In sweltering September 2011, Fresno could have used more trees. Temperatures climbed, winds died and lung-searing ozone spiked the season's highest readings on three days.
Worse yet, all three peaks broke the one-hour federal ozone standard between 3 p.m. and 4 p.m. on weekdays when children were outside after school.
An extensive canopy of trees over streets, parking lots and driveways might have kept ozone-cooking heat down just enough to avert those dangerous peaks, say researchers. Plus, trees actually take pollutants out of the air.
It's time to talk seriously about using trees and other city-cooling ideas, such as reflective or cool roofs, to end the San Joaquin Valley's decades-long quest to achieve the federal one-hour ozone standard, say air-quality leaders.
These days, only a few parts per billion of ozone on a few days a year separate the Valley from the achievement.
"Ten years ago, it might not have made as much sense to everyone to pursue these strategies," said Seyed Sadredin, executive director of the San Joaquin Valley Air Pollution Control District. "But we've passed many rules, made many advances, and we're so close to compliance on the one-hour standard now."
The one-hour threshold is 125 parts per billion, which the Valley had no prayer of achieving in the past. This 25,000-square-mile bowl allows dirty air to build up for days -- it's an incubator for one of the worst ozone problems in the nation.
With cleaner-running vehicles and ever-tightening regulations on everything from dairies to urban sprawl, ozone peaks have dropped from the 150s to the 130s over the last decade.
University of California at Davis research suggests that if Fresno aggressively pushed city cooling efforts, temperatures could drop as much as 4 degrees. Up to 7 parts per billion could be trimmed off ozone peaks.
The stakes are high in this fight. When the standard is achieved, it will eliminate a $29 million annual penalty, most of which is paid by Valley motorists in their vehicle registration fees.
But money isn't the best reason to fight ozone, health researchers say. Ozone is a corrosive gas that damages lungs, eyes and skin. It is linked to heart and lung ailments as well as early mortality.
The Valley's climate creates ideal conditions for ozone, which forms best in heat, sunlight and stagnant air. Scientists say turning down the heat just a little is a logical approach to shave off the peaks on bad days.
It's a fight against the phenomenon called the urban heat island. Cities become heat islands as they trap energy from the sun in asphalt, rooftops and buildings, particularly in places as sunny and warm as Fresno or other Valley cities.
Drive from downtown Fresno into the surrounding farmland on most any summer day. Feel the temperature drop several degrees. Streets and parking lots of this 112-square-mile city hold the heat long after dark.
"Think of it as a heat dome over the city," said meteorologist Paul Iniguez of the National Weather Service in Hanford. "It's not a perfect dome, because there are green spaces in cities, such as parks. But it has the characteristics of a dome."
As the climate warms over the next century, scientists expect heat islands to become more intense and more of a factor in ozone problems. The cost of cooling homes and businesses will no doubt rise, scientists say.
Lawrence Berkeley National Laboratory has a heat island research team that has worked on several cooling approaches, including vegetation, reflective materials for roofs and pavement.
In roofing, for instance, materials might include titanium dioxide to reflect infrared light. Though human eyes don't perceive such light, it contains about half the energy in the sunlight that hits Earth.
Experiments have shown dramatic differences with the reflective material. In a side-by-side comparison of a reflective parking lot and a more standard blacktop parking lot, scientists recorded a 30-degree difference on a June day in Berkeley.
"The darker materials absorb more heat," said Benjamin Mandel, graduate research assistant at Berkeley Lab.
In Fresno, Berkeley researchers studied the difference between a light-colored concrete-tile roof and a dark asphalt-shingle roof during the five hottest months last year. The light-colored, more reflective roof saved a total of $350 over the five months.
Mandel said that if all Fresno homes had the reflective roof, the savings would be about $60 million each year.
But such a radical change in a city of half a million might be a lot to expect, he said. A more realistic scenario would be modest improvements over a smaller percentage of the city amounting to a few million dollars of savings -- still a worthy investment, he said.
California is pushing toward more energy- and water-efficient construction, but the new state building code, called CALGreen, has only voluntary measures for cool or reflective roofs for new homes or roof replacements on older homes.
The California Energy Code requires such roofs for new commercial buildings.
The city of Fresno does not mandate cool roofs, but officials are reviewing the development code, which includes a provision about trees in the landscaping of buildings and homes.
Since 1993, Fresno has required a tree for every two parking spaces in lots around the city, said Arnoldo Rodriguez, interim city planning manager.
"We're looking to reduce the number of parking spaces and the size of parking lots in the future," he said. "We're also exploring the idea of reducing the width of new streets with hopes of getting less paved area in the city."
Fresno needs to turn greener with trees, says Lee Ayers, executive director of Tree Fresno. His organization is pushing to make trees a priority in the city.
"I don't think there's any doubt that we all would benefit from more trees," he said. "It's not just a matter of planting new trees. We need to replace trees that have died and retain mature trees in this city."