*3.5.1 Mapping*

#### *3.5.1.1 NH4 +*

In **Figure 12**, it can be observed that during warm dry and rainy seasons, the lowest ammonium deposition fluxes were registered, unlike cold dry season, when the highest levels were observed. During all study period, the highest ammonium

**Figure 11.** *Frequency histogram for (a) cold dry season, (b) for warm dry season, and (c) for rainy season.*

**57**

Guanajuato and Silao.

*−*

Blvd. and Mariano Escobedo Oriente Blvd.

*3.5.1.2 NO3*

**Figure 12.**

*rainy season.*

*Deposition map of NH4*

*+ (kg ha<sup>−</sup><sup>1</sup>*

 *year<sup>−</sup><sup>1</sup>*

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

atmospheric deposition fluxes were found at the southeast of the city (CICEG-Bomberos and Instituto Tecnológico de León, both with an industrial land use). It is worth mentioning that both sites are influenced by the emissions released by a great vehicular fleet that circulates daily on the streets, especially near monitoring station CICEG-Bomberos which is located on the main route of entry to the city from

*) in León City, (a) cold dry season, (b) warm dry season, and (c)* 

In the case of nitrate, from **Figure 13**, it can be observed that the highest nitrate deposition fluxes were found during the cold dry season. Regarding seasonal patterns, it can be observed that the highest nitrate deposition fluxes were registered at de Southwest of the city, specifically in site X, which corresponds to site of Loma Blanca. This zone has an urban land use with the highest altitude in the city (elevation of 1874 m), in which, there are many commercial areas and avenues with high vehicular traffic such as Miguel de Cervantes Av., Miguel Torres Landa Oriente

Since nitrate deposition fluxes were higher during the cold dry season, it suggests the origin of nitrate and its precursor in local sources. In addition, wind velocities are lower during the cold dry season in comparison with the other two seasons; therefore, there is a minor dispersion of pollutants in the region.

*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*

#### **Figure 12.**

*Spatial Variability in Environmental Science - Patterns, Processes, and Analyses*

To carry out the meteorological analysis at regional level, 24-h backward air-masses trajectories at 500, 1000, and 1500 m of altitude were obtained (a total of 85 trajectories) from HYSPLIT Model (National Oceanic and Atmospheric Administration), and choosing as representative site to CICEG-BOMBEROS, located at SE of the metropolitan area. In addition, meteorological surface data were obtained from SINAICA (National System of Air Quality Information) to estimate wind roses to identify the prevailing wind direction during the study period.

From surface analysis, it could be observed that wind direction showed a great variability between climatic seasons, for example, the prevailing wind direction during cold dry season was from SW (**Figure 11a**), during warm dry season was from NE (**Figure 11b**), and during rainy season was from E-NE (**Figure 11c**).

In **Figure 12**, it can be observed that during warm dry and rainy seasons, the lowest ammonium deposition fluxes were registered, unlike cold dry season, when the highest levels were observed. During all study period, the highest ammonium

**3.4 Meteorological analysis**

**3.5 Mapping and reference values**

*3.5.1 Mapping*

*+*

*3.5.1.1 NH4*

**56**

**Figure 11.**

*Frequency histogram for (a) cold dry season, (b) for warm dry season, and (c) for rainy season.*

*Deposition map of NH4 + (kg ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> ) in León City, (a) cold dry season, (b) warm dry season, and (c) rainy season.*

atmospheric deposition fluxes were found at the southeast of the city (CICEG-Bomberos and Instituto Tecnológico de León, both with an industrial land use). It is worth mentioning that both sites are influenced by the emissions released by a great vehicular fleet that circulates daily on the streets, especially near monitoring station CICEG-Bomberos which is located on the main route of entry to the city from Guanajuato and Silao.

#### *3.5.1.2 NO3 −*

In the case of nitrate, from **Figure 13**, it can be observed that the highest nitrate deposition fluxes were found during the cold dry season. Regarding seasonal patterns, it can be observed that the highest nitrate deposition fluxes were registered at de Southwest of the city, specifically in site X, which corresponds to site of Loma Blanca. This zone has an urban land use with the highest altitude in the city (elevation of 1874 m), in which, there are many commercial areas and avenues with high vehicular traffic such as Miguel de Cervantes Av., Miguel Torres Landa Oriente Blvd. and Mariano Escobedo Oriente Blvd.

Since nitrate deposition fluxes were higher during the cold dry season, it suggests the origin of nitrate and its precursor in local sources. In addition, wind velocities are lower during the cold dry season in comparison with the other two seasons; therefore, there is a minor dispersion of pollutants in the region.

