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The Habitable Planet: A Systems Approach to Environmental Science 

Atmospheric Pollution Interview with Charles Kolb

Interviewer: How did Aerodyne Research, Inc. get started?

CHUCK: Aerodyne was founded in late 1970 by a couple of scientists who had worked at Avco-Everett Research Laboratories, another research facility in the area. It was originally started to investigate how military systems could be visualized, detected, things like missiles in the atmosphere, reentry vehicles in the atmosphere, and so it has a basis of a lot of fundamental chemistry and physics and also understanding of the atmospheric system.

Interviewer: How did you first become involved with Aerodyne?

CHUCK: I joined them to worry about how satellites could see rockets flying through the atmosphere. This was at the height of the Cold War, so there was a lot of concern about whether or not we could detect Soviet missiles and Chinese missiles and whether, if they had new kinds of rockets, we could actually see them coming.

Interviewer: What got you interested in science?

CHUCK: I’m a child of the Sputnik era. My father worked at a facility that the Navy owned that designed rockets for military use, and I got to know rocket scientists by meeting his friends and colleagues from work. I was in junior high school when the Russians launched the first satellite and it became a matter of national priority for people to go into chemistry and physics and engineering so that we could compete with the Russian success.

Interviewer: How did your interest in rocket science lead to your interest in atmospheric science?

CHUCK: I got interested in the atmosphere first because we were interested in finding out how rockets flying through the atmosphere could be detected, what sort of trail they left, and how reentry vehicles coming back into the atmosphere could be detected and what sort of signature they left in the atmosphere. But I also have a strong interest in air pollution. I grew up in Appalachia, where there’s a lot of coal burning and a lot of heavy atmospheric pollution from industrial sites. And it always seemed to me that we should not be turning the atmosphere into something that was dark and gray and ugly.

Interviewer: When you were working on detecting rockets, were you actually aware that everything that was being emitted into the air was having an effect on people’s health?

CHUCK: Back in the 1960’s, when I was in high school and then in college, we were just beginning to understand what a large range of chemicals were in the atmosphere and how they impacted people’s health. Our knowledge today is much more sophisticated and much more extensive.

Interviewer: Why study the atmosphere? Why is it important to people?

CHUCK: Air is kind of fundamental. It’s important for more than blowing up basketballs. Most of us can only survive a minute or so without a fresh breath of air. And if the air contains substances which are going to really hurt your health, you’d hate to think that you’re shortening your life with every breath of air you take. So it’s really a fundamental human need and probably a fundamental human right to have good, clean air to breathe.

Interviewer: What are the big research questions you’re trying to answer?

CHUCK: We’re interested in a range of atmospheric pollution issues. The most immediate would be are there toxic compounds, compounds that directly effect your health, being emitted in high enough quantities in various places so that people’s well being is immediately threatened. So detection of toxic air pollutants and their control is an important topic to us. Beyond that, many of the chemicals that are emitted into the air aren’t immediately harmful. The sun provides a lot of energy to the atmosphere in the form of photons. And these photons can start chemical reactions, initiate chains of chemical reactions that can turn relatively benign chemicals into chemicals that are significantly less benign. It can also turn gas-based chemicals into small particles which we now know can have a significant amount of impact on people’s lungs and their hearts. Beyond that, beyond the immediate impact of air toxic emissions and air pollution, there are larger questions of the impact of pollutants on the climate, for instance, both in terms of green house gasses, which trap the heat from the sun, and in terms of particles, which can have a variety of influences on climate.

Interviewer: What are the capabilities that you have for measuring pollutants that don’t exist anywhere else?

CHUCK: Since we have an interest in understanding where pollutants come from and how they change their chemical identity in the atmosphere, we’ve developed some very capable and very fast research instruments that can be deployed in the atmosphere and measure right away what’s there. This is an advance over the traditional method of chemical sampling, where you pull a sample of air into a metal bottle and take it back to the lab and analyze it sometime later. That type of analysis has problems because the chemicals that you sample may or may not be there later on when you try to analyze the sample.

Interviewer: What are the major pollutants that are emitted into the atmosphere?

