This research derives and validates an equation to predict rainwater pH using the Air Quality Index (AQI) based on Fick's law of diffusion. Considering the surface area and diffusivity coefficient parameters, the mathematical model equation improves the understanding of mass-transfer mechanisms between pollutants and rain droplets. Validating the results obtained in this work with existing data showed an initial prediction deviation of 47.3 %, which was further reduced to 41.06 % using a conversion factor. This result demonstrates the accuracy of the mathematical modeling reported in this work. The modified equation also offers a practical tool for environmental monitoring, aiding in the mitigation of acid rain effects. This work supports making decisions for environmental management and contributing significantly to atmospheric science by providing a quantitative method for assessing acid rain potential and guiding effective mitigation strategies.
