The 16th-century Fountain of Moses, a testament to the power of Pope Sixtus V, sparkled after a restoration was finished in 1988 in Rome. But now the likeness of the biblical hero that adorns the fountain is turning black, the victim of a constant barrage of traffic exhaust and other pollutants. Tour buses that come to the city are believed to be a major contributor to the pollution. With few parking spaces available in a city filled with historical monuments, most buses have idled at the curb during each stop on their tour. Such idling produces as much exhaust as driving. Rome has now provided parking that accommodates a third of the tour buses, so damage to Rome's artistic monuments from the buses' exhaust will diminish significantly.
Which of the following, if true, most strongly supports the argument?