Nitrogen and sulfur compounds in ambient air and in wet atmospheric deposition at Mexico City Metropolitan Zone

E. Rodolfo Sosa, J. Ana Luisa Alarcón, B. María Del Carmen Torres, A. Pablo Sánchez, H. Elías Granados, P. Mónica Jaimes, H. Armando Retama, David Gay, Christopher Lehmann

Research output: Contribution to journalConference articlepeer-review


Particulates and sulfur dioxide (SO2) were identified as the main atmospheric pollutants three decades ago in the Mexico City Metropolitan Zone (MCMZ). In order to reduce emissions of these pollutants, replacing fuel oil with natural gas, given this is one of the most important industries located inside MCMZ. This replacement strategy resulted in the reduction in the ambient air levels of both pollutants. SO2 no longer exceeds its ambient air quality standard; however acid rain remains a significant issue, being sulfate the principal component in the wet atmospheric deposition. In this study, spatial and temporal variations in the chemical composition of rain in Mexico City between 2003 and 2016 were analyzed; sulfate and nitrate ions and pH were obtained weekly at 16 sampling stations located in the MCMZ. Furthermore, sulfur dioxide (SO2) and nitrogen oxides (NOx) were evaluated from 1990 to 2016 at the MCMZ air quality monitoring network. SO2 levels have decreased from 1990 to 2016 by about 90%, while those of NOx by 20%. The SO2 / NOx ratio has declined about 60% indicating more effective strategies in reducing SO2 than for NOx emissions. The NOx emission sources are more diverse than for sulfur, and NOx has more complex mechanisms of atmospheric deposition and photochemistry. In 2003 a difference among the sampling sites was observed in the SO42- to NO3- equivalents ratio; sites located in the north presented a higher ratio of 2, while the sites located in the south the value was 1. In 2014, a homogeneous distribution was observed, where the ratio was the same in all the Mexico City sampling sites: 1.5 (µeq/L SO42- to µeq/L NO3-). The pH values of the samples at the stations located in the south were more acidic than the samples for the stations in the north. This result is in line with meteorological conditions, prevailing winds blowing from the north to the south, as well as emission sources located in the north sector, both inside as outside MCMZ.

Original languageEnglish (US)
JournalProceedings of the Air and Waste Management Association's Annual Conference and Exhibition, AWMA
StatePublished - 2018
Externally publishedYes
EventAir and Waste Management Association's 111th Annual Conference and Exhibition - Charting the Future: Environment, Energy and Health - Hartford, United States
Duration: Jun 25 2018Jun 28 2018


  • Air quality
  • Mexico City
  • Nitrogen and sulfur compounds
  • Wet atmospheric deposition

ASJC Scopus subject areas

  • General Energy
  • General Environmental Science


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