Faulty Pollution Science in California? Think again.

It’s easy to get carried away with faulty science claims with the significant changes of late to the California Air Resources Board’s diesel emissions inventory and to estimates of the health impacts of air pollution.  Let’s keep some perspective here: The fact is that trucks and off-road construction equipment remain a major source of diesel pollution in California, and that fine particles (which often come from diesel) are responsible for vast amounts of illness including asthma, and thousands – Yes, thousands – of premature deaths each year according to US EPA.  Given the tremendous health toll of polluting equipment, the air board’s diesel regulations provide important statewide public health protections.  But let’s walk through the underpinnings of these regulations, which have been called into question.

Why did the emissions inventory change so much?  Well, part of the changes were a result of the economic downturn that hammered the construction industry – nobody could have predicted that when the off-road regulation was adopted in 2007.  The other issue that is responsible for most of the downward adjustment of the inventory is an obscure emission modeling assumption called a load factor.

Snooze alert: This is about to get technical.

A load what?  Think about a construction site with some bulldozers, graders and backhoes.  That equipment is operating at different times but probably sitting idle most of the day.  When it does operate, it may not work as hard as its full horsepower rating.  The air board’s off-road model assumed that construction equipment was working a lot harder and a lot longer than in reality; they used a higher load factor and assumed the equipment was used more frequently.  You might expect obscure yet important details like these to come to light during the over two years when this rule was developed.  No, the construction industry was not in a sharing mood with their data at the time. 

Now that data has come in showing much lower engine loads by construction equipment in use, the air board responded to the new data by adjusting their off-road model.  US EPA had the same problem of under-estimated load factors; they had to make similar corrections.  In reality, emissions inventories are never static, they are constantly adjusted, updated and tweaked as our understanding of emissions progresses with new data.   It’s tempting to tag inventory changes as faulty science, but in fact, what happened is just part of the usual process of adjusting the inventory to account for new information.  The incredible thing here is how quickly the air board responded.  They recognized the significance of correcting load factors in their model and set about adjusting the entire emissions inventory right away.

As for the changes to the health estimates from air pollution, this is another case of updating the science to reflect the latest research.  The interesting thing about the health estimates is that while the emission inventory for diesels was adjusted downward, we now know that serious health effects are occurring at much lower levels of pollution than previously thought.  For more on that, see an earlier post.  No matter what you think about all of these changes, diesel pollution remains a potent health hazard, contributing to asthma and heart attacks, stunted lung growth in children, birth defects, more emergency room visits and higher death rates.

California’s Air Board has a proven track record as a global leader in protecting public health, having launched world renowned programs to clean up cars, fuels, transportation and now more broadly, address climate change.  Sometimes the price paid for cutting edge policies is that things don’t always come out perfect the first time; corrections must be made.  In this case, the Air Board has been quick to respond, making the corrections they need to maintain the important programs that we rely on to protect the health of all Californians.

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