Molecular and Ionic Signatures in Rainwater: Unveiling Sources of Atmospheric Pollution

Atmospheric deposition through rainfall plays a significant role in transporting various anthropogenic contaminants to terrestrial and aquatic ecosystems. However, rainwater’s integrated ionic and molecular composition remains underexplored in semiurban environments. This study provides a comprehensive chemical characterization of rainwater collected during seven precipitation events from February to April 2025 in Athens, Georgia, USA. This semiurban area is characterized by substantial vehicular traffic, seasonal agricultural activities, and ongoing construction, while lacking significant industrial emissions. Targeted spectrophotometric analyses revealed heightened concentrations of nitrate (ranging from 2.0 to 4.3 mg/L), sulfate (17 to 26 mg/L), and phosphate (2.4 to 3.1 mg/L), with peak concentrations observed during high-intensity rainfall events. These findings are consistent with enhanced wet scavenging of atmospheric emissions. Concurrently, both targeted and non-targeted gas chromatography-mass spectrometry (GC-MS) analyses identified a diverse array of organic pollutants in the rainwater, including organophosphate, organochlorine, and triazine pesticides; polycyclic aromatic hydrocarbons (PAHs); plasticizers; flame retardants; surfactant degradation products; and industrial additives such as bisphenol A, triclosan, and nicotine. Furthermore, several legacy contaminants, such as organochlorines, were detected alongside currently utilized compounds, including glyphosate and its metabolite aminomethylphosphonic acid (AMPA). The concurrent presence of elevated anion and organic pollutant levels during significant storm events suggests that atmospheric washout can be the primary deposition mechanism. These findings underscore the capability of semiurban atmospheres to accumulate and redistribute complex mixtures of pollutants through rainfall, even in the absence of large-scale industrial activity. The study emphasizes the importance of integrated ionic and molecular analyses for uncovering concealed pollution sources. It highlights the potential of rainwater chemistry as a diagnostic tool for monitoring atmospheric contamination in urbanizing environments.