Well, it’s not a vast conspiracy by all those cats wandering around out there.
The explanation is a lot more complicated.
The cat-urine-like odor mystified experts for years, but it’s been showing up since the late 1980s.
It was difficult to pinpoint because, as it turns out, it doesn’t come from a single source.
It wasn’t until 1998 that air quality experts determined that the pungent odor is a concoction that can include swamp gas and fumes from a number of industrial plants along the Cape Fear River.
Alone, many of these things are not noticed in the air, but when they combine in the right way, it stinks.
Just ask Brad Newland, who is currently the acting regional director for the N.C. Division of Air Quality office in Wilmington.
He has a vast file of reports, studies, data and complaints about this smell, dating back for years.
“There are a few facilities that potentially can emit that odor,” Newland said. “While they may smell similar, they’re not easily discernible.”
Atmospheric conditions, such as temperature inversions, often contribute to the problem.
“A lot of the odor complaints are weather-related,” Newland said.
One culprit that has been identified is a compound known by the chemical name of 4-Mercapto-4-methylpentan-2-one.
As ominous as that might sound to the chemistry-challenged among us, it’s actually not anything toxic.
The compound commonly occurs in fermentation and some types of baking.
It also contributes to the bouquet of cabernet sauvignon wine and it shows up in the aroma profile of basil.
So how does it end up making the Cape Fear region smell like a litter box?
Well, 4-Mercapto-4-methylpentan-2-one is what’s known as a volatile thiol, which means it sometimes doesn’t play well with other chemicals. Combined with certain other things, it holds the potential of malodorous magnificence.
(Newland relates a story about a bakery that ran a laboratory experimenting with different baking techniques and ingredients. Workers accidentally concocted something with a concentration of this stuff that resisted all efforts to eliminate the smell. It was so bad the company closed down the lab.)
Among other things, 4-Mercapto-4-methylpentan-2-one reacts with hydrogen sulfide, which is commonly emitted by a number of industries and can come from decomposing vegetation in swamps and marshes. The Cape Fear region has an abundance of both sources.
(The same compound also contributes to the odor of – yes, you guessed it – cat urine.)
While it may be smelly, it is not considered harmful, so it is not regulated under the Clean Air Act.
One known source of the compound is a plant operated by Fortron Industries, which manufactures polyphenylene sulfide, or PPS. PPS is a high-performance, heat-resistant plastic used in a wide variety of applications, such as airplane wings, car parts, power tools and circuit boards.
Fortron has worked with state air quality experts in efforts to minimize the compound emitted from its site.
“The company does go well above what is required of them by the regulations in efforts to address this issue,” Newland said.
Division of Air Quality specialists did an extensive study at one point around the Fortron plant, but instruments picked up only minute concentrations, he said.
One of the reasons it is hard to pinpoint the exact source is that the smell actually gets worse as the compound moves away from its point of origin
“As it gets more dilute, the odor gets stronger.” Newland said.
Date posted: February 16, 2010
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