Apportionment of Midway Spring
The apportionment of Midway spring has been a thorn in our
side for several weeks. On the surface it seems simple: the aerosol contains a
large component of desert dust and a smaller component of pollution, both of
which are generally supposed to have originated in China and environs and been
transported to the mid-Pacific by the prevailing westerlies. Demonstrating that
with elemental tracers has proven to be something else again, however.
Until recently, we could not track neither the crustal component or the pollution component back to Far Eastern sources. Now with the latest refinement of signatures, it seems possible. We also had to eliminate the primary marine elements Na, Mg, and Ca as well as the secondary marine Se in order to reach a successful solution.
We illustrate a single thread below, which may be called the Chinese solution.
|Midway spring, 12 elements|
|Step 0||Nothing chosen|
|Step 2||Sea and Chinese dust added, fit 1.26|
|Step 3||Yellow sea added, fit 0.29|
|Step 4||Beijing suburbs added, fit 0.24|
Midway step 0, with nothing chosen, shows high F-ratios wherever there is strong crustal aerosol or coal flyash. Oahu, also in the mid-Pacific, resembles it most strongly. for the moment we reject choosing Oahu because it is a parallel receptor. Although Oahu tells us something about where the aerosol was sampled, it does not lead to its ultimate sources.
Step 2, after sea and Chinese dust are chosen, offers a pattern of F-ratios that has a broad but irregular crest in East Asia. The highest value within that area is shown by Yellow Sea (April), which is then chosen in step 3. This produces the surprisingly good fit of 1.26. Most of the reason for this good fit is the dominance of Chinese dust in Midway spring.
Adding the Yellow sea (April) in step 3 improves the fit to the very good 0.29. Beijing suburbs is the highest remaining F-ratio in East Asia. It is added in step 4.
Adding Beijing suburbs in step 4 improves the fit to 0.24. The F-ratios that look high for the Atlantic cannot be tapped, because they yield negative coefficients.
Thus the final solution for Midway spring is large amounts of Chinese desert dust with traces of Chinese pollution aerosol.
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