Field Notes: Mapping Pollution in Allegheny County


Not just resigned to the laboratory, researchers at the Center for Atmospheric Particle Studies are often collecting measurements in the field to better understand atmospheric phenomena. Day or night, rain or shine, CAPS researchers work to collect important measurements from the Pittsburgh region and around the world. These are their stories. 


Over the past year, residents of Allegheny County, Pennsylvania may have noticed a unique vehicle driving on local roadways or parked in their neighborhoods. With several metal tubes extending upwards from the roof, this vehicle can be (and has been) mistaken for some type of surveillance vehicle. While this is partially true, the vehicle in question – Carnegie Mellon University’s Center for Atmospheric Particle Studies (CAPS) mobile laboratory – is not being used to intercept communications. Rather, CAPS researchers are using the mobile lab for an altogether different type of investigation – a surveillance of air quality. Equipped with a wide variety of instrumentation capable of measuring concentrations of particles and gases in the atmosphere, the mobile lab provides a specialized platform for use in air pollution research projects. We are currently using the CAPS mobile lab to study the spatial variability of air pollution in Allegheny County.

Quantifying human exposure to harmful air pollutants is a complex problem. Exposure is directly related to the concentration of air pollutants in the air that people breathe. Concentrations of these species are in turn dependent on many factors and are subject to spatial and temporal variability. For example, concentrations of pollutants emitted by motor vehicles are typically elevated downwind of roadways, particularly during rush hour. The Allegheny County Health Department (ACHD) operates a network of stationary air monitors to measure concentrations of a number of air pollutants throughout the county ( This network provides a robust picture of air quality and is necessary for the measurement of nationally regulated air pollutants. However, due to the limited number of monitoring sites in the network, important small scale variations in air pollutant concentrations may be overlooked. For instance, pollution “hot spots” near roadways or industrial sources of emissions are not fully characterized by the stationary monitoring network.   

With our mobile sampling project, we aim to supplement the existing ACHD monitoring network by utilizing the unique capabilities of the CAPS mobile lab. The mobile lab enables us to make measurements at a large number of sites with varying degrees of influence from air pollution sources such as traffic or industrial facilities. We are also able to investigate the impacts of altitude on air quality by comparing measurements made at river valley sites with upland sites at higher elevations. Our measurements will help us to develop a better understanding of how these factors influence concentrations of harmful air pollutants and to determine whether certain subgroups and communities are experiencing high exposure conditions. To date, we have conducted hundreds of hours of measurements at sites across the county. Our goal is to use this data to develop county level maps showing concentrations of air pollutants, including criteria pollutants such as ozone and particulate matter, as well as other pollutants of concern such as metallic species. These maps will support future investigations into the public health impacts of air pollution in the county and will provide regulators and decision makers with more detailed information on important emission sources.   


Written by Tim Dallmann, Photos by Peter Leeman         


Documerica: The Environmental Protection Agency’s Ambitious, Once Forgotten Photography Project from the 1970s

Peter Leeman

 In the late 1960s and early 1970s a new environmentalism went mainstream. Precipitated from the infamous ‘60s counterculture, a heightened concern for the state of the environment inspired action and media attention across the country. The momentum of public outcry led to a fury of federal action on the environment. In 1969 the National Environmental Policy Act was passed, then came the Clean Air Act (1970), the Federal Water Pollution Control Act (1972), The Coastal Zone Management Act (1972) and the Endangered Species Act (1972). And to oversee it all: a newly consolidated, still fledgling federal agency called the Environmental Protection Agency (1970).

Eager to please and garner support for environmental protection, the EPA green-lighted Documerica, an ambitious photography project which sought to document the state of the environment throughout the 1970s. Gifford Hampshire, a former National Geographic editor turned career bureaucrat in the EPA’s Public Affairs office, brought the idea to EPA leadership and directed the program until its end. The Documerica project lasted six years and hired approximately 70 photographers for about 115 assignments in all 50 states. In the end, Documerica produced 22,000 images from all across the country.

Hampshire wanted to create “a visual baseline” of the environment from which progress could be measured. Taking inspiration from the Farm Security Administration’s lauded documentary photography project during the 1930’s, Hampshire also wanted to document “any beauty worth saving.” The motto for Documerica was Barry Commoner’s Law of Ecology: “everything is connected to everything else.” Photographers spent time capturing environmental degradation, research, testing and pollution. They also photographed people in their communities, painting a more general picture of life in the 1970s.

Approximately 15% of the Documerica pictures show research and testing of pollution and environmental degradation. Pictures of air quality research are shown below.

From 1973 to 1975, photographer John L. Alexandrowicz went on assignments for Documerica in the Pittsburgh region. He took pictures of heavy industry like the Clairton Coke Works, tagged along with the Department of Environmental Protection while they tested water quality, and also captured moments of everyday life in many neighborhoods around Pittsburgh.

