An ion mobility spectrometer (IMS) was used to study the negative ion chemistry of bromine and monitor its concentration in a series of laboratory experiments and in the ambient air of a chemical production facility. Under the conditions of the IMS, three negative ions, Br-, Br2- and Br3-, were produced from bromine. The relative abundance of Br3- increased with the bromine concentration, whereas those of Br- and Br2- decreased owing to the ion-molecule reactions they undergo with bromine. The presence of chlorine, other bromides and chlorides did not adversely affect the determination of bromine. In all field measurements, the maximum bromine levels measured were below 30 ppb, well below its 8-h time-weighted average threshold limit value (TWA-TLV) of 100 ppb. The rapid response of the IMS was evident from the effect of changes in wind direction or velocity on the measured concentrations.
