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The Habitable Planet: A Systems Approach to Environmental Science 

Atmospheric Pollution Interview with Luisa T. Molina

Interviewer: When did you realize that you wanted to develop a career in atmospheric science?

LUISA: I grew up in the Philippines, in Manila and Manila is a very, very polluted city. It’s one of the worst mega-cities. When I was a child, I got very sick because of gas, heat, high temperatures, but mostly from dust in the air. My sister has asthma. We are allergic to a lot of the pollutants there. So I was very interested when I was young in environmental problems.

Interviewer: Was there a specific moment that you realized you wanted to study air pollution?

LUISA: When I was working at MIT, before I worked on urban pollution, I was involved in stratospheric ozone and depletion and I did a lot of work related to the upper atmosphere. But lots of my colleagues at MIT were interested in looking at mega-city problems. We were always wondering, with so many mega-cities that are growing, what would be the impact on not just air pollution, but on the global climate.

The Mexico City Project actually started in the late 1990s as a continuation of the environmental study that we had at MIT. We wanted to look at the lower atmosphere. We were concerned about the problems of air pollution and we also wanted to know how to deal with it. Growing up in a city like Manila and spending quite a bit of time in Mexico as well, I am aware that environmental problems are not something that you can just rely on science and technology to fix. There are many other aspects, such as cultural, social, economic, and political issues so we created these integrated programs on urban, regional, and global air pollution with many colleagues at MIT. Myself, I’m an atmospheric scientist, but we also contacted colleagues in other disciplines.

We contacted people in Mexico that are involved in urban development and land use. But if you want to make suggestions for a strategy to mitigate the air pollution, then you also have to consider economics. It’s not just a matter of saying, okay, fine, let’s do this; you need to do an analysis of what would be the most cost effective way to do that strategy. So we started with these integrated programs on urban regional global air pollution and we used Mexico City as a case study. It’s one of the largest mega-cities in the world.

Interviewer: What is a mega-city?

LUISA: A mega-city usually refers to a city with a population of over 10 million. But it’s loosely defined because it depends on the boundary. There are more than 20 mega-cities in the world. But there are also at least 100 cities with populations of between 7 and10 million. And these cities are often adjacent to many other cities and they form a metropolitan area. Many of these cities with these very large urban centers have very similar problems as a large mega-city. I was in China, for example, and they were telling me in China that the largest mega-cities are not Beijing and Shanghai, but there are others that are even larger- large metropolitan areas with surrounding cities that actually become like a megalopolis.

Interviewer: Why should we care about pollution?

LUISA: Why should people care about pollution? There are many harmful effects from pollution. I think the driving force for studying air pollution really is the effects on the health of the population. Ozone, particulates, and other air toxins can really affect people’s health. It’s very expensive when people get sick and when children miss school because of ozone alerts. And elderly people also are affected with premature mortality.

There are lots of studies that show the harmful effects of air pollution. The quality of life is diminished when you go to a very nice national park and it’s covered with haze. These are all effects of air pollution. And then there is damage to ecosystems, to crops on regional and global scales. Regionally, it affects climate and the weather. And globally it affects the climate. Citizens might be aware of the local pollution that affects them, their health, and their visibility, but the regional and global impacts are also very serious.

Interviewer: Describe the scale of the effects of pollution.

LUISA: In a mega city or an urban center you have pollution from the burning of fossil fuels, from cars, from industry, and from burning trash. The pollutants that you burn locally would affect the health of the population and the air quality. There is also the regional impact, which would affect ecosystems. And the global impact that would affect climate. Then there’s also this intercontinental transport of pollutants. So a source that is in a mega-city could be transported far away. This is why is we are very concerned about air pollution.

There are lots of mega-cities and there are many people who are moving to large cities. The populations of cities are growing, and more and more mega-cities are being formed. Currently there are about 20, 21 mega-cities, but it’s expected that in about 2 to 3 decades that number could go up to 30, or even higher. So that’s something that we are concerned about: what would be the impact of these growing numbers of mega-cities?

Interviewer: How is it possible for pollution to be a global and not just local issue?

LUISA: Some of the pollutants are water soluble, so they can be washed out. But some of them react in the presence of sunlight. They transform into other species. And they have no boundary. Once you emit something to the atmosphere, pollution can transport from one region to another.

