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What causes an odor like cat urine that is sometimes in the air around here?

Merton Vance

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.

User-contributed question by:
Dixie Dobyns

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7 Responses to “ What causes an odor like cat urine that is sometimes in the air around here?”

  1. On February 16, 2010 at 7:28 pm mike lynds wrote:

    I have lived in Wilmington for years, all the locals I know have always contributed the smell to the paper mill, International Paper. The odor varies depending in the direction of the wind.

  2. On February 17, 2010 at 7:00 pm Bryan wrote:

    Actually, the Riegelwood smell is something completely different (and much more foul). I don’t know how to describe it, but you’ll smell a similar odor around any paper mill that does its own pulping. It comes from something called a ‘digester,’ which is very aptly named. That’s where heat, pressure, and extremely caustic chemicals break wood down into the pulp from which paper is made. It’s chemically similar to human digestion, and the output is also quite similar.

  3. On February 20, 2010 at 10:34 am Elizabeth Scott wrote:

    That was a very eye-opening answer to the question about cat-litter smell. I live in Brunswick County (Bolivia then Calabash) and noticed a “smell” from day one upon moving here 10 years ago. I was told it was from the lumber mills. When I asked natives, they never noticed it. I guess one can get used to anything. Well, I too got used to it. I still smell it once in a while here in Calabash. Can you clarify that yes indeed lumber mills do emit a similar smell – maybe sweeter – or is it the same as the Wilmington area smell. Oh my, we do have sensitive noses don’t we!

  4. On December 30, 2010 at 1:38 pm Sheila wrote:

    Drive by the Invista plant on 421 North and you will have your answer.

  5. On September 24, 2013 at 1:27 pm a citizen wrote:

    p-xylene is one of the biggest culprits of the “odor” and you failed to mention it.

    Here is a CDC link:

  6. On September 24, 2013 at 3:12 pm Si Cantwell wrote:


  7. On January 15, 2014 at 9:11 pm Ricky Turner wrote:

    Everytime we pass by the Invista plant on 421, the smell in overwhelming!! I sometimes wonder if it’s safe for people to breathe in! I live in Long Creek, 15 miles north of the plant and on some days we can smell it at our house!!

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