GIS Based Chemical Fate Modeling: Principles and Applications

Chapter 18

GIS Based Models in Practice: The Multimedia Assessment of Pollutant Pathways in the Environment (MAPPE) Model

Alberto Pistocchi and Dimitar T. Marinov

18.1 Introduction

The description of chemicals in space may be highly uncertain: we often have vague ideas about the distribution of emissions, and we may not know very well which are the processes actually driving a chemical's fate. For instance, we may lack knowledge on the partitioning of a substance between gas and aerosol phases in the real atmosphere, or on the exchange of gas between air and vegetation. This lack of knowledge requires flexibility in the adjustment of models by changing equations as well as data used in model parameterization: in the different cases, we might need to switch from an adsorption to an absorption model, and/or we might need to compute partitioning as a function not just of aerosol concentration but also of aerosol chemical composition; we might need to add a vegetation component to air–ground exchange models; and so on. In order to be flexible, models should be kept to a minimum of computational complexity, by adding process descriptions and assumptions only when strictly necessary, and by using the minimum possible number of parameters. When two possible representations describe equally well a certain phenomenon, the simplest of the two should be trusted: this is often referred to as the principle of Occam's razor.

At the same time, we are highly attracted by spatially distributed ...