Nice of a little overnight rain to clean the sky. This time of year our murky air is mostly old-fashioned smog, stuck in the basin and cooked by the summer sun into a thick cloud. But recent studies confirm that a lot of dust and "black carbon particulate pollution" is reaching us from China. Science columnist Robert Lee Hotz reported in the Wall Street Journal:

An outpouring of dust layered with man-made sulfates, smog, industrial fumes, carbon grit and nitrates is crossing the Pacific Ocean on prevailing winds from booming Asian economies in plumes so vast they alter the climate. These rivers of polluted air can be wider than the Amazon and deeper than the Grand Canyon.

"There are times when it covers the entire Pacific Ocean basin like a ribbon bent back and forth," said atmospheric physicist V. Ramanathan at the Scripps Institution of Oceanography in La Jolla, Calif.

On some days, almost a third of the air over Los Angeles and San Francisco can be traced directly to Asia.

The plumes have a complex influence on the climate, seeding more powerful thunderstorms over the Pacific and exerting both cooling and warming effects.