Sulfate and nitrate in wet atmospheric deposition in the Gulf of Mexico and possible source regions of their precursors.

Rodolfo Sosa E.1, Humberto Bravo A.2, Ana Luisa Alarcón J.3, Maria del Carmen Torres B.4, Pablo Sánchez A.5, Mónica Jaimes P.6 and Elías Granados H.7

The Gulf of Mexico has important sources of acid rain precursors, both on land and at sea, so that is very important study of the chemical composition of the wet atmospheric deposition in this region. For several years in the coast of the United States it has evaluated the chemical composition of rain, resulting acidic values. Studies on the Mexican coast have recorded the presence of acid rain since 2003. In relation to acid rain, pH determination it is essential, in addition to the composition of sulfates and nitrates that are formed from its main precursors, sulfur dioxide and nitrogen oxides, respectively. The aim of this study was to evaluate pH, sulfate and nitrate concentrations in wet atmospheric deposition, collected daily from 2003 to 2014 in a sampling site located in the coast of Mexico (La Mancha) and compare the registered values, with the NADP sampling sites located in the coast of the Gulf of Mexico from Texas to Florida.

HYSPLIT back trajectory model was applied in order to identify the regions where the emissions sources of acid rain precursors are located.   Trajectories showed an important transport to the sampling site from the East during rainy season (June-October). The region located east to “La Mancha” is the Gulf of Mexico presenting offshore operations for the exploration and production of petroleum. The annual VWM pH in wet deposition at “La Mancha” sampling site was in the range of 4.78 to 5.40 during the study period (2003-2014) and for the year 2014 was 5.01, which is similar for the USA sites; the VWM concentration of SO42-  was in the range of 16 to 32 μeq/L, and for the last year  was 26 μeq/L, which is similar  than the higher level registered in the USA at TX10 site; the VWM concentration of NO3-  was in the range of 4 to 15 μeq/L and for 2014 was 6 μeq/L, which is lower than in the USA sites. The ratio SO42-/NO3- found for the site in Mexico in 2014 was 4, being the highest value compared to other sites in the Gulf of Mexico whose ratios were between 1.25 and 1.7. Therefore it is important to pay attention to the sulfur dioxide emission sources in Mexico. It is recommended to extend the atmospheric deposition sampling to other sites in Mexico and Cuba.


1Universidad Nacional Autonoma de México (UNAM),
6Gobierno de la Ciudad de México,