CHUCK: Combustion sources, things that burn fossil fuels — natural gas, oil, coal – can produce a wide variety of pollutants because the combustion process doesn’t always burn the fuel completely. So combustion systems in cars, in power plants, in factory furnaces, can produce gases, and the ones we worry about most are fuel fragments, which we call volatile organic compounds: carbon monoxide, sulfur dioxide, and most importantly, nitrogen oxides, which are composed of nitrogen and oxygen molecules in various combinations. Combustion can also produce tiny particles. We call these sub-micron particles because they’re less than a millionth of a meter in diameter, so that many particles would have to be lined up to be the width of a human hair. These very small particles can go directly into our lungs and lodge there, carrying chemicals with them that may not be good for us.

Interviewer: Do people only have to worry about air pollution that they can see?

CHUCK: The tiny particles that we worry about people breathing, as well as most of the gasses are, of course, invisible. They don’t show up in the light we can see with our eyes. But we can detect them at other wavelengths and we find that they can be widely spread in the atmosphere even when the air looks perfectly clear. So while we can sometimes see a smoke plume from a vehicle or from a factory stack, it’s not at all necessarily to be able to see the pollutants to be exposed to them.

Interviewer: Why do you need all of these specialized instruments to measure air pollution when I can just take my car into the mechanic and measure the emissions?

CHUCK: When you get your car exhaust checked, when you have your automobile inspected, of course, they’re looking directly at the tailpipe where the pollutant levels can be very high. Typically they’re looking for pollutants at the level of tens to hundreds of parts per million in the exhaust gas. Out in the atmosphere, we worry about pollutants in the parts per billion or parts per trillion range, which would be a thousand to a million times lower than one part per million. It turns out that pollution can be harmful even at these very low levels, but to measure pollutants at very low levels, you need very specialized instruments.

Interviewer: What was the first project you conducted here with atmospheric pollution measurements?

CHUCK: Our first big project here was to understand how much methane, which is a simple molecule, the main molecule in natural gas, was leaking from the natural gas system because methane is an important greenhouse gas and, next to carbon dioxide, it’s the most important greenhouse gas that we emit. We were paid by the Environmental Protection Agency and by the natural gas industry to determine how much was leaking from their wells, from their transmission pipes, from their distribution systems within cities.

Interviewer: How did you go about measuring methane pollution?

CHUCK: In order to measure the emissions from the natural gas system, we invented a special laser that could measure methane directly in real time, so that we could drive around in a van with this laser and detect plumes of methane, which are invisible but could be detected by our instrument. We could trace those plumes back to the leak sources and we could use the laser to measure how much methane was leaking out of each source.

Interviewer: What did this truck that measured the methane look like?

CHUCK: It looked like a small delivery truck with some tubes poking out the front to draw air in. And the methane laser and other instruments were inside the van along with a scientist or two to keep them running.

Interviewer: What is the Aerodyne Mobile Lab?

CHUCK: Our current version of our Aerodyne Mobile Laboratory is a FedEx style van which has roughly a million and a half dollars worth of high level instruments inside, measuring both the fine particles in the atmosphere and the pollutant gasses. And we use instruments that we’ve developed here to measure some of those, and we use some high quality instruments that are manufactured by other companies, as well.

Interviewer: How did the idea of having a Mobile Lab originate?

CHUCK: When we were first approached about finding the leaks in the country’s natural gas system, that’s a huge, a huge job. There are thousands of miles of pipelines and big fields of gas wells and lots of other facilities. We needed to be able to sample a representative number to understand what the leakage from the whole system would be. We needed to be able to take our instruments to many states in the U.S. and to have them investigate many facilities. So it made a lot of sense to package up the lab in a small van and use it to get to the sites that we thought might be representative of the whole natural gas system.

Interviewer: How qualified do the operators on the Mobile Van need to be?

CHUCK: The people on board our Mobile Laboratory are largely PhD. level scientists because the instruments are very advanced and you need skill to run them. We also usually have students on board, graduate students or post-doctoral students from some of the university groups that collaborate with us on Mobile Lab measurements.

Interviewer: What information do you get from the Mobile Lab that you couldn’t just get back in a normal lab?

