Dept. Of Energy Analysis Hits Diesel 'Toxics' Calculation

Diesel Fuel News, Oct 1, 2001 by Jack Peckham

California Air Resources Board (CARB) and South Coast Air Quality Management District (SCAQMD) have miscalculated the relative threat and relative contribution of diesel exhaust to "toxic" air pollution, a new analysis by U.S. Department of Energy indicates.

Compounding that error was another study by state air regulator group STAPPA/ALAPCO (see Diesel Fuel News 3/20/2000, p1), the DOE analysis contends.

The analysis points out that neither U.S. EPA, nor its science advisors, nor the prestigious Health Effects Institute term diesel exhaust as a "known" carcinogen, since the scientific studies show only "weak" cancer links. (see: www.trucks.doe.gov/plain-talk/cancer.html).

This is in sharp contrast to CARB and SCAQMD "toxic air contaminant" findings and calculations for diesel particulate matter (PM), which include "unit risk" calculations claiming that hundreds or even thousands of people might get cancer if exposed to rather high levels of diesel exhaust over a 70-year lifetime.

Problem: SCAQMD's "Mates-2" study, drawing on 20-year-old data, attempts to ascribe "diesel PM" as the main cancer-causing "air toxic." This "flawed" study, DOE's analysis says, incorrectly uses a problematic elemental carbon surrogate for ambient diesel PM. What's more, DOE notes that SCAQMD only counted this "diesel PM" and ignored the other 67% of the [PM.sub.2.5] captured at SCAQMD's own air monitoring stations, as EPA's own science advisors first pointed out last year (see Diesel Fuel News 3/6/2000, p12).

In any case, people don't breathe just "diesel exhaust," but rather, they breathe everything that's in the air, including both gasoline and diesel PM, gasoline refueling vapors (partly due to flawed Stage 2 vapor controls), industrial and agricultural pollution, ozone, sulfates, nitrates, tire wear PM, road dust, water vapor and other natural substances.

Colorado's Northern Front Range Air Quality Study (NFRAQS) recently discovered that gasoline cars account for 2.5-3 times the ambient [PM.sub.2.5] contribution from diesel engines (see Diesel Fuel News 7/23/98, p7).

"This fraction [gasoline PM at more than twice the diesel PM contribution] closely matches the unaccounted residual particulate carbon from the SCAQMD [PM.sub.2.5] air monitoring sites," DOE's new analysis points out.

Meantime, a separate DOE-sponsored study on relative pollution contributions in the SCAQMD area is underway. If these study findings mostly mirror the NFRAQS findings, then this could indicate that SCAQMD logically ought to finger gasoline PM, not diesel, as its number one "ambient air toxic."

But irony piles upon irony: Neither EPA nor CARB have ever bothered to investigate whether gasoline or other alternative-fuel PM deserve heavy scrutiny like that given to diesel PM health probes (see Diesel Fuel News 8/20/98, p9). That's odd, since gasoline PM toxicological rating is almost identical to diesel PM (see Diesel Fuel News 8/23/99, p9), and might be even more dangerous, since it tends to be smaller and thus more easily penetrates deeply into lungs.

What's more, the SCAQMD area seems to suffer more from excess hydrocarbon (HC) emissions, rather than excess NOx, in the formation of ozone. Merely cutting heavy-duty diesel NOx, without a prior steep cut in HC from gasoline and other non-diesel sources, actually increases ambient ozone, which explains the "weekend effect" in metro Los Angeles (see Diesel Fuel News 9/11/2000, p11).

"This is especially true of heavy-duty vehicles: they contribute about 50% less of ozone precursor emissions on weekends than they do on weekdays," DOE's analysis says. "The data are beginning to suggest that in urban locations, non-methane organic compounds [HCs] are more important than NOx in determining ozone concentrations."

Ironically, SCAQMD's recent ban-diesel-engine policies and alternate fuel mandate schemes now seem to be missing the primary causes of PM "air toxics" and ozone. This also leaves taxpayers and fleets holding the bag for SCAQMD's enormously expensive (and ultimately futile, since they're not economic) compressed natural gas (CNG) mandate schemes, which recent studies show might be more "toxic" than clean-diesel.

A fuel-neutral policy would allow clean-diesels to cut more pollution -- at far lower taxpayer cost -- as fleets have been trying to tell SCAQMD for years, without anybody listening so far.