PHILADELPHIA Scent of burning leaves has scientists sniffing around

Do burning leaves remind you of fall? It may depend on when you were born.
PHILADELPHIA (AP) -- A Montgomery County man says he gets at least two weeklong permits each year so he can savor an old-fashioned, and fast-vanishing, pleasure of autumn.
"There's something about raking a big pile of leaves, setting it on fire, and sitting for a half an hour and watching it burn and doing nothing," said Bruce MacBain of Lower Frederick Township, one of a shrinking number of places that still allow controlled leaf burning.
The fragrant mix of carbon, wood and carcinogens is becoming rare enough to interest a Long Island, N.Y., perfumer in bottling it, and interest Philadelphia researchers in testing whether its hazy allure is built into the human brain or is a learned nostalgic response.
Christopher Brosius has created the fragrance Bonfire for his fragrance company, Demeter, based in Great Neck, N.Y. Brosius said the scent, bottled in Sunbury, Northumberland County, is based on memories of burning leaves with his father in Dalmatia, also in Northumberland County.
"Smoke is one of my favorite smells, and from the point of view of re-creating that smell, it's fairly easy," he said.
Experiment waiting to happen
Such memories may be fading, however, which intrigues olfactory scientists. While MacBain can still get permits to burn leaves, most Pennsylvania townships are snuffing out the fires, and New Jersey and Delaware banned leaf-burning almost a decade ago.
"It's an experiment waiting to happen," said Charles Wysocki, a neuroscientist at Monell Chemical Senses Center in Philadelphia.
"Some people believe that you're born with a nose that's a clean slate, and acquire meaning to odors because of memory. Others believe that there's an inborn mechanism for thinking that some odors are disgusting," Wysocki said.
If the association of leaf smoke with autumn fades, that's an opportunity for researchers, according to Rachel Herz, an assistant professor of psychology at Brown University.
"Leaf smoke kind of has a sharp quality to it; it gets in your throat and can get kind of irritating," she said. "So if children right now have a burning-leaf-free environment, as a 20-year-old, if they're exposed to the smell, they might find it unpleasant because they don't have any positive associations previously formed to the smell."
Deadly elements
While evoking pleasant memories for many, the smell can be deadly for a few. The smoke includes small amounts of carcinogens, particularly benzoapyrene, believed to be a factor in lung cancer from cigarette smoke.
John Bachmann of the Environmental Protection Agency, who has studied particulate matter for more than 20 years, said on a particularly heavy burning day in South Bend, Ind., he has measured 100 micrograms per cubic meter of particulates, compared with a maximum safe limit set at 65 micrograms.
That may not be a problem for the average adult, but can be for children with asthma or elderly people with heart problems, he said.
"We don't say leaf burning kills people, but we know that on days with higher amounts of particulates in the air, more people die," he said. "And the people who are dying appear to be sensitive to asthma and cardiovascular diseases."