The Columbia River Gorge Air Quality and Visibility Study

Transcription

1 feature em The Columbia River Gorge Air Quality and Visibility Study by Mark Green, Marc Pitchford, and Chris Emery The Columbia River Gorge ( the Gorge ) is a narrow gap in the Cascade Mountains of Washington and Oregon with outstanding natural features, including steep forested mountainsides and numerous high waterfalls. Cut by the flow of the Columbia River, the Gorge is approximately 190 km in length, 5 km wide (at river level), and 1 km deep. The elevations at river level are less than 100 m above mean sea level. The Portland, OR/Vancouver, WA metropolitan area, with a population of approximately 2 million, is located at the western terminus of the Gorge. This article briefly describes a several-year study of the causes of visibility impairment in the Gorge and the development of a strategy to improve visibility in the area. For detailed information, the reader is encouraged to refer to the journal articles and project reports referenced in this article. In 1986, the U.S. Congress afforded special protection to this area when it passed the Columbia River Gorge ational Scenic Area Act. Pursuant to this act, the Columbia River Gorge Commission was established to develop and enforce policies and programs that protect and enhance the scenic, natural, cultural, and recreational resources of the Gorge, while encouraging compatible growth within existing urban areas of the Gorge and allowing economic development outside urban areas consistent with resource protection. It is noteworthy that the people of the Pacific orthwest have decided to take steps beyond what is required by any law or regulation to understand and improve visibility in the Gorge. In 2001, a technical study plan focusing on atmospheric visibility (haze) was developed that included comprehensive data collection and analysis and modeling components. Haze is caused mainly by scattering and absorption of light by particles suspended in the atmosphere (i.e., aerosols). umerous urban, industrial, and natural sources in the region emit gaseous or particulate air pollution that may contribute to light scattering and absorption in the Gorge. These sources include the Portland, OR/Vancouver, WA metropolitan area; numerous pulp and paper mills (mainly west of the Gorge); coal-fired electric generating units (the largest regional source of sulfur dioxide is the Boardman plant, east of the Gorge); highway, railroad, and barge vehicles that travel through the Gorge; and Mark C. Green, Ph.D., is a research professor at the Desert Research Institute, Reno, V; Marc L. Pitchford, Ph.D., is a meteorologist with the ational Oceanic and Atmospheric Administration s Air Resources Laboratory, Las Vegas, V; and Chris Emery is a manager with EVIRO, ovato, CA. mark.green@dri.edu. 20 em june 2008

2 small cities in the Gorge, such as Hood River and The Dalles. These sources emit substantial quantities of primary particulate matter, which scatters light as well as significant quantities of sulfur dioxide and nitrogen oxides that react with other compounds to form light-scattering secondar y particles (e.g., sulfate and nitrate). Other significant sources of haze include Figure 1. Location of study monitoring sites. forest fires, biogenic emis- ote: The Portland metropolitan area is located at the bottom left edge of the figure. sions, and ammonia from scattering and surface meteorology at nine locations confined animal feeding operations, agricultural fertilizer through the Gorge (Figure 1 shows the locations of study application, and other sources. The main objective of the monitoring sites) to look at spatial and temporal patterns technical study was to identify sources, source categories, of light scattering and how it varied with wind speed and/or geographical regions that contributed to haze in and direction. Winds within the Gorge are channeled the Gorge and, to the extent practicable, quantify those by the terrain so they blow either upriver (west-to-east) impacts. or downriver (east-to-west), depending on seasonal forcings (i.e., winds blow from high to low pressure). Thus, Overview of Study Methods much information about the transport of haze through The initial phase of the study was the haze gradient the Gorge can be ascertained by having monitors along study,1,2 which was conducted from July 2003 to Februa line through the Gorge. ary The study used hourly measurements of light Until now, improving AERMOD runtimes took extraordinary effort. It says here we can make a test run at breeze-software.com/em. BREEZE Remote Modeling System up to 100 times faster! Do more in less time o proprietary software interface required Submit data anytime, day or night, and receive your results via +1 (972) Achieve incredibly fast runtimes (e.g., 8 hour runs reduced to 5 minutes) breeze-software.com Visit breeze-software.com/em for FREE model run details. BREEZE is a registered trademark of Trinity Consultants, Inc. june 2008 em 21

