**5. Conclusions**

Results found in this research work suggest that NO3 atmospheric deposition in the study site has a local origin, and is mainly distributed along the urban zone, being its deposition higher during the dry season. On the other hand, NH4 <sup>+</sup> highest deposition fluxes were distributed at the east edge of the island just during the dry season, suggesting a local origin, probably from light- duty vehicles emissions and agricultural activities developed in nearby rural areas. Regarding SO4 2- , its deposition has its origin in both, local and regional sources, being this contribution higher when the Island was subjected to the influence of "Norths". It was quite evident that in addition to local industrial sources in Carmen Island, background levels were enhanced by the long- range transport of SO2 emissions from offshore platforms in the Gulf of Campeche during the "Norths" season when prevailing winds came from NE.

Exceedance of critical loads represents a potential risk indicator of acidification as well as its impacts on ecosystems; therefore, in order to assess the vulnerability of the mangrove ecosystems in Carmen Island, it is necessary to establish the critical loads and to estimate their exceedances. Only then, it will be possible to develop emissions control programs and propose prevention policies and local regulations focused to protect these ecosystems.

Interpolation of field measurements is one of the most convincing methods to explore N and S budget, even though the accuracy is limited by the characteristics of measured data and uncertainties associated with the interpolation technique.

This research work constitutes the first step to quantify the current status of N and S deposition in the study site. A long- range monitoring network over Mexico will be established in a shorttime for estimating nitrogen and sulfur deposition fluxes and their distribution along the country. A series of monitoring stations should be set down in order to keep the uniformity in the measured data, allowing comparability and considering not only urban and industri‐ alized sites but also rural and remote sites. Maps based on measurements are also required in Mexico to validate and calibrate three- dimensional transport models.
