Measuring and Modelling Aerosol Indirect Effects

October 31, 2019

Dr. Rachel Chang
Dalhousie University - Department of Physics and Atmospheric Science

Aerosols affect radiation indirectly by acting as cloud condensation nuclei (CCN) for liquid droplets. As aerosol and cloud droplet number concentrations increase, clouds become brighter and more reflective (first indirect effect) and also have longer lifetimes due to reduced precipitation (second indirect effect). Both of these effects result in reduced solar radiation reaching the earth’s surface. Despite their importance to the earth’s radiation budget, neither of these effects are well-understood or parameterized in models. This talk presents measurement and modelling studies undertaken by my group to characterize the two aerosol indirect effects. Visibility in coastal fog was used as a proxy for clouds to study the first indirect effect and low Arctic clouds were studied for the second indirect effect.


Dr. Rachel Chang’s research is motivated by atmospheric processes that take place in marine and polar environments. One aspect is in studying the sources, transport and loss processes of aerosol in the atmosphere in these regions. Another aspect is in understanding how carbon cycles in permafrost regions.

photo of Dr. Rachel Chang