For five winter seasons and running, Bay Area residents have observed Spare the Air, curbing their wood- burning activities on select days to promote cleaner air.
Has it worked? The Bay Area Air Quality Management District reviewed pollution levels from the last few years and concluded that Spare the Air, along with other factors, has pushed particulate matter levels (known simply as ‘PM’) lower each year for the last several.
“What we’ve seen over time is a decrease in the peak levels of PM concentration in the winter time,” said Eric Stevenson, the group’s director of technical services, “and what we believe that’s caused by is the decrease in smoke that’s emitted from individuals’ fireplaces.” A closer look at the numbers reveals that average peak PM levels have indeed dropped the last few years, based on testing sites located throughout the Bay Area.
Some areas, like Livermore, Concord, Redwood City, Vallejo, Santa Rosa and Gilroy, demonstrated fairly significant drops. More urban cities like San Francisco, Oakland and San Jose either saw small reductions or in Oakland’s case, a slight increase. For fuller context, however, it’s interesting to note that PM levels fell precipitously when measured over a broader time horizon.
The biggest drop occurred from 2000 to 2003, when total PM in the Bay Area shrank by 32 percent. Since that point in time, it’s fallen another 22 percent. “It’s really difficult to make definitive types of statements when there are a tremendous number of variables [involved],” added Stevenson, who said that the timing and frequency of storms, for example, can greatly skew the numbers in one direction or another. Nonetheless, he said after accounting for changes in weather, the Bay Area Air Quality Management District is “pretty confident that the program has had a very large effect on getting us under national standards” for PM levels.
During the 2012-2013 season, there were a total of 10 Spare the Air days observed. We asked Berkeley professor and environmental engineer Robert Harley if a modestly-used program like Spare the Air could really sway pollution levels over a period of several years. Harley said he hadn’t looked at the data specifically, but believes “in the short-term, the best thing you can do is to ask people not to burn wood on those problematic nights,” calling the Spare the Air program well-targeted.
The longer-term effects, however, aren’t as clear. “It’s still helpful, but it has much less leverage on the annual average of particulate matter (PM), and it’s much more focused on the high winter episodes,” Harley said.
The professor has been conducting field research on gasoline and diesel emissions since the mid-1990s, and believes that higher fuel standards, better technology in the motor industry and more state controls over industrial practices has had a more obvious impact on pollution levels in the long-term.
“I can tell you for sure that the gasoline and diesel engine sources are going down over time,” Harley said.
Car and truck emissions, according to the BAAQMD’s own research, contribute about 32 percent of winter time pollutants. Wood-burning, by contrast, is around 28 percent, the single largest source. “If you look over a long time scale, over 10 or 20 years, there’s been a steady march downward,” Harley said.
“And that’s in a good direction, right? That’s progress in improving air quality.”