We analyze Nash-stable coalition partitions in a differential game with heterogeneous player populations; as a leading application, we study an asymmetric game of pollution control. Type-I players are non-vulnerable to pollution and do not internalize damages in their production choices, whereas Type-II players fully internalize the damages. We characterize optimal feedback strategies under alternative coalition partitions, establish conditions for Nash-stable partitions for fixed numbers of Type-I and Type-II players, and identify when vulnerable players can incentivize non-vulnerable players to cooperate in emission control. We prove that, under a non-transferable payoff scheme, no Nash-stable coalition partition exists, whereas under a transferable scheme with the CIS value, a stable partition can be achieved. We also provide a compact compute-allocate-verify module that, given the model parameters and a feasible-partition set, computes feedback Nash equilibrium, allocates CIS values, and verifies unilateral deviations to identify Nash-stable coalition partitions.