It's been a banner year for breezes and clean air in the Valley
By Elizabeth Lester
The Sacramento Bee
The Sacramento Bee
Published: Thursday, Aug. 11, 2011 - 12:00 am | Page 1B
© Copyright The Sacramento Bee. All rights reserved.
Sacramento is enjoying cleaner air, which officials attribute to this year's cool spring and summer, the lack of major forest fires and continued success in state vehicle emission-control programs.
The summer's air quality is good news for those taking advantage of outdoor recreation – gardening, jogging, golfing, hiking and finding pleasure in the region's scenic views.
According to the Sacramento Metropolitan Air Quality Management District, air quality has generally held in the "good" range, on par with 2009-10.
This year, the air quality district has issued one "unhealthy" day warning for people to exercise moderately because of bad air – compared with six last summer, although most of those came later in the season. They have issued 15 warnings for pollution-sensitive groups including children and those with respiratory ailments. Both in 2008 and 2009, the agency issued nearly three dozen of those warnings.
Cool ocean breezes from the southwest have prevailed in the Sacramento Valley this summer, reducing fire risk and keeping temperatures out of the 100s.
"So far it's been a moderate year. We haven't seen any large fires," said Daniel Berlant of the California Department of Forestry and Fire Protection, or Cal Fire.
Wildfires, often a staple of California summers, can put heavy concentrations of particulates into the air. For example, the intense wildfire season of 2008 cast a heavy haze, contributing to four "very unhealthy" air days in the Sacramento region. That's the only time in the past decade that regulators told people to remain inside.
This year has been cooler and wetter than usual. The National Weather Service says the low pressure keeping Northern California relatively cool circulates the air, diluting the ozone and particulate matter that often stagnates in the Valley in summer.
Ozone, an invisible component of smog and the major pollutant of summer in Sacramento, forms from the action of sunlight on byproducts of fossil fuel combustion, and volatile organic compounds released in solvent fumes – produced by vehicles, factories and household paints. Heat accelerates the reaction.
Michael Kleeman, professor of civil and environmental engineering at the University of California, Davis, attributes the cleaner air to the work of state regulators.
"The emission-control program has put us on a long-term downward trend," he said. "There's no question that there's a long-term, decade-to-decade improvement.
"It used to be that temperature had a big impact, back in the 1980s. Less so in the 1990s, even less so now, because the atmosphere is getting less reactive, and that has to do with emissions," he said.
At ground level, ozone triggers asthma, bronchitis and heart attacks. Sacramento ranks fifth in the American Lung Association's 2011 list of the nation's worst ozone cities. Eight of the top 10 are in California.
Despite strict state emissions standards and improved results, California cities perennially hold top ranks for both photochemical smog and small airborne-particle pollution.
"A lot of it has to do with our topography, because we are surrounded by mountains here in the Valley," said Eric Kurth of the National Weather Service's Sacramento office. High atmospheric pressure can bring both heat and stagnant air.
"The warmer air above acts as a lid" over the bowl of the Valley, Kurth said, concentrating dirty air.
Automobile tailpipes are the major source of that bad air, spewing particles as well as ozone precursors.
Less traffic – whether the result of the recession, high gas prices or road closures – translates into cleaner air.
This was illustrated dramatically by a 10-mile closure of Interstate 405 in Los Angeles in July. A notable drop in pollution accompanied the 36-hour closure.
"We have seen a clear reduction, across the freeway, of small particles, less than 100 nanometers in size," said Yifang Zhu, professor of environmental health sciences at UCLA's School of Public Health.
Zhu said low traffic on Los Angeles-area streets and other highways during the I-405 closure reduced the amount of fine particles in the air.
The summer's air quality is good news for those taking advantage of outdoor recreation – gardening, jogging, golfing, hiking and finding pleasure in the region's scenic views.
According to the Sacramento Metropolitan Air Quality Management District, air quality has generally held in the "good" range, on par with 2009-10.
This year, the air quality district has issued one "unhealthy" day warning for people to exercise moderately because of bad air – compared with six last summer, although most of those came later in the season. They have issued 15 warnings for pollution-sensitive groups including children and those with respiratory ailments. Both in 2008 and 2009, the agency issued nearly three dozen of those warnings.
Cool ocean breezes from the southwest have prevailed in the Sacramento Valley this summer, reducing fire risk and keeping temperatures out of the 100s.
"So far it's been a moderate year. We haven't seen any large fires," said Daniel Berlant of the California Department of Forestry and Fire Protection, or Cal Fire.
Wildfires, often a staple of California summers, can put heavy concentrations of particulates into the air. For example, the intense wildfire season of 2008 cast a heavy haze, contributing to four "very unhealthy" air days in the Sacramento region. That's the only time in the past decade that regulators told people to remain inside.
This year has been cooler and wetter than usual. The National Weather Service says the low pressure keeping Northern California relatively cool circulates the air, diluting the ozone and particulate matter that often stagnates in the Valley in summer.
Ozone, an invisible component of smog and the major pollutant of summer in Sacramento, forms from the action of sunlight on byproducts of fossil fuel combustion, and volatile organic compounds released in solvent fumes – produced by vehicles, factories and household paints. Heat accelerates the reaction.
Michael Kleeman, professor of civil and environmental engineering at the University of California, Davis, attributes the cleaner air to the work of state regulators.
"The emission-control program has put us on a long-term downward trend," he said. "There's no question that there's a long-term, decade-to-decade improvement.
"It used to be that temperature had a big impact, back in the 1980s. Less so in the 1990s, even less so now, because the atmosphere is getting less reactive, and that has to do with emissions," he said.
At ground level, ozone triggers asthma, bronchitis and heart attacks. Sacramento ranks fifth in the American Lung Association's 2011 list of the nation's worst ozone cities. Eight of the top 10 are in California.
Despite strict state emissions standards and improved results, California cities perennially hold top ranks for both photochemical smog and small airborne-particle pollution.
"A lot of it has to do with our topography, because we are surrounded by mountains here in the Valley," said Eric Kurth of the National Weather Service's Sacramento office. High atmospheric pressure can bring both heat and stagnant air.
"The warmer air above acts as a lid" over the bowl of the Valley, Kurth said, concentrating dirty air.
Automobile tailpipes are the major source of that bad air, spewing particles as well as ozone precursors.
Less traffic – whether the result of the recession, high gas prices or road closures – translates into cleaner air.
This was illustrated dramatically by a 10-mile closure of Interstate 405 in Los Angeles in July. A notable drop in pollution accompanied the 36-hour closure.
"We have seen a clear reduction, across the freeway, of small particles, less than 100 nanometers in size," said Yifang Zhu, professor of environmental health sciences at UCLA's School of Public Health.
Zhu said low traffic on Los Angeles-area streets and other highways during the I-405 closure reduced the amount of fine particles in the air.
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