Chemical composition of precipitation in a Mexican Maya region

The chemical characteristics of wet precipitation in Puerto Morelos, Quintana Roo State, Mexico, were measured from April 1994 to December 1995. Puerto Morelos is located in the Caribbean Mayan coastal region of the Peninsula of Yucatan, and is normally exposed to winds from the Caribbean region. Wetfall was analyzed for pH, conductivity and Cl−, NO3−, SO42−, Na+, NH4+, K+, Mg2+ and Ca2+ ion concentrations. Volume–weighted mean pH for the whole sampling period was 5.35, although values as low as 4.6 were measured in several rain samples. Concentrations of all species correlated negatively with rain volume. Sea-salt aerosols contributed with most of the Na+, Cl−, Mg2+, K+ and SO42− found in wet precipitation. The mean [SO42−excess] was 9.7 μEq l−1, which agrees with the background hemispheric values of ≈10 μEq l−1 reported elsewhere. The mean [NO3−] was 11.4 μEq l−1, almost four times higher than the background hemispheric value of ≈2.5 μEq l−1 reported elsewhere. However, a major component causing the slight acidity character of rain in Puerto Morelos seems to be H2SO4.