While the micrometeorological and energy impacts of certain surface modification strategies can be demonstrated and evaluated in the field, the potential large-scale effects from such surface modifications are relatively unknown and can currently be assessed only via numerical modeling. Increased built-up surface albedo and vegetative cover, for example, have been shown to reduce cooling electricity use in summer in the United States, but their regional environmental impacts are more difficult to ascertain, because of uncertainties in meteorological and photochemical models and input data. Thus more up-to-date modeling is necessary if more accurate estimates of such impacts are sought.

This study consists of two phases, the first of which is summarized in this report. This first phase involved modification, update, improvement, and application of state-of-science mesoscale meteorological and photochemical models (MM5 and CAMx) and related emission models in evaluating the potential impacts of these strategies in California during two episodes. The findings suggest both positive and negative impacts depending on location, time, and level of modifications. Peak ozone concentrations in southern California can increase during certain times of the episode; whereas, in central California the peaks decrease considerably. In terms of area-averaged indices, all regions experience reductions in ozone levels. In the future, multiepisodic and seasonal evaluations may be needed.

In the second phase of the study, a new generation of mesoscale (urbanized) meteorological models will be used in further evaluating these positive and negative air-quality impacts to determine the dominant and overall effects.