“...we presented, for the first time, chemical evidence of the polymer formation using new analytical techniques as well as a first quantitative estimate showing that up to 50% of the total aerosol mass could be composed of polymers.”

The formation of polymers in secondary organic aerosol (formed by a reaction of gaseous precursors) was discovered a few years ago (Jang and Kamens, Environmental Science and Technology, 2001), however, those experiments had been performed under highly acidic conditions which did not mimic atmospheric conditions, and only indirect experimental evidence for polymer formation was given. In our paper, we then showed that indeed the process also works under conditions closer those found in the real atmosphere. And we presented, for the first time, chemical evidence of the polymer formation using new analytical techniques as well as a first quantitative estimate showing that up to 50% of the total aerosol mass could be composed of polymers.

It is both. First, it is a new discovery which has triggered follow up work at various institutes. In addition, some of the techniques, especially laser desorption/ionisation mass spectrometry has been applied by us for the first time to such samples. Other groups then started to use the same method as well in their research.

For more than 20 years the chemical composition of most of the organic aerosol mass has been unknown. With the discovery and the quantitative estimation of the polymers it became clear that this class of compounds might represent most of the aerosol mass that was missing so far. These polymers have a very low vapor pressure such that aerosol particles consisting of such polymers are far less volatile than previously assumed, i.e., they are much more stable in the ambient atmosphere during summer days or in warm climates. The longer lifetime of these aerosol particles in the atmosphere increases their significance for many aspects in climate-related research such as cloud formation potential or radiative properties. The implications for health effects remain to be explored.

Both of us had spent a one-year sabbatical/postdoc at the California Institute of Technology (1989/1990 and 1999/2000, respectively) and were involved there in smog chamber experiments. When the Laboratory of Atmospheric Chemistry was founded at the Paul Scherrer Institute (PSI) in 2000, personnel resources were sufficient to successfully start its own smog chamber activity at PSI as a collaborative project with ETH Zurich. Planned as a user facility, the activity fitted nicely into the strategy of PSI to attract collaborating scientists for joint experiments at the chamber. From the beginning, the close collaboration between ETH Zurich and PSI proved to be highly fruitful, due to their complementary expertise. The discovery of polymer formation within the secondary organic aerosol occurred very rapidly, such that this paper in Science is actually the very first paper resulting from our own smog chamber activities.