A Global Look at Urban Air Quality, with Pallavi Pant

Notable Quotes

• Much air pollution has a common source: “In very simple terms, if we think about air pollution, a lot of it comes when we burn things. You could be burning a piece of paper, you could be burning incense sticks in your home, you could be burning fossil fuels to produce energy—all of it is going to potentially lead to air pollution if the combustion is not efficient and not complete.” (3:49)
• Air pollution triggers diseases: “The impacts of air pollution aren’t limited to just our respiratory organs. We have substantial evidence of the role of air pollution in chronic heart diseases, in stroke, in certain types of cancer—especially lung cancer—and in other types of chronic diseases like type 2 diabetes. For some countries, the contribution of air pollution to these types of diseases can be very big. Growing evidence shows that air-pollution exposures also can impact neurodegenerative diseases like dementia, which are becoming more and more important as populations age around the world.” (8:50)
• Improving air quality is a long-term project: “Progress generally takes time when it comes to air pollution. So, even if countries or cities were to implement measures today, we won’t really see the results in two months or six months. We need long-term, sustained resources and funding to keep doing it.” (28:15)

Top of the Stack

• “Air Quality and Health in Cities: A State of Global Air Report” from the Health Effects Institute
• Agents of Change in Environmental Justice podcast

The Full Transcript

Kristin Hayes: Hello and welcome to Resources Radio, a weekly podcast from Resources for the Future. I'm your host, Kristin Hayes. My guest today is Dr. Pallavi Pant, head of global health at the Health Effects Institute, or HEI.

Dr. Pant is the lead author on a new study that came out earlier this year called “Air Quality and Health in Cities,” which is part of HEI's State of Global Air series. Our conversation today focuses on the findings of that report, which explores the prevalence of fine particulate and nitrogen dioxide pollution in more than 7,000 cities worldwide. Given the large-scale impacts of air pollution on human health and the sheer number of people who live in cities, this report has important lessons for, quite frankly, a substantial portion of humanity. Stay with us.

Thanks so much for joining me today, Dr. Pant. It's great to have you here.

Pallavi Pant: Thank you so much. It's great to be here.

Kristin Hayes: Quickly, before we dive into the substance of the report, I always like to ask guests to share a little bit about their backgrounds and, in particular, I'd love to know how you became interested in research on air pollution and on health broadly.

Pallavi Pant: I grew up in Delhi, which some people may have heard about, because it often is in the news for being one of the most polluted cities in the world. Apocalyptic pictures emerge from time to time during winter. Growing up in Delhi, we've had phases of air-pollution problems, but it wasn't the immediacy of air pollution that put me on this spot.

My first interaction with air pollution was when we were being taught in schools that fireworks that are used extensively during one of the major Hindu festivals, Diwali, are not that great for the environment, and you can have bad exposures to pollutants and metals that are coming from them. There were other issues related to it, but the idea that burning something and being very close to it was bad for your health and the environment stuck.

Over time, college, and afterwards, during my masters, I started focusing a little bit more on air pollution as an issue. It was very immediate, around us, and something that you could do something about. That's how it started. Over the years, I've been fortunate to keep working in India on air pollution–related issues and also to get to work with colleagues from different parts of the world to figure out why the air pollution is there, what the sources are, and also hopefully figure out ways to reduce it and improve people's health.

Kristin Hayes: I wanted to start by asking about the types of air pollution that you actually looked at in this study. My understanding is that there are two primary types: fine particulates and nitrogen dioxide. Where do those two types of pollution typically come from, and how do they impact human health? Can you say a bit more about how fine particulates and nitrogen dioxide typically get into the air—and then, why do we care? What are they doing to human bodies that make them so problematic?

Pallavi Pant: In very simple terms, if we think about air pollution, a lot of it comes when we burn things. You could be burning a piece of paper, you could be burning incense sticks in your home, you could be burning fossil fuels to produce energy—all of it is going to potentially lead to air pollution if the combustion is not efficient and not complete.

So, combustion is one major category of sources that result in air pollution—both the fine particulate matter, which are these tiny particles that are often invisible to the human eye because of their very small size; and also gases like nitrogen dioxide that come from combustion-related sources. Think about coal being used for energy production and about cars and other types of vehicles where we are using fuel, gasoline, or diesel to run them.

We can think about industries where there are a number of different processes where, again, combustion is happening. In some countries, especially in lower-middle-income countries, we also know that sources like waste can be a contributor to air pollution, especially particulate matter, mostly because in the absence of very structured waste-management practices, it can be hard to get rid of all of that waste.

We end up burning it, which then results in air pollution. There are also some more natural sources of air pollution. For people here in the United States, every year, we hear very consistently about wildfires. While we can debate how they started, the burning of forests essentially releases a lot of particles and gases into the air. That is a form of air pollution, as well.

In other parts of the world where we have deserts, the dust from the desert can contribute to poor air quality. Often the particles tend to be bigger in size, and we won't necessarily see gases like nitrogen dioxide. But, for particles, that is also a source of higher levels of PM2.5, even PM10, which is a larger particle. So, we normally try to classify these particles by size; fine particulate matter, or PM2.5, is what is 2.5 microns in diameter or smaller. We cannot see them with our eyes. A single strand of hair is about 50–70 microns, in comparison.

Those are some of the common sources of air pollution in different parts of the world. Some sources are very similar between PM2.5 and nitrogen dioxide, because of the nature of how the pollution occurs. In principle, when we think of nitrogen dioxide or nitrogen oxides in general, which are a bigger class, they're often most closely linked with traffic-related air pollution, which is also why, for populations and cities, this can be a big contributor to where and how they might get exposed to air pollution.

Industries and power plants are other major sources. For fine particulate matter, it's a mix of power plants; industries; in some cases, construction; waste burning, in some parts of the world. We also see burning of agricultural waste in certain seasons and during certain times of the year, which can contribute to the creation of particles. What's unique in the case of fine particulate matter, PM2.5, is that we not only emit it from certain sources, it can also be created in the atmosphere in the presence of other pollutants. A whole range of sources can contribute to these pollutants.

Kristin Hayes: Can you say a bit more about what the fine particulates and the nitrogen oxides are doing to our lungs and, maybe, to other systems in the body?

Pallavi Pant: There's been a lot of research over the last few decades trying to understand how air pollution affects our health. In many instances, we tend to think about air pollution impacting our lungs and respiratory system, which, of course, is a major organ system within our body that is affected by air pollution. For many people, this means living with chronic respiratory diseases like chronic obstructive pulmonary disorder, or COPD. Asthma is another disease that has been linked with air-pollution exposure, both in terms of exacerbation if someone has asthma, and, in some cases, developing asthma as a result of exposures to air pollution.

But in reality, the impacts of air pollution aren't limited to just our respiratory organs. We have substantial evidence of the role of air pollution in chronic heart diseases, in stroke, in certain types of cancer—especially lung cancer—and in other types of chronic diseases like type 2 diabetes.

For some countries, the contribution of air pollution to these types of diseases can be very big. Growing evidence shows that air-pollution exposures also can impact neurodegenerative diseases like dementia, which are becoming more and more important as populations age around the world.

It's a variety of organ systems and a variety of ways in which air pollution affects our health. All of this is long-term exposure. We're getting exposed to air pollution over months and years of our life. In some cases, when we are only thinking about the 20- or 30-minute exposure that may happen if you're walking next to a road, or sometimes when air-pollution levels just get really high, those can increase hospitalization. More people are going to visit the emergency department. For people that are already living with diseases, like lung diseases and heart diseases in particular, we can see exacerbation of those. For a lot of people, water in your eyes or difficulty breathing occurs when pollution levels get particularly high, as I've experienced a few times in Delhi.

Kristin Hayes: Let's turn to the specific report focused on cities. I wanted to ask a bit about the data. This is a robust picture—7,200 cities—that were covered in this report. That's a lot of data that you need to put together in order to provide that robust of a picture. Where did you combine the data that you use for this study, and how did you combine it to be able to present this global picture?

Pallavi Pant: It's definitely one of the most important questions in relation to this report. We worked with our collaborators at George Washington University: Dr. Susan Annenberg was one of our primary collaborators, and also colleagues at the Institute for Health Metrics and Evaluation, or IHME. Some people may have heard about IHME more recently in the context of COVID. They have a long-running project on understanding the global burden of disease linked with a variety of risk factors, which includes air pollution, but really includes a host of other factors like malnutrition, physical inactivity, etc.

