The evaluation of atmospheric deposition at regional scales requires international collaboration to adequately characterize the occurrence of potential impacts and establish measures to mitigate them. The central theme for the 2017 NADP Meeting, “NADP data: making the world a better place, one monitor, one network, one study at time,” gives us the direction to evaluate atmospheric deposition in the Gulf of Mexico Region.

The Gulf of Mexico Region has important sources of acid rain precursors, both on land and at sea, located in countries bordering the region, such as the USA, Mexico and Cuba.  It is very important to study the chemical composition of atmospheric wet deposition through international cooperation. Studies on the Mexican coast have recorded the presence of acid rain since 2003. The aim of this study was to evaluate the major ions (Na⁺, NH₄⁺, K⁺, Mg²⁺, Ca²⁺, SO₄^2-, NO₃^- and Cl^-), pH and conductivity in atmospheric wet deposition, collected daily from 2003 to 2015 at a sampling site located along the coast of Mexico (La Mancha, Veracruz) and compare the values with the NADP sampling sites located along the Gulf of Mexico coast from Texas to Florida.

Among the major findings: all ions were present in greater levels in “La Mancha” in comparison with each one of the sampling sites in the USA, with exception of nitrogen compounds (NO₃^- and NH₄⁺ ), which were comparable to the USA sites. The levels of sulfates in Mexico were comparable to the highest US NADP sites. The ratio of SO₄^2- to NO₃^- has been used as indicator of the effectiveness of SO₂ and NOx emissions reductions in the USA. The SO₄^2-/NO₃^- ratio found for “La Mancha” in 2015 was 4.8, the highest value when compared to other sites in the Gulf of Mexico, which had ratios between 1.03 and 1.87. Due to the high levels of SO₄^2- and the ratio SO₄^2-/NO₃^- found at “La Mancha,” it is important to monitor the sulfur dioxide emission sources in Mexico. 

In addition to “La Mancha” sampling site, two additional sampling sites, in Mexico, have recently been incorporated to the atmospheric deposition study: one in the City of Campeche and another in the Port of Veracruz. Initial results from these sites will be shown.

The establishment of the international network for the evaluation of atmospheric deposition in the Gulf of Mexico represents a great opportunity for international collaboration. NADP protocols for sampling and analysis will be adopted, including quality-assurance and quality-control protocols, to ensure that information generated is comparable between current participating countries, USA and México and possibly Cuba.