**4. Conclusions**

In general, a strong seasonality in both, N and S atmospheric deposition fluxes was observed. Regarding to spatial variability, it was found that, in each climatic season, fluxes stayed homogeneous and uniformly distributed as a result of meteorological conditions prevailing in each season, having a regional origin during the rainy season and a local origin during the rest of the year. NH4 + and NO3 <sup>−</sup> showed a similar spatial and temporal pattern in their deposition fluxes. According to the analysis by season, the highest N deposition flux was found during the cold dry season, followed by warm dry season and rainy season, respectively. It could be explained due to the occurrence of a minor dispersion of pollutants resulting from lower wind velocities, and the frequent occurrence of thermal inversions during the cold dry season. On the other hand, dilution phenomena could play an important role during the rainy season, resulting in lower fluxes during this season. From spatial analysis of N deposition fluxes, it can be concluded that the site with the highest N deposition was Loma Blanca (Site X). In general, all sites where the highest N deposition fluxes were found are urban sites located in the suburbs of the city, with high vehicular traffic, where some agricultural sites are located. It suggests that the main sources of NO3 <sup>−</sup> are vehicular emissions, whereas the main source of NH4 + is the intensive use of fertilizers in these agricultural zones. However, since significant differences were not found between sampling sites by land use, it can be concluded that fluxes could be uniformly distributed, confirming their local origin. It agrees with the residence time of NO2 in the atmosphere of 1 day, time in which, it is deposited as NO3 <sup>−</sup> or NH4 + at ground level, being their concentrations higher in the surroundings of the emission point. Since in León city, there was not a territorial ecological order in the past, the city growth and development along the years was not planned, resulting in the coexistence of different type of land use in a given zone.

On the other hand, S deposition fluxes showed a different pattern, suggesting their regional origin. From seasonal analysis, it was found that the highest atmospheric deposition flux occurred during the rainy season, followed by warm dry and cold dry seasons. It agrees with the regional character of SO2 (sulfate precursor) which has a residence time in the atmosphere of 1–5 days [24, 25], being able to transport long distances before to be deposited finally at ground level. From air masses trajectories analysis, it could be concluded that, during the rainy season, this pollutant is long-range transported from the South of United States and from the North of Gulf of Mexico, explaining in this way, why during this season, a relative sulfate enrichment is observed in comparison with the other two seasons.

From analysis by sampling site, the site with the highest S atmospheric deposition flux was Instituto Tecnológico de León followed by Zoológico (sites IV and VI), these sites have an industrial and urban land use, suggesting that both vehicular and industrial emissions could contribute to background sulfate levels, which in turn were temporarily increased during the rainy season due to the long-range transport of air masses from distant sources (South of United States and North of Gulf of Mexico).

**61**

**Author details**

Campeche, México

Rosa María Cerón Bretón1

Reyna del Carmen Lara Severino1

María de la Luz Espinosa Fuentes2

and Lizbeth Cisneros Rosique1

Ciudad de México, México

3 Instituto Politécnico Nacional, Guanajuato, México

provided the original work is properly cited.

\*Address all correspondence to: rosabreton1970@gmail.com

*Mapping and Estimation of Nitrogen and Sulfur Atmospheric Deposition Fluxes…*

\*, Julia Griselda Cerón Bretón1

1 Facultad de Química, Universidad Autónoma del Carmen, Ciudad del Carmen,

2 Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México,

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

, Marcela Rangel Marrón1

,

, Simón Eduardo Carranco Lozada<sup>3</sup>

,

*DOI: http://dx.doi.org/10.5772/intechopen.90878*

*Mapping and Estimation of Nitrogen and Sulfur Atmospheric Deposition Fluxes… DOI: http://dx.doi.org/10.5772/intechopen.90878*
