1. Department of Earth Sciences, University of Toronto, M5S 2B1 Toronto, Canada
2. Department of Physical and Environmental Sciences, University of Toronto Scarborough, M1C 1A4 Toronto, Canada
3. Air Quality Processes Research Section, Environment and Climate Change Canada, M3H 5T4 Toronto, Canada
4. Department of Life Sciences, University of Siena, via Mattioli 4, 53100 Siena, Italy