Periodycal #22: Ci wins a thing, aeroplane air and summer hair

Plus a rallying call to join the X exodus

Aug 29, 2024

Hello and welcome to another edition of the Periodycal newsletter! As summer winds down, we’re taking a look at some last-minute summer-themed hair chemistry as well as the science behind the air you breathe on flights to holiday destinations. There’s also a neat new resource that puts air pollution in context and the usual round-ups of interesting chemistry news and features. But I should probably start with the big news…

Award for Interpreting Chemistry for the Public

I’m delighted and honoured to have been selected as the 2025 winner of the ACS James T. Grady–James H. Stack Award for Interpreting Chemistry for the Public. There are some huge names on the list of previous winners (Raychelle Burks, Sir Martyn Poliakoff, Bassam Shakhashiri and Harold McGee, to name but a few) and it’s both surreal and flattering to be mentioned on the same page as them!

The timing of the award feels apt, coming just after I’ve reached the point of ten years of making chemistry infographics on Compound Interest. I’m thankful to those who nominated me and everyone who shares the graphics: those who share them on social media, teachers who share them with students, scientists who use them in outreach, and more. Without this sharing, my infographics wouldn’t have had the impact they have had, so thank you.

Airplane airs

Infographic on the chemistry that cleans the air you breathe on a plane, as well as the reactions that produce oxygen in an emergency.
Airliners pressurize their onboard air to make flights more comfortable. In the cabin, the air pressure is 75.1 kPa, compared with 101 kPa at sea level. Cabin air is a mix of fresh air from outside and filtered inside air and is renewed up to 30 times an hour. High-efficiency particulate air filters remove bacteria, fungi, and viruses.
Airplanes cruise in the lower stratosphere, where the ozone concentration is slightly higher than at ground level. This can lead to increased ozone levels in the aircraft’s cabin, which can cause headaches and breathing problems. Ozone can also react with compounds in skin oils to form irritant aldehydes. Many planes use devices to convert ozone in air into oxygen before it enters the cabin. They also reduce cabin odors.
A chemical system produces the oxygen provided by masks that drop from an airplane’s ceiling during an emergency. Pulling the mask down releases a firing pin from the oxygen generator cylinder. This release ignites a mixture of an oxidizer (commonly sodium chlorate) and iron powder. The heat from burning iron decomposes the oxidizer, a process that produces oxygen. The generator produces oxygen for 15–20 min, long enough for the plane to descend to an altitude at which ambient air is breathable. — Click to view and download this graphic on the C&EN site

The idea for this latest edition of Periodic Graphics came to me, perhaps unsurprisingly, while sat on a flight to Budapest listening to the safety briefing. I realised I had no idea how life vests inflate when you pull their cord, nor how the oxygen in the masks that drop from an aeroplane’s ceiling in an emergency is generated.

The former turns out to be quite mundane (the vests inflate from a pressurised carbon dioxide canister) but the emergency oxygen generator turns out to be an interesting bit of chemistry sitting above every passenger’s head. And there’s also some interesting chemistry relating to ozone, too, as the graphic explains.

Summer hair colour changes

Infographic looking at the chemistry behind how some summer activities may alter some hair colors. The first column of the graphic highlights the three layers of hair: the medulla, a soft inner layer with an uncertain composition and role; the cortex, formed from long keratin protein strands and containing melanin, which gives hair color; and the cuticle, layers of dead cells, which protect the inner layers of hair. Copper in swimming pool water, often from copper-containing algicides, can turn light-colored hair green. Chlorine oxidizes the copper, producing green copper compounds, which bind to keratin proteins in hair strands. The resulting discoloration is known as chlorotrichosis. Shampoos with chelating agents can remove this discoloration.Lemon juice contains citric acid. When squeezed on hair and exposed to the sun’s ultraviolet light, it penetrates the hair cuticle and breaks down melanin, lightening hair color. Avobenzone is a UV-absorbing compound used in some sunscreens. When it interacts with iron in pool water or shower water, it can form complexes that turn clothes, light-colored hair extensions, or dyed hair orange or pink.

Summer is coming to an end in the northern hemisphere, and some in the UK might dispute whether it ever really started. At any rate, here’s a summer-themed edition of Periodic Graphics from last month which examines how the sun, sunscreen and swimming pools can all affect your hair colour, particularly if you have light-coloured hair.

Air pollution stripes

Graph showing air pollution for London, UK. The graph shows air pollution increasing to poor/very poor levels between 1900 and 1960, before falling to fair levels in the present day

Climate stripes are a ubiquitous image of the climate crisis. They show a stark contrast between the climate’s relatively recent past and the path we find ourselves hurtling down in the coming decades. Now, they’ve inspired similar graphics highlighting air pollution, specifically PM2.5 concentrations in cities worldwide over the past 150 years or so.

These paint a slightly cheerier picture than the climate stripes, showing how action and legislation can have a positive impact. Take the graph for London, showing the gradual creep of poor air quality peaking in the 1960s before the 1956 Clean Air Act helped to reverse the trend. These could make for great contextual resources when teaching about air pollution in chemistry.

Join the X exodus

The site formerly known as Twitter is an increasingly unpleasant place to be, but plenty of us stay there because we tell ourselves it’s where everyone else is. So it’s been good to see some inroads being made into that with the ongoing establishment of a chemistry education community on Bluesky.

If you don’t already have an account there, you can kick off with this “starter pack” created by the Chat Chemistry team, which includes a list of chemistry educators to follow and the #ChatChemistry feed. You can also find me and Compound Interest there. So far my feed there has been refreshingly free of clickbaity threads and reassuringly full of chemistry conversation (and cat photos, obviously).

Chemistry news and features

Here’s the regular selection of chemistry news and features I’ve found interesting over the past few weeks:

Shingles vaccine may delay dementia – This story is a month or so old now, but I only came across it last week. It’s fascinating, both in that the shingles vaccine may well be accidentally more effective in delaying dementia than many tried and failed (and expensive) drug trials and in that it suggests a possibility of herpes virus involvement in some forms of dementia.
Jane Richardson and protein ribbon diagrams – If you’ve studied biochemistry to any degree you’ll have seen the protein ribbon diagrams used to depict the complex 3D structures of proteins - but did you know about the scientist who created them?
Dora Kulka and British beer – A profile of another little-known woman in science and her impact on the British beer industry.
Why cats like cat food – Why do cats go nuts for some cat food and turn their nose up at others? Well, this article doesn’t really answer that, but it does provide some interesting insight into what cat food chemistry cats find appealing!

That’s all for this issue! Look out for upcoming graphics on the Northern Lights and coffee chemistry. Let me know if there are topics I’ve yet to cover that you’d like to see graphics on!

Thanks for reading,

Andy