A study of the diurnal variation of biogenic volatile halocarbons

The diurnal variation of a number of naturally produced volatile halogenate d 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 produc tion 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 a fter sunset, probably caused by algal respiration. The production rates wer e found to be equal during light and dark conditions. The measured rates co rrespond well to our earlier laboratory experiments. A rapid decrease in th e concentration of VHOC in the water was observed, and the magnitude of the decrease is compared with the calculated emission of VHOC to the atmospher e. The diurnal cycle of chlorinated and brominated compounds, as well as fo r 1-iodobuthane, differed from those of iodomethane and 2-iodopropane, prob ably due to different formation pathways. (C) 1998 Elsevier Science B.V. Al l rights reserved.