3 Figure 2. Diurnal variation in particle light scattering (b sp ) for four western and central Gorge sites and one eastern Gorge site, summer (June August). ote: The eastern propagation of higher b sp levels late morning to early afternoon at the western and central Gorge sites. Sites noted in legend are ordered from west to east. The second phase of the study was conducted concurrent to the initial phase. Within the 20-month haze gradient study were embedded three periods with additional monitoring: December 2003 February 2004, July ovember 2004, and December 2004 February The additional measurements included high time resolved measurements of sulfate, nitrate, and carbon aerosol at the two Interagency Monitoring of Protected Visual Environments (IMPROVE) sites in the Gorge (Mt. Daily average bsp (Mm -1 ) /1 11/3 11/5 11/7 11/9 11/11 11/13 11/15 11/17 11/19 Figure 3. Daily average light scattering by particles (Mm -1 ) at the Gorge study monitoring sites for the ovember 2004 episode. ote: Sites in legend are ordered from west to east. Zion and Wishram) and at a mid-gorge site at Bonneville Dam. The additional measurements were used for qualitative assessment of episodes and for evaluation of the chemical transport model simulations. Following the field study, chemical transport modeling was conducted using the Comprehensive Air Quality Model with Extensions (CAMx) 3 for two haze episodes (August and ovember 2004). The modeling used a 2004 emissions inventory prepared for the study and a 2018 emissions projection to consider current source contributions to haze and to project future haze levels. 4,5 Summary of Study Results The study design provided for in-depth monitoring and wide geographical coverage for emissions inventory and modeling analyses for the Gorge area. The study provided insight on both man-made and natural sources of haze. Of most interest are the man-made emission contributions, as those are the focus of emission reduction strategies that can lead to reduced haze in the Gorge. During certain periods, natural and very distant sources contributed significantly to haze in the Gorge. The haze gradient study found that the highest haze conditions occurred in winter when flow was easterly (i.e., from the east) and that haze levels decreased with distance Sauvie Is Steigerwald Mt Zion Strunk Rd Bonneville Memaloose 7 mile Wishram Towal Rd into the Gorge. This suggests that sources east of the Gorge were mainly responsible for the haze. In summer, winds are nearly always from the west and haze levels are highest in the western part of the Gorge and decrease with distance eastward due to vertical and horizontal dilution. The summer data clearly show an influence of the Portland, OR/Vancouver, WA metropolitan area as a slug of hazy air gets transported from west to east through the Gorge when the winds increase in mid-to-late 22 em june 2008

4 morning in summer (see Figure 2). On some occasions when winds shifted in direction during the day, analysis of monitoring data indicated sources within the Gorge contributing to haze. The August 2004 episode saw elevated levels of organic carbon and sulfate aerosols. The ovember 2004 episode saw high levels of nitrate, sulfate, and organic carbon. Figure 3 shows a time series of daily average particle light scattering (b sp ) at the nephelometer sites. Haze levels were highest at the eastern sites and decreased to the west. Figure 4 shows photographs from Wishram at the height of the episode and during pristine conditions. The CAMx chemical transport model results indicated that for the ovember episode most of the haze was caused by man-made sources within the region (Oregon and Washington), while for the August episode a majority of the haze was due to natural (vegetation and wildfires) and more distant sources. Figure 5 summarizes the modeled source impacts at the western Gorge Mt. Zion site for the August episode and the eastern Gorge Wishram site for the ovember episode. Of the 41% impact at Mt. Zion from local man-made sources in August, approximately half was due to the Portland area, a finding consistent with the summer diurnal haze pattern shown in Figure 2. At Wishram for the ovember episode, 57% of the haze came from sources east of the Gorge with 32% from electric Figure 4. View looking west into the gorge from Wishram for (a) pristine conditions and (b) ovember 2004 episode day (1200 PST 10 ovember 2004, b sp = 267 Mm -1 ). The episode was characterized by daily average bsp over 200 Mm -1, high relative humidity, and high concentrations of nitrate, sulfate, and organic carbon aerosols. june 2008 em 23

