**2. Study area**

trees growth and losses of vitality in forest [5- 6]. In addition, N and S deposition can cause deterioration to historical monuments and diverse materials and can cause damages to human

In Mexico, N and S deposition monitoring, its spatial and temporal distribution, and its effects on historical and cultural heritage and sensitive vegetation species have not been sufficiently studied. Comparing current conditions with ten years ago, S emissions' scenarios have decreased as a result of reformulation of fuels and the application of rigorous regulations focused to reduce them; however, it has been reported that the relative importance of N

The coast of the Gulf of Mexico is characterized to be a complex region where the co- existence of oil refineries, offshore platforms and other facilities for oil and gas exploration and produc‐ tion, historical monuments, archaeological zones, and many valuable aquatic and terrestrial ecosystems (this region has the widest mangrove forests cover in the country) occurs. Cam‐ peche State is located at the southeast of the Gulf of Mexico and it constitutes the most important oil and gas producer in the country. A total annual emission of 205.64 Gg of NOx and 336.79 Gg of SO2 has been reported for this state, mainly produced by urban and industrial sources. Consequently, it is expected that N and S deposition, in ecosystems located downwind from these sources, would be high. This region has important natural reserves, national parks, protected natural areas, historical monuments and archaeological sites that constitute the main support of the eco- tourism industry which generates significant economical resources for Campeche State. Only in Campeche State, mangrove cover accounts for 29.98% of the total country cover, which is, approximately 196,552 ha. Therefore, the potential ecological effects derived from atmospheric deposition on these sites constitute a key concern for this region. Critical loads estimation method allows to quantify the grade of damage derived from atmospheric pollutants deposition on ecosystems. A critical load can be defined as the input of one pollutant at levels below of which harmful ecological effects do not occur in the long term. To establish these critical load values and estimate their exceedances in a given site, atmospheric deposition measurements in field are required. N and S levels, their spatial and temporal distribution and their deposition fluxes are used in order to determine the actual inputs of these pollutants to ecosystems. This information is commonly represented in deposition maps, most of them are based on three- dimensional chemical transport model results which need to be validated by comparison with field measurements [8- 10]. Such studies represent an opportunity for policy- makers to identify the potential impacts associated with different emission sources and their spatial and geographical distribution. Sensitivity mapping

and the critical load approach are methods that may allow analysis of these risks.

can be high as a result of the prevailing meteorological conditions.

Particularly, in Mexico, measurement- based maps are required to assess the current deposi‐ tion fluxes and the vulnerability of the ecosystems. Considering that studies about critical loads and their exceedances are scarce in tropical humid forests, this research work had the following aims: 1) To establish a solid base line about throughfall deposition of N and S in mangrove ecosystems, and 2) To assess the temporal and geographical distribution of N and S deposition along Carmen Island in order to identify critical zones and seasons in which N and S deposition

health.

148 Current Air Quality Issues

deposition has increased [7].

This study was carried out in Carmen Island, Campeche, Mexico. This site constitutes a complex area due to its closeness to the most important offshore zone for gas and oil explora‐ tion and production. In addition, the urban area is located within the buffer zone and in the surroundings of the Natural Protected Area of "Terminos Lagoon". Climate in this site is subhumid warm with rains occurring along the summer. Annual mean precipitation is 1300 mm and annual average temperature is 27 °C. Prevailing winds blew from NE from March to October (when the island is under the influence of cold fronts called "Norths"); and from SE during the rest of the year (from April to September) when this site is influenced by tropical maritime air as a result of the trade winds. In Figure 1. is presented a typical wind rose and backward trajectory for Carmen Island during the study period. Additionally, Carmen Island is all time under the influence of sea and land breezes as a consequence of differential heating. In this research, a multiple transect sampling schema was designed (13 sampling points were considered along the island) in order to assess N and S deposition temporal and spatial distribution along Carmen Island. Specific sampling points are presented in Figure 2.

**Figure 1.** Typical wind rose and backward trajectory for Carmen Island during the study period.

**Figure 2.** Sampling sites location along Carmen Island, Campeche, Mexico.