CHUCK: If you just have a fixed site lab, you can measure what’s in the air at a particular point. But that might not at all be representative of the area around that measurement. For instance, if an air monitoring station is near a busy highway, it might have a much higher level of pollution than the neighborhoods beyond, a little further away from the highway. With a mobile laboratory, you can actually map out the distribution of the air pollutants, so that you have a much better picture of how the pollutants are dispersed around, say a city, or around a factory complex. In addition, you can locate sources of pollutants, because you can see a concentration in a plume and you can then use a mobile laboratory to actually follow the plume back to the source. So one can identify situations where a factory or a facility is emitting pollution directly into the atmosphere.

Interviewer: What are the different types of situations for which you use the Mobile Lab? Can you describe your New York City bus project?

CHUCK: We want to use our Mobile Laboratory to look at two types of situations. One is to understand pollutants that are directly emitted into the atmosphere. We call those primary pollutants. We’ve worked with the Metropolitan Transit Authority in New York City that runs about a third of the city’s buses, to determine which types of buses emit what kinds of pollutants. So one can take the Mobile Lab and follow the buses as they go about their routes in the city. And as they stop and start, take on passengers, accelerate, slow down, one can see how both the particle pollutants and the gaseous pollutants they emit, change. Then you can take the same type of bus and put some emission control technology on it – maybe a trap that traps and burns the particles – and you can see what effect that has on the particle emissions and also what effect on the gaseous emissions. We’ve worked in New York City with four or five types of bus technology to see which ones do the best job of minimizing the pollution from the diesel buses in the city.

One can also look at diesel trucks, at light duty vehicles, cars and pickup trucks and SUV’s. One can look at emissions from boats and trains and airplanes, all of which we’ve done. You can build up a database of emissions and determine what kinds of transportation or what kinds of factories, what kinds of power plants are emitting the worst types of pollutants and identify what kind of regulation or what kind of technology you might use to reduce the primary emissions.
The second big job with the Mobile Lab is to go out and actually see what happens to those primary pollutants as they cook in the atmosphere, as the sunlight starts chemical reactions which convert them to new and different pollutants. We worry about two kinds of pollutants being created in the atmosphere. We call those secondary pollutants. The first kind are oxidant compounds that can hurt our cells, the cells in our lungs, the cells in our blood if we’re exposed to them.

Interviewer: Can you explain how the atmosphere actually can make pollutants even worse by altering them?

CHUCK: Besides characterizing the pollutants that are emitted directly into the atmosphere from power plant stacks and from vehicle exhaust pipes and other sources, it’s very important to understand what happens to those pollutants once they get into the atmosphere. The atmosphere can be thought of as a kind of a cool fire. The sun comes out and it actually starts chemistry that is very similar to the kind of chemistry that occurs when fuel burns, like the wood in your fireplace. This chemistry can create what we call secondary pollutants. It can chemically change the pollutants that were emitted into the atmosphere into different and sometimes more dangerous chemicals. And it can also produce a lot more fine particles. Not all fine particles are emitted from tailpipes or from power plant stacks. In fact, in a city, most of the particles most of the time will have been made in the atmosphere from this kind of fire chemistry that goes on.
There are actually two kinds of chemicals that we worry about or two kinds of chemistry that we worry about in the atmosphere. The organic compounds that get emitted from combustion sources that don’t burn the fuel completely and those from painting operations, from dry cleaners, from McDonalds when they charbroil your hamburger and put the smoke out the roof stack, that can react with the nitrogen oxides which also come from combustion processes, but may also come from things like the fertilizer decomposing on your lawn, and the interaction of the photons from the sun. The nitrogen oxides and the organic compounds create a kind of a fire which can produce oxygenated compounds, what we call oxidants. The one that most people have heard about and the one we worry about the most is called ozone. It’s made up of three oxygen atoms, rather than the two oxygen atom molecule that we normally breathe. Ozone is a very powerful oxidant. It can bleach the cells in your body and can create a lot of serious problems to people, to other animals, and to plants. So ozone gets formed as a secondary pollutant. It’s not emitted directly and it’s important to understand not only how much ozone is in the atmosphere, but how much of its precursor chemicals are there so we can predict what the ozone will look like as the wind blows that chemical mixture across the countryside.

The second thing we worry about are these fine particles that can get created. As the atmospheric fire burns, it creates molecules that are heavier than the ones it started with, and those can condense, can come out of the gas and form tiny particles which again, if we breathe them into our lungs, can lead to a number of medical complications, including not just lung disease – emphysema, asthma, possibly lung cancer – but can also put a very high strain on your heart and can lead to heart attacks in people who are susceptible.

