The reactive uptake of ClONO2 onto O-18-labeled ice and onto organic liquids was measured in a cylindrical flow tube reactor using chemical ionization detection. The hydrolysis of CIONO2 on (H2O)-O-18 ice produced primarily (HOCl)-O-18, indicating that the Cl-ONO2 bond is broken upon hydrolysis on ice. The loss of ClONO2 onto Liquid organic surfaces (ethylene glycol, cyclohexanone, decanol, and tridecane) was found to be efficient (reaction probability > 0.06), and the product HNO3 was detected in the gas phase. This suggests that dissociation or ionization are not prerequisites for heterogeneous reactions of ClONO2.