It is well known that plumes can travel. For example, in the case of a stratospheric ozone story, which I did for a number of years: CFC’s are released in industrial areas. These chemicals are so stable that they don’t get washed out by rain, and they don’t react with other chemicals. When they were first made, they were called the miracle compound because you used them as a refrigerant, as an aerosol, as a propellant. So these are very stable compounds. And then what happened? People found out that they eventually rise up to the stratosphere and these CFC’s are photolyzed by the strong radiation up there and then they form radical species and other chemicals. Then eventually they damage the ozone layer. Where did we find the largest ozone hole? In Antarctica. That’s far away from the source, so that shows that the pollutants that you release here can go a long distance.

The impact of these pollutants depends on how long they stay in the air. Ozone concentration in the northeast United States actually has increased. Why is that? The transports are coming from Southeast Asia- over a very long range, a very long distance.

Interviewer: There are many mega-cities around the world. Why did you choose Mexico City as a case study?

LUISA: There are many reasons for selecting Mexico City. First of all, Mexico City is one of the largest mega-cities. It has about 20 million people. Mexico City is in a tropical latitude, so it’s representative of many of the future mega-cities, which will be in Asia, in Africa, and the developing nations. And one of the very important reasons for choosing Mexico City is that we already have done quite a bit of work there. We started this from an integrated program at MIT. We have very good collaborations with local investigators and government officials. And Mexico City has an excellent infrastructure. It has atmospheric monitoring stations. What we hope is that what we learn from Mexico City will provide insights and understanding that can be applied to other and future mega-cities.

Interviewer: What is the name of your study and what does it stand for?

LUISA: “MILAGRO” stands for Mega City Initiative Local and Global Research Observation. We were very, very pleased that we were able to find an acronym, MILAGRO, that not only fit the themes of our management campaign, but it also means miracle in Spanish.

Interviewer: What is the objective of MILAGRO?

LUISA: The objective of this study, of MILAGRO is not just to look at local pollution but at the export of the pollutants. The main objective is to follow the plumes and find out where and how the plumes are transported to other regions. It is very important for us to not only just to look at one site but we actually look at various sites. With ground based measurements you can only cover so much, so you need even larger scaling and that’s why we have aircraft and then this is complemented with satellite measurements.

Interviewer: How many people and institutions are contributing to MILAGRO?

LUISA: MILAGRO is actually composed of four different components. The first one is to look at what are the impacts of the emissions from a mega-city on a regional and global scale. We wanted to not just study the emissions in the city, but we wanted to look at the export of the fumes. The National Science Foundation, Department of Energy, and NASA are able to participate because this is not just looking at local pollution. It’s looking at the regional and global impacts. It’s an extension of the work that we did in 2003, but on a much larger scale.

The National Science Foundation supports “MIRAGE” – that’s Mega-city Impacts on the Regional and Global Environment. The Department of Energy participated with “MAX-MEX” or the Mega-city Aerosol Experiment. And NASA is looking at the intercontinental transport of air pollution, so they participated with “INTEX-B.”

These are the four components. The total number of people participating inside Mexico is over 400, but this doesn’t include NASA, based in Houston, where they have another 100 investigators. And in terms of number of institutions, we have from the US, from Mexico, as well as from Europe about 150 to 160 institutions participating.

In order to look at the plumes, it’s very important for us to have different measurements. So we have what we call the super sites for ground-based measurements that follow forecasts and meteorological modeling. We set out to find the sites where the plumes are more likely to be exported from Mexico. Then we set up lots of sites all over Mexico City. This is the ground-based study. I would say that the total area that we are looking at is over 60 kilometers.

Then we have 6 aircraft from DOE, NASA, and NSF. The NASA DC-8 is based in Houston. In addition to aircrafts NASA provided satellite observations to the project. So there are three different platforms: ground base, aircraft, and satellite. And for ground based measurements, in addition to the fixed sites, we also have mobile labs, such as the Aerodyne mobile laboratory, and other mobile labs that look at the vertical profile of aerosols. And we have lots of meteorological measurements.

Interviewer: How do you oversee so many projects and people?

LUISA: I am the lead scientist for the ground-based campaign. But then there are lead scientists for NASA, for NSF, and for DOE. But because I already did a lot of work in Mexico City I know the local investigators and I coordinate the logistics inside Mexico City.

Interviewer: Why did you decide to do all these measurements at the same time?

