#Chlorine atom free

#Chlorine atom free

Therefore, it is likely that ClNO 2 production from reactions in aerosols will continue to occur in the free atmosphere and at regional and global scales. However, in the atmosphere, higher humidities lead to droplets with more water. ( 2) suggest that their mechanism should be operative even when relative humidity is higher than in their experiments because the catalytic behavior of water makes their mechanism faster. Figure was prepared with the assistance of Debra Dailey-Fisher. suggest a heterogeneous pathway ClNO production. Currently, there are no established multiphase schemes for the formation of ClNO. The rates, mechanisms, and the availability of reaction media (i.e., solid surfaces or liquid droplets) all determine the overall effect on the atmospheric production of ClNO 2.

Here, the chemicals do not enter the substrate of the suspended particle or other solid surfaces exposed to air. ( Left) The new mechanism involving a surface, proposed by Raff et al. This mechanism has been shown to be effective by laboratory and field observations of N 2O 5 loss and ClNO 2 production.

( Right) Formation of ClNO 2 via the established multiphase reaction scheme in which the gas-phase reactant enters an aerosol particle or water droplet, reacts within the liquid medium, and expels the product. Two mechanisms for the reaction of N 2O 5 to produce CINO 2. Now the question is: What will it be in the troposphere? Will ClNO and ClNO 2 be produced via surface reactions or multiphase reactions?įig. have observational and ab initio calculation evidence that water would catalyze these surface reactions! This mechanism is shown in Fig. To make matters more interesting, Raff et al. They evoke the formation of ClNO, a molecule that has not been widely considered significant even though its formation was observed in the laboratory via NO 2 reaction with salt more than 35 years ago ( 13). These authors suggest a surface reaction where HCl reacts with an ion pair formed by the uptake of NO 2 or N 2O 5 to form ClNO or ClNO 2, respectively. ( 2) has not been considered within atmospheric chemistry models it is an exciting, new, and somewhat puzzling pathway for producing tropospheric atomic chlorine. The liquid-phase reactions involved are reasonably understood and the overall mechanism can be independently verified from individual reaction rates and physicochemical parameters such as solubility coefficient and diffusion constants. 1 Right shows the ClNO 2 production according to the multiphase reaction scheme from a droplet. These highly photolabile species are then proposed as sources of chlorine atoms.įormation of ClNO 2 from multiphase reactions has been proposed and proven in the laboratory and the atmosphere ( 8– 11). ( 2) have proposed a rapid and, potentially, copious production pathway in which HCl reacts heterogeneously on surfaces with NO 2 and N 2O 5 to produce, respectively, ClNO and ClNO 2. Therefore, for chlorine atoms to be important in the troposphere, one needs a mechanism that can produce copious amounts of them from stable gases (i.e., have a large flux), especially from stable species such as HCl or chloride ions in particles, such that the rapid production can compensate for the rapid removal. Further, reactive chlorine atoms quickly end up as HCl, which is removed via rainout. However, unlike the stratosphere, where harsh UV radiation is available to produce chlorine atoms from stable species and mechanisms are available to sustain them, there are only a few known pathways for making chlorine atoms in the troposphere none of them have been shown to be efficient until recently. It has been proposed that the chlorine atom could be a significant reactive free radical in the troposphere ( 6), as it is in the stratosphere, where it is responsible for ozone depletion ( 7).