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The Bonneville Power Administration is an American federal agency operating in the Pacific Northwest. BPA was created by an act of Congress in 1937 to market electric power from the Bonneville Dam located on the Columbia River and to construct facilities necessary to transmit that power. Congress has since designated Bonneville to be the marketing agent for power from all of the federally owned hydroelectric projects in the Pacific Northwest. Bonneville is one of four regional Federal power marketing agencies within the U.S. Department of Energy . Wikipedia.

NEW YORK--(BUSINESS WIRE)--Fitch Ratings has assigned an 'A-' rating to the Public Utility District No.1 of Klickitat County's (KPUD, or the district) series 2015 A ($45.75 million) and series 2015B ($34.55 million, federally taxable) electric system revenue and refunding bonds. The bonds are scheduled to price the week of August 10th, with a final maturity of Dec. 1, 2036. Bond proceeds will fund certain capital expenditures; refund and restructure a portion of outstanding (series 2006B) debt; fund the debt service reserve account requirement; and pay costs of issuance. In addition, Fitch affirms the following parity lien ratings: The bonds are secured by net revenues of the electric system, after the payment of operating expenses. The district's water and wastewater system is separately financed and secured. NONTRADITIONAL RETAIL UTILITY: KPUD predominantly provides its customers with retail electric service. The district's electric operating profile is somewhat unique, as it extends beyond the delivery of power to its native load, and incorporates wholesale power and transmission activities. Although these activities generate margins and help offset costs to customers, they also expose bondholders to added risk. RENEWABLE AND CARBON-FREE POWER SUPPLY: The district's power supply is mostly purchased hydropower, with 88% contributed by the Bonneville Power Administration (BPA), along with wind and landfill (methane) gas-to-energy resources. Together, these provide a favorable mix of renewable and carbon-free resources. RELIANCE ON WHOLESALE REVENUES: The current rating reflects KPUD's reliance on wholesale power revenues, which are largely derived from near-term and spot sales of excess power supply and are inherently volatile. Wholesale power revenues accounted for 23% of total operating revenues in fiscal 2014 and are projected to remain in the 22%-27% range through 2019. Although some improvement is forecast, low wholesale market prices will continue to challenge operating margins over the near term. MODESTLY IMPROVED FINANCIAL PERFORMANCE: The District's financial performance has shown some improvement from its low point in FY2012 when significantly lower electricity market prices and step-up in debt service curtailed cash flow and debt service coverage (DSC) (1.03x consolidated). The district subsequently implemented three rate increases (totaling 21%), focused on its hedging strategy and recently increased its DSC target from 1.40x to 1.50x. More conservative Fitch calculated DSC equaled 1.15x and 1.17x, on a consolidated and electric-system only basis, respectively, for FY2014. DEBT EXTENSION PLANNED: The proposed 2015 debt offering includes a four-year debt extension of a portion of outstanding debt (approximately $70 million) to 2035, to levelize debt amortization and alleviate an upcoming rise in debt service. Fitch views the debt extension as credit neutral, as it will provide members near-term rate relief, but continue to amortize debt in-line with the operating life of the generating asset. FAILURE TO ADEQUATELY MAINTAIN FINANCIAL TARGETS: Given Klickitat County Public Utility District's greater exposure to volatile wholesale electricity prices and sales and its high leverage, any failure to offset weaker margins through additional rate increases, meet projected performance or maintain solid liquidity would likely result in downward rating pressure. Klickitