Conversations: DeCarlo on Philly Air Quality

“Conversations” features faculty members addressing topical, occasionally polemical issues from an engineering perspective.

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The explosion in June at the Philadelphia Energy Systems refinery and the subsequent decision to close it down and sell the property raises a host of broader questions about the competing interests of economics and health; among them, Philadelphia’s air quality and the factors that define it. Dr. Peter DeCarlo, an associate professor in the Department of Civil, Architectural and Environmental Engineering (CAEE) whose research on air quality has spanned the globe, sat down for a Q&A on the air Philadelphians breathe and the issues he believes should be addressed today for a cleaner tomorrow.   

How is Philly’s air quality?

In terms of ranking in population, we’re sixth. And I think in terms of air quality, we’re 18th or better depending on the pollutant. So, proportionate to size we’re doing better than other cities. Air pollution is going to be due in part to population—the more people you have in an area, the more driving, the more industrial activity, the more pollution you typically have. When you add up all the different sources, you get your total emissions. We’re also on the eastern seaboard. From DC up to Boston, we have a huge population and that I-95 corridor is a massive economic activity engine. If you look at air quality, it’s regional as much as it’s urban. For reference, New York City a few weeks ago had ozone over 100 parts per billion. Our national air quality standard is 70, so it’s significantly exceeding what we deem safe for air quality.

What is ozone and why is it a bigger problem in the summer?

Basically, ozone is a pollutant that’s formed in the atmosphere. It’s not emitted. It needs a mix of what we call volatile organic compounds (VOCs), and these come from things like evaporated gasoline, but can also come from trees. So, if you’re in a pine forest, that pine smell … those are also VOCs, and those react with nitrogen oxide (NOX), which comes from combustion sources. So between cars, driving and industry, anytime we have a high temperature combustion process you create a little bit of NOX. When they mix in the atmosphere, you generate ozone. Higher temperatures mean chemical reactions happen faster. Really hot days mean you can generate more ozone and faster, and since you really can only generate it when the sun is out—because that’s another ingredient needed to kick off that chemistry—hot summer days are when we have our worst ozone conditions.

How do you measure air quality?

One of the projects I’ve been working on since I’ve been at Drexel has been looking at the relationship between indoor and outdoor air quality. So in my lab, we actually have an inlet that goes out through the roof of AEL. We bring in air from outside to my lab, where we have a bunch of different instruments that can measure the composition of the particulate matter with one-minute time resolution, 24-7. And then we’ve also made measurements in a classroom next to my lab. That is where we found the residual cigarette smoke contribution reported in the press last year.

What does it look like inside and outside, winter and summer? It gives us this contrast between what is the composition of particulate matter and what are the different sources seasonally. In summer, for instance, we definitely get more cooking aerosols that don’t happen in the winter. In the winter, we see sulfate and nitrate and ammonium. The sulfate almost exclusively comes from coal burning. It leaves the coal-fired power plant as sulfur dioxide, which oxidizes in the atmosphere to become sulfuric acid, which then can go into the particles to pair with ammonia to make ammonium sulfate. A lot of that coal burning is happening in the Ohio River Valley and Western Pennsylvania and Virginia. That air moves to the East Coast—most weather systems go from west to east—and it brings with it all those pollutants.

What are the biggest threats to air quality in Philly?

The thing in Philly is that roughly 80% of the particulate matter is regional, and so we get a little bit of a bump in the city and those are going to be due to activities in the city and immediate areas—the airport, traffic, and the refinery will be a problem if its’ going to continue as a refinery. The more vehicles you have in the city, the more of a problem you’ll have with emissions. So those are the biggest sources to think about here. And then you have the regional source and what’s happening in the vicinity of the city that also contributes.

How can we improve our air quality?

If you could improve air quality in DC and Baltimore and Wilmington, that would also affect our air quality. But in Philly, it’s largely about reducing vehicle emissions, and there are two ways to do that. The worst thing for air quality is cars sitting and not going anywhere and burning fuel and emitting that into the atmosphere. Cars moving freely are going to emit less per mile driven. The activities that California has actively pursued are to build more roads and bigger roads, and for each road they build they get a little bit of a benefit from less congestion for a period of time. But, of course, eventually that gets backed up too, and there is a limit to how big you want to build your roads and how many roads you want. So the other strategy is just to reduce the need for cars: improve public transportation, make it more convenient.

When I lived in Switzerland for two and a half years, I didn’t have a car and I didn’t need one. The bus and rail system ran incredibly well. It was on time and it got people to where they needed to be, and a huge fraction of the population utilized that. I could go anywhere in Switzerland I needed to go with my pass. I could get on my bike and bike as far as I could possibly go in one direction, then I’d find a train station and come home on the train.

There are ways that public transportation can be done well. There are people who’d say, well, the population density is much higher in Switzerland and so it’s easier to do that kind of infrastructure. But we can find ways to improve our infrastructure, and we can make our trains go faster. However, there has to be a political will to do that, and that gets into issues of climate change and when we actually recognize that as a problem we need to address.

