<p>Emerging pollutants (EPs) in aquatic environments require treatment strategies that are both effective and operationally sustainable. While solar photocatalysis is widely investigated, its performance is rarely characterised under realistic outdoor irradiance conditions, limiting its engineering translation. This study presents a field-validated evaluation of a solar-driven TiO₂-based photocatalytic system operated in a 10 L compound parabolic collector (CPC) reactor under natural sunlight. Real-time global horizontal irradiance (GHI) was recorded at 1-min resolution and statistically coupled to apparent first-order degradation rate constants (k_app) using a linear mixed-effects model. Across six representative emerging pollutants (carbamazepine, diclofenac, sulfamethoxazole, atrazine, benzotriazole, and bisphenol A), removal efficiencies exceeding 90% were achieved under optimal noon conditions (GHI ≈ 850 ± 40 W m⁻²), with total organic carbon (TOC) mineralisation up to 63%. In natural river water matrices, degradation remained substantial (75–88%) despite light attenuation and radical scavenging effects. The statistical model confirmed GHI as a significant predictor of k_app (β_GHI = (1.1 ± 0.2) × 10⁻³ m² W⁻¹ min⁻¹, p &lt; 0.001), with irradiance explaining 62% of kinetic variability. Operational scheduling within the 11:30–14:30 window enhanced pollutant removal by 23–41% compared with morning or afternoon operations. Catalyst durability was demonstrated over ten reuse cycles with 87% activity retention. By establishing quantitative irradiance–kinetics parameterisation under genuine outdoor conditions, these findings support the practical implementation of solar photocatalysis under environmentally variable operating conditions.</p>