Where personal-care siloxanes go in US air
CMAQ puts cyclic siloxanes highest in cities, with oxidized products peaking downwind at far lower concentrations than the parents.
Source
Comprehensive atmospheric modeling of reactive cyclic siloxanes and their oxidation products
Inspect source passages
Where personal-care siloxanes go in US air
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
Atmospheric lifetimes are approximately 5–10 days at typical OH.
Atmospheric lifetimes () are approximately 5–10 days at typical hydroxyl radical (OH) concentrations; accordingly, long-range transport (; ; ; ; ) of cVMS occurs.
Average D5 concentrations up to 432 ng m−3 and average o-D5 up to 9 ng m−3.
The oxidized product concentrations are significantly lower than the parent compounds with average D 5 concentrations up to 432ngm −3 and average o-D 5 up to 9ngm −3 .
What they did
Authors added D4, D5, D6 and single-OH oxidation products to CMAQ 4.7.1 at 36 km over North America for four months in 2004, using population-based emissions and OH rate constants.
What they found
Lifetimes are about 5–10 days. Urban D5 can average up to 432 ng m−3 while oxidized D5 averages up to 9 ng m−3 downwind. Cities are emission-dominated; rural air tracks transport and OH. D4/D6 have larger errors than D5 because emissions are less certain.
The limits
What it doesn't show
Particle-phase oxidized siloxanes are not simulated; indoor exposure is not modeled; D6 molecular weight was capped by CMAQ’s dry-deposition limit.
Key terms
- cVMS
- Cyclic volatile methyl siloxanes such as D4, D5, and D6 from personal-care products.
- D5
- Decamethylcyclopentasiloxane, the dominant emitted cyclic siloxane.
- o-D5
- OH-oxidation product of D5 represented as a lumped silanol.
- CMAQ
- Community Multiscale Air Quality chemical transport model.
- Urban–rural gradient
- Concentration drop from populated source regions to remote air.
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Typical cVMS lifetime:
Common questions
Typical atmospheric lifetime?
About 5–10 days at typical OH.
Peak modeled mean D5?
Up to 432 ng m−3 in urban air.
Where are oxidized products highest?
Downwind of major urban centers.
Which species is best constrained?
D5 personal-care emissions.
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