Conversation Piece

Andrea Polli's Particle Falls draws the attention of a passerby on Philadelphia's Broad Street. (Conrad Erb)

Andrea Polli’s Particle Falls draws the attention of a passerby on Philadelphia’s Broad Street. (Conrad Erb)

How does an artist capture something invisible? Andrea Polli chose light to illustrate a pressing hidden concern: what are we breathing, and is it hurting us?

Particle Falls turns local readings of airborne pollution into real-time light projections. The more pollution, the more active the installation becomes. Polli’s project was most recently on display at Philadelphia’s Wilma Theater as part of CHF’s Sensing Change project. Each time a bus idled beneath the air sampler on Philadelphia’s Broad Street, golden flares erupted inside the blue waterfall of light.

The air sampler at the heart of Polli’s installation is a nephelometer, which uses reflected light to measure air quality. Every 15 seconds the nephelometer samples the air for particulate matter, detecting particles as small as 2.5 microns. To put that number into perspective, a grain of table salt is about 80 microns; common allergens—dust, pollen, and mold—come in at around 10 microns. At 2.5 microns and smaller—the size produced by the diesel engines found in trucks and buses—particles are small enough to get deep into a person’s lungs and even into the bloodstream, where in sufficient quantities they can wreak havoc with a person’s health.

During the first iteration of Particle Falls in San Jose, California, some viewers egged on the projection by smoking near the nephelometer. Such experimentation was unexpected, but the problem of rewarding bad behavior had worried Polli from the start. More pollution would make a better show, so she added falls of blue light that keep flowing even when the air is clear. Polli was only partially successful, I’d say: the falls are eye-catching, but my fellow observers and I soon found ourselves scanning the streets for fuming gas guzzlers.

But what’s the point of this installation? By turning abstract data into something as visible as a three-story waterfall of light, Polli hopes, at least in part, to trigger a public conversation about air quality. In the United States, she says, there is a long tradition of weather monitoring by ordinary citizens. Why not the monitoring of pollution?