Absorption cross sections for gaseous ClNO 2 and Cl 2 at 298 K: Potential organic oxidant source in the marine troposphere

The absorption cross sections for gaseous ClNO 2 in the 200–370 nm region and for Cl 2 in the 270–400 nm region have been determined at 298 K. The cross sections for Cl 2 are in excellent agreement with the literature. At λ < 300 nm the absorption cross sections for ClNO 2 are in good agreement with those of lilies and Takacs (1976/1977) and Nelson and Johnston (1981) but are higher than those of Martin and Gareis (1956) from 220 to 240 nm. In the tropospherically important region beyond 290 nm our results, which have been corrected for impurity Cl 2 using a combination of mass spectrometry and UV absorption, fall between those of Martin and Gareis (1956) and lilies and Takacs (1976/1977) and are in excellent agreement with the values of Nelson and Johnston (1981). Estimates of the photolysis rate constants and photolytic lifetimes for ClNO 2 for various solar zenith angles at the Earth's surface are reported. It is shown that atomic chlorine from ClNO 2 photolysis may be a significant initiator of organic photooxidation in both moderately polluted and remote marine atmospheres.