We did not find particularly good agreement between filter and impactor concentrations for times when the C-130 was near Cape Grim or Disco. The obvious question is whether this disagreement is due to the fact that we were not sampling exactly the same air (30 minute C-130 samples were compared with 4 hour Disco impactor samples or 3 hour CG filters) or a disagreement between the measuring systems. Since we did considerably better during the PSI-3 impactor intercomparison and since the agreement on the IC pass-around unknowns was excellent, we do not believe these data represent an indictment of our measuring systems.

We decided not to abandon the search for comparison times, however. We will jointly look for times when the homogeneity of air during a long surface sample time (as judged by continuous samplers such as nephelometers and OPC's) suggests that that sample can be used as a comparison with a shorter sample from another platform. If suitably-simultaneous samples can be identified, we will then use them to evaluate the potential that inlet systems or other factors may have limited the comparability of the data from the various platforms.