  The holistic approach to sustainable urban planning implies using different
models in an integrated way that is capable of simulating the urban system. As
the interconnection of such models is not a trivial task, one of the key
elements that may be applied is the description of the urban geometric
properties in an "interoperable" way. Focusing on air quality as one of the
most pronounced urban problems, the geometric aspects of a city may be
described by objects such as those defined in CityGML, so that an appropriate
air quality model can be applied for estimating the quality of the urban air on
the basis of atmospheric flow and chemistry equations.
  In this paper we first present theoretical background and motivations for the
interconnection of 3D city models and other models related to sustainable
development and urban planning. Then we present a practical experiment based on
the interconnection of CityGML with an air quality model. Our approach is based
on the creation of an ontology of air quality models and on the extension of an
ontology of urban planning process (OUPP) that acts as an ontology mediator.