LUISA: It is very important for us to do an integrated measurement. In order for you to look at the outflow, not only do you need ground-based measurements, but you also need to have a larger coverage, so the airplane measurements are essential. The satellite observations provide even larger coverage from space. This information is all very important for us to put into models so it’s important for us to do all of these measurements during the same time period. We wanted to use different techniques that compliment each other. And, in fact, some of the measurements during the campaign were designed exactly for that purpose. We have the C-130 from NSF and the G-1 from DOE that actually went on the same flight path so that we can have confidence in what we put into our models.

Interviewer: Describe the different ground sites that are part of MILAGRO?

LUISA: Air pollution depends on topography and on meteorology. Mexico City is like Los Angeles; it’s in a basin, surrounded by mountains. The mountains trap the pollutants. Mexico City is at a high altitude, 2,240 meters above sea level, so the solar radiation is quite intense. The urban area is around 1,500 square kilometers, but the population’s density is very high in the center of the city. In fact, it’s something like 1,200 people per kilometer, compared with Los Angeles where it’s something like 800 people per kilometer.

We wanted to look at the pollution coming up from Mexico City. We have one site which is right in the city cente at the Mexican Petroleum Institute; we call it IMP. Moving up another 35 kilometers northeast, we have the second site, and that is what we call the T-1. And then further up north we have another site and that’s in the state of Hidalgo, T-2. These are the three super sites. We call them super sites because we put a large number of state of the art instrumentation from many different institutions. Some are measuring, providing meteorological information. Some are for measuring aerosols, and radiation. In addition, we also have many other mini-sites.

Then we have the mobile labs. The one from Aerodyne, in 2003, was used mostly for chasing vehicles. But in 2006 they were located at fixed sites. We wanted to look at the emissions coming up from different types of vehicles, from taxis, from diesel buses, from trucks.

There are 35 air quality-monitoring stations in Mexico City. Those are routine measurements. Every time the Aerodyne Mobile lab went out in 2006, it was located side by side next to a monitoring station, because the Aerodyne Mobile Lab has a lot more very sophisticated instruments. We compare with some of the measurements obtained by the RAMA station and validate some of the data.

Let me also mention that one very, very important component of the campaign is to look at health impacts. We looked at the local emissions transport from transportation. We received financial support from the Mexican government to support local Mexican investigators. And two groups specifically looked at health impacts. One is to look at the damage to DNA from particulates. And the other one is to look at the impacts of the pollutants on children. Those are two very large health studies.

Interviewer: Does the quality of the fuel that is used in cars make a difference for pollution?

LUISA: The largest emissions come from vehicles. The vehicles now currently in Mexico City use diesel and gasoline. Cars are becoming cleaner- they adapted a lot of the technologies from the U.S. I believe in 1993 they actually phased out lead in gasoline. Before of course, lead had very harmful health effects.

And they have been trying to lower the sulfur content which requires major investment in the refinery- actually billions and billions and billions of dollars. But then recently the government agreed that they’re going to lower the sulfur content. So, hopefully, the Mexican’s fuel is actually quite, quite good. And that of course improves the emissions.

Interviewer: Why do you use balloons for obtaining data?

LUISA: There are different kinds of balloons for meteorological measurements. We want to look at vertical profiles. Again that’s very essential, understanding the radiation and meteorology.. The meteorological measurements we have measure the pressure, temperature, relative humidity, and the wind speed and the wind direction. These all affect the transport of the pollutants. Some of the balloons have all these sophisticated instruments. Some of the balloons actually had a canister of VOC because we wanted to look at the VOC’s, the volatile organic compounds, hydrocarbons coming out from cars and paints and other solvents and gasoline and things like that. We wanted to look at vertical profiles. As the balloon rises, you measure. Some of these go up to about a thousand meters. But that is still limited. And that’s why you have airplane measurements. It’s important for us to have this information.

Interviewer: Why does MILAGRO have an outreach component?

LUISA: One of the most important components is education and capacity building. The project initially was supported by the Mexican government. The Metropolitan Environmental Commission from Mexico City funded our project along with MIT.

First of all, before you make any suggestion or recommendation, you have to have proper knowledge. We looked at all of the problems in Mexico City. We looked at transportation. We looked at health impacts. We compared Mexico City with Los Angeles.