Interviewer: Can air pollution kill people?

CHUCK: Unfortunately, we now believe that air pollution can kill people directly. People look at admissions to hospitals and deaths in hospital during and after big air pollution episodes in cities and we now know that there is a significant number of excess deaths when people who have been exposed to air pollution, particularly high particle levels, are taken ill and end up in the hospital. The most famous air pollution event in terms of hurting people was in London when the so-called killer fogs actually killed about 6,000 people over about a week and a half, beyond the number who would normally die in London. In the late 1940’s when London still consumed a lot of coal, they had very heavy particle events, where it almost looked like the city was enveloped in fog. In fact, we now call that kind of pollution “smog.” The particle loading got so heavy in London during one episode that many thousands of people died over just a 10 or 15 day period. That kind of event is not seen now, but the particle levels in many cities get high enough in the summertime that there are quite a number of people admitted to the hospital and a fraction of those people do die before they would have normally.

Interviewer: If the number of particles emitted is reduced, does that solve the problem?

CHUCK: The natural gas propelled buses don’t make many particles at all. Unfortunately, they can emit gaseous pollutants, which are not good for you at all. For instance, we found the CNG buses in New York emitted a large amount of formaldehyde, which is a very nasty, toxic air pollutant. The diesel buses with particle traps did, indeed, emit only about a quarter of the particles that normal diesel buses emitted, but they did emit a large amount of nitrogen dioxide, which is, again, a gas that is a toxic air pollutant, much more than the diesels without the particle traps. So you have to be careful when you’re trying to solve one pollution problem, that you don’t create a second pollution problem, which may be as serious as the first one.

Interviewer: When you’re out there in the Mobile Lab, are you just getting one point of data at a time?

CHUCK: The Mobile Lab is equipped with instruments that can measure every second or so. We can follow a vehicle and measure its exhaust plume more or less continuously as it drives around a city or as it drives around its normal route. In terms of measuring what’s in the background atmosphere, the ambient atmosphere, of course as we move along at 10 or 20 or 30, even up to 60 or 70 miles an hour, measuring every second, you actually then create a map of the pollutants along the route you’re traveling.

Interviewer: What is the reason for measuring the emissions every single second?

CHUCK: If you’re characterizing an emissions source and its emissions are changing second by second, as a vehicle might as it stops and starts or accelerates or goes up a hill, down a hill, if you don’t measure second by second, you won’t get the right answer. Also if you’re trying to map out the pollution distribution and you’re doing that from a moving vehicle so you can cover a lot of area, if you’re not measuring rapidly, snap, snap, snap, you’ll only be seeing a spot every hundred yards, or every 200 yards, depending on how fast the vehicle is going. But if you’re measuring every second, you may have then a point every 10 yards.

Interviewer: When you see the data coming in real time, do you have to make any analysis?

CHUCK: When we’re trying to understand the emissions from a vehicle, we have to figure out how much the exhaust is diluted when we actually intercept the exhaust plume. So we measure the combustion gases, the CO and CO2, and use them to calculate how much the plume is diluted. What we’ll find is that if a vehicle is cruising along at a moderate speed, it generally will be operating fairly efficiently and the ratio of the pollutant gases and the pollutant particles we’re measuring to the carbon dioxide that the engine is making as it burns the fuel is relatively low. On the other hand when an engine is under strain – when the vehicle is going up a hill or when it’s stopping and then starting again – you’ll find that the levels of unburned fuel and the levels of particle pollutants created by the combustion process may spike up quite a bit. So we analyze the data in terms of what the state of the vehicle is that’s emitting the plume we’re studying.

Interviewer: Can you describe how emissions create so many different polluting gases and particles?

