Chemical Interactions of Tropospheric Halogens on Snow/Ice

It has become clear in recent years that ice surfaces can efficiently promote chemical reactions between neutral gas phase species. The best known example involves the activation of chlorine in the presence of polar stratospheric clouds through the reaction of HCl with chlorine nitrate (ClONO₂) [e.g., Molina et al., 1987; Tolbert et al., 1987; Hanson and Ravishankara, 1991] or with HOCl [Hanson and Ravishankara, 1992; Abbatt and Molina, 1992]: 1$$ HCl + ClON{O_2} \to C{l_2} + HN{O_3} $$2$$ HCl + HOCl \to C{l_2} + {H_2}O $$