Montfort A. Johnsen, Ph.D.
Neutral or malevolent for aerosols?
Oxygen is ubiquitous. In molecular and combined forms, it constitutes about 50% of the
earth’s crust. The oceans, lakes and rivers are 88.2% combined oxygen. Rocks and soil
contain 46.2% and the troposphere holds 23.14% (20.95% oxygen by volume). Without
oxygen, mankind would perish within a few minutes. Still, oxygen challenges us. It can
react with organic and inorganic substances, even at ambient temperatures, to produce both useful and
Oxygen has six isotopes. Three are radioactive and three are stable. 16O2 comprises 99.759% in
abundance. 17O2 and 18O2 total 0.241%. 18O2 (“labeled oxygen”) is used to parse certain organic
compounds to learn their synthesis pathways. Liquid oxygen is blue, liquid ozone is deep blue and explosive,
pure hydrogen peroxide is blue and explosive and certain forms of water (ice) range from light
blue to deep blue with a purple tinge. All are colorless when in diluted liquid form.
Oxygen is very active, forming
oxides, peroxides and related compounds
with every known element
except helium, neon and possibly
argon. A vast number of oxygenated
organic compounds, alcohols, ethers,
aldehydes, etc. are also recognized.
Many can be created at ambient
temperatures, such as the corrosion
of iron (forming rust), which is both
widespread and very complex.
Atmospheric (ground state) oxygen
is paramagnetic and is more technically
described as triplet oxygen, 3O2.
It is relatively inactive unless heated.
However, under the influence of UV
light and sensitizers, it can be converted
to singlet oxygen, 1O2. This,
and the related anionic free radical
(O2-•), are extremely active, attacking
many organic compounds to produce
hydroperoxides that can degrade into
various other compounds, some of
which may be clinically troublesome.
These oxidations do not take place in
aerosol cans because of the absence of
light, but they may affect applied skin
and hair care products unless they are
protected by such naturally present
enzymes as catalase and superoxide
dismutase (SOD). If these defenses
are overcome, skin problems such as
acne, irritation, comedogenic lipids
and carcinomas may result. Chemical
antioxidants do not prevent the formation of singlet oxygen species.
A wide variety of sensitizers have been alluded to in industry literature, such as Rieger, M.M., et al.,
Cosmetic & Toiletries, 104, (October 1989). They include enzymes, flavins, porphyrins, melanines and
such urban air pollutants as benzene and nitrogen dioxide. The rate of singlet oxygen oxidation of
ascorbic acid increases hugely if catalytic traces of copper ion are present.
28 Spray June 2018
For nitrosols and compressed air dispensers, a directional dot should be
used to help prevent depressurizing the head space. The actuator must be
aligned to the dot during production.