We worked with both of these groups together to produce this report. One of the biggest challenges we face, when we start looking at air pollution at the global scale, is that we don't know nearly enough about the reality of air pollution in many parts of the world.

That's partly because we don't have sufficient monitoring stations at scale. In some countries, including the United States, we have a relatively high density of air-pollution monitors, especially for fine particulate matter, PM2.5. But in other parts of the world, if we look at entire continents like Africa, we have very limited data. For this report, we combined what we have from ground monitoring stations, which are stations in different cities and in some cases in rural areas or at places where there are no immediate sources of air pollution. But we still had a lot of gaps.

Then, we looked upward. There are a lot of satellites around that capture data on various types of pollution. In the last few years, there have been a lot of advancements in ways that we can use the satellite data effectively. We combined ground-based data with satellite data and then used atmospheric models to really understand what the patterns of exposure are in different parts of the world. You can get a relatively consistent picture for countries around the world.

The data set is comparable enough within itself that we know we're using the same parameters and data set. The good thing with an approach like this is that we are able to talk about cities around the world. In the report, we included about 7,200 cities. There are estimates available for even smaller locations: places that may have smaller populations, but are classified as urban centers. But one of the challenges, still, is that we do not have sufficient ground-based data from certain places. There are some things where we still need to improve, but it was this combination of different types of data sources that led us to the analysis and finally producing these figures for cities around the world.

Kristin Hayes: I struggled a little bit to know what exactly I wanted to ask you about the specific, city-level findings. The core question is not to call out winners and losers in this game. Ultimately, the question that I wanted to ask was what do the cities with the worst outcomes in these two types of pollution—PM2.5 and nitrogen dioxide—have in common?

Pallavi Pant: We do tend to look at who's doing well and who's not doing so well. So, I really appreciate your question, and there are a few things that become evident as we start looking at these global patterns. I'll start with PM2.5.

Over the last many years, we've started to get this understanding that the levels of PM2.5 vary quite significantly across continents and across countries. We have a lot of countries in Asia, including countries like India and China, that often get a lot of coverage for air pollution, but also countries like Nepal, Pakistan, and South Asia, or some of the southeast Asian countries, have relatively high levels of PM2.5. There are countries in Africa that have really high levels of PM2.5. On balance, if we look at global maps, parts of Asia and parts of Africa tend to stand out in terms of how bad the air pollution, or PM2.5, levels are there.

When we look at the city-level data, similar things show up. The cities with the highest levels of PM2.5 tend to be in South Asia, in Africa, in southeast Asia. A lot of them are cities that are rapidly growing; more infrastructure is being built. The vehicle-technology measures may not be as stringent as they are in other parts of the world, especially if we look at North America and Europe, where PM2.5 levels tend to be lower.

They're in that process where there is growth and development, and, with it, air-quality management slowly is being built in. But sources may not be as strongly tackled yet. That includes energy production, vehicles, sources like waste-burning.

But when we start to look at nitrogen dioxide levels, a slightly different picture emerges. We don't see cities from India or Nigeria or Pakistan on the top of the list. We see that cities in areas that are considered more high income have relatively higher levels of nitrogen dioxide exposures. A lot of cities from the Middle East show up when we start looking at higher levels. Central Asia, another place that wouldn't necessarily come on the top of our list for PM2.5 exposures, has a lot of cities with high levels of nitrogen dioxide exposure. Eastern Europe is another place that comes to the top of the list. When we start to think of the countries or the cities with highest levels of air pollution, and we have PM2.5 in mind, we have a list that comes up, and you would expect places like Delhi to be on that list, and you might expect some cities from African countries to be on that list.

But with nitrogen dioxide, a whole other list shows up. We start to see cities from countries like Russia and Iran and Turkey and Uzbekistan among the highest levels of nitrogen dioxide exposure. In a lot of places where we see higher nitrogen dioxide exposures, we also know that, in many cities of that kind, we have older vehicles that may be more polluting or using fuels that have higher content of sulfur and other additives.

The vehicles may not be running on all of the control technology that we see in high-income countries. It is also very interesting to see that some of the cities that have over many years put in place stringent controls in terms of what vehicles can emit and what types of technology goes in—they are still trying to figure out how to reduce nitrogen dioxide exposure. Even in cities such as London in the United Kingdom, or in Paris, France, we see relatively high levels of nitrogen dioxide exposure. These are also some places where we see more use of diesels for passenger vehicles. The stories are vastly different depending on which pollutant you start to focus on.

