Measurement technique for the determination of photolyzable chlorine and bromine in the atmosphere

Abstract

Abstract.A technique has been developed to enable measurement of photolyzable chlorine and bromine at trace levels in the troposphere. In this method, ambient air is drawn t•ough a cylindrical flow cell, which is irradiated with a Xe arc lamp. In the reaction vessel of the photoactive halogen detector (PHD), photolyrically active molecules Clp (including C12, HOC1, C1NO, C1NO2, and C1ONO2) and Brp (including Br2, HOBr, BrNO, BrNO2, and BrONO2) are photolyzed, and the halogen atoms produced react with properie to form stable halogenated products. These products are then sampled and subsequently separated and detected by gas chromatography. The system is calibrated using low concentration mixtures of C12 and Br2 in air from commercially available permeation sources. We obtained detection limits of 4 pptv and 9 pptv as Br2 and C12, respectively, for 36 L samples.

Chlorine chemistry in urban atmospheres: a review

“…[66] The authors suggest that a mechanism aside from photolytically driven aqueous phase mechanisms [64,72] is needed to explain these observations. A study in the arctic coastal location of Alert, North-West Territories utilised the photoreactive halogen detector method [73] to detect levels of photolysable Cl, which ranged between ,9 and 100 pptv. Concentrations were reported as Cl 2 , although they may have also included HOCl or other photolysable species.…”

Rate constants for the reactions of chlorine atoms with a series of unsaturated aldehydes and ketones at 298 K: structure and reactivity

“…22 Non-HCl inorganic gaseous chlorine compounds, hypothesized to be mainly Cl 2 ranging from 13 to 127 ppt were measured indirectly using mist chambers at coastal sites. 23,24 Photolyzable chlorine compounds [25][26][27] have also been identified in the Arctic during surface ozone depletion in the spring. Such photolytically labile chlorine compounds will be photolyzed at sunrise and generate chlorine atoms.…”

Heterogeneous reactions of Cl2 with sea salts at ambient temperature: Implications for halogen exchange in the atmosphere

“…Using a tandem mist chamber method, C12', including Cl 2 and HOCI not trapped in the acidic mist chamber, has been measured in the range < 26 to 254 pptv CI in the marine atmosphere . Using a photoactive halogen detector with scavenger hydrocarbon molecules, photolytically active molecules Clp (including C12, HOCI, CINO, C1NO 2, and C1ONO2) have been detected in the range < 9 to 100 pptv as C12 in the Canadian Arctic at Alert [Impey et al, 1997a, b].…”