5 Figure 5. Source contributions to haze during August and ovember 2004 episodes at Mt. Zion (August) and Wishram (ovember) from CAMx modeling. generating units (EGUs). The dominant EGU east of the Gorge is the Portland General Electric (PGE) coal-fired plant near Boardman, OR. Based on a weight of evidence approach considering the modeling, data analysis, and emissions inventories, the PGE Boardman plant is responsible for a substantial fraction of the haze in the Gorge during certain winter conditions with easterly winds. It should be noted that ammonia emissions are required to achieve the high levels of winter time nitrate particulate. Confined animal feeding operations (CAFOs), including dairies, are expected to comprise much of the ammonia emissions east of the Gorge. Substantially reducing emissions from the PGE Boardman plant and CAFOs would be expected to quite noticeably improve visibility in the Gorge on some winter days with easterly winds. The modeling for 2018, which accounts for future state and federal emission reduction strategies, suggested little change in summer haze (1 3% improvement) and approximately 10% improvement in winter haze in spite of a projection of increased population. Receptor modeling using Positive Matrix Factorization (PMF) for all samples 6,7 showed broadly similar results to the CAMx modeling. 5 PMF attributed much of the haze to two broad categories secondary sulfate and secondary nitrate factors potentially containing many source types. PMF did specifically identify paper mills, responsible for 7% of haze at Mt. Zion and oil combustion (mainly shipping) responsible for 10% of Mt. Zion haze averaged over the two years. Strategy for Accomplishing Visibility Improvements The Oregon Department of Environmental Quality (ODEQ) and the Southwest (Washington) Clean Air Agency (SWCAA) are developing a strategy to manage visibility in the Gorge. 8 The proposed strategy is based on a four-pronged approach: continued implementation of existing strategies; development of new strategies based upon current regulations; development of future strategies based upon future regulations; and a consensus-based Gorge Solutions Initiative. The agencies propose to report back to the Columbia River Gorge Commission on progress in improving Gorge visibility in The Regional Haze Rule will provide some benefit because there are Federal Class I areas near the Gorge, including Mt. Hood Wilderness (30 km south) and Mt. Adams Wilderness (50 km north). However, in winter, the Class I areas are by and large located at a higher elevation than the haze that affects the Gorge; thus, emissions affecting the Gorge may not affect the Class I areas at times. Also of note is a commitment by ODEQ to recommend emission controls for the PGE Boardman plant in 2008 as part of the Best Available Retrofit Technology analysis for regional haze. Furthermore, the Oregon Dairy Task Force is exploring options for reducing emissions and will issue a report by July em References 1. Green, M.; Xu, J. Transport of Atmospheric Aerosol by Gap Winds in the Columbia River Gorge; J. Climate Appl. Meteorol. 2008, 47, Green, M.; Adhikari,.; Xu, J.; ikolich, G. Columbia River Gorge Haze Gradient Study. Prepared for the Southwest Clean Air Agency, Vancouver, WA, 2006; available online at (accessed 3. User s Guide: Comprehensive Air quality Model with Extensions, Version 4.40; EVIRO International Corporation Inc., ovato, CA, 2006; available online at 4. Emery, C.; Tai, E.; opmongcol, U.; Johnson, J.; Morris, R. Modeling Analyses Conducted for the Columbia River Gorge ational Scenic Area Air Quality Study: Final Report (2007); available online at html (accessed 5. Pitchford, M.; Green, M.; Morris, R.; Emery, C.; Sakata, R.; Swab, C.; Mairose, P. Columbia River Gorge Air Quality Study: Science Summary Report (2008); available online at (accessed March 2008). 6. Green, M.; Xu, J.; Adhikari,.; ikolich, G. Causes of Haze in the Gorge (CoHaGo). Prepared for the Southwest Clean Air Agency, Vancouver, WA, 2006; available online at (accessed 7. Green, M.; Xu, J. Causes of Haze in the Columbia River Gorge; J. Air & Waste Manage. Assoc. 2007, 57, Columbia River Gorge Air Study and Strategy, Draft Report, February 29, 2008; Oregon Department of Environmental Quality and Southwest Clean Air Agency, 2008; available online at (accessed 24 em june 2008