**Figure 13.** *Deposition map of NO3 <sup>−</sup> (kg ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> ) in León City, (a) cold dry season, (b) warm dry season, and (c) rainy season.*

Another important factor is the lack of rain, contributing to a minor dilution or washing of the atmosphere. Levels found were homogeneously distributed as a result of local sources, and it agrees with residence time in the atmosphere of NO2.

#### *3.5.1.3 SO4 2−*

In the case of SO4 <sup>2</sup><sup>−</sup>, its deposition fluxes were uniformly distributed in the metropolitan area of León (**Figure 14a**–**c**). In all seasons, the highest levels were found at NE (Site VI: Zoológico) and at SE (Sites I and IV corresponding to CICEG Bomberos and Instituto Tecnológico de León), all of them, with an industrial land use. On the other hand, the lowest sulfate deposition fluxes were found at North of the city.

The highest value for sulfate atmospheric deposition flux was found during the rainy season; however, this difference was not statistically significant in comparison with the other two seasons. Some hot spots were identified: at NE (Site VI), at SE (sites I and IV), and at SW (Site X).

#### *3.5.2 Reference values*

It has been proposed a critical load value of 5 Kg N ha<sup>−</sup><sup>1</sup> year <sup>−</sup><sup>1</sup> for alpine ecosystems, which are more sensitive than ecosystems in lowlands [17], whereas in Nuevo México and California, a critical load value of 3–8 and 4–7 Kg N ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> , respectively, has been proposed [18]. Regarding to Mexico, reference values

**59**

**Figure 14.**

*rainy season.*

*Deposition map of SO4*

*<sup>2</sup><sup>−</sup> (kg ha<sup>−</sup><sup>1</sup>*

 *year<sup>−</sup><sup>1</sup>*

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

hand, for S, it has been proposed a critical load value of 3 Kg S ha<sup>−</sup><sup>1</sup>

<sup>2</sup><sup>−</sup>) in metropolitan area of León were 5.82 N and 13.77 Kg S ha<sup>−</sup><sup>1</sup>

year<sup>−</sup><sup>1</sup>

Cerón et al. [22] in metropolitan area of Monterrey (4.88 N Kg ha<sup>−</sup><sup>1</sup>

In this study, mean deposition fluxes for N (as N-NH4

et al. [19] in Carmen Island, Campeche (2.15 N Kg ha<sup>−</sup><sup>1</sup>

[20] in Orizaba Valley, Veracruz (1.44 N Kg ha<sup>−</sup><sup>1</sup>

to compare N and S atmospheric deposition fluxes are not available. On the other

tive areas in Europe, whereas for natural forests, values between 2 and 5 Kg S ha<sup>−</sup><sup>1</sup>

respectively. In the case of N, exceeds the value reported for alpine ecosystems, but is near the reference values for Nuevo México and California. N deposition levels found in metropolitan area of León were twice as that reported by Cerón

five times as that reported by Cerón et al. [23] in Atasta-Xicalango, Campeche

With respect to S, deposition fluxes exceeded almost 4.5 times the critical load value proposed for sensitive areas in Europe, whereas for natural forests, reference value was exceeded almost three times those values reported by Cerón et al. [19]

Therefore, it can be inferred that, N and S atmospheric deposition fluxes constitute

year<sup>−</sup><sup>1</sup>

year<sup>−</sup><sup>1</sup>

year<sup>−</sup><sup>1</sup>

+

year<sup>−</sup><sup>1</sup>

); also exceeding those values reported by

year<sup>−</sup><sup>1</sup>

), and twice the value reported by Cerón et al. [23]

year<sup>−</sup><sup>1</sup>

*) in León city, (a) cold dry season, (b) warm dry season, and (c)* 

+ N-NO3

for sensi-

) and

<sup>−</sup>) and S (as

 year<sup>−</sup><sup>1</sup> ,

); by Cerón et al.

year<sup>−</sup><sup>1</sup>

); and by López [21] in

) and by López [21] in Mérida,

). However, values reported

year<sup>−</sup>1) and by Cerón et al.

) were not exceeded.

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

have been proposed [18].

Mérida, Yucatán (2.7 N Kg ha<sup>−</sup><sup>1</sup>

 year<sup>−</sup><sup>1</sup> ).

