Every lungful of air we suck down is mostly made up of nitrogen, with a generous helping of oxygen, and a dash of carbon dioxide.
But dusting this atmospheric soup is a whole encyclopedia of different compounds and elements, some of which we can only speculate about.
One of those mysteries just came into focus, however. Chemists have shown that a reactive class of compounds called organic hydrotrioxides exists in the atmosphere, and while these chemicals last only briefly, they could have effects we don't know about.
In fact, by the researchers' calculations, you just sucked up a few billion molecules of them while reading this.
Exactly what this means for your health, not to mention the health of our planet, is literally and figuratively up in the air. But given that we've just discovered this new ingredient in Earth's atmosphere, it's well worth looking into.
"These compounds have always been around – we just didn't know about them," says chemist Henrik Grum Kjærgaard from the University of Copenhagen in Denmark.
"But the fact that we now have evidence that the compounds are formed and live for a certain amount of time means that it is possible to study their effect … and respond if they turn out to be dangerous."
Quite often in chemistry, the addition of just a single new component can radically change how a material behaves.
Take water, for example. Thanks to the way its pair of hydrogens and single oxygen interact, organic chemistry can mix and swirl into an evolving phenomenon we call life.
Add just one more oxygen, though, and we get hydrogen peroxide – a far more reactive compound that can tear living chemistry apart.
Stick one more oxygen onto this angry little molecule, and the result is hydrotrioxide. To make it you just need the right kind of lab equipment, some saturated organic compounds, and some dry ice.
It's not exactly the kind of party trick you'd use to spice up a margarita, but chemists have used their manufacture in the generation of a specific flavor of molecular oxygen as a step in producing various other substances.
Being highly reactive, there's been an open question as to whether hydrotrioxides can easily form stable structures in the atmosphere.
It's not just an academic point of speculation, either. So much of the way our atmosphere operates, from the intricate ways it influences personal health to the massive scale of global climate, emerges from the way trace materials in it interact.
"Most human activity leads to emission of chemical substances into the atmosphere. So, knowledge of the reactions that determine atmospheric chemistry is important if we are to be able to predict how our actions will affect the atmosphere in the future," says Kristan H. Møller, also a chemist from the University of Copenhagen.
The team's investigations now provide the first direct observations of hydrotrioxide forming under atmospheric conditions from several substances known to be present in our air.
This allowed them to study the way the compound is likely to be synthesized, how long it sticks around for, and how it degrades.
One such emission, called isoprene, can react in the atmosphere to generate around 10 million metric tons of hydrotrioxide each year.
That's just one potential source, though. Based on the team's calculations, just about any compound could in theory play a role in the atmospheric formation of hydrotrioxides, which remain intact for anywhere between a few minutes to a few hours.
In that time, they can participate in a slew of other reactions as a powerful oxidant, some of which could be sheltered inside microscopic solids drifting on the winds.
"It is easy to imagine that new substances are formed in the aerosols that are harmful if inhaled. But further investigation is required to address these potential health effects," says Kjærgaard.
Since aerosols also affect the way our planet reflects sunlight, knowing how their internal chemistry causes them to grow or degrade could change how we model our climate.
Further investigations will no doubt begin to unravel the role hydrotrioxides play in our planet's atmospheric cocktail. As University of Copenhagen researcher Jing Chen notes, it really is just the start.
"Indeed, the air surrounding us is a huge tangle of complex chemical reactions," says Chen.
"As researchers, we need to keep an open mind if we want to get better at finding solutions."
This research is published in Science.