Rachel Chang

Home Research Publications CV
Current Research
I am currently interested in the effect that climate change, specifically increasing temperatures, will have on the greenhouse gas emissions from permafrost in the Arctic. The Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) consists of aircraft measurements over Alaska. In situ measurements of carbon dioxide, carbon monoxide and methane will be combined with radar measurements of soil temperature and moisture as well as total column measurements of greenhouse gases in order to learn more about what controls the emissions from permafrost and project how climate change will affect them.
PhD Research
We investigated this by conducting aerosol-CCN closure studies in which we compared measured CCN concentrations with those predicted from a Kohler model and using measured aerosol chemical composition. By looking at what parameters needed to be changed in the Kohler model in order to achieve good agreement, we can get an idea of the significance of the organic fraction in droplet activation as well as the sensitivity of CCN-activation on the different parameters. In order to study different types of continentally-influenced air, sampling campaigns took place at a semi-rural site in southern Ontario during the fall of 2005 and the spring of 2007, as well as a forested site in British Columbia in the spring of 2008. Our findings show that the CCN-activity of ambient aerosol is mostly dominated by the inorganic component, however, there are sites where understanding the hygroscopicity of the organic fraction is important.

I also investigated the sources of aerosol in the Canadian Arctic archipelago as well as the central Arctic Ocean. During the Surface Ocean Lower Atmosphere Study in the Canadian Arctic in 2007 and 2008, nucleation events were observed to coincide with elevated dimethyl sulphide (DMS) levels. Box-modelling showed that it is possible that DMS caused the observed nucleation events. In the central Arctic Ocean, as a part of the Arctic Summer Cloud Ocean Study in 2008, I measured the aerosol composition with an aerosol mass spectrometer and used statistical techniques to apportion the aerosol mass to continental and marine biogenic sources.