Effective photon–medium coupling induced by urban clouds

We propose a framework inspired by effective field theory (EFT) to describe how photons interact with the disordered medium of an urban atmosphere. Specifically, we examine UV attenuation driven by the interplay between aerosols and cloud stratification. By defining an effective coupling constant, geff Π , we link an observational proxy for the photon self-energy to the near-surface PM10 concentration. This approach yields a physically motivated metric for the radiative impact of particulate matter. Our results reveal a distinct regime-dependent response: the nature of the photon–medium coupling changes sign under different cloudiness classes, suggesting that cloud topology acts as a macroscopic control parameter for the effective-medium description [1–3].