A CONTINUOUS-FLOW INSTRUMENT WITH FLOW REGULATION AND AUTOMATIC SENSITIVITY RANGE ADAPTATION FOR THE DETERMINATION OF ATMOSPHERIC H2S

A set-up for continuous measurements of atmospheric H2S concentrations in the range between 0.138 mu g/m(3) and 17.5 mu g/m(3) is described. All flows are regulated by flow sensors which are connected to the re spective pump by a feed back circuit. The instrument is working in two sensitivity ranges. One is provided for low H2S concentrations (lower than 1.75 mu g/m(3)) and the other for higher levels (higher than 1.7 5 mu g/m(3)). During continuous measurements the set-up enables an aut omatic adaptation of one of the sensitivity ranges to ambient H2S conc entrations. The critical step of absorption of gaseous H2S into the li quid phase of the continuous flow system could be stabilised by the de velopment of a new fluid level control system. After numerous test mea surements under laboratory conditions the instrument was tested for th e first time in June 1993 during field measurements in the tropics. Th ese measurements took place in the environment of natural and industri al sources of H2S in the vicinity of Salvador da Bahia in Brazil. Data are presented which prove the ability of the instrument.