Sensing Change: Particle Falls

Part of the yearlong Sensing Change initiative, Particle Falls was a large-scale, real-time visualization of air-quality data created by digital media artist Andrea Polli. The light installation was projected on the wall of the Wilma Theater at Broad and Spruce Streets in Philadelphia.

Air—it’s invisible. We can’t really see it, touch it, know that it exists.

—Andrea Polli

On a background of falling blue light, spots of bright, fiery color emerge and crackle, representing the presence of fine particulate matter, as detected by a nearby air monitor. Fewer bright spots over the falls mean fewer particles in the air.

Particle Falls draws our attention to the invisible particles that surround us and that may affect our health. While the visible smog that plagued many U.S. urban centers decades ago has been mitigated by technology and regulatory measures, microscopic threats to our air continue to exist and often go unnoticed. Particle Falls is one way we can learn more about the quality of air around us.

Philadelphia has come a long way in improving the quality of the air we breathe, but our work isn’t done. Particle Falls makes it possible to see—in real time and vivid color—the challenges we continue to face.

—Thomas Huynh, Director, Air Management Services, City of Philadelphia

An interview with artist Andrea Polli about her public art installation, Particle Falls.

The value of art in science-related issues.

How It Works

Behind the visual spectacle of Particle Falls lies complicated science. Read below to learn more about how the work processes particulate data. 

The Visuals

Particle Falls displays concentrations of particulates in bursts of bright color over a constant background of falling blue light. Increasing frequency of the crackling dots of color indicates a greater concentration of particles. The image updates with new particulate data every 15 seconds.

The Tools

An instrument called a nephelometer monitors and samples the air to generate the data for Particle Falls. The nephelometer used in this art installation is an E-Sampler developed and manufactured by Met One Instruments. The E-Sampler combines two different technologies: light scattering and the gravimetric filter method.

Light scattering operates by pulsing a beam of light through a sample of air. The particulates in the air scatter the beam of light, which is collected and concentrated onto a photodiode in the E-Sampler. That light is then converted into an electric signal, which is proportional to the concentration of particulates in the air. That electric signal is converted to usable data and sent to the projector via a computer software program. Also used in scientific analysis is the E-Sampler’s gravimetric filter system. After measurement via light scatter, the sample is drawn onto a filter. The filter can be taken for lab analysis as a second method of measurement of air particles.

The Particles

The Particle Falls nephelometer measures particles in a gas sample that are smaller than 2.5 micrometers (or PM, particulate matter) in diameter. Particulate matter comprises water droplets and a variety of small particles made up of organic chemicals, soil, dust, metals, and acids like sulfates or nitrates, among other materials. Particles smaller than 10 micrometers can pass into the nose and throat, thus posing potential health risks to humans. 

Particles fitting this description are called “fine” particles and can come from a variety of combustion sources, like diesel exhaust. Not visible to the naked eye, these particles are key components of air pollution in Philadelphia, leading to Philadelphia’s ranking as one of the cities in the United States with the most polluted air.


Particle Falls provided a real-time visualization of particulate concentrations in the air surrounding the Wilma Theater in Center City Philadelphia. However, Particle Falls tells only part of the story about air in Philadelphia. Have you ever wondered about the past and present state of our air, and what you might be able to do to promote, maintain, or advocate for air quality? Click on the links below.

We’re proud that Particle Falls is closely aligned to the work of a variety of organizations that provide monitoring, advocacy, and educational services to the greater Philadelphia region regarding its air:

  • Air Management Services is Philadelphia’s air-pollution control agency.
  • Pennsylvania’s Department of Environmental Protection administers Pennsylvania’s environmental laws and regulations.
  • Clean Air Council is a nonprofit environmental health organization dedicated to improving the Mid-Atlantic region’s air quality through public education, outreach programs, community advocacy, and government oversight.
  • Air Quality Partnership is a public-private coalition dedicated to improving air quality in the greater Philadelphia region by providing air-quality advisories and educating the public about air-quality issues.

We also recognize for their efforts to help make Particle Falls possible Air Management Services, Applied Video Technology, Avenue of the Arts, Post Brothers, the Wilma Theater, and the following City of Philadelphia agencies: the Office of Arts, Culture, and the Creative Economy; the PhillyRising Collaborative/Office of the Managing Director; and the Streets Department. 

Andrea Polli is a digital media artist whose work merges art, science, and technology to address how natural and manmade systems are connected. Since 1999, Polli has focused on environmental-science issues in her work and has collaborated extensively with atmospheric scientists. Polli has worked with scientists to develop systems for understanding climate through sound using sonification, a process by which data is translated into sound.


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