The proliferation of air conditioners (ACs) has established them as vital demand response resources in urban power systems. The energy consumption of ACs is directly determined by the surrounding microclimate, while the corresponding waste heat raises the ambient temperature. In this paper, we study the capacity allocation of ACs for demand response considering interaction with surrounding microclimate. First, a unified thermal model integrated with ACs and urban microclimate is established to analyze the micro-scale heat flux transfer. This thermal model can quantify the interactions between extra energy demand of ACs and rising temperature of building blocks. Second, we formulate a two-stage optimal response capacity allocation model of ACs for providing peak-valley regulation services. In the first stage, load aggregators (LAGs) engage in a cooperative game to maximize response benefits considering response revenues as well as indoor and outdoor temperature deviation penalties. In the second stage, the LAGs implement state-of-charge equalization to allocate the first-stage capacity, enforcing consistent comfort levels for individual buildings. Additionally, we design a parameter equivalence and differential linearization algorithm to solve model efficiently. Finally, we validate the proposed method on all 4,739 individual buildings in the Macau Peninsula. Numerical results show that the proposed strategy can effectively increase the response benefits and satisfy individual comfort requirements.