Catalyzes the degradation of carbonyl sulfide (COS) to hydrogen sulfide and CO(2) (PubMed:23406161, PubMed:29199215). May function as one of the microbial sinks for ambient COS, which is an atmospheric trace gas leading to sulfate aerosol formation, thereby participating in the global radiation balance and ozone chemistry (PubMed:23406161). Shows little CO(2) hydration activity and poor carbon disulfide (CS(2)) hydrolysis activity (PubMed:23406161). carbonyl sulfide + H2O = CO2 + H(+) + hydrogen sulfide Binds 1 zinc ion per subunit. Weakly inhibited by thiocyanate (SCN(-)). kcat is 58 sec(-1). Homotetramer. Two pairs of subunits form tightly associated dimers. Belongs to the beta-class carbonic anhydrase family.