1. Could you explain the significance of your article to the non-specialist? (50-100 words)

We used an electrodynamic balance (EDB), in combination of a Raman spectroscopic system, to monitor the changes in the mass (and size) and chemical composition of individually levitated particles. Raman spectroscopy was used to probe the state of selected components during phase transformation and hygroscopic growth of mixed particles. Taking advantage of the ability to levitate a particle virtually indefinitely in an EDB, we studied chemical reactions and their mechanisms of organic particles at atmospherically relevant conditions such as low ozone concentrations. Such an EDB/Raman system can be used to study a number of problems involving gas-particle interactions.

2. What has motivated you to conduct this work?

We have been using an EDB to make hygroscopic measurements of chemical systems of atmospheric relevance for a number of years. When we started to examine multicomponent aerosols, the mass change alone determined from the balancing voltage measurements of the EDB was not adequate in providing insight on what was happening to the different components of the particles.

Raman spectroscopy is an attractive tool for examining the changes such as the formation, disappearance, and the state of different components.  We are currently using it to study heterogeneous reactions of atmospheric aerosols.

3. Where do you see this work developing in the future?

The EDB is a very versatile platform for investigating a number of problems involving gas-particle interactions.  Most applications to date are related to hygroscopic growth and more recently heterogeneous reactions of atmospheric aerosols.  Investigating chemical reactions through functional group analyses is attractive.  Slow reactions (in the time frame of hours) that involve multi-component systems appear to be good candidates.  The use of other non-intrusive techniques for in-situ monitoring of chemical reactions is also possible.  Applications on gas-particle interactions beyond atmospheric problems (e.g., pharmaceuticals and powder processing) and at extreme conditions (e.g., temperature and RH) are potential developments in the future. 

4. Are there any particular challenges facing future research in this area? 

It would be exciting to study smaller particles (e.g., submicron particles) in an EDB/Raman system. Spectroscopic imaging of the particles undergoing chemical reactions would be very useful in a number of applications. Most studies so far have used "model" systems under very well controlled conditions that are sometimes not most relevant to real world situations. Extending these studies to real world situations would be most useful.