CHUCK: Most of our energy comes from burning fossil fuels: gasoline, diesel fuel, coal, oil or natural gas. All of these fuels have carbon and hydrogen in them, so if you burn them right, they make primarily carbon dioxide and water. But no engine burns perfectly and so fuel fragments are not completely consumed, and they combine to form many different organic molecules, molecules made out of carbon and hydrogen as well as sometimes oxygen, nitrogen, sulfur, that get emitted from the exhaust pipe or the stack of the combustor. In addition when the air that’s used in combustion gets heated up, you make nitrogen oxide molecules, molecules of nitrogen and oxygen, which, when they get out into the atmosphere, can generate a whole range of chemicals that can drive atmospheric chemistry and make new species in the atmosphere. Finally, if the combustion is not handled exactly right at each instance, some of the fuel can actually condense into soot particles, which don’t get burned and get emitted. So the combustion sources that we rely on to power our vehicles, to make most of our electricity, to power our factories, to heat our homes, can produce this wide range of pollutants. And some of those are bad for our health and bad for the plants and animals that live around us directly. Others can be turned into pollutants that are bad for us by chemical reactions in the atmosphere. So it’s important to understand both the emission, which chemicals are emitted and how much and where and when, as well as then understand how those chemicals can change into different gaseous chemicals or into additional fine particles under the influence of reactions in the atmosphere, primarily driven by the sun.

Interviewer: What are the sources of these emissions?

CHUCK: Combustion systems of all kinds are a major source of pollutants. That includes all kinds of motor vehicles, diesel and gasoline vehicles, cars, trucks, boats, trains, airplanes. It also includes off-road vehicles like bulldozers and even your lawn mower or your ATV. But there are other sources of pollutants. Landfills can emit a wide variety of pollutants. Sewage treatment plants emit pollutants. When we fertilize our lawns or our golf courses, the microbes in the soil turn the fertilizer into various gaseous pollutants, which come up into the atmosphere. Farming operations can produce a lot of pollution from the animal waste as it decomposes. And then nature produces pollutants. Trees emit various chemicals when they’re under heat stress, or when they’re under insect attack. Grasses, grass when it’s mowed can emit various chemicals – the smell of freshly mowed grass is a sign that various organic chemicals are being emitted by the grass as it dries out.

Interviewer: At what time during the day is pollution at its worst?

CHUCK: On a working day, the heaviest levels of directly emitted pollutants are generally in the morning rush hour, and there are two reasons for that. One, when the concentration of vehicles is highest on the highway, there are more vehicles emitting pollutants than any other time of day. And second, at night the atmosphere does something which we call inverts, meaning that there’s a relatively shallow layer of air, which we call a boundary layer, near the surface and that doesn’t mix well with the main bulk of the atmosphere above. If the boundary layer is in place, it may be only about a football field high, the length of a football field high. The pollutants that are emitted in the morning are then trapped in that much atmosphere. So it’s like pouring some chemicals into a relatively small bottle. It doesn’t take as many chemicals to get a high concentration in the bottle. When the sun comes out strongly and really begins to heat the atmosphere, the boundary layer begins to rise. The heat causes it to expand and eventually it may expand as high as half a mile, or a mile. And then the chemicals that are emitted into the atmosphere from vehicles or from factories or from power plants mix into a much larger bottle. And therefore, the concentration of pollutants near the ground can be much less, even though the emissions are still pretty high.

Interviewer: What is the Mexico City Project?

CHUCK: In collaboration with a number of university and US government laboratory scientists, we’ve been working in Mexico City since 2002. Mexico City is the largest city in North America and the best example we have of a developing mega-city. Within the Valley of Mexico and the Mexico City metropolitan area, there are almost 20 million people. All of the pollution associated with the transportation and the cooking and the heating and the jobs they do is trapped within that one valley each day. In the spring of 2006, we took part in a multi-government agency, multi-national project called “MILAGRO”, which means miracle in Spanish, where about 350 scientists from the United States, Mexico and several European countries, all spent the month of March in Mexico City and in the area around Mexico City measuring what the pollutant levels were in the city and how they evolved, and then following the pollutant plumes as they moved out of the city either northeast, up towards the Gulf of Mexico and the United States, or southward into the southern part of Mexico.

Interviewer: Why should people care about pollution in Mexico City?

CHUCK: Pollution in Mexico City is representative of pollution in the large, developing mega-cities around the world. There are a tremendous number of people, many hundreds of millions now, living in this type of a city. Mexico City is characteristic of a class of cities we call developing mega-cities. There are many dozens of cities, which have five to fifteen or twenty million people, scattered around the world. Hundreds of millions of people are living in these kinds of cities and the demographic projections are that when we get to the middle of this century that will be multiplied many times over. If the people living in these developing mega-cities have their health severely impacted by air pollution, these cities are not going to thrive, and they’re going to be global problem spots for the entire world.

