A team of scientists assigned tones to different air pollutants. Here are the results.





Take a listen.

The Caldecott Tunnel, Oakland, CA


Bakersfield, California


Pasadena, California


Because it is so close to LA and major shipping ports, you would expect Pasadena to sound the same as Bakersfield, or perhaps the Oakland tunnels. But in Southern California winds blow in from the ocean and trap the smog of LA at the foot of the surrounding San Gabriel Mountains before carrying it down to Pasadena. The usual hydrocarbon slurry then has a chance to "cook" in the oxidizing atmosphere of the hot mountain foothills. The resulting soundscape is more bubbly than the pure hydrocarbon samples above, as you can hear the new presence of complex oxygenated compounds.

The High Sierras

In a remote pine forest deep in the Sierra Mountains we gathered particulate data from the top of a swaying tower, which was installed to take measurements from above and inside the tree canopy. This soundscape starts with bubbly, diverse tones -- the result of small compounds (smaller compounds show up earlier in the data and hence earlier in the soundscape) that plants release to attract or repel insects. When you smell the sharp tang of pine pitch or fragrance of mountain laurel, you are smelling the volatile chemicals produced by the plant, which have evaporated and taken to the air, where hungry herbivores and pollinators can detect them.

Despite the remoteness of the study site, you can hear the influence of vehicle emissions later in the soundscape, as low, Bakersfield-type drones fill in. Though this site is far from any major cities or highways, winds bring emissions up from Sacramento during the day and back down the mountain at night -- a common pattern in the Central Valley of California -- making the influence of humanity nearly impossible to escape.

Lingering Pollution

The negative influence of human emissions on forests and remote areas is a problem that is increasing throughout the country and the world, and it is leading to one of the major issues currently being tackled in the scientific community. When human and natural emissions interact, as they do outside our cities, more particulate matter (smog and haze) is formed than we expect. This leads to inaccuracies in pollution models and, unsurprisingly, makes improving air quality more difficult. In some places, like the American Southeast, these poorly understood interactions have resulted in unpredicted, large-scale trends in regional warming and cooling.

These interactions are also, incidentally, one of the reasons President Reagan once said that trees pollute more than people do.

In short, to better understand and regulate our changing climate, the consequences of mixing those bubbly, natural tones with that droning, fossil-fuel chord need to be better studied.

Data analysis contributing to this project was performed by the research group of Dr. Goldstein at UC Berkeley. We'd like to thank the research groups of Dr. Harley (UC Berkeley) and Dr. Surratt (UNC Chapel Hill) for collecting samples.

Top image: Dan Riedlhuber/Reuters

This post originally appeared on The Atlantic.

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