Air’s eternal cycling quality does not apply to many pollutants and organic compounds that are broken down by chemical reactions before they can complete round-the-world jaunts. (For that reason you will also not inhale any alcohol vapors from Caesar’s last glass of wine.) Still, a good number of noxious chemicals can hang around long enough to have serious effects. Recent studies show that emissions from ships crossing the Atlantic, forest fires in Canada, and factories in Russia have all made their way to the North Pole, where they generate a warming haze of sulfates, ammonia, soot, and nitrates. Renyi Zhang, an atmospheric scientist at Texas A&M University, has found that prevailing winds carry soot and sulfates from factories in China and India out thousands of miles over the Pacific. Computer modeling and satellite observations suggest that these tiny particles can increase storm-cloud cover over certain regions of the North Pacific by 20 to 50 percent, enough to alter storm tracks in some cases. “This is going to have a major impact on global weather,” Zhang says. There are also upsides to air’s restless movements. Many plants, including cereal grains like corn and wheat, depend on wind to spread their pollen. Dust from the Sahara brings surprising gifts. Wafting over the Atlantic, it may have lessened the intensity of the 2006 hurricane season. It also seems to carry crucial mineral nutrients to the Amazon’s rain forests.
Indoors, air takes on a whole additional range of qualities. Air in the average home contains chlorine gas from household cleaning products, fragments of cockroaches and other bugs, and microscopic dust mites kicked up from carpets or couches. While changing our clothes, we dispatch 100,000,000 inhalable microbes into the air per minute. After flooding, indoor mold can become an irritating, or even deadly, part of the air.
The workplace is hardly pristine, either. A typical cubic meter of office air contains several hundred fungal spores, 89 micrograms of ethanol, 42 of acetone, 16 of formaldehyde, half a microgram of chloroform, and the by-products of human flatulence, a major source of methane and hydrogen sulfide.
There may be benefits to breathing in such a hodgepodge of stuff, according to Eoin Brodie, a microbiologist at the Lawrence Berkeley National Laboratory in California. He is part of a team cataloging the microbial diversity of U.S. air—in which the scientists have picked up, among other things, very small concentrations of bacteria related to anthrax. Brodie suspects that low-level exposure to other microbes may fortify our immune systems. “It may actually be protecting us,” he says.
And some impurities in the air are more than compensated for by the atmosphere’s protective qualities. Air incinerates all but the biggest space rocks before they pummel our planet; the vast majority never even make it past the stratosphere. The trade-off is a constant rain of cosmic dust. Every year, statistically speaking, you will inhale three particles shorn off a meteoroid as it burned through Earth’s atmosphere.
Air connects us to the most distant reaches of this planet, to all the life that has ever lived, even to the universe beyond. “If it exists on Earth,” says McGill University chemist Joe Schwarcz, “there will be some remnant of it in the air.”