A study of the diurnal variation of biogenic volatile halocarbons

The diurnal variation of a number of naturally produced volatile halogenated organic compounds (VHOC) in a pool at Gran Canaria, Spain, is shown. The diurnal cycle was studied both in water and air samples. The highest production rates of VHOC were observed at mid-day, when the photosynthesis of the algae was assumed to be maximal. A second production period was observed after sunset, probably caused by algal respiration. The production rates were found to be equal during light and dark conditions. The measured rates correspond well to our earlier laboratory experiments. A rapid decrease in the concentration of VHOC in the water was observed, and the magnitude of the decrease is compared with the calculated emission of VHOC to the atmosphere. The diurnal cycle of chlorinated and brominated compounds, as well as for 1-iodobuthane, differed from those of iodomethane and 2-iodopropane, probably due to different formation pathways.