Yucatán (4.07 S Kg ha<sup>−</sup><sup>1</sup>

in Carmen Island, Campeche (4.7 S Kg ha<sup>−</sup><sup>1</sup>

in Atasta-Xicalango, Campeche (8.57 S Kg ha<sup>−</sup><sup>1</sup>

year<sup>−</sup><sup>1</sup>

by Cerón et al. [20] in Orizaba Valley (55.16 S Kg ha<sup>−</sup><sup>1</sup>

[22] in metropolitan area of Monterrey (25.03 Kg ha<sup>−</sup><sup>1</sup>

a potential risk of acidification for ecosystems in the region.

year<sup>−</sup><sup>1</sup>

SO4

(1.15 Kg ha<sup>−</sup><sup>1</sup>

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

to compare N and S atmospheric deposition fluxes are not available. On the other hand, for S, it has been proposed a critical load value of 3 Kg S ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> for sensitive areas in Europe, whereas for natural forests, values between 2 and 5 Kg S ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> have been proposed [18].

In this study, mean deposition fluxes for N (as N-NH4 + + N-NO3 <sup>−</sup>) and S (as SO4 <sup>2</sup><sup>−</sup>) in metropolitan area of León were 5.82 N and 13.77 Kg S ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> , respectively. In the case of N, exceeds the value reported for alpine ecosystems, but is near the reference values for Nuevo México and California. N deposition levels found in metropolitan area of León were twice as that reported by Cerón et al. [19] in Carmen Island, Campeche (2.15 N Kg ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> ); by Cerón et al. [20] in Orizaba Valley, Veracruz (1.44 N Kg ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> ); and by López [21] in Mérida, Yucatán (2.7 N Kg ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> ); also exceeding those values reported by Cerón et al. [22] in metropolitan area of Monterrey (4.88 N Kg ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> ) and five times as that reported by Cerón et al. [23] in Atasta-Xicalango, Campeche (1.15 Kg ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> ).

With respect to S, deposition fluxes exceeded almost 4.5 times the critical load value proposed for sensitive areas in Europe, whereas for natural forests, reference value was exceeded almost three times those values reported by Cerón et al. [19] in Carmen Island, Campeche (4.7 S Kg ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> ) and by López [21] in Mérida, Yucatán (4.07 S Kg ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> ), and twice the value reported by Cerón et al. [23] in Atasta-Xicalango, Campeche (8.57 S Kg ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> ). However, values reported by Cerón et al. [20] in Orizaba Valley (55.16 S Kg ha<sup>−</sup><sup>1</sup> year<sup>−</sup>1) and by Cerón et al. [22] in metropolitan area of Monterrey (25.03 Kg ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> ) were not exceeded. Therefore, it can be inferred that, N and S atmospheric deposition fluxes constitute a potential risk of acidification for ecosystems in the region.

#### **Figure 14.**

*Spatial Variability in Environmental Science - Patterns, Processes, and Analyses*

**58**

year<sup>−</sup><sup>1</sup>

**Figure 13.**

*rainy season.*

*3.5.1.3 SO4*

the city.

*2−*

In the case of SO4

*3.5.2 Reference values*

(sites I and IV), and at SW (Site X).

It has been proposed a critical load value of 5 Kg N ha<sup>−</sup><sup>1</sup>

*Deposition map of NO3*

*<sup>−</sup> (kg ha<sup>−</sup><sup>1</sup>*

 *year<sup>−</sup><sup>1</sup>*

Another important factor is the lack of rain, contributing to a minor dilution or washing of the atmosphere. Levels found were homogeneously distributed as a result of local sources, and it agrees with residence time in the atmosphere of NO2.

metropolitan area of León (**Figure 14a**–**c**). In all seasons, the highest levels were found at NE (Site VI: Zoológico) and at SE (Sites I and IV corresponding to CICEG Bomberos and Instituto Tecnológico de León), all of them, with an industrial land use. On the other hand, the lowest sulfate deposition fluxes were found at North of

The highest value for sulfate atmospheric deposition flux was found during the rainy season; however, this difference was not statistically significant in comparison with the other two seasons. Some hot spots were identified: at NE (Site VI), at SE

ecosystems, which are more sensitive than ecosystems in lowlands [17], whereas in Nuevo México and California, a critical load value of 3–8 and 4–7 Kg N ha<sup>−</sup><sup>1</sup>

, respectively, has been proposed [18]. Regarding to Mexico, reference values

*) in León City, (a) cold dry season, (b) warm dry season, and (c)* 

year <sup>−</sup><sup>1</sup>

for alpine

<sup>2</sup><sup>−</sup>, its deposition fluxes were uniformly distributed in the

*Deposition map of SO4 <sup>2</sup><sup>−</sup> (kg ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> ) in León city, (a) cold dry season, (b) warm dry season, and (c) rainy season.*
