Air quality control: Understanding atmospheric pollutants with Christian Salvador

While completing his undergraduate studies in the Philippines, atmospheric chemist Christian Salvador caught a glimpse of the horizon. What he saw concerned him: a thin, black line hovering above the city.

The line, Salvador later learned, was a layer of small particles suspended in the atmosphere. These particles, called atmospheric aerosols, are often emitted directly into the air from urban and industrial activities. They also have a considerable impact on the environment, from climate to human health, especially for the vulnerable parts of the population.

 “The bad thing with air quality is that everyone is exposed: the rich, the old, young and poor,” Salvador said. “You could be totally healthy, but still you’re exposed to bad air quality. Even if you’re a nonsmoker, you can still get lung cancer because of bad air quality. You can still get sick.”

With the black line slowly suffocating the city, Salvador knew he wanted to understand it and, more importantly, learn how to diminish its impact.

Salvador now works with the Environmental Risk and Energy Analysis group at the Department of Energy’s Oak Ridge National Laboratory, finding ways to improve our understanding of how atmospheric pollutants affect ecosystems and their impact on future climate conditions.

Aerosols and where they come from

Salvador works alongside biologists and environmentalists to determine how plant processes are impacting atmospheric chemistry. He uses mass spectrometry to gather real-time information about volatile organic compounds, or VOCs, and particulate matter emitted into the air during certain processes.

Many people are familiar with urban emissions; the particles often enter the atmosphere from cars and industrial activities. But there are naturally occurring emissions as well, and these are often emitted by plants, Salvador explained. As an example, peeling an orange releases a fruity smell into the air. That is limonene — an active gas that, once airborne, reacts to form the particles that can serve as a seed to cloud formation.

Alongside ORNL colleagues Melanie Mayes, Lianhong Gu and Kevin Birdwell, Salvador is studying the impact of meteorological conditions on the emission and transformation of urban and biogenic, or naturally produced, VOCs. Utilizing the Missouri Ozark AmeriFlux Site, or MOFLUX, where instruments atop a 106-foot-tall tower gather continuous data on local forest emissions, Salvador hopes to understand how gas emissions react with each other in the atmosphere. With the instruments at MOFLUX taking measurements 10 times per second, Salvador receives about 30 gigabytes of data each day. He’s using the data to observe how the concentrations of different VOCs are changing spatially and over time.

Closer to home in Knoxville, Tennessee, Salvador and Mayes are gathering and analyzing data in urban areas to understand how the natural and built environments interact. They are seeking to measure the impact of atmospheric aerosols on urban heating. The data will also be used to improve ecosystem and atmospheric models in simulating urban heat island effects, which could help scientists understand how natural ecosystem components like green spaces could mitigate climate warming.

This research focus is relatively new, Salvador explained, since aerosols were not seen as contributing to the urban heat problem until recently. New research is demonstrating that aerosols can increase temperatures more in urban heat islands than in rural areas.

Salvador is also working with a group of researchers led by ORNL’s Dave Weston to determine how plants respond to a future climate characterized by higher temperatures and carbon dioxide levels.

“Right now,” Salvador said, “scientists are just looking at the VOCs that are already out in the air and how they’re changing the atmosphere. But here at ORNL, we’re going further. How are these VOCs emitted by plants? What are the underlying molecular and physiological mechanisms? How are these VOCs going to respond in the future? We want a whole idea of what’s happening from the biosphere to the atmosphere.”

“We try to understand what the plants are emitting at the leaf level, which VOC concentrations are heavily impacted, and the VOC distribution as we change different meteorological conditions,” Salvador said. The research could help scientists understand how the changing climate could impact plant emissions in the future.

A father’s influence

Salvador’s interest in science began when a high school research class required him to conduct experiments outside the classroom. His father, an agriculturalist working at a national laboratory in the Philippines, took Salvador to his office, where several of his colleagues set out to get the high schooler excited about science.

“I was able to perform microbial analysis. I started thinking ‘OK, science is fun!’” he recalls.

After that experience, Salvador graduated and traveled to Quezon City — one of the most populous cities in the Philippines — to study chemistry at the University of the Philippines. There, he caught his first glimpse of the black line, but it would not be the only time, or place, where he noticed it.

After his undergraduate studies, Salvador enrolled in an Earth system science Ph.D. program in Taiwan, hoping to utilize his chemistry background to understand atmospheric pollutants.

SPRUCE-ing up the atmosphere

Today, Salvador is leading an atmospheric research project at DOE’s state-of-the-art Spruce and Peatland Responses Under Changing Environments, or SPRUCE project, a whole-ecosystem-manipulation experiment in the boreal peatlands of northern Minnesota.

The SPRUCE site was developed for terrestrial ecosystem measurements, with several large, temperature-controlled enclosures that scientists use to measure how the region’s climate-sensitive ecosystems will change in response to rising temperatures and atmospheric carbon dioxide levels. Salvador’s project is extending the facility’s capabilities into atmospheric chemistry: taking both gas and particulate measurements and observing aerosol formation.

Using the unique facility, Salvador is seeking to understand how future climate conditions will impact the formation of atmospheric aerosols and their impact on global warming.

When temperatures rise, plants emit a higher concentration of gases, said Salvador. An elevated gas concentration can generate more atmospheric particles, which modifies cloud formation. Clouds ultimately impact how heat is reflected into the atmosphere and back to the ground. It’s a feedback loop.

At SPRUCE, Salvador is trying to determine at what point the higher temperatures and CO₂ concentration will impact this loop.

In the past, these kinds of experiments were only done in small chambers, Salvador said. Small chambers do not capture what is really happening in the environment. With SPRUCE, researchers have a more accurate representation of what has happened — and what is going to happen in the future.

“Thanks to this capability at ORNL integrating biology and environmental science into atmospheric science, we are now looking at the complete picture — from microbial scale to a plant scale into the climate scale — which I think is beautiful,” he said. “We are not looking at segments of the atmosphere anymore. It gives us the whole idea of what’s happening from the biosphere to the atmosphere and how we can tackle climate change in the future.”

On the horizon: Diminishing the black line

Away from the lab, Salvador lives with his wife in Oak Ridge, where they enjoy riding bikes around the greenways and natural spaces near their apartment. In a small city like Oak Ridge the skyline is clear of the haze of atmospheric pollutants, but this is not the case when Salvador visits his home in the Philippines.

“When I go back, the black line — it’s still there,” he said. “I hope that in five to 10 years we can diminish that line — just make it less and less. Aerosols are a big part of the climate future and they’re going to impact a lot of industries — a lot of livelihoods. Visualizing that black line getting smaller, I think that somehow my small contribution will change what's going to happen in the future.”

UT-Battelle manages ORNL for DOE’s Office of Science, the single largest supporter of basic research in the physical sciences in the United States. The Office of Science is working to address some of the most pressing challenges of our time. For more information, visit energy.gov/science. — Michaela Bluedorn