The chemical composition of the marine atmosphere is still poorly understood even though the Earth’s surface is 70% of the ocean. For example, it is common knowledge that sea spray aerosols from the ocean are dominated by NaCl by mass. However, their size, number concentration and actual composition remains poorly constrained, especially at sizes smaller than 1 µm, where climate implications are the most important. Furthermore, even less is known about the processes leading to secondary marine aerosol formation from the condensation of low-volatility gases emitted from the ocean. To address these gaps in our knowledge, this talk will present results suggesting that secondary marine aerosols in the Canadian Arctic summer are primarily organic, likely formed from the condensation of organic vapours from the nearby open waters. Although these particles are not very hygroscopic, they nevertheless grow large enough to activate as cloud droplets, potentially affecting climate. The second part of the talk will present results showing that the emission of laboratory sea spray aerosols can be altered by a surfactant, with the resulting aerosols being smaller, less numerous and less hygroscopic, and therefore less likely to contribute to cloud droplet formation. Preliminary results from the recent Tracer Release EXperiment (TReX) on the St. Lawrence River will also be presented, showing the potential for improved estimates of sea spray aerosol emissions. Together, these results further our understanding of primary and secondary marine aerosols in Canadian waters.
Rachel Chang is an associate professor in the Department of Physics and Atmospheric Science at Dalhousie University and a Tier 2 Canada Research Chair in Atmospheric Science. She completed all of her education at the University of Toronto with a BASc in Engineering Science, a MASc in Chemical Engineering and a PhD in Chemistry. She was an NSERC post-doctoral fellow at Harvard University before joining the faculty at Dalhousie University. Her primary research interests are studying the sources of and processes affecting marine and polar aerosols, including understanding the effect of these aerosol particles on liquid cloud and fog droplets. Her group uses a combination of ambient measurements, laboratory experiments, and modelling at different scales to explore these questions.