Shifting weather patterns mean sunnier skies and poorer air quality today across the Bay Area, triggering the Bay Area Air Quality Management District to declare today a Spare the Air Day.
Today's smog alert is the third such alert this summer -- the first two Spare the Air days occurred last week during a heat spell that flirted with record high temperatures.
Officials with the air district are reminding Bay Area residents to take daily action to reduce air pollution across the region over the long term and not just during the smog alerts.
"Taking transit, carpooling, walking or biking will help everyone breathe easier," air district executive officer Jack Broadbent said in a statement.
Clean air choices recommended by the air district include biking to work or around town, working at home or telecommuting, stringing together errands for fewer driving trips, and cooking indoors rather than on outdoor grills or barbecues.
The air district monitors daily air pollution levels and produces air quality forecasts every day based on an index developed by the U.S. Environmental Protection Agency.
When the index indicates unhealthy concentrations of ground-level ozone -- commonly known as smog -- the air district issues the Spare the Air alerts.
Smog, which can cause throat irritation, congestion and chest pain, is the major contributor to poor summertime air quality. Long-term exposure to ozone can reduce lung function. Short-term exposure can trigger asthma, inflame the lining of the lungs and worsen bronchitis and emphysema.
Motor vehicle exhaust, gasoline vapors, industrial emissions and household chemicals contain volatile organic compounds and nitrogen oxides the combine with oxygen in the presence of heat and sunlight to form smog.
Ozone and particulate matter -- microscopically small solid particles or liquid droplets -- are the two primary culprits behind poor air quality in the Bay Area.
There is no free transit tomorrow, and there is no wood burning ban in place. Wood burning bans are common during winter Spare the Air alerts because of the particulate matter contained in wood smoke.
The Bay Area Air Quality Management District is a regional agency chartered with safeguarding air quality in the nine-county Bay Area.
For more information about the Spare the Air program, visit www.sparetheair.org.