CFD-based numerical investigation of solar chimney effect on urban air pollution and AQI reduction: a case study of Tehran.

Urban air pollution arises from the interplay of natural and anthropogenic drivers and remains a major challenge for megacities. This study numerically investigates how a solar chimney can improve the air quality index (AQI) by enhancing near‑field ventilation around the structure. The solar‑chimney system and its surrounding outdoor domain were modeled to evaluate near‑field ventilation. Within this framework, we quantified the affected radius, the fraction of polluted air displaced, and the resulting changes in pollutant concentrations and AQI. We also examined the effects of collector radius, chimney height, and pollution‑layer height. The model was validated against a well‑documented experimental dataset. Increasing the collector radius from 200 to 1000 m expands the affected radius from about 550 to about 1,850 m, corresponding to an approximately 11.3‑fold increase in area. By contrast, increasing chimney height-especially at higher values-has little effect on system performance; for example, raising the height from 50 to 100 m increases the affected radius by about 11.6%, whereas from 450 to 500 m it increases by only about 0.6%. The pollution‑layer height is identified as the dominant external limiter: as it increases, the surrounding polluted volume grows and the portion that can be cleaned within a day shrinks. The analysis extends beyond the system to the outdoor near-field and identifies design limitations not captured in prior studies. On this basis, the performance of the solar chimney in reducing air pollution is assessed.