Steady‐state concentrations of carbonate radicals in field waters

Abstract The carbonate radical [•CO−3] is a secondary radical that results from the scavenging of hydroxyl radical (•OH) by carbonate/bicarbonate. N,N-dimethylaniline was found to be a selective probe for measuring the steady-state concentration of this radical in a variety of natural waters. The pH, nitrate, total carbonate/bicarbonate, and dissolved organic carbon (DOC) in selected field waters were quantitatively analyzed. It was assumed that hydroxyl radicals were produced primarily from the slow photolysis of nitrate and DOC and then were scavenged by carbonate/bicarbonate that were competing with DOC. Steady-state carbonate radical concentrations [•CO−3]ss in natural waters were measured by irradiating solutions of natural waters containing N,N-dimethylaniline in a photoreactor with varying intensity as well as using natural sunlight. The measured steady-state concentration of carbonate radicals was found to be strongly dependent on light intensity and ranged from 5 × 10−15 to 10−13 M. Further kinetic analysis of the data showed that carbonate radical concentrations were related to the concentrations of nitrate and dissolved organic carbon in natural waters through a simple linear relationship.