A clearer look at haze
A clearer look at haze
28 March 2007
published by www.thedalleschronicle.com
USA — The Portland area is important, but it isnt asimportant as sources on the east end of the gorge, Dr. Dan Jaffe told theColumbia River Gorge Commission March 13.
Approximately 40 percent of the worst airquality days come from sources east of the gorge, he said. Thats sortof the take-home message.
He was hired by the Yakama Nation to review airquality data gathered over an 11-year period from a monitoring station nearWishram.
Jaffe, who has a Ph.D. in chemistry from theUniversity of Washington, and is a full professor at the universitys Bothellcampus, stopped short of identifying specific pollution sources, or saying thatpollution in the gorge is getting better or worse.
Jaffe has published more than 60 papers onatmospheric pollution in peer-reviewed journals.
He said his goals were to evaluate possiblesources of pollution and the chemical composition of that pollution for theworst air quality days in the Columbia River Gorge, and to evaluate whether airquality in the gorge is improving or deteriorating.
He characterized his review report to the gorgecommission as preliminary, because it had not been peer-reviewed forjournal publication.
The Wishram station that provided the data is partof the national Interagency Monitoring of Protected Visual Environments (IMPROVE)program. According to the IMPROVE website, the program is designed toestablish the current visibility conditions, track changes in visibility anddetermine causal mechanism for the visibility impairment in the National Parksand Wilderness Areas.
The Columbia River Gorge National Scenic Area isneither a national park nor a wilderness area, though the Mark O. HatfieldWilderness area in Oregon does adjoin the scenic area along the ridgeline nearCascade Locks. (The Mt. Adams Wilderness Area does not adjoin the scenic area.)
Nevertheless, the station above Wishram has beencollecting particulate matter data (PM) twice a week since June 1993.
Between August and December 2006, Jaffe analyzeddata from 1,139 days between June 1993 and December 2004, the most recentavailable at the time.
Jaffe chose to examine data from the the 50 worst air quality days in that 11½-yearspan.
Its probably not those nice days that reallydrive environmental impacts, health effects or ecological impacts, Jaffe toldthe gorge commission. Its probably the haze days that are more important.
To determine the worst pollution days, Jaffe usedmeasurements of the smallest size of particulate matter, 2.5 micrometers indiameter or smaller (PM2.5), typically found in smoke or haze.
By comparison, the average human hair is about 70micrometers in diameter making it 30 times larger than the largest fineparticle.
Heres an overview of that data:
Average PM2.5 for all 1,139 days: 5.9 microgramsper cubic meter.
Average PM2.5 for the 50 highest days: 18.3micrograms per cubic meter.
Highest PM2.5 day (Nov. 7, 2002): 34.7 microgramsper cubic meter.
The Environmental Protection Agency has proposed a24-hour standard of 35 micrograms per cubic meter for particulate matter mass.
Very likely the gorge is not going to violatethis new standard, Jaffe told gorge commissioners. But at the same time,the high days are approaching the standard. I think thats important. Thereason for that is there is evidence in the scientific literature that there arehealth effects even below the federal standard.
He also found the worst days tended to be in asingle month. Eighteen of the 50 worst days (36 percent) took place in November.A four-month period from April through June, by contrast, had only two of theworst days. The second highest month was July, with eight, or 16 percent.
Jaffe then integrated that data with historicNational Oceanographic and Atmospheric Administration (NOAA) data on windpatterns. He used HYSPLIT (Hybrid Single-Particle Lagrangian IntegratedTrajectory) modeling to determine the direction of the haze source.
Trajectories cannot be used to quantitativelyassign source contribution, Jaffe said. Trajectories can identify a likelysource in one direction, compared to an alternate source in another direction.
Jaffe calculated wind flows at 0, 100 and500-meter arrival height above ground level at Wishram. For each 24-hour sample,trajectories were calculated at 2-hour intervals, for a total of 13 trajectoriesper sample.
Heres what he found. In 15 of the 50 worst airquality days, Jaffe said he was very confident the airflow was comingdownstream from sources on the east end.
PM2.5 readings on those days, averaged 20.5micrograms per cubic meter.
For an additional four days, he was less confident, but said his best guessis that its also coming downstream.
PM2.5 readings on those days, averaged 20.1micrograms per cubic meter.
Those two categories account for 38 percent of the worst air days.
Jaffe gave the same high confidence to sources on the west end of the gorge forfive of the worst 50 days (averaging 14.8 micrograms per cubic meter).
An additional four days (averaging 17.7 microgramsper cubic meter) were characterized as possibly from the west.
Those two categories account for 18 percent of theworst air days.
The remaining 22 days were classed unassignedor other.
Jaffe also examined chemical components of thehaze on the 50 worst days. In the interests of time, he said, he had notprepared specific detailed information for presentation to the commission.
He did say, though, that the numbers jump outat you when comparing the nitrate content of the haze with likely sourcedirection.
He said 30 percent of the aerosol mass was due tonitrates on days when the sources of pollution appeared to be east of the gorge,compared to just 11 percent nitrates in all other cases.
So these sources on the east end of the gorgeare very nitrogen rich, and are important, and produce about 40 percent of theworst air quality days, Jaffe said.
He noted those results were consistent with themore in-depth Causes of Haze in the Gorge (CaHaGo) study which identifiedsources on the east end of the gorge as significant contributors.
While Jaffe did not specify those sources in hisverbal testimony, Jaffe did present a powerpoint slide illustratingback-trajectories on Nov. 8, 2004, one of the worst air pollution days, with ared burst labeled, Boardman, Oregon.
Is gorge air quality improving or declining?
This is one of those questions that depends onwhich side of the elephant youre looking at, Jaffe said.
There is some improvement in annual average butthe result is not statistically robust.
By that, Jaffe explained, data from a single year 2000 fell considerably outside the general trend of the other years. Ifthat outlier year is left out, he said, the improvement in the annualaverages would be statistically significant.
Is it legitimate to throw out data you dontlike? Jaffe asked. No, he answered.
Of the 50 worst days, Jaffe said, there is noevidence that the air quality is improving.
He noted it takes two things to make a bad air dayin the gorge: an inversion and sources.
Meteorological condition is not something wecan control, Jaffe said. This would suggest that sources at this point arenot changing dramatically. Its my conclusion that there is no evidence thatits getting better.