1. Atmospheric and Environmental Research, Inc., Lexington, MA 02421, USA.
2. Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
3. Department of Environmental, Earth, and Atmospheric Sciences, University of Massachusetts Lowell, Lowell, MA, USA.
4. The Hebrew University of Jerusalem, Institute of Earth Sciences, Edmond J. Safra Campus, Jerusalem, Israel.