[kidd]

Radiation levels in downtown Tokyo—which had also risen earlier Tuesday, though they remained well below levels that could damage human health—also fell sharply later in the day.

Irrelevant. Prevailing winds have been such that Tokyo is upwind of the nuclear plants. With all the widespread destruction in Tokyo (granite dust is very mildly radioactive), and with people burning coal to stay warm (coal is very mildly radioactive), it is unlikely that the source of minor radiation spikes are from the nuke plants. But the article fails to mention that.

[bvw]

Wow, I wanted to post something along those lines last night, and forgot. Great job!

I also suspect that earthquake event itself would have released some extra activity into the sea, and then the atmosphere via sea foam and forth. That would be dust forms, in addition to the significant amounts of Radon released before, during and after quake events.

Also you should include the crushing to dust, or the burning of, radioactive elements in medical equipment and supplies and other common sources like smoke detectors.