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rjs banner AOSC Chemistry & Biochemistry ESSIC UMd Click For More Info On This Photo

     Our research focuses on quantification of the effect 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 (Oman et al., JGR, 2010).  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 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 the supply of bromine to the stratosphere may be strongly influenced by organic bromocarbons produced by biological processes in the ocean (Salawitch, Nature, 2006; Salawitch et al., GRL, 2005).  Recently, we have used three dimensional models to examine measurements of bromine monoxide (BrO) obtained by ground-based, aircraft, and satellite instruments during the NASA ARCTAS and NOAA ARCPAC field campaigns, which initially appeared to present a contradictory picture of atmospheric halogen abundances. We offered an explanation that reconciles these apparent differences, based on the premise that many satellite BrO hotspots are actually caused by the compression of stratospheric air masses to high pressure (low altitude) rather than surface release of bromine at high latitudes (Salawitch et al., GRL, 2010). We have also re-examined the understanding of polar ozone photochemistry in light of a new laboratory observation that had suggested photolysis of the ClO-dimer proceeds more slowly than previously thought (see SPARC report for preliminary results) and participated in an effort to evaluate the accuracy of the chemical mechanism used by various coupled chemistry climate models (CCMs).  Groups members also contributed to the 2010 WMO/UNEP Scientific Assessment of Ozone Depletion report as co-author, contributor, and reviewer.


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 (NOx) 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 NOx 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 present research is 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.  We are in the process of analyzing data collected by the DISCOVER-AQ mission, occurring in the mid-Atlantic region during summer 2011.


The Global Carbon Cycle.  Carbon dioxide (CO2) is the most important anthropogenic greenhouse gas and, quite literally, the 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) (Crisp et al., Advances in Space Research, 2004), 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).  We are excited to be involved in the formulation of the NASA Orbiting Carbon Observatory 2 mission (OCO-2), the successor to OCO scheduled for launch in 2013.

Please visit our Atmospheric Chemistry site that shows real time conditions in College Park, Md:


and the rest of the webpage that hosts this data to learn more about Atmospheric Chemistry at UMd.

Click here to see a list of the UMd PhD Dissertation and Prospectus Committees on which I have served.

Department of Atmospheric and Oceanic Science                                           College of Computer, Mathematical, and Natural Sciences

Department of Chemistry and Biochemistry                                                                                  The University of Maryland Newsdesk

Earth System Science Interdisciplinary Center                                                                                             The University of Maryland

This page last updated on Thursday, 07 July 2011                                                                                                                                                 Home