*Listen* to some of America's most pristine and polluted airways.
In the flat lands of California's Central Valley, oil pumps obscured by waving lines of fuel-richened air dip and rise on the horizon. Two hundred miles to the north and west, aging eighteen-wheelers pound through an urban bypass tunnel, staining the walls black with diesel fumes. Farther to the north, High Sierra pines scent the mountain air with notes of cinnamon and nutmeg, sending blue wisps of haze trailing gently upward.
Air is not the same everywhere. Across the extremes of the human environment, in both urban areas and wild, powerful natural and human forces combine to create intricate mixtures of chemicals that compose the air we breathe, seek for pleasure, or avoid. And now that air is made audible.
We created sounds from air samples (atmospheric particulate matter collected on filters) by first using gas chromatography to separate the thousands of compounds in the air (try it with markers at home) and then using mass spectrometry, which gives us a unique "spectrum" for chemicals based on their structure, to identify the compounds and assign them tones. Some compounds end up sounding clear and distinct, while others blur together into unresolvable chords. The result is a qualitative, sensory experience of hard, digital data. You can actually hear the difference between the toxic air of a truck tunnel (clogged with diesel hydrocarbons and carcinogenic particulate matter) and the fragrant air of the High Sierras.
In the following soundscapes you can listen to the air quality at study sites established across California by air pollution scientists at the University of California-Berkley's Department of Environmental Science, Policy, and Management, where new efforts are underway to better understand the air we breathe and to devise new efforts to improve our polluted areas.
Take a listen.
The Caldecott Tunnel, Oakland, CA
The Caldecott Tunnel cuts east from Oakland through the Berkley Hills, linking greater Contra Costa County with the Bay area. To capture the direct emissions of cars and trucks (which often vary greatly from projected emissions) we dangled an air sampler from a ventilation passageway above the busy road. What you hear in the soundscape is an eerie mixture of highly unsaturated compounds called "polycyclic aromatic hydrocarbons" (those distinct chirps at the beginning) and complex, saturated heavy hydrocarbons (the long, low droning chords at the end). Both of these result from burning fossil fuels. And many are dangerous carcinogens, mutagens, and teratogens -- linked to cancers, gene mutations, and birth and developmental defects.
The town of Bakersfield sits in the middle of California's Central Valley on swampland reclaimed from the nearby Kern River. It hosts, supposedly, the world's largest ice cream plant (Dreyer's Grand!) and sits in one of our country's most productive oil counties (Kern County). It is also, according to the American Lung Association, America's most air-polluted city. You'll notice it sounds a lot like a contained highway tunnel -- the result of fresh hydrocarbons from a main trucking highway and oil and gas fields surrounding the sampling site.
Several years ago almost 100 air and climate scientists joined forces to resolve a lingering question in atmospheric science: Why do existing air quality models under-predict urban particulate (unhealthy airborne particle) concentrations by a factor of between two and 10? Their efforts met on the campus of Caltech in Pasadena, which sits just downwind of greater Los Angeles.