**2.2 Sampling**

Since passive sampling is defined as hydrologic flux to soil of ions and other compounds in solution, passive sampling provides a useful estimation of atmospheric inputs to a given site, because of it includes both, wet and dry deposition. Considering the high cost and the difficulty of measuring dry deposition fluxes, passive collectors constitute a useful alternative to measure annual atmospheric inputs at ground level [4, 9]. Additionally, automatic collectors are very expensive, for this reason, passive collectors constitute a good sampling choice in a given area, since they allow to increase the number of sampling sites at a low cost and take samples simultaneously in different locations in a specific region.

Therefore, it is possible to obtain complex spatial patterns of N and S atmospheric deposition in a given area by using monitoring equipment of low cost, easy to operate, and that does not require frequent field visits. Collectors based on IER

**Figure 1.** *Study area location.*

beds have been used to measure atmospheric deposition in forest ecosystems with a high spatial resolution [10].

This type of passive collectors consists in a funnel connected to a column which contains 30 g of ionic exchange resin (IER) [11]. Glass wool is placed in both, bottom (as a support) and top (as a filter) sections. Samples are collected through the funnel, and hydrologic flux is channeled to resin mixed bed through the column where ions are retained. The funnel is connected to IER column by a PVC tube (1.27 cm × 35.6 cm), in addition, a double-wall shadow tube is placed around resin column to avoid that solar radiation damage the resin. Resin used for IER collectors was a mixed bed of polystyrene to exchange both, anions and cations (Amberlite IRN-150™). In the top of sampling devices, a fine mesh is placed to avoid the input of insects, leaves, and so on. The PVC column has a valve which must be open all time to let the pass of hydrologic flux through the collector.

The main advantage of this kind of collector is that can be used during long exposition periods (i.e., months), the equipment has a low cost, and let to display a great number of them to characterize deposition spatial patterns with a high resolution [12].

Sampling was carried out from January 1 to December 31 of 2018, with three sampling sub-periods considering three climatic seasons: cold dry, warm dry, and rains. At the end of each sampling sub-period, resin tubes were changed by tubes containing fresh resin. Later, retained ions (sulfate, nitrate, and ammonium) were extracted from resin tube by using an extraction solution (KCL 2N solution) and analyzed by turbidimetric and colorimetric methods, respectively.

### **2.3 Chemical analysis**

Atmospheric deposition samples were sent and analyzed in Environmental Protection Laboratory of Chemistry Faculty of Autonomous University of Carmen. NH4 + was determined by molecular absorption spectrometry by using blue indophenol method [13]. SO4 <sup>2</sup><sup>−</sup> was determined by turbidimetric method [14], whereas NO3 <sup>−</sup> was analyzed by colorimetric method using the brucine method [15].

#### **2.4 Meteorological analysis**

To identify possible natural and anthropogenic sources and to analyze transport processes which could influence on N and S levels in atmospheric deposition in the study area, a meteorological analysis was carried out at both, surface and altitude. For this, surface meteorological data were obtained from meteorological portable stations (Davies Vantage Pro II). Later, to carry out surface meteorological analysis, wind rose graphs were obtained by using WRPLOT View™ (Lakes Environmental), to identify prevailing wind direction in the study area.

For the altitude meteorological analysis, backward air-masses trajectories for 24 h were obtained from HYSPLIT model (Hybrid Single-Particle Lagrangian Integrated Trajectory) from NOAA (National Oceanic and Atmospheric Administration of United States) to identify the origin of air masses and to identify the main transport processes contributing to N and S deposition during the study period.

#### **2.5 Statistical analysis**

To obtain descriptive measurements, to analyze the morphology and symmetry of data, univariate, bivariate, and multivariate analysis was carried out by using XLSTAT 20016 program. Likewise, non-parametric tests (Friedman test) were applied to establish if, there were significant differences between treatments (sites and sampling seasons) [16].

**49**

**Figure 2.**

*Sulfate atmospheric deposition fluxes by season.*

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

To obtain deposition maps in the study area, a geo-statistical procedure was applied to interpolate field measurements (kriging interpolation) and to obtain a continuous spatial pattern for the variables (concentration iso-lines) to increase the

To assess the seasonal variability, deposition fluxes were analyzed for three climatic

year<sup>−</sup><sup>1</sup>

in site VI, which corre-

in site IV

year<sup>−</sup><sup>1</sup>

year<sup>−</sup><sup>1</sup>

in sites III and VI, located at NE and at

year<sup>−</sup><sup>1</sup>

year<sup>−</sup><sup>1</sup>

) was

periods: cold dry, warm dry, and rainy. During the cold dry season, a mean flux of

, with a maximum value of 25.82 Kg Ha<sup>−</sup><sup>1</sup>

(Instituto Tecnológico de León), located at SE, whereas the minimum value (1.81

Finally, during rainy season, the mean value obtained was 15.52 Kg Ha<sup>−</sup><sup>1</sup>

From **Figure 2**, it can be observed that mean deposition fluxes for sulfate were relatively higher during the rainy season and lower during cold dry season. With respect to extreme values, the highest values were observed during warm dry

year<sup>−</sup><sup>1</sup>

downtown of the city, whereas the minimum value (11.77 Kg Ha<sup>−</sup><sup>1</sup>

obtained for site I (monitoring station CICEG-Bomberos) (**Figure 2**).

) was found in site III, which corresponds to monitoring station IMSS

sponds to Zoológico, located at NE, whereas the minimum value of 6.58 Kg Ha<sup>−</sup><sup>1</sup>

, with a maximum of 17.14 Kg Ha<sup>−</sup><sup>1</sup>

was obtained for site VII that corresponds to Universidad de León (**Figure 2**). On the other hand, the mean value obtained during warm dry season was

**2.6 Kriging interpolation and mapping deposition fluxes**

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

number of points in the maps.

**3. Results and discussion**

year<sup>−</sup><sup>1</sup>

year<sup>−</sup><sup>1</sup>

with a maximum of 18.43 Kg Ha<sup>−</sup><sup>1</sup>

T-21, located at downtown of the city (**Figure 2**).

*3.1.1 Seasonal variability*

**3.1 Sulfate**

10.89 Kg Ha<sup>−</sup><sup>1</sup>

13.98 Kg Ha<sup>−</sup><sup>1</sup>

year<sup>−</sup><sup>1</sup>

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*