It turns out, of course, that the world only has one atmosphere. And so the pollution that’s created in Mexico City may well influence Miami at some point. The pollutions that are created in the large mega-cities in China can deliver very high levels of pollutants all across the United States, just as the pollution that’s created in the Midwest and the eastern part of the United States reaches all the way to Europe. It only takes about two weeks for air to go all the way around the world. The chemical lifetime of many of these pollutants can certainly be a week, two weeks, sometimes even months. So pollutants, which are created in one part of the world can influence the air quality a continent or two continents away.
Beyond that, we also know that these air pollutants, particularly some of the long-lived trace gases and the fine particles, have a big impact on climate. So again, the world only has one global climate. And the particles or gases that are created in one part of the world can influence the climate in every part of the world. We don’t have the luxury of thinking that it’s other people’s air pollution problems, other people’s climate problems. If they’re having problems, we’re going to have problems, too.

Interviewer: Why did you take measurements from Pico de Tres Padres?

CHUCK: When we deployed our mobile lab in Mexico City during the “MILAGRO” campaign, one key experiment involved first measuring how the chemicals evolved near the center of the city at a major super site where many groups had deployed instruments, but where we would park our mobile lab and follow the chemical patterns through the day, so we would understand what the system source term looked like in terms of pollution. Then we deployed to the north-northeast of the city, on top of a very impressive small mountain called Pico de Tres Padres. It’s well known in Mexico City because it’s the site of the TV transmission towers for the main television networks. Pico de Tres Padres is about 900 meters, or more than a thousand yards, higher than the already high altitude of the main city. So during the night it’s actually above the boundary layer and sees relatively clean air. But in the morning, when the sun bakes the air in the city, the boundary layer lifts, then the winds which prevail to the north-northeast that time of year, can bring the pollution plume from the city up and up over the top of the mountain. So ordinarily in the early morning, say between 6 and 8 or 9 AM, one can stand up on the top of Pico de Tres Padres and look as the smog in the city gets deeper and deeper in color, and uglier and uglier. Then as the boundary layer lifts, that cloud of gray pollution is lifted up, over and envelops the peak. And this enables us to see what happened to the chemical mix we had previously measured near the center of the city, and how the several hour transport time from the city up over this spot at the very outer edge of the city, how those chemicals had changed and what the pollution mix had now looked like.

Interviewer: What results did your Mobile Lab discover in the Mexico City project?

CHUCK: Our work both during “MILAGRO” and in previous measurement campaigns in Mexico City has shown that although there are only about three million vehicles in Mexico City, there is an extremely high level of vehicle exhaust pollution. This is partly due to the fact that there’s still quite a number of vehicles in Mexico City that are over 10 years old and don’t have the kind of pollution controls that the newer vehicles do. Also only three million vehicles to serve almost 20 million people, so they tend to work very hard. A lot of them are taxis or small transit buses, which are running many hours a day, all day. Finally, Mexico City is at a very high altitude, about 7,500 feet. And the thin air means that the combustion engines aren’t necessarily as efficient as they would be at closer to sea level. And we believe that leads to significantly higher emission levels for certain kinds of pollutants.

Interviewer: Did you discover anything unexpected during the Mexico City Project?

CHUCK: One of the most interesting things about Mexico City is the fact that the pollution each day gets so bad, but at night, most of the pollution is actually removed from the city. Even though it’s ringed in on three sides by mountains, there’s enough air flow through the passes and even up over some of the lower mountains, so that the pollution actually gets dispersed. But each morning with the strong emissions from the vehicles and from the factories and the trapping nature of the valley, you start a whole new chemical soup and by the end of the day, that soup is pretty thick and pretty nasty. So that’s one of the big surprises, that it wasn’t a multi-day pollution episode, like those in Los Angeles, or the ones we get along the east coast of the United States where the air moves from city to city.

Interviewer: What happens to all the pollution in the atmosphere. Do these particles just stay there forever?

