DEVELOPMENT OF A NEW REAL-TIME METHOD FOR MEASURING S(IV) IN-CLOUD WATER USING A COUNTER-FLOW VIRTUAL IMPACTOR

A new method of analysis for S(IV) is described incorporating a counte r-flow virtual impactor for collection and evaporation of cloud drople ts with an SO2 analyzer. This technique allows analysis of aqueous S(I V) concentration in real-time and overcomes some sampling or analysis problems of conventional sampling with bulk cloud water collectors and wet chemical analysis methods. The technique is demonstrated by the c orrelated responses of the S(IV) instrument and instruments measuring physical properties of clouds while passing in and out of clouds. Meas ured aqueous S(IV) concentrations ranged from the detection limit (0.1 nmol per m3 of air) to 1.8 nmol m-3 in clouds in Ohio. S(IV) molar co ncentrations (moles/l of cloud water) were not calculable from these m easurements, but can be calculated when a measurement of the liquid wa ter content of the collected cloud water is made simultaneously.