researchers are now proposing is not only to reduce the precursor pollutants but also to cool the oven.

Heat, of course, is dangerous in its own right, as recent events have demonstrated. In the heat wave of 1980, more than 1,000 Americans died. In 1995, a heat wave killed 500 people in the city of Chicago alone. In the European heat wave of 2003, some 2,000 people died in Italy and at least 10,000 (perhaps as many as 15,000) died in France. In these and numerous other places, Akbari noted, those who suffered heat-related deaths were usually older people living in upper-floor apartments. He noted that something simple such as a cooler roof for these buildings would probably have saved many lives.

Humanity’s basic way to stay cooler—use light-colored surfaces and plant trees—was actually known, pre-air conditioning, for thousands of years, and it can certainly be reinstituted with the aid of modern, technology-derived materials to improve the heat island problems in a big city such as Houston, said Akbari. This can happen at a steady, although not rapid, pace. Within the next 10 to 15 years, when the time comes to change roofs on houses, he suggested that people should consider a cooler roof. This could save approximately $100 per Houston household per year, he estimated, and the consequently reduced air-conditioning would require less power from the power plant, leading to reduced emissions of CO₂, SO₂, NO_X, VOCs (volatile organic compounds), and ultimately, lower ozone and smog levels.

Another aspect of heat island mitigation is the treatment of paved surfaces, particularly for a place such as Houston whose land area is covered so extensively with concrete pavement. When roadway sections or sidewalks have to be replaced, new high-reflectance types of pavements can be used to produce cooler surfaces and, as a result, lower air temperatures. As shown in a demonstration of three different asphalt types (Figure 5.7), a 35°F difference is readily achievable.

Meanwhile, planting trees throughout a metropolitan area can also reduce air temperature and smog formation, Akbari pointed out. In Los Angeles, for example, planting 11 million trees—about 3 trees per house—could lower the temperature of some sections of the city by as much as 5–6°F. These plantings (in combination with cool roofs and cool pavements) could decrease the concentration of ozone by about 30 to 40 parts per billion—an effect comparable to that of making half of the cars in the Los Angeles basin electric.

Akbari and his colleagues have computed that if all these heat island reduction steps were taken in Los Angeles, the smog level would be reduced by 12 percent, some $350 million dollars per year could be saved in health costs, and energy savings could amount to $170 million (Rosenfeld et al., 1998). Similarly, annual reductions in Houston’s energy consumption for air conditioning could be about $80 million. These model-derived estimates are not numbers you can take to the bank, he acknowledged, but they do indicate huge opportunities for improving air quality that should be explored.