Air pollution levels have declined considerably since air quality monitoring began in Sonoma County in the early '70s, largely because some of our strongest sources of emissions have come under conscious control via state and local regulation. Efforts are now turning to new and less tractable sources for further pollution reductions, including stationary sources of toxics and particulates, and home-based and recreational activities. Meanwhile, some pollutant readings appear to have stalled at their new low levels, indicating that the continued growth of our population, paired with our dependence on polluting technologies, particularly cars, could overtake clean air advances. Still more restraint is called for if we're to achieve federal and state clean air objectives in the coming years.
Sonoma County encompasses portions of two air basins, divided along the line of coastal and inland hills running west and north of Santa Rosa. Around Santa Rosa and to the south and east, Bay Area air circulates, and pollution levels in the southern county are closely related to those of nine other jurisdictions, including Napa, Solano, Contra Costa, Alameda, Santa Clara, San Mateo, San Francisco, and Marin counties. This air basin is monitored and managed by the Bay Area Air Quality Management District, which has two stations for common pollutants in Santa Rosa and Sonoma (a third in Petaluma closed in 1979). To the north, Sonoma County air quality regulation falls in with that of other coastal counties up to the stateline, including Mendocino, Humbolt, Trinity and Del Norte counties. North Sonoma County air quality is monitored and managed by the Northern Sonoma Air Quality Management District, with monitoring stations in Cloverdale, Healdsburg, and Guerneville, and in locations downwind of the Geysers.
Residents in Sonoma County released slightly fewer common pollutants in overall estimated tons per day and pounds per capita daily (overlay) between 1989 and 1991.
For each day of 1991, Sonoma County residents released an estimated 539.4 tons of common pollutants into the air--about 2.64 pounds per person. From its southern air basin, the county contributed about 5.5% of the Bay Area's total estimated air pollutants, roughly equivalent to our relative population. In the north county, which holds one-fifth of the north state's air basin population, residents contributed one-eighth of that basin's estimated pollutants.
These emissions are considerably less than what they've been in the recent past. In fact, the air pollution story is one of the most successful of our attempts to clean up the environment: over the last 20 years, we've seen a 20 to 60% drop in the five-year average measurements for ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, and particulates.
Pollutant Reports: Ozone (O3)
Photochemical smog, of which ozone is a major component, is one of the most visible indicators of warm-season air pollution, although visibility is also affected by weather, wind erosion, pollen, and airborne salt-water and sand particles. In high concentrations, photochemical smog appears as a brown haze, formed from a chemical reaction between nitrogen oxides (NOx) and reactive organic gases (ROG) in the presence of ultraviolet sunlight. These
reactive organic gases arise from the evaporation of aerosol sprays, paints, inks, solvents, and gasoline; both they and nitrogen oxides also have their source in the combustion of various fuels, including wood. Together, they form a mix of air pollutants, including peroxyacetyl nitrate, formaldehyde, hydrogen peroxide, and acrolein.
Initially measured along with other oxides, ozone has been an object of regulatory concern since the early 1960s. It is known to harden and crack rubber and affect paint and other synthetics, irritate the eyes, damage lung tissue and cause premature aging of the lungs, and to severely impact the health of those with compromised respiratory systems. Children and seniors are most susceptible to its effects, but even athletic performers can be adversely affected by ozone pollution. It is also known to stunt growth and reduce the yield of crops and affect many varieties of landscaping plants.
In 1991, activities in Sonoma County yielded an estimated 111 tons of reactive organic gases daily; of this, 60% came from natural sources; another 22% from mobile sources, and a little more than 8% from solvents.
Ozone levels, still measured in the cities of Santa Rosa and Sonoma, now hover near state standard (9 parts per hundred million/1-hr.; federal, less than 12 pphm; Alert Level, 20 pphm.)
