Effective-field description of UV photon propagation in correlated urban cloud-aerosol media

Abstract We develop an effective-field framework for ultraviolet (UV) photon propagation through a heterogeneous urban atmosphere, modeled as a correlated dielectric disorder field $\delta\varepsilon(\mathbf{x})$ embedded in a stratified cloud--aerosol canopy. Using a Born-like approximation for the transverse photon self-energy, we derive closed-form analytical solutions for the damping proxy, emergent photon mass, and effective dielectric function. Crucially, our model identifies an exact topology-driven critical transport scale at $k\xi=1/2$, separating a Rayleigh-type dissipative regime from a strongly forward-peaked, screening-like phase. Furthermore, we show that atmospheric stratification naturally induces a macroscopic birefringence ($\Delta n_{\mathrm{eff}} \sim 10^{-4}$). Finally, observational validation using NASA POWER UV irradiance and CETESB PM$_{10}$ data over S\~ao Paulo ($N=149$ days) confirms the predicted sign inversion of the effective coupling across cloud-cover regimes. These results provide a rigorous, physics-first route to connect macroscopic radiative-transfer phenomenology with effective-field language in complex media.