Acid rain in a Mexican site on the coast of the Gulf of Mexico

Abstract

The activities taking place along the coast of the Gulf of Mexico are of great economic importance; however, these activities are potential sources of acid rain precursors. Potentially sensitive receptors to acid deposition in the coastal region of the Gulf of Mexico are lakes, rivers, forests, soils and monuments of cultural heritage. The aim of this study was to evaluate the chemical composition, enrichment factors and trends of wet atmospheric deposition at La Mancha, Veracruz, from 2003 to 2014. The major ions, pH and conductivity were analyzed daily during rainy and dry seasons. The following value ranges of the annual volume weighted mean (VWM) were: pH: 4.78-5.40; SO₄^2–: 16-32 μeq L^–1; NO₃^–: 4-15 μeq L^–1, among others. The principal findings were found: (1) acid rain has been present for more than a decade along the coast of the Gulf of Mexico; (2) the non-marine ions in decreasing order were: NO₃^–, NH₄⁺, Ca⁺ and SO₄^2–; (3) all of the ions were present in major concentrations during the dry season due to minimal precipitation; (4) in several cases, the value of the pH events was low during the rainy season due to the low presence of chemical species that could favor neutralization; (5) the VWM pH in wet deposition was in the range of 4.78 to 5.40 during the study period (2003-2014), and (6) a significant increasing trend for pH was observed during the entire study period, while an increasing trend occurred from 2003 to 2008 for SO₄^2–, NO₃^–, K⁺ and Ca²⁺, which decreased until 2011 and then increased until 2014.