Page 31

the limited available remote sensing data in combination with measurements from the range of available in situ platforms.

These integrated measurement programs form a core component of the overall research framework needed for the study of global air quality change. Models comprise another core component of this research framework, since they are needed to fulfill at least three important roles: (i) helping to determine the optimal locations for long-term observational sites and short-term process studies, in order to maximize the usefulness of the data collected; (ii) assimilating the observations acquired from different platforms and helping to place isolated measurements in a larger context; and (iii) providing a prognostic capability for predicting future air quality trends, for estimating transboundary pollution fluxes, and for assessing the impacts of coupling between climate and air quality changes. Fulfilling all of these roles will require careful integration of various types of modeling tools. For instance, process models can be embedded in regional models to provide detailed representation of certain critical processes; and likewise, regional models can be embedded in global models to expand the spatial and temporal resolution in areas of particular interest.

Coordinating measurements among various remote sensing and in situ platforms, and integrating these measurements with detailed modeling studies presents an immensely complex research challenge. This approach is being developed in focused process studies such as the Southern Hemisphere ADditional OZonesondes project (SHADOZ, which coordinates a network of balloon-borne ozonesondes with TOMS remote sensing measurements), and the INDOEX, TRACE-P, and ACE-Asia field campaigns (studies aimed at understanding the impacts of pollution outflow from the Asian continent). This level of integration, however, does not yet exist in an ongoing, operational sense or extend over the range of scales needed to accomplish the research objectives highlighted in this report.