• Trade-offs will be inevitable, because various choices among control strategies will have differential impacts on different receptor sites throughout the region. Also, the ratio of ROG to NO_x reductions will affect pollutants other than ozone, in differing degrees, and for different receptor sites.

• NO_x reductions may actually increase ozone in regions of the airshed with high emissions. But as receptor sites further downwind are considered, the impact of reducing NO_x throughout the basin tends to reduce ozone. The crossover point seems to be 3 to 4 hours of downwind travel time. Associated ROG controls are most effective in those areas where high NO_x levels are maintained and radical concentrations suppressed through midday.

• PAN concentrations seem to follow the same general pattern as ozone. Thus a combination of ROG and NO_x controls—such as have been in effect for about a decade in California—is advisable.

• Inorganic nitrate levels follow base-line levels of NO_x and OH. Thus reducing NO_x reduces inorganic nitrate pollution.

• The foregoing points suggest that a strategy solely reliant on ROG emission reductions may be inadequate, as the EPA now recognizes, and under certain conditions could never succeed in attaining the required ozone standard, without correlative substantial reductions in NO_x Moreover, only by a strategy that combines both ROG and NO_x controls can simultaneous reductions be expected in ozone, PAN, and inorganic nitrates.

• Any conclusions drawn about the effects of pollution based only on peak receptor sites will distort the picture that emerges from more revealing models. These suggest that only by considering numerous receptor sites throughout the region and over time, and evaluating at least PAN and inorganic nitrates in addition to ozone, can a strategy be developed that embraces the known major trade-offs.

Thus it can be seen from the work authored by Milford, Russell, and McRae that atmospheric scientists very often assume a strongly proactive stance about their conclusions. As McRae affirmed at the outset of his presentation at the Frontiers symposium, convincing people about the right thing to do in response to the problems he is analyzing is part of his charge. He and Winer and Lloyd each in his own way revealed a consciousness informed by science, but fueled with a passion for implemented solutions. And as McRae's career and his model attest, modern supercomputing provides a very useful