The rate of asthma in children younger than five increased 160
percent between 1980 and 1994.

But asthma researchers are still very much working to figure out what, besides changes in the way asthma is diagnosed, might account for the 160 percent rise in the rate of asthma in children younger than 5 that took place between 1980 and 1994. Our QUEST TV story looks at one interesting hypothesis, called the "hygiene hypothesis." The hypothesis proposes that as certain types of bacteria have become less and less present in our lives, we have developed allergic diseases in response.

I also asked researchers if their findings allowed them to make recommendations to parents on what they might be able to do to help reduce the risk of their children developing asthma. Although our two interviewees were careful to caution how little scientists know with certainty at this point, they were willing to venture some advice, which you'll see in our Web-only video.

Watch the Asthma television story online.

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The California Air Resources Board is expected to vote on a new diesel-emissions regulation when the board meets on December 11 and 12 in Sacramento. As Dan Sperling, head of the Institute for Transportation Studies at UC Davis, explains in this clip, diesel trucks haven't been regulated the same way cars have been.

It would require all trucks on California roads to meet the lower 2010 emissions standards. The cost to retrofit a diesel truck could run anywhere from $10,000 to $25,000 per truck. There are roughly a million diesel trucks driving through the state – but not all of them are going to get the retrofit.

About half of the trucks traveling through California are from out of state. And almost all of those are long-distance freight trucks, which drive so many miles that they only last about three years – so most of the out-of-state trucks will meet 2010 standards in time.

That leaves about half-a-million California trucks, and of those, only about 200,000 are estimated to need retrofitting. From the truckers' point of view, that's still a tough haul in today's economy. Here's Bob Ramorino, President of Road Star Trucking in Hayward and head of the California Trucking Association, discussing how the new regulations could affect his business.

Overall, the expected cost is about $5.5 billion. About $1 billion of bond money will be available to make that transition easier for truckers.

And not just for truckers. Diesel buses will need to meet the requirement, as well. And blood centers are concerned about retrofitting their bloodmobiles.

If retrofitting really old diesel trucks doesn't quite make financial sense – that is, if the cost of retrofitting isn't worth the mileage left in some old diesel trucks — some truckers have the choice of junking those trucks and springing for new ones. But for bloodmobiles, with their specialized and complicated and expensive layouts, buying new could be financially crippling.

There's one more number to compare to all the others. According to the Air Resources Board, California loses about $40 billion a year due to lost job time and illnesses attributable to diesel exhaust. In the clip above, Dr. Tom Dailey, chief of pulmonary medicine at Kaiser Permanente, Santa Clara talks about some of those health dangers.

Listen to the Get the Soot Out radio report online.

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