Kristin Hayes: How much do you know from the body of knowledge that the community has generated around why that differentiation occurs? Is it still a mystery, or do you feel like the air-pollution-and-health community has a sense of why those two concentrations or exposures would diverge so much?

Pallavi Pant: There are some answers and some clues that we have. For example, nitrogen dioxide as a pollutant tends to be higher closest to the source. If you have urban environments where there are lots of vehicles—and especially if these vehicles tend to be higher-emitting vehicles—we might experience higher levels of nitrogen dioxide in those places. But even within a matter of a few kilometers away from the source, we start to see the levels of nitrogen dioxide decline.

Spatially speaking, nitrogen dioxide is a pollutant of which you see really high concentrations closest to the source, whereas, for pollutants like particulate matter, we can see very similar levels over kilometers of space because there are regional sources that are also contributing to the generation of these pollutants. The other factor, which is important to keep in mind, is that we have a lot more information on particulate matter from the ground monitoring stations than we do for nitrogen dioxide.

Countries have invested more in setting up monitors for PM2.5; we've known that PM2.5 is a consistent predictor of health effects, so investments have been made into monitoring and measuring what the levels of particulate matter are. Some of it comes down to how the sources are being addressed or tackled. As you would appreciate, air pollution is an issue, but it often connects very strongly with other decisions that are made in transportation, in energy production, etc.

What vehicles are on the road where some of the other sources of air pollution might be with respect to the city—whether it's industries or power plants, which can also emit nitrogen dioxide—can make a lot of difference. Some of the other competing sources for PM2.5, for example, may not be as strongly present in some of the cities, resulting in higher nitrogen dioxide exposures, but not really high exposures for PM2.5.

Kristin Hayes: Imagine it's October, 1952. There's no such thing as the Clean Air Act or Clean Water Act. There are no federal fuel standards for cars and the Environmental Protection Agency doesn't yet exist. That was the year Resources for the Future (RFF) was created, 70 years ago this week. Ever since October, 1952, RFF has been developing innovative policy solutions for the most pressing environmental, energy, and natural resource issues. As we commemorate RFF’s founding, please consider donating to help us carry on this critical work for another 70 years. Visit rff.org/donate to make your gift to RFF today.

So, Pallavi, this is a report that's focused on cities, but it is part of a long series that HEI has been putting together with partners on the state of global air. Because there is that longevity, I'd welcome any thoughts you have on what this report shows in terms of levels of pollution either abating or getting worse, and then what's driving some of those changes.

Pallavi Pant: With reports like these, which cover data both over spatial differences and over time, we are able to look at where we are making progress and where we may need to pay more attention. Consistent with what we have been hearing and looking at in the data over the last few decades, a lot of cities and high-income countries have been making progress in improving air quality. This is very evident when we start to look especially at the data for nitrogen dioxide. Cities including Los Angeles, which within the United States tends to be a place with relatively high air-pollution exposures have seen big declines over the last 10–20 years. That is consistent with the policy decisions that have been made to try to reduce emissions.

That is a narrative that we hear about a lot. We know that countries in North America and countries in Europe have been investing in improvements of different emissions from sources. But what we are also seeing at the same time is that there are cities which are rapidly developing and growing, including some in Eastern Africa, Latin America, and Southeast Asia, which are starting to see levels of nitrogen dioxide go up, which is somewhat worrying.

That's perhaps an area that we need to keep focusing on. A couple of examples have been encouraging, because the quest for clean air takes a lot of time and resources and, in many countries, you have the competition of where the money and time gets spent and which problem is bigger. But in the case of China, we've seen with data at the national level—in our previous reports, we see some of it here in the city level data, as well—that the policies and the programs that have been brought about over the last eight or so years have resulted in improvements that are visible.

We're already beginning to see in the data significant improvements both in PM2.5 levels and in nitrogen dioxide levels over time—even though the levels for both PM2.5 and nitrogen dioxide are high when we start to look at the guidelines that the World Health Organization has put forward. But we are seeing progress, and we're seeing improvement.

