Aerosol Scientist Spotlight: Five Questions with Roby Greenwald

Roby Greenwald
Associate Professor and MPH Program Director
School of Public Health
Georgia State University

How did you get involved in the aerosol science community?

My motivation for pursuing aerosol science was primarily its role in climate change. In the mid-90’s, I volunteered for the Peace Corps after I finished my undergraduate degree, and I was posted to the Sahel region of West Africa. During this time, many of the farmers I worked with struggled with crop-losses and other impacts related to desertification, and this experience solidified my desire to devote my career to addressing this issue. I pursued my PhD at Georgia Tech, and the first projects I worked on investigated how aerosols influence plant growth and crop production, and I’ve been doing something related to aerosols ever since.

Which people or programs in our field have been the most influential to you and your path, or who have most influenced your ideas about aerosol research?

The most important influences in my career have been Mike Bergin, my PhD advisor, and Jeremy Sarnat, a mentor when I was starting out as a research faculty member at Emory University. Mike introduced me to all the basics of aerosol science as well as the essentials of performing intense field measurements in challenging situations, and he also gave me several outstanding opportunities with very interesting research projects in exciting places all around the world. Jeremy expanded on that base by introducing me to the important methods for assessing human health response following PM exposure and assisting me in many of the practical aspects of building a research career.

What is the most interesting research contribution you’ve made so far?

This is a bit of a subjective question, I suppose. Oddly enough, the paper that consistently generates the most inquiries is a crop modeling paper from my first years in grad school. Even 20 years later, I still get several citation alerts a year and a couple of random emails asking for my FORTRAN code. It was a very simple approach: we used a radiation model to calculate direct and diffuse solar radiation as a function of aerosol optical depth (AOD), then we took a well-validated crop model and adjusted the radiation use efficiency term to account for diffuse radiation. The model then calculated the harvestable yield for rice, maize, and wheat under various PM loadings, and I think what generated the most interest was that it increased yield at modest AOD when everything else was left unchanged. For myself though, I think the more interesting contribution is the influence of physical activity on PM exposure. I developed a model for estimating the volume of air an individual inhales based on simple personal characteristics like age, height and sex plus heart rate data that can be easily collected with wearable devices. We cross-validated the model using a huge pooled-data set from a diverse group of previous projects and came up with an exposure model that is about as good as can be expected from wearable technologies.

What challenges were completely unexpected as you began and continue to grow your own research group?

The most unexpected challenge over the last several years was definitely COVID-19. After a couple years of effort gathering preliminary data and confirming support from all the required research partners, my team had a great project lined up that involved PM-exposure and outcomes in toddlers. Then COVID hit, and our funding opportunity was diverted to pandemic-related projects. This was on top of my other projects being paused and our labs being closed for months at a time. Thankfully, the non-profit funder of some of our other projects saw the value in this study, and we were able to begin the study a few years later than initially planned.

Are there new research directions that you see as particularly important or interesting?

Over the last five years, I have begun to gradually shift my focus to projects related to the built environment. I think there is a probably broad understanding in the PM and human health community that the most important sources in many parts of the world are motor vehicle emissions. This is certainly true in the United States (and especially in Atlanta where I live). The impact of motor vehicles extends beyond just being a source of PM exposure; they are the single-biggest carbon source in the U.S., the biggest source of noise-exposure, a huge contributor to fatal and non-fatal traumatic injuries, a major reason for reductions in physical-activity rates, and part of the cause of the housing affordability crisis, social health inequities, and decreases in social connectivity. The list goes on quite a ways actually. None of these problems are going to be successfully resolved if we don’t seriously address how our cities are built and how people get around, so I’ve begun collaborating with some of my colleagues in Policy and Urban Studies at Georgia State to include built environment factors in our health effects studies. There are numerous built environment interventions proven to improve public health outcomes, mostly in other parts of the world, but building local support for infrastructure that makes it safe, pleasant, and convenient for people to get around without an automobile will be an important focus for the remainder of my career, unless this issue is resolved sooner, in which case I will happily shift my focus to other challenges.