Some of the most engrossing pictures of the Documerica project were completely social documentary efforts in places like El Paso’s 2nd ward, Chicago’s African-American communities or Coal Miners homes in Virginia. Hampshire said of his project’s scope, “Where you see people, there’s an environmental element to which they are connected. The great Documerica pictures will show the connection and what it means.” 

Technically, the Documerica project was a failure. It was originally supposed to last for 10 years and have a cultural impact on par with the Farm Security Adminstration’s photos, which were crucial to the development of documentary photography and helped sell the New Deal to the public. Due to managerial priorities and differences, the funding for Documerica was gradually cut. Even though some of most acclaimed photographers of that time contributed photos to Documerica, the images were filed away and almost completely forgotten until recently. Giff Hampshire might not have achieved the original goal of the project, but the Documerica photos provide an immense and vivid view into almost an entire decade of history, all in the rich, true color tones of government provided Kodachrome film.


An exhibit of Documerica photos is currently being shown at the National Archives Gallery until September, 8th, 2013:

The National Archives has digitized 16,000 Documerica photos, which are searchable online:

They have also put a selection of photos on flickr:


Shubinski. B. (2009) “From FSA to EPA: project documerica, the dustbowl legacy, and the quest to photograph 1970s America.” PhD. Thesis, University of Iowa.

The National Archives (


A tale of two particles

Dan Westervelt

Imagine yourself as an atmospheric particle. You are blowing in the wind and perhaps interacting with other particles and gases.  Your goal in life is to grow to about 100 nm in diameter so that water will form around you and you will become a cloud. Where did you come from? Many would say you were a product of some kind of combustion process, maybe from a power plant or a vehicle.  But no, you are a special particle. You are a nucleated particle, formed by a nanoscale process known as nucleation.

Besides direct emission, new particles can be introduced into the atmosphere in only one other way: nucleation. Nucleation is the formation of particles from an existing gas such as sulfuric acid. Sulfuric acid is the main nucleating gas and is formed from sulfur dioxide, a power plant by-product.

It turns out that nucleation can form thousands to millions of particles within one cubic centimeter of the atmosphere. This is typically a higher number than direct emission, so perhaps you, the nucleated particle, are not that special.  Not only that, but also you and all your companions are only about 1 nanometer in diameter, whereas the directly emitted particles are born at about 20 to 30 nm.  Suddenly, your friends start disappearing! They are colliding, or coagulating, with larger particles, which is a major loss mechanism for nucleated particles.

You are lucky. You have managed to grow by condensation while avoiding death by coagulation. Congratulations, you’ve made it to the 100 nm finish line! But you look around and only about 5-10% of friends are as lucky as you.

This percentage is called the survival probability; that is, the likelihood that a nucleated particle will grow by condensation and avoid coagulation for long enough to act as a cloud nucleus. In recent work under peer-review in Atmospheric Chemistry and Physics, our research team studied survival probability using ambient measurements of particles as well as a global, 3-dimensional model of the atmosphere. We find that in both the model and measurements, nucleated survival probabilities are relatively low (5-10%).  Since directly emitted particles are larger and do not coagulate as much, they make up a much larger percentage of the cloud nucleus population.

It’s a hard knock life out there for a nucleated particle. 


Burning the midnight oil (and forming PM)

Daniel Tkacik

It’s 2:53 in the morning on a Wednesday. I’m at the Ft. Pitt Tunnel, a traffic tunnel that Interstate 376 passes through, and I’m writing this post in-between turning some knobs on an instrument that is converting exhaust vapors in the tunnel into particulate matter (PM).

Some other researchers and I are currently monitoring the air inside this traffic tunnel— not because we want to know if the air is dirty or not (of course it’s dirty), but because this gives us a nice, concentrated sample of real-life traffic emissions. What are we doing with these emissions? Let’s back up a bit.

When a car or truck is tested for its emissions, it’s given a rating that describes how much of its emissions is PM. This rating, however, may not fully account for all of the particles in a vehicle’s exhaust. There’s a catch: after leaving the tailpipe, the vapors in the exhaust may undergo chemical reactions that turns them into “secondary” PM. This happens hours, or even days, after the exhaust is initially emitted (certainly not while the car inspector is looking).

Here at the tunnel, we are trying to simulate that vapor-to-PM conversion. We are doing that by pulling the exhaust-filled tunnel air into an instrument called the Potential Aerosol Mass chamber that exposes the air to high levels of oxidants—roughly 1000 times higher than the atmosphere typically has. Why so high? So the formation of secondary PM happens immediately (rather than the hours or days it normally takes in the atmosphere). Knowing how much PM is created from vapor oxidation can then help us better understand the impact of vehicles on air quality.

So why am I here at 3 o’clock in the morning? Right now is prime time for catching big tractor-trailers and other large vehicles transporting cargo across the country, and we want to see if their exhaust looks any different (or if it acts any differently, in terms of producing secondary PM) than light-duty vehicles like gasoline-powered cars and SUVs.

I’m hoping all goes well with this experiment, not only for science, but so I can get some sleep.