The purpose of this research was to study the chemical composition of rainwater to assess the impact of marine aerosol and anthropogenic emissions by using back air-mass trajectories. Fieldwork was done from July to November 2004, in a coastal site probably impacted by gas and oil industry in Campeche, Mexico: San Antonio Cardenas. Na + , Cl -, and Mg
2+, were the most abundant ions, being sea-salt aerosol their unique source. A significant portion of K + and Ca 2+ originated from non-sea-salt sources; and the sulphate excess exceeded the background level reported for remote marine sites, suggesting that besides of marine aerosol, there was a significant contribution of SO 4 2-from anthropogenic sources. NO 3 -concentrations in San Antonio Cardenas exceeded the background level reported for coastal sites with minimal anthropogenic influence and showed a significant correlation with SO 4 2-, suggesting a common source. Agricultural practices are null, for this reason NH 4 + levels were low. Mean pH value was 4.64, this acidity showed a good correlation with SO 4 2-and NO 3 -levels, and with the local meteorology. A sour gas recompression plant located 10 km at NE from San Antonio Cardenas was identified as the main source of this strong acidity.