We are talking in the shadow of the Philadelphia Energy Solutions (PES) refinery explosion. You were asked to sit on the mayor’s advisory group on PES?

Philadelphia Energy Solutions (PES) refinery
The Philadelphia Energy Solutions refinery (in a 2016 photo) was shut down following a fire in June, 2019.

Yes, I’m a member of the mayor’s advisory group. The first meeting was in late July. My expertise is going to be environmental air quality and particularly air quality issues associated with the refinery. I’m trying to also work with colleagues to get some more information about other health impacts and costing that out and trying to bring that voice to the table. It’ll be interesting. The group has a lot of people who have worked for the refinery for years and have very strong opinions about its future.

Ultimately, none of this is up to us. It’s up to whether PES can find a buyer, and if not, what the plan is going forward. And so, what can the city do to incentivize that land in a way that is beneficial to the city? I think that is our charge. I’m there to try to keep an environmental voice in that conversation.

How is PES going to impact air quality going forward?

PES is not going to fire the refinery back up, but if there’s another buyer that comes in and wants to continue operating as a refinery, that’s a possibility. PES can sell to whomever they want. We can’t stop them from doing that. But the economics don’t look good. PES was about to go into bankruptcy again. It’s going to be hard to see any kind of smart business coming in and accepting that risk of potentially losing money.

So the question becomes, what would be next? That leads into a whole host of other questions about what can you do with that land. It’s been a refinery for 150 years. It’s incredibly contaminated. We didn’t have automobiles when it started, so the gasoline fraction of the product was just dumped on the ground early on since there was no market for it. The lead levels are high. The heavy metal content of the soil is untenable for anything other than an industrial site. But it still has to be remediated to be able to use it. So, what level of remediation will that land get? Who would be willing to take it, balancing jobs, balancing the environment, balancing neighborhoods, and people in the area? Lots of questions to think about.

Where’s the balance between economics vs. what puts air quality at risk?

There’s a reason that industry in Philadelphia has for the most part left and gone outside of the city. And the reason is, that balance can’t be found in neighborhoods. Putting heavily polluting industries in an urban populated area is a health risk. You can cost those out—incidences of asthma, missed work days, early death from a host of diseases like cancer. When you do those calculations, the cost of having an industrial facility in a highly populated area is outweighed. The economic benefit isn’t there.

“Ultimately, none of this is up to us. It’s up to whether PES can find a buyer. What can the city do to incentivize that land in a way that is beneficial to the city? I think that is our charge.”

If you look at any modern standard, PES would never be built where it is today. If we had to site a refinery in this region, the confluence of two rivers in an urban, populated area is not where you would put it. It’s been grandfathered for over 150 years. But now we are going to have to ask the question, what else can we do with this land that isn’t going to be as damaging to the city and the people who live around it?

What are the bodies charged with tracking our air quality?

In Philadelphia itself, it’s the Philadelphia Air Management Services, which is a part of the Health Department; in Pittsburgh, it’s the Allegheny County Health Department; and for the rest of Pennsylvania, it’s the state Department of Environmental Protection. The EPA is the federal agency charged with making sure air quality is safe. EPA provides funding to state and local agencies to do air quality monitoring and these types of assessments. Larger cities tend to have their own air monitoring, with states picking up the rest of the areas for monitoring.

In Philadelphia, there are nine monitoring sites that are run by the city. But not all of them have the full suite of measurements. There are seven sites that are more regulatory; five of those have two or fewer measurements. So really, there are only two sites that have a pretty big suite of air quality measurements.

A little background on this: in 1970, the first Clean Air Act was written and the EPA was formed; in 1990 there was a big amendment; in 1997 there was another amendment. If you look at the present, ozone and particulate matter (PM) are the two areas that we’re struggling to stay in compliance with. With ozone, we’re on the edge. With PM, we’ve just come into compliance. From a regulatory perspective, we are doing much better than we used to. So if we’re in compliance with most of the pollutants, we don’t necessarily need to be measuring them all the time. That’s the thinking for not having every measurement at every site. We do measure ozone and PM at multiple sites because those are the ones where we’re closer to the limits.

From a science perspective, though, understanding ozone means understanding what the NOX concentration is. Some of the ozone sites we have, we don’t have that complementary monitor for NOX. There’s no parallel measurement. Understanding those two simultaneously is really important. From a regulatory perspective, what they care about is looking at the ozone and making sure we’re not going to exceed the designated level for what is considered safe. But from a science perspective, I want to know what the NOX is, too, because the NOX concentration is really important for understanding what the chemistry is and what’s happening.

That’s a long-winded way of saying the city is fulfilling its regulatory capacity, which is what it’s charged to do. But in my work, we really seek to understand the chemistry of what’s going on in the atmosphere and how different sources play a role in that. If I had my way, I’d love to see more monitoring.

If air quality is also a regional issue, then are we talking with others?

