**2.1 Study area**

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

wet deposition. Gases and particulate matter are deposited in dry form, while completely soluble components are deposited by the rain action (wet deposition). Dry deposition of gases and particles occurs through complex processes such as sedimentation, impactation, and adsorption and can contribute in a significant way to local deposition of atmospheric components, being particularly important near urban and industrial areas, where particle concentration and dust can be relatively high [1]. On the other hand, wet deposition occurs as rain, fog or snow and plays an important role in the removal processes of soluble wastes in the atmosphere [2]. Some of components of atmospheric deposit (as nitrate and sulfate) are precursors of acidification, being able to harm the aquatic and terrestrial ecosystems not only in the surroundings of sources but also in nearby

Thus, it is necessary to measure the total atmospheric deposition of N and S, to estimate the inflows and outflows, their effects on the balance of biogeochemical cycles, and to assess the biologic and ecologic response to the current atmospheric pollution levels and their relationship with emission patterns. Since the effective design of public politics requires of surveillance and monitoring programs to understand and to quantify the current conditions, by comparison with historical data and reference values, measurement chemical composition, and physical characteristics are required. This will allow to propose environmental politics focused to protect not only public health but also ecosystems and diagnose the real effects of N and S deposition as a result of the current emission patterns [3]. Deposition maps are very useful tools to carry out this kind of assessments, since they allow to analyze the spatial distribution and temporal variability of N and S deposition in a given area; likewise, they allow to visualize those areas in which exceedances to threshold values of critical loads are occurring. In this way, the decision makers can implement control strategies of regionalized emissions to protect different receptors. Several exceedance ranges can be established and be related to sensitivity categories, from which, it is possible to diagnose in a preliminary way, the vulnerability of ecosystems to the inputs of N and S. However, the main problem during this process is to have enough and reliable data of N and S

Dry deposition fluxes for ecosystems are obtained from theoretical models, due in part to the lack of monitoring standardized methods. On the other hand, in the case of wet deposition, the estimation depends on the occurrence of rain events, resulting in the case of arid or semiarid regions in insufficient data to study the spatial and temporal variability at long-term. In addition, atmospheric sampling devices for atmospheric deposition comprise manual and automatic collectors. Although the first choice in more economical, it is hard to implement in field in the case of remote sites, while in the case of automatic collectors, these are expensive and must meet specific criteria for installation and operation. Fenn and Bytnerowicz [4] proposed a collector based on ionic exchange resin (IER) to quantify atmospheric deposition in forests. In this regard, comparison between conventional collectors and passive sampling devices of atmospheric deposition have been carried out [5, 6], concluding that passive collectors can be used to quantify total sulfur deposition and report a strong correlation between N Deposition and the presence of nitrate in soils. From combined use of mapping and measurement of N and S deposition fluxes, it is possible to study the spatial and temporal variability of deposition. Therefore, this study was aimed to estimate N and S atmospheric deposition fluxes using passive collectors to assess their spatial distribution and temporal variability in Central Region of México known

**46**

as "Bajío."

regions.

deposition fluxes.

Study area is located in Central México within an area known as "Bajío," in metropolitan area of León, in Guanajuato. León City is the most populated in Guanajuato state with a population of 1,578,626 inhabitants [7]. Climate is semi-dry semi-warm [8].

The main economic activities in this region are shoe manufacturing, tanned skin, cardboard production, and chemical industry; however, economical activities are not only based on these sectors, but also building, plastics, mining, manufacturing, textile, and automotive industries. There were selected a total of 10 sampling sites considering in first place the site accessibility and the land use; as well as safety of sampling devices, preferring public buildings to safely house the equipment. In **Figure 1**, study area and sampling site location are shown.