CHUCK: People often ask what happens to the pollutants that are emitted into the atmosphere and we like to point out that there’s a kind of a Newton’s law of atmospheric chemistry: what goes up eventually must come down. So it’s true that pollution comes back out of the atmosphere. But how long it stays in the atmosphere and where it comes out is controlled by a very complex mixture of both chemistry and physics. Pollutants can change their chemical identity. They can change their physical form, going from a gas to a particle, or even from a particle back to a gas. And as the chemistry of the atmosphere works on them, much of the pollution is eventually rained out. It gets incorporated into cloud droplets. Clouds make up about 10 percent of the atmosphere. And those little water droplets in clouds can absorb many of the chemicals and particles that are emitted. And then if that cloud actually turns into rain or snow, it conveys those chemicals back down to the surface. Generally that can be benign, but in the case of acids in the atmosphere, that turns into acid rain, which can ruin lakes and forests.

Interviewer: What has been done about air pollution?

CHUCK: In most parts of the United States, the Clean Air Act is working. Since 1970, we’ve had fairly strict laws which have helped stop the increase in bad air pollution episodes and in fact in most cities have decreased them. But in cities with rapid growth, and with challenging climates, climates that can lead to a lot of chemistry in the air and a lot of pollution, secondary pollution formation, there are certainly still big challenges left. In the city of Houston, for instance, which is the site of a big air pollution monitoring episode in the summer of 2006, it has been a problem with air pollution getting increasingly worse over the 1990’s and into the 21st century. Any place where the population is growing has to work hard to reduce the emissions attributable to each person, or the air will inevitably degrade.

Interviewer: What research questions are you still trying to answer?

CHUCK: One of the biggest concerns we have is about the fine particles, and not just the soot particles that are emitted by combustion sources, but the secondary fine particles that are created in the atmosphere by the pollution chemistry. What we would like to know is what’s the detailed chemical composition of those particles, and what is it in those particles that seems to make them such a threat to human health and why they have such a high impact on climate. In order to do that, we really have to measure the chemical content. And if we’re going to control these fine particles in the future, we’ve got to determine which of the primary emissions are really resulting in the heavy loadings of secondary particles. In Mexico City, the secondary particles are actually primarily organic material. They’re made up of carbon, hydrogen and oxygen. There is some sulfuric acid, nitric acid and ammonia in them. But they’re primarily organic compounds, so we want to know what gaseous organic emissions are being oxidized and turned into these fine particles.

Interviewer: Given the current state of the environment, what do you see looking forward?

CHUCK: One of the real facts that we all have to deal with is that people make pollution, and as the population of the earth grows, unless we’re very clever and work very hard, the levels of pollution we all have to live with will grow along with it. And that’s certainly happening. We have to understand which pollutants are the ones that we must control, and we have to come up with either changes in our technology or changes in our lifestyles which reduce the heavy pollution burdens that we emit into the atmosphere.

Interviewer: Can you make a prediction for 25 or 30 years from now?

CHUCK: The consequences of not controlling what we emit into the atmosphere could be pretty grim. Nature has a way of limiting damage. If we don’t control the changes we make to the atmosphere, the atmosphere may begin to control how many of us are left on the planet. So it’s pretty important – it’s vital that we understand what happens to the pollutants we emit, and we understand how to better control them so the planet can continue to be a habitable place for both people and the rest of the creatures we share it with.

As the population grows, and we each emit a lot of pollution into the atmosphere, if we don’t learn to control that level of pollution, the atmosphere may change enough that it begins to control us. In other words, if the air is dirty enough, people will die sooner. Crops will fail. The climate may change, and the ability of the earth to sustain the number of people it has now may be severely diminished. That, of course, would be a tragedy for people all over the world, and it’s something that we’d like to avoid.

Interviewer: What about this subject is so fascinating to you?

CHUCK: The atmosphere is a fascinating system. It doesn’t seem like much to us. We only really sense it when it rains hard or when the wind blows. But it’s chemically very complex and it has to do an enormous amount of work if we’re going to survive on this planet. It has to provide fresh, breathable air. It has to somehow deal with all the pollutants that we inject into it, and it has to not change so much that our climate changes to the point where large parts of the earth aren’t habitable any more. So just understanding that system and understanding what we as a population are doing to it, and what we as a population need to develop in the future to avoid an atmosphere we can’t live with, is a great task. And it’s just a lot of fun to try to understand and work on that problem.

Series Directory

The Habitable Planet: A Systems Approach to Environmental Science 


Harvard Smithsonian Center for Astrophysics in association with the Harvard University Center for the Environment. 2007.
  • ISBN: 1-57680-883-1