Can we reduce pollution?

Speed read

• Daily human activities impact the environment, especially air quality

• The COVID-19 pandemic forced many people to severely restrict travel

• This scientist takes a close look at how reduced mobility correlates with better air

Asking someone if they believe in climate change is like asking a toddler if they were the one who scribbled on the wall. It doesn’t really matter if they own up, the mess is still there.

Pandemic stay-at-home orders meant weeks of parked cars and empty streets. Could a parallel decrease in nitrogen oxide air pollutants be related? Courtesy kgbo. (CC BY-SA 4.0)

The study of climate change isn’t about convincing people—it’s about understanding what’s happening to our world. That’s the attitude Brian McDonald, an environmental engineer at the National Oceanic and Atmospheric Administration (NOAA), takes toward his work.

In his ongoing research studying the impact of human activity on air quality, McDonald soon saw evidence that pandemic stay-at-home orders seemed to have lowered the quantity of some pollutants present in the air, particularly nitrogen oxides. He believes this marked decrease in NO2 concentrations will help him assess how well earth monitoring and modeling capabilities are able to track changes in human activity.

“There have been some changes in directly emitted species, like nitrogen oxides,” says McDonald. “As far as how the total emissions have changed, I think that's still an ongoing question. And how those total emissions change is going to affect our understanding of how ozone and particulate matter levels have been affected.”

Ozone is found in both the upper stratosphere and the troposphere. Unhealthy levels of ozone can cause shortness of breath, increase asthma attacks, and damage the lungs. Courtesy Randy Russell, UCAR.

While the danger of particulate matter is easy to understand—small particles get in your lungs and harm your body—ozone is a little more complex. A highly-reactive gas made up of three oxygen atoms, ozone can be found in the upper stratosphere and in the troposphere that we live in. Much of the ozone in the air we breathe comes from pollution, and it can contribute to smog.

The COVID-19 pandemic occurred in the middle of general air quality research McDonald was already conducting, and as such he’s reluctant to give any hard conclusions. That said, it’s pretty clear that more people at home instead of out polluting has an effect on the air we breathe.

Human impact

The idea that “less people polluting = less pollution” isn’t new, but McDonald is interested in exploring the bigger picture. What’s more, he’s relying on some pretty cool technology to get the job done.

McDonald relies on the Tropospheric Monitoring Instrument (TROPOMI) on board the polar-orbiting Copernicus Sentinel-5 satellite to capture snapshots of chemical species in the atmosphere around midday across the globe.

Pollution detector. A monitoring instrument on board the Sentinel-5 satellite captures daily snapshots of chemical species in the atmosphere. Courtesy European Space Agency.

“The satellites we use can see nitrogen dioxide, which is a species that you can see from space that gives you an understanding of NOx emissions,” says McDonald. “There have definitely been changes in those satellite retrievals. We know that NOx emissions have likely decreased.”

NOx refers to a group of oxides of nitrogen, which are all gases that contribute to air pollution. Without making hard conclusions from an incomplete study, it’s likely that much of this NOx emissions drop came from the reduction in cars on the road.

However, that isn’t the end of the story. McDonald points out that while widespread stay-at-home orders took a lot of individual drivers off the road, the pandemic may have also affected air quality in other ways.

“Freight traffic these days is a relatively significant source of NOx emissions,” says McDonald. “And it's not clear that there's been a big reduction in freight. I see Amazon and UPS and FedEx trucks all the time.”

McDonald’s early reading of the data points to the conclusion that individual human activities are contributing to poorer air quality. However, the problem is much bigger than that. From shipping the goods we need to producing the food we eat, modern living makes it nearly impossible to avoid a negative impact on the environment. Climate change might lessen if we begin to make better choices as individuals, but we’ll need bigger alterations than that.

Letting the machine do the heavy lifting

McDonald’s work focused on 12 square kilometer sections of the country, which helped give him a granular look at air quality across vast swathes of the US. Therefore, the best way to do meaningful research is with high-performance computing (HPC) machines.

McDonald relied on Hera, NOAA’s 2.7 petaFLOPS supercomputer. While the data load itself was intensive—this work incorporated data from hundreds of monitoring sites—McDonald also reflects on the complexity of the system he’s studying.

What matters most. While individual drivers stayed off the road during pandemic closures, freight traffic—a significant source of nitrogen oxide emissions—did not decrease. Computational models help researchers determine which changes have the greatest effect on air quality. Courtesy Elvert Barnes. (CC BY-SA 2.0)

“If you're looking at something like air pollution or air quality, you take into account the emissions that occur at the surface ,” says McDonald. “But that's going to be transported by winds and other wind dynamics. And then you also need to use linear algebra to solve matrices of chemical reactions in the atmosphere as it's being transported.”

With the power of Hera, McDonald relied on a model that connects surface emissions to ozone and hazardous particulate matter formation. The computer also helps McDonald recognize if this decrease in air quality is really due to emissions or to other factors.

Again, McDonald is quick to point out that he’s not done with this research. Regardless, he’s very aware of how important this work is. What’s more, he’s optimistic that we can learn from it.

“These changes in traffic—do they give us insights into a future where you can reduce traffic emissions?” says McDonald. “Not just from a reduction in driving, but from electric vehicles, better public transport, or other technologies? There's a variety of ways that emissions can decrease beyond the pandemic.”

COVID-19 has ravaged communities, the physical and mental health of hundreds of thousands of people, and the global economy. We can easily recognize it as one of the worst events of the 21st century, but that doesn’t mean we should ignore any lessons it’s taught us.

Convincing people that climate change is real is no longer the goal, if it ever was. It may be a beneficial side effect of work like this, but we’ve moved well past that. We don’t need studies like McDonald’s to compel non-believers—we need them to remind us that we can stop this madness any time we want.

We just need to decide what’s most important to our species.

Originally posted on Science Node