Group 10. Lagrangian chemical analysis (Huebert)

In Lagrangian A, we do not have a balloon trajectory to confirm that our third flight was in fact in the same airmass as the first two. However, the meteorological profiles suggest that we were following the evolution of very nearly the same air. A comparison between nearly-simultaneous measurements of sub- and super-micron MSA and NSS on the C-130 and Disco with a C-130 external sample suggests that the aircraft's CAI inlet system removed about 20% of the supermicron MSA and NSS. Unfortunately, the loss of a pump in the external sampler system means that we have only one defendable "total" sample for the two Lagrangians. In practice, this means that we cannot close the aerosol sulfur budget, since we do not have a measure of the change of supermicron NSS with time. Since oxidation of SO2 on seasalt may be an important mechanism, we will not be able to distinguish between dry deposition and seasalt oxidation as loss mechanisms for SO2.

The increase of aerosol concentrations across sunrise is particularly striking. We have derived slopes for the day and nighttime intervals, and will use these for comparisons with the sulfur gas chemistry. The DMS and SO2 diurnal variations look very much like those observed at Xmas Island: DMS increasing as SO2 decreases at night, followed by a DMS decrease and SO2 increase when the sun comes up.

The Lagrangian B analysis is very promising, since the dynamics have been well-characterized by Russell and Lenschow. The supermicron NSS concentrations apparently decreased early in the experiment, which we have trouble explaining. It may be that humidity changes caused the supermicron NSS mass to shift relative to the CAI cutoff (which we believe to be around 3 um), thereby causing an apparent decrease in NSS, even as the submicron NSS and MSA increased.