The EPA has divided the country into 10 regions. We’re in Region 3 and their headquarters are in Philadelphia. So the EPA has a regional office in the city. It’s Pennsylvania, Delaware, Maryland, Virginia and DC, so you’re talking the whole Mid-Atlantic. Pennsylvania interfaces a lot with New Jersey because New Jersey is downwind of Pennsylvania. And then there is an organization called MARAMA, the Mid-Atlantic Regional Air Manager Association, Inc. They hold a meeting annually where all the state, local, and regional air quality experts get together to discuss what they’re seeing. There are also international interactions; the US and Canada, and the US and Mexico have treaties discussing air quality crossing borders.

The US population is getting more urbanized: how essential is it that we grapple with urban air quality now?

We have been continuously improving our air quality since the founding of the EPA and you can track the concentrations of all the pollutants. It does look like we’re kind of bottoming out, though. There’s only so many more improvements you can make, and the population and population density is really important when you’re looking at air quality. So as we urbanize it potentially becomes more of an issue.

“Philly has a great opportunity right now to make decisions that are going to last another 150 years and be something that we can be proud of, realizing that climate change is a massive problem.”

Under the Obama Administration, the fuel efficiency standards for vehicles were supposed to be getting better. I think the Trump Administration is trying to roll those back. But those are steps that if you do that and you’re burning less fuel per distance traveled, then you’re going to have less emissions. Electric vehicles are another benefit because they don’t emit in the city. Power generation that provides the electricity emits pollutants elsewhere, so electric vehicles don’t have that street-level emission where people live, work, and play.

And then if you talk about generating electricity cleanly—and I include nuclear in that as a possible clean or non-fossil source—and renewables with wind and solar and hydro, anything that’s not burning something to make power is going to improve air quality. Just electrifying vehicles is a step to take, and then cleaning up our electricity generation is a second step.

Are you hopeful?

I am. I think Philly has a great opportunity right now to make decisions that are going to last another 150 years and be something that we can be proud of, realizing that climate change is a massive problem. A lot of the projections for climate change go out to 2100. I won’t be here in 2100 but my kids might be, and my grandchildren certainly will be if they choose to have kids. I want what’s best in 2100, for them. We can make decisions now that do have an impact on that. I think it’s time to recognize climate change now for the threat it is, and take the steps now to make a better world.

What are you currently working on?

I’m working on a host of things. One project is continuing the third-hand smoke work we published last year, and expanding it to e-cigarettes. So those are the indoor things. We participated in this HOMEChem study (at the University of Texas-Austin with a huge group of collaborators from a bunch of different institutions), the largest indoor air quality field campaign. And then, our Nepal work is continuing. We also currently have an instrument in India flying through clouds to look at particles and how they make clouds and are changed by clouds.

Who funds your participation in these projects?

The Nepal work is a National Science Foundation-funded project. The instrumentation I need to do what I do is quite expensive, and the countries that can afford it—US, Europe, China’s investing in this stuff—have bought the “toys” and the analytical equipment. So we have a very good idea what air quality is in the US and Europe, and a better idea now of China.

But there are huge parts of the world where we have very little understanding. We have these blank spots in the world about what air quality is, southeast Asia being a big one. Africa is also a place where we have very little idea of what urban areas in those regions look like. Since ours is a shared atmosphere and all of these are climate relevant—especially on the regional scale—understanding those emissions are really important. That was the motivation for us going to Nepal. The work we’re doing in India is a collaborative work, and this is a pilot study.

Where else you have taken monitoring equipment?

Antarctica was a big one. There are about five orders of magnitude of difference between Nepal and Antarctica. It was just enormous. But the cool thing is the instrument is sensitive enough to make really good measurements in both a pristine place like Antarctica and what we would nominally call a very dirty city.

The instrument is called an Aerosol Mass Spectrometer. It takes particles in the air, brings them into an instrument, shoots them at a heater and when they hit the heater they vaporize; we ionize that vapor and that gives us the composition of the particles, their history, their source, and basically acts as a window into where that air has been. It’s an instrument I helped develop during my PhD. I have a very long history with it, and it’s been a great tool for my research.

What’s the air like in Antarctica?

Most of the stuff in Antarctica is natural. There are a couple things we found—basically snow on that sea-ice surface. When the wind picks up, it can actually generate little particles and they are mostly based of sodium chloride (salt). And then there’s also other stuff. Oceans are filled with life and that biological activity actually generates gases that can then oxidize to make particles. There’s this whole feedback system and we see traces of that in the particles.

Where do you most want to go next?

Kenya. I did a year of volunteer work in Kenya before I went to grad school and I have a little piece of my heart in that country. I’d love to go back and see some friends and take measurements.

Essentially, one of the goals of the research that we do is to identify what the main sources of the particulate matter are through the composition measurements that we make—whether it’s open burning or traffic or industry—so we can start to identify what policies focused on the key source will give us the best benefit for air quality. So once we have that information, we find the strategies we can take to really target the biggest bang for your buck in air quality improvement.