Sulfur and nitrogen compounds in wet atmospheric deposition on the coast of the Gulf of Mexico from 2003 to 2015.

The Gulf of Mexico region has important sources of acid rain precursors, located in all of the countries; U.S., Mexico and Cuba, and so it is very important to study the chemical composition of the wet atmospheric deposition in all coastal areas. For many years along the U.S. Gulf Coast, acidic precipitation has been measured. Measurements along the Mexican Gulf Coast were begun in 2003. The aim of this study was to evaluate pH, sulfate, nitrate and ammonium concentrations in wet atmospheric deposition, collected daily from 2003 to 2015 at La Mancha (LM), Veracruz and compare the values with the National Atmospheric Deposition Program (NADP) sampling sites located along the U.S. coast of the Gulf of Mexico. The annual Volume Weighted Mean (VWM) pH in wet deposition at La Mancha site ranged from 4.81 to 5.40, which is similar to the U.S. Gulf sites. Additionally, the annual VWM SO concentration was from 15 to 31 μeq/L, which is higher than the U.S. sites. Annual VWM NO concentrations were from of 3.5 to 15 μeq/L, which is lower than all the U.S. sites. At the Mexican site, the SO/NO ratio was 4.90 and higher than all of the U.S. sites, which were between 1.03 and 2.38. For LM, the median NH/NO ratio was 0.77, similar to the Florida sites (0.53-0.91), and below the values measured for Louisiana and Texas (1.07-1.5). The Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT) was applied in order to identify the emission sources for the pollutants seen at LM. Trajectories showed an important transport to LM from the East (open water) during the rainy season. The region located East of La Mancha shows offshore petroleum operations as sources of acid rain precursors and deposition of acidifying and nitrogen containing compounds. It is important to consider the sulfur dioxide emission sources in the Mexico Gulf region, and to extend the atmospheric deposition sampling to other sites along the Mexican Gulf coast and Cuba.