Ross J. Salawitch

Our research focuses on the quantification of the effects of human activity on atmospheric composition. We develop computer models that are used to analyze a wide variety of observations. Our focus is on stratospheric ozone depletion and recovery, air quality, and the global carbon cycle.

Stratospheric Ozone Depletion and Recovery. Our research on stratospheric ozone is motivated by the desire to define how the ozone layer will evolve now that industrial production of ozone depleting substances (ODSs) has been banned. As else being equal, the protective stratospheric ozone layer should return to levels that were present prior to the anthropogenic release of ODSs. However, rising levels of greenhouse gases (GHGs) will alter the expected recovery of the ozone layer by imposing changes on stratospheric temperature and circulation. We have published an analysis of 40 years of data collected in the Arctic polar vortex that shows during years when the stratospheric experiences cold conditions, which is conducive to ozone loss, temperature tends to be much lower during the past decade than at any other time in the data record (Rex, Salawitch et al., GRL, 2006). Whether or not this change is due to rising levels of GHGs is an area of active research. We have also postulated that, contrary to the assumptions made in most ozone photochemical models, the supply of bromine to the stratosphere may be strongly influenced by organic bromocarbons produced by biological processes in the ocean, rather than dominated by industrial sources gases (Salawitch, Nature, 2006; Salawitch et al., GRL, 2005). Presently, we are working on the development of a model that can account for ground-based, aircraft, and satellite observations of bromine monoxide (BrO) obtained during the NASA ARCTAS field campaign that, initially, appeared to present a contradictory picture of atmospheric halogen loading.

Air Quality. Industrial activity leads to lower levels of stratospheric ozone (“good ozone”) and increased levels of tropospheric ozone (“bad ozone”) (Salawitch, Scientific American, 2007). Increased levels of tropospheric ozone result in respiratory problems that have been linked to increased morbidity and mortality in humans as well as significant damage to crops and plants. High levels of surface ozone are caused by human release of nitrogen oxides (NO_x) and hydrocarbon. These pollutants are released by the exhaust of power plants, factories, and vehicles. Severely bad air quality is linked also to specific meteorological conditions: in the mid-Atlantic, “ozone alerts” are typically associated with days when the air is hot and stagnant, forced by a weather pattern known as the Bermuda high. We have recently published an analysis of 21 years of surface ozone and temperature measurements that shows surface ozone improved considerably during hot summer days in the mid-Atlantic starting around 2002, when emissions of NO_x from power plants began to fall due to measures imposed by the Environmental Protection Agency (Bloomer et al., GRL, 2009). We also were able to quantify the relation between surface ozone and temperature, termed the “climate penalty factor”, that allows projections of how much surface ozone will increase due to future climate change. Our research is also focused on the use of aircraft and satellite observations to define how emissions released from a particular geographic area affect air quality at downwind locations.

The Global Carbon Cycle. Carbon dioxide (CO₂) is the most important anthropogenic greenhouse gas and, quite literally, the single greatest waste product of modern society. About half of the CO₂ released by human activity is taken up the world’s oceans and terrestrial biosphere. The precise location and magnitude of these carbon sinks is unknown, yet is of enormous importance for defining interactions within the global carbon cycle that might be altered by climate change and also for future management of the global carbon cycle. We helped design a NASA satellite mission, the Orbiting Carbon Observatory (OCO), which would have revolutionized our understanding of the global carbon cycle. Unfortunately, the launch of OCO was not successful. Presently we are part of a collaboration between the OCO Science Team and colleagues from Japan that is applying ground-based assets and tools developed for OCO to the analysis of CO₂ measurements collected by the Japanese Greenhouse gases Observing SATellite (GOSAT) instrument, which was successfully launched on 23 January 2009. Our research in this area builds on prior work on modeling changes in the global carbon cycle that occurred at the K-T boundary (when dinosaurs became extinct) (Ivany and Salawitch, Geology, 1994) and at the most recent glacial-interglacial transition (Marino et al., Nature, 1992).