Resumen
The present study reports the chemical composition of atmospheric wet deposition in Monterrey, capital of the state of Nuevo León and the most important industrial city in northeastern México, where air quality presents a serious problem due to dust particles emitted. The sampling period was from January to December 2007. The station was mounted on the roof of the College of Chemical Sciences at the University of Nuevo León which is located in the north of the Metropolitan Area. Thirty-two samples of rain were collected with an automatic sampler and analyzed for pH, ion concentrations (SO4-2, NO3-, Cl-, Ca2+, Na+, K+, NH4+) and conductivity. The results show that the average weighted pH value of the rainwater was 6.58 due to neutralization. Rainwater chemistry showed high contribution of Ca2+ and Mg+2 in cations and SO4-2 and Cl- in anionic species. Low concentration of H+ found in rainwater samples from Monterrey N.L. suggests that an important portion of H2SO4 and HNO3 have been neutralized by alkaline particles in the atmosphere. In order to find possible association between ions in precipitation, and consequently, the possible sources of pollutants correlation study was applied using the program SPSS v.12. Weak correlations were found between the H+ ions and SO4-2 or NO3-1 because of neutralization. The local dust cement factories and surrounding limestone environment might be causing high concentration of Ca+2 and Mg+2. The results of this research will be used to evaluate the composition of atmospheric deposition, to evaluate air quality and to develop strategies to implement preventive measures and control of the atmospheric emissions in Nuevo Leon. This work represents the first study of rainwater chemical composition in the northeast of México.