A comprehensive overview of the ionic composition of rainwater across Latin America

Wet atmospheric deposition, primarily through rainfall, plays a crucial role in removing atmospheric pollutants, particularly water-soluble particles and dissolved gases, thereby contributing to atmospheric cleansing. This review article examines the ionic composition of rainwater in Latin America, based on scientific studies retrieved from the Web of Science and Scopus databases. The findings reveal that anthropogenic sources of ionic compounds in rainwater include fossil fuel combustion, fertilizer application, vehicular emissions, and industrial activities, which primarily contribute to acidifying compounds. In contrast, neutralizing compounds (e.g., Ca 2+ and Mg 2+ ) originate from both human activities and natural sources, such as marine aerosols and dust resuspension. Elevated concentrations of acidifying compounds have been documented in urban and industrial areas, whereas rural regions predominantly exhibit neutralizing ions. In certain countries, such as Brazil and Costa Rica, reductions in the sulfur content of fuels have led to trends of rainwater neutralization. The ratios of ionic compounds (e.g., SO 4 2 − /NO 3 − and NH 4 + /NO 3 − ) and rainwater pH were analyzed to identify emission sources and regional patterns, revealing geographical, seasonal, and local influences on emissions. However, documentation on the impacts of rainwater acidification in Latin America remains limited, with most studies focusing on Brazil. Mexico, Argentina, and Brazil have been identified as the most productive countries in this research area. Nevertheless, studies on the ionic composition of rainwater in Latin America remain scarce and have declined over the past 5 years. This decline is concerning given the region’s rich biodiversity, which may be adversely affected by rainwater acidification.