Ozone levels have dropped steadily in Sonoma County since monitoring began in Santa Rosa in 1969 and in Sonoma in the early '70s. Readings at that time exceeded state and federal standards as many as 14 days out of the year. Traditionally the less polluted of the two because of its relatively open
surroundings, Santa Rosa last exceeded the more stringent state limit for ozone highs in 1987, while the city of Sonoma, sheltered from wind, continued to experience days of ozone pollution above the state standard--three in 1989 and again in 1991. Current readings for both locations have remained around or just under the state standard since the late 1980s.
For the Bay Area as a whole, days in which ozone levels exceed state standards have dropped 85% since the 1960s. Health Advisory Alerts--when children and seniors were advised to stay indoors--were posted an average of seven days a year during the late '60s, triggered by readings in excess of 20 parts per hundred million. In the latter part of the '80s, air was considered safe to breathe in all Bay Area locations year-round, and "ozone season," when readings tend to exceed clean air standards, retreated from ten down to seven months of the year. Residents of Livermore, where Bay Area air pollution collects, have experienced an average of 11 high-ozone days above federal standards in recent years, down from 40 in 1969. Bay Area pollutants, including ozone precursors and other emissions from Sonoma County, are known to accumulate in air basins around Livermore, the San Joaquin Valley, and Sacramento.
In the relatively less-polluted north Sonoma County, ozone concentrations are mounting, reaching their highest levels on hot summer afternoons during ozone season when winds are from the south. The north county air pollution control district speculates that the elevated readings are a combination of local traffic pollution and emissions from southern Sonoma County and adjacent Bay Area counties. The district's Healdsburg Airport monitors show a steady rise since measurement there began in mid-1991; peak days coincide with Bay Area smog alert forecasts. Although ozone is currently not a problem pollutant for the north district, the district's status is likely to change within a few years should the trend persist, bringing upon it new regulations and controls like those now imposed on the Bay Area.
Carbon monoxide (CO)
Odorless and invisible, carbon monoxide is another prevalent pollutant emitted from heated and burning petrochemicals, wood, and other fuels. Carbon monoxide acts to displace oxygen in the blood, reducing the function of heart, brain, lungs, and other tissues.
In Sonoma County, passenger car and light truck emissions accounted for 59% of an estimated 227 tons of CO emitted daily during 1991 (more than a pound per person). Mobile sources in general accounted for 82%.
Local carbon monoxide pollution levels are within limits (state standard, 9 parts per million/8-hr.; federal, 9 ppm/8-hr.)
The average for the highest eight hours of carbon monoxide readings measured per day in Santa Rosa has dropped to half its previous levels, from 8.9 ppm in the early and mid-'70s to 4.5 ppm in recent years; and the trend continues downward. Days in violation of standards numbered as high as three a year in 1973. No CO violations have occurred in Santa Rosa since the '70s.
Nitrogen dioxide (NO2)
A product of combustion, nitrogen dioxide pollution appears "whiskey-brown" in concentration, and can cause airway constriction in asthmatic individuals and bring about sore throat, breathing difficulties and respiratory infections in others. At high concentrations it will damage beans, tomatoes, and other sensitive crops. It is one of the two oxides of nitrogen (NOx)--which also includes nitric oxide--that interact with reactive organic gases to form ozone.
In 1991, the state Air Resources Board estimates that a total of 27 tons of oxides of nitrogen were emitted from Sonoma County sources daily; of that, 90% came from mobile sources on land and from airplanes.
NOX pollution levels averaged a little over 9 parts per hundred million/1-hr. in recent years (state standard, 25 pphm/1-hr.; federal 5.3 pphm/annual av.)
The average for the highest hour readings of the day for nitrogen dioxide has dropped by 40% from the early '70s in Santa Rosa, from a previous average of 15.2 parts per hundred million to 9.2 pphm in recent years. Readings continue to fluctuate a little above this level.
Nitrogen oxide readings in the north county district have remained within state parameters since monitoring began there in 1992, rising and falling with local commute traffic levels. Though within acceptable bounds, the NOx pollution appears to be a contributor to the district's ozone problem.
Mobile sources account for more than 50% of our carbon monoxide air pollution in Sonoma County.
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