The Bay Area's cool summer weather may have restricted sunbathing and slowed tomato growth, but it has delivered one good thing — cleaner air.

The region is on pace to enjoy one of its least smoggy years on record. Not a single violation of the federal public health standard for smog has been recorded in the nine-county air basin, and six weeks remain in the five-month smog season.

The Bay Area had eight violation days in 2009, 12 in 2008, and one in 2007.

The region also is headed for another milestone. It's the first year without a single Spare the Air advisory in the warm season. The health alerts advise the public on smoggy days to avoid strenuous outdoor exercise and minimize driving or other polluting activities.

Clean air regulators credit the cool weather for providing a welcome shortage of the conditions that brew smog: consecutive days of hot stagnant air with temperatures in the 90s or hotter.

Hot spells are ideal for converting car and factory exhaust into ozone, the lung-stinging ingredient in smog that causes asthma

attacks, watery eyes and can retard children's lung development.

"It has been a wonderful year for air quality. We've had unusual conditions," said Kristine Roselius, a spokeswoman for the Bay Area Air Quality Management District. "But we can't rest on our laurels and relax our efforts to reduce air pollution. You never know when it will get really hot."

The smog season began May 2 and ends Sept. 30 in the air district, which covers all of seven counties, and the southern parts of Solano and Sonoma counties.

Elsewhere in the nation, many urban areas outside California have had hot temperatures and high smog levels.

Bay Area clean air regulators said the hottest day in region this year was June 27, when the mercury reached 101 degrees in Livermore and 102 degrees in Concord. However, winds that day disrupted smog formation, Roselius said.

"Weather is a huge factor in the ozone concentrations we get," she said. "It takes time for the smog to build up."

The air district is forecasting good air quality at least through Sunday.

Although the normally breezy Bay Area is less smoggy than most urban areas in the country, the federal government still considers the region marginally out of attainment with the federal smog standard — a ruling based on smog readings over three years.

On Sept. 15, the air district's 22-member pollution board is scheduled to consider adopting a blueprint for more than 50 new or

expanded measures to reduce smog-forming pollutants from oil refineries, digital printers, dairies, cement kilns and other sources.

Contact Denis Cuff at 925-943-8267. Read the Capricious Commuter at Follow him at