MEASUREMENT TECHNIQUE FOR THE DETERMINATION OF PHOTOLYZABLE CHLORINE AND BROMINE IN THE ATMOSPHERE

A technique has been developed to enable measurement of photolyzable c hlorine and bromine at trace levels in the troposphere. In this method , ambient air is drawn through a cylindrical flow cell, which is irrad iated with a Xe are lamp. In the reaction vessel of the photoactive ha logen detector (PHD), photolytically active molecules Cl-p (including Cl-2, HOCl, ClNO, ClNO2, and ClONO2) and Br-p (including Br-2, HORr, B rNO, BrNO2, and BrONO2) are photolyzed, and the halogen atoms produced react with propene to form stable halogenated products. These product s are then sampled and subsequently separated and detected by gas chro matography. The system is calibrated using low concentration mixtures of Cl-2 and Br-2 in air from commercially available permeation sources . We obtained detection limits of 4 pptv and 9 pptv as Br-2 and Cl-2, respectively, for 36 L samples.