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.