Rainwater chemistry at the eastern flanks of the Sierra Madre Oriental, Veracruz, Mexico

A rainwater chemistry study was carried out at a single site in Xalapa located at the eastern flanks of the Sierra Madre Oriental, Veracruz, Mexico, during the rainy and dry seasons under the influence of different meteorological conditions. Rain samples were analyzed for the most important ions. The statistical results indicated that there were significant differences at the 95% confidence level between the ionic concentration measured in Samples collected in both seasons. The lower concentration values found during the rainy season could be attributed to dilution processes since in this season 79% of the annual precipitation occurs, compared to only 21% in the dry season. High and positive ion-pair correlations were found among the most important ions in both seasons. Although Xalapa is situated at less than 100 km from the coast, marine contribution of SO42- and Ca2+ is negligible compared with the nonmarine contribution. In the rainy season, enrichment of SO42-, NH4+, and NO3- is due to upwind medium-and long-distance emission sources of Veracruz, as back trajectories of the predominant winds from the southeast indicate. On the other hand, in the dry season this enrichment is due to emission sources situated in Tampico, Madero, and Poza Rica and south-southeastern Texas, as indicated by the predominant winds from the northeast. Finally, wet deposition rates were, as expected, higher during the rainy season in spite of the dilution processes.