Last week, Dan Jaffe’s atmospheric research group at the University of Washington released the results of a study of particulate emissions associated with rail traffic here in Seattle and along the Columbia River. That study was motivated by the controversy over coal exports, and was funded by contributions from the Sierra Club and through crowdfunding. We have been watching how this study has been received by the public and used by both sides of the coal export debate, and thought it would be useful to provide some context for Dr. Jaffe’s research, especially because this research is a good example of how science, policy, and law interact.

The paper is fairly readable even by someone who lacks a scientific background and is worth the read. To summarize, Dr. Jaffe and his group sampled particulate matter at two locations in Washington, a porch of a house located about 25 meters from train tracks in the Blue Ridge neighborhood in Seattle, and a location along the Columbia River. The Blue Ridge site is the subject of the most analysis. What the researchers observed there was a spike in fine particles as trains passed by. For passenger and freight trains, that spike occurred when the beginning of the train passed the site, and was attributed to diesel emissions from the locomotive. Coal trains had two spikes, one associated with the locomotive and a second associated with larger particles attributed to the coal contained in open-topped cars.

The part of the paper that is receiving the most media coverage is a back-of-the-envelope calculation in the final paragraphs where the authors conclude that a 50% increase in train traffic “would bring the PM2.5 concentrations at [the Blue Ridge] site up to about 14 ug/m3, which is higher than the new U.S. National Ambient Air Quality Standard (NAAQS) of 12 ug/m3 (annual average).” Media and bloggers are using this conclusion to proclaim that coal trains are “degrading” air quality, such as this article in The Olympian, and Cliff Mass’s blog post from March 3rd.

This theme emerging in media in reaction to Dr. Jaffe’s research is what we wanted to explore in more detail.

Dr. Jaffe’s extrapolation that a 50% increase in train traffic will result in a violation of the NAAQS for PM2.5 is likely not true because he compares the results of his extrapolation to the wrong NAAQS for PM2.5. The standard Dr. Jaffe compared his extrapolation to is an “annual” standard (12.0 ug/m3) and is, according to EPA’s NAAQS regulations, only comparable to data collected that are representative of area-wide air quality conditions. 40 C.F.R. 58.30. “Area-wide” impacts are defined by EPA to be conditions throughout a reasonably homogenous urban area, on the scale of a few kilometers or larger. (See Appendix D to 40 C.F.R. Part 58). Relatively unique micro-scale, localized hot spot, or unique middle-scale impacts are more properly compared to the 24 hour NAAQS (35 ug/m3 nationally, with a 25 ug/m3 “goal” locally in the Puget Sound Region). Consistent with this regulatory framework, all of Washington’s PM2.5 monitoring sites that are comparable to the lower annual standard are at the neighborhood scale or larger. Ecology’s Ambient Air Monitoring Network Report for 2013 demonstrates this in detail. If you review the PM2.5 monitoring station details starting on page 24 of the report, you can see that only one–near I-5 in downtown Seattle–is monitoring at the micro-scale, and Ecology very clearly notes that data from this station are not comparable to the annual PM2.5 standard (see page 30 of this report). The Blue Ridge site is most likely not representative of neighborhood scale (a few kilometers or more) or larger atmospheric conditions because it was sited so close to the rail corridor, and is more like the I-5 monitoring station in place So, Dr. Jaffe’s comparison of possible future emissions from trains to the NAAQS PM2.5 standard should have been done to the higher 24 hour standard. Placed in this context, and assuming Dr. Jaffe’s extrapolation is otherwise scientifically defensible, a 50% increase in locomotive traffic will not lead to an exceedance of the applicable NAAQS for PM2.5.

It is important to place PM2.5 rail emissions in context in terms of the magnitude of those emissions compared to other sources. The first source of this context is Ecology’s annual report discussed above, which details why individual NAAQS sites were chosen and the targeted scale of the monitoring efforts. For PM2.5, the vast majority of NAAQS sites monitor impacts to air quality from home heating and wood burning–one of the dominant sources of fine particles to the atmosphere in Washington.

Further, emission inventory data show that about 76,000 tons of PM2.5 are emitted from a variety of sources annually in Washington, and less than 1% of those total emissions come from locomotives. PM2.5 emissions from diesel combustion tell a similar story, with almost two thirds of the total emissions coming from on road or off-road sources (i.e., construction equipment) and the relative emissions from on-road and railroad sources demonstrates the negative impact of efforts to reduce rail traffic in Washington, which could shift cargo to roads, resulting in higher particulate emissions per unit of cargo traveled per mile.

It is also important for Washington to consider whether PM2.5 is a pressing issue that needs to be addressed through future regulatory activities. Thanks to a variety of factors, the answer to this question is no. Only one county does not meet the current annual PM2.5 NAAQS, which compares to 29 counties in California. In a time of increasingly limited resources for regulatory activities, devoting those resources to particulate emissions from railroads likely won’t lead to a proportionate environmental benefit.

Put in the above context, we believe particulate emissions from railroads are not a pressing concern in Washington, and will not become such a concern in the future. It is also worth putting these arguments against rail traffic in the overall context of Washington’s economy. Washington depends heavily on exports and rail capacity to move commodities to market. Attacking rail traffic now because the cargo those trains are carrying is controversial may limit Washington’s ability to grow its economy, now and later.