GreehnouseGases program of the International Institute of Applied Systems (IIASA), whose reports on the methodology of GAINS greatly allowed me to extend the modules of AERIS under my own perspective. I also acknowledge the United States Environmental Protection Agency that supports and makes available the CMAQ modeling system through the Community Modeling and Analysis System (CMAS); the Spanish and Portuguese Ministries of the Environment and EMEP for making available the emission datasets and monitoring data used throughout this work; Dr. Maximilian Posch and Dr. Jean Paul Hettelingh of the Coordination Centre for Effects for providing the VSD model for estimating critical loads on soils; Dr. Panos Panagos for making available the SPADE and MEUSIS databases on European soils; Dr. v Acknowledgements Chad Monfreda of the University of Minessota for providing the shapefiles with crop covers and yields; Dr. John Douros of the Aristotle University of Thessaloniki for his advice; Dr. Niko Karvosenoja of the Finnish Environment Institute and Dr. Rob Maas of RIVM for their fruitful contributions to the thesis; and Dr. Marialuisa Volta of the University of Brescia for making the documentation of the Opera and APPRAISAL projects publicly available. I am especially grateful with CONACyT (Mexico), which partially funded my doctoral dissertation.On a more personal perspective, I would like to express my gratitude to my friends Rubén Vásquez and Margarita Hernández for being the persons who initiated me into research and who encouraged me to follow postgraduate studies. Naturally the help and support that my family provided was essential for me to carry on with my career. I would like to thank my parents, Michel Gérard and Patricia for their unconditional support, love and empathy and for understanding my success as their own. Finally, I would like to thank Stephanie for her love, acceptance, support and sense of humor, but above all, for being there.