**3. Results and discussion**

#### **3.1 Sulfate**

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

time to let the pass of hydrologic flux through the collector.

analyzed by turbidimetric and colorimetric methods, respectively.

to identify prevailing wind direction in the study area.

processes contributing to N and S deposition during the study period.

high spatial resolution [10].

**2.3 Chemical analysis**

phenol method [13]. SO4

**2.5 Statistical analysis**

and sampling seasons) [16].

**2.4 Meteorological analysis**

NH4 +

NO3

beds have been used to measure atmospheric deposition in forest ecosystems with a

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

This type of passive collectors consists in a funnel connected to a column which

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

Atmospheric deposition samples were sent and analyzed in Environmental Protection Laboratory of Chemistry Faculty of Autonomous University of Carmen.

<sup>−</sup> was analyzed by colorimetric method using the brucine method [15].

was determined by molecular absorption spectrometry by using blue indo-

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),

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

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

<sup>2</sup><sup>−</sup> was determined by turbidimetric method [14], whereas

**48**

#### *3.1.1 Seasonal variability*

To assess the seasonal variability, deposition fluxes were analyzed for three climatic periods: cold dry, warm dry, and rainy. During the cold dry season, a mean flux of 10.89 Kg Ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> , with a maximum of 17.14 Kg Ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> in site VI, which corresponds to Zoológico, located at NE, whereas the minimum value of 6.58 Kg Ha<sup>−</sup><sup>1</sup> year<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 13.98 Kg Ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> , with a maximum value of 25.82 Kg Ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> in site IV (Instituto Tecnológico de León), located at SE, whereas the minimum value (1.81 Kg Ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> ) was found in site III, which corresponds to monitoring station IMSS T-21, located at downtown of the city (**Figure 2**).

Finally, during rainy season, the mean value obtained was 15.52 Kg Ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> with a maximum of 18.43 Kg Ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> in sites III and VI, located at NE and at downtown of the city, whereas the minimum value (11.77 Kg Ha<sup>−</sup><sup>1</sup> year<sup>−</sup><sup>1</sup> ) was obtained for site I (monitoring station CICEG-Bomberos) (**Figure 2**).

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

**Figure 2.** *Sulfate atmospheric deposition fluxes by season.*

season, suggesting that the lack of dilution during this season could result in higher values in the region. Applying the Friedman tests, significant differences in sulfate atmospheric deposition fluxes were found between seasons.