That has come about with very consistent policymaking, trying to reduce emissions at source, and trying to find ways to cut down on what is being emitted into the atmosphere in the first place. We are also seeing, in some African countries, very good progress being made to improve our understanding of air quality, and we are starting to understand what the levels of air pollution are and how we can make progress on those.

We highlight some examples in our report, but two that I'll point out are Accra in Ghana and also Addis Ababa in Ethiopia, both of which have taken significant steps in recent years to try and understand the sources of air pollution and come up with plans to improve our understanding of how these sources are affecting the air quality and people's health and also have put in place measures that will eventually lead to improved air quality.

But progress generally takes time when it comes to air pollution. So, even if countries or cities were to implement measures today, we won't really see the results in two months or six months. We need long-term, sustained resources and funding to keep doing it.

Kristin Hayes: You did say in China that the progress had been measurable in 8–10 years, which, in the scheme of things, is a pretty rapid improvement. That's heartening to hear that changes can be felt and seen in less than the span of a lifetime, which is important.

I wanted to ask you another temporal question. This one struck me when I noticed that the data that are underlying this report are from 2010 to 2019. What's so interesting to me about that time period is that, as the entire global population is all too aware, 2020 was crazy. The pandemic rapidly changed the ways that people travel and work; these patterns were shifted in very significant ways. If you do a report in a decade, let's say, what will that radical disruption in the typical patterns of vehicle usage and of other facets of urban life do—what do you think you'll be able to learn from the shock to the system of the pandemic?

Pallavi Pant: That's a fascinating question, and one we've all been thinking about quite a bit. Because, in the early days of the pandemic when countries and cities were trying to figure out how to really control the pandemic, efforts were made to shut down as much activity as possible. Despite the massive amounts of loss that we have seen as a result of the pandemic, this was the time when a lot of people in different places were able to experience what clean air can look like. It gave them hope that perhaps it is not a moonshot to think, “Can we really clean up our air, and is it ever going to work?”

A slight dampener on the hope message is that, even as lockdowns were lifted and people started going back to some business as usual with some new ways of living and commuting and all of it, there have not been as many longer-lasting changes to some of the air pollution–related issues.

For example, one unfortunate thing in some places that has happened is that, as a result of the pandemic, more people are using their own vehicles, which means we have more cars or more passenger vehicles on the road. And because of the economic impact of very strict lockdowns, some places have also made decisions to push for more industrial activity or push for certain ways of doing things, which would mean perhaps more air pollution in the short to medium term.

One example is, again, China, which has seen a lot of progress over the last 8–10 years: In the wake of the very stringent lockdowns, we did see the coal consumption levels go up quite a bit. It remains to be seen what we will observe in a report like this 10 years from now.

It's going to be a mixed bag again, perhaps, because cities and countries are trying to understand what they can take away from the lockdowns, what we learned from them, and what we learned from this whole experience. Perhaps similarly to what we've seen already, there are going to be differences across regions, depending on what approach we take and what types of decisions we make to give people choices that would be cleaner, whether it is investing in cleaner energy, making public transportation easier, etc.

But the biggest takeaway for me and, I think, for many other people, has been this hope that, “Clean air is doable, here's what it looks like, and we can make it happen.”

Kristin Hayes: I appreciate you taking the time to talk through the report findings. I certainly encourage listeners to go take a look at the wonderful detail that is in the report.

I wanted to close our time together with our regular Top of the Stack feature, and I'd welcome any suggestions you have for more good content. Again, it can be on this topic or another that our listeners might want to take a look at. So, what's on the top of your stack?

Pallavi Pant: I would like to highlight another podcast that I've been listening to for some time now, which features younger environmental health researchers, community practitioners who are trying to make a difference through their work. It's called Agents of Change, and it was established by an academic, but they've been growing the program, and it brings together wonderful, uplifting, and inspiring stories of how and where change can happen, or even, in some cases, just raising those uncomfortable, difficult questions that we need to come to grips with, both in terms of interpersonal interactions and what our biggest environmental health problems are that we need to tackle today and into the future. That’s definitely on top of my list, and they've announced a new cohort of fellows, so I'm excited about hearing and reading what they have to share with us.

Kristin Hayes: Fantastic. I appreciate the recommendation and all the insight that you've shared with us. It's been a pleasure. I hope we can talk again soon.

Pallavi Pant: Thank you very much.

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