atmosphere. Over daily periods, atmospheric conditions can range from high stability, where the vertical gradients of ambient concentration are enhanced due to very small diffusivity, to highly unstable conditions, in which concentration gradients are small due to the intense turbulent activity of the surface layer. The large vertical gradients generated by high stability would bias the estimate of the actual flux: to avoid this, the COTAG system samples conditionally, within a carefully refined range of stability. A comparison with a continuous flux gradient system suggested that the removal of stable conditions from the sampling period does not substantially modify the evaluation of the long-term fluxes.
authors.affiliation: Centre for Ecology and Hydrology-Edinburgh, Bush Estate, Penicuik, EH26 0QB, Scotland, UK. danf@ceh.ac.uk
authors.forename: D
authors.initials: D
authors.lastname: Famulari
authors.forename: D
authors.initials: D
authors.lastname: Fowler
authors.forename: E
authors.initials: E
authors.lastname: Nemitz
authors.forename: K J
authors.initials: KJ
authors.lastname: Hargreaves
authors.forename: R L
authors.initials: RL
authors.lastname: Storeton-West
authors.forename: G
authors.initials: G
authors.lastname: Rutherford
authors.forename: Y S
authors.initials: YS
authors.lastname: Tang
authors.forename: M A
authors.initials: MA
authors.lastname: Sutton
authors.forename: K J
authors.initials: KJ
authors.lastname: Weston
mesh_terms: D004784:Environmental Monitoring / Q000191:economics* / Q000379:methods*; D008962:Models, Theoretical; D000644:Quaternary Ammonium Compounds / Q000032:analysis*; D013458:Sulfur Dioxide / Q000032:analysis*
chemical_list: D000644:Quaternary Ammonium Compounds; D013458:Sulfur Dioxide