And we found that it is very important to take an integrated approach. You cannot just do one thing at a time. If you want to clean up local pollution- for example, one of the very polluted vehicles is the taxi – well, it’s not enough to just go in and say okay, fine, you guys, this is a bad taxi. You’re going to buy a new one. What happens to the taxi driver? He would not have money to do that. You have to take that into consideration.

We made a lot of recommendations. And these recommendations we submitted to the Mexican government. They have become their air quality management programs for 2000 to 2010. The ten year management program is based on our study. We advised them that it is very important to have public transportation. It’s very important to provide incentives to the taxi driver and to set a low interest loan so that they can buy a new taxi.

And you have to raise the awareness for the citizen. You have to start with young children. We had a lot of workshops in Mexico during the time that we were working on the project. We even had a training workshop for the media to inform them because they are really the vehicle to publicize the environmental problems to the public and we wanted to make sure what they reported was accurate.

We had a set of eighteen posters that the National University of Mexico displayed in their science museum. In addition we also have posters at the sites. We had public lectures. We set up two kinds of lectures, one where we invited the U.S. and international participants to talk in English, and then, the other in Spanish. Every week, we had guided tours for school children at the high school level. We also had some workshops for younger students to demonstrate some of the meteorological instruments and how they work. And we are planning to have a workshop for high school teachers: How Can We Improve the Environmental Situation in Mexico?

Interviewer: What are the results of your study?

LUISA: We are in the process of looking at the data. I can tell you some of the preliminary results. I call it preliminary because we have so much data. We are still working on it. We already published more than twenty-five papers based on the 2003 campaign. We know that the chemistry in Mexico City is very reactive. The radicals, what they call O-H and H02 are very, very high compared to other cities. And we also know that in Mexico City, the main pollutants, the largest sources of emissions, are coming from mobile vehicles.

In fact, in 2003, we did the campaign in April. One week was the Holy Week and we noticed some data during that time which was very striking. I was invited to give a presentation to the Mexican government, because they are very concerned about particulates. I showed them this graph that showed the PM concentration during the April Holy Week was almost down to the base line. We also know that the toxins are very high in the air. Air pollutants during the night just go away and then build up again during the day from all of the emission sources and photochemistry.

Interviewer: So, with all the data you got from March 2006, is MILAGRO finished?

LUISA: What do you mean? MILAGRO is not finished. MILAGRO is just beginning. It’s going to take at least another five to ten years before we analyze all of the data. You’re talking about information from many of the instruments taken at a frequency in seconds so there is lots and lots of data.

Once we analyze the data, then we have to put it into models and then we have to make some simulations, evaluate the data, and find out how do we make recommendations to the government in terms of improving the air quality locally. Then, for the people who are doing the climate modeling, they can use this information and fit it into their models so that they can look at the impacts of the pollution on the global climate. It is going to take many, many years for this project.

Interviewer: Given the current state of the global environment, what do you see when you look into the future?

LUISA: Well, I think I am optimistic. I think that we have learned a lot. I remember when I first went to Mexico City many, many years ago, I used to cry because of PAN, peroxy acetyl nitrate. That was in 1997. But in 2003, the levels were rather low. So some of these emissions are actually lower.

Lead and sulfur readings are low. Ozone and Pm are still high. But the fuel quality has improved.

So, I would say that, yes, things have changed. But you still need to educate the public and you need to work with government officials to create more public transportation.

What we learn from Mexico City we should be able to apply to many of these other mega-cities. Hopefully we will work with the world community to make sure that many of these emerging cities have air quality monitoring. When people say that Mexico City is one of the worst mega-cities in the world, well, that’s only because a lot of those mega-cities do not even have air quality monitoring stations. So how dirty they are, no one knows. But I’m optimistic that things are changing. In Mexico City children are concerned and these are the future leaders. And they could really have an impact.

Interviewer: Have you seen improvement in other mega-cities besides Mexico City?

LUISA: Yes. I have visited many other cities, like Beijing in China. Beijing, of course, has a lot of problems with haze – you almost literally could not see from one building to another. But the government is really moving forward to clean up the city. Of course, their motivation is because of the 2008 Olympics, but that’s fine. You can have any kind of motivation, but the bottom line is that they are doing a lot of work trying to clean up the city. So, yes, by extension of what we see in Mexico City, we think that this can be done in other cities as well, as long as there is political will. You really need political will and you need pressure from citizens. That’s what got a lot of things done in Los Angeles.

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