| Ozonesondes are instruments commonly used to measure ozone concentration in the atmosphere. Essentially an electrochemical cell, air is pumped into the cathode chamber where ozone reacts with a dilute solution (typically 1.0% or 0.5%) of potassium iodide, forming iodine. A current is generated as two electrons for every iodine molecule flow from the anode to the cathode. This current is directly proportional to the amount of ozone entering the cathode chamber. Theoretically, one molecule of iodine is produced for every molecule of ozone reacting in the solution. However, past studies have suggested that additional reactions, which may be due to phosphate buffers included in the potassium iodide solution, occur, producing more iodine and thus causing erroneously high concentrations of ozone to be documented. The overall goal of this project was to determine, using the most widely used cathode electrolyte concentrations (1% full buffers and 0.5% half buffers), if the stoichiometry of the reaction is indeed 1:1. After exposing cathode electrolytes to known amounts of ozone (&sim200 ppb), the iodine which formed in the electrolyte was titrated using a solution of sodium thiosulfate. It was anticipated that the ratio of iodine to ozone would be at least 1:1, following the chemical equations of the reaction. However, this was not the case. The laboratory results yielded less iodine than ozone. A typical lab test generated 1.24E-07 moles of ozone, with some of this ozone escaping the sensing electrolyte (&sim2.62E-08 moles). Assuming no other ozone loss was occurring, total ozone reacting in the solution was approximately 9.78E-08 moles. Titrations of iodine show that approximately 7.75E-08 moles of iodine were formed during the test. This is equivalent to a stoichiometric ratio of 0.79:1 (iodine to ozone). This is a result that has not been documented in past work, and though attempts were made to increase this stoichiometry, the tests never yielded ratios of 1:1. Several components of the experiment may need to be altered for future stoichiometric determinations of ozonesondes including more precise burets to perform the titrations and higher ozone concentrations to produce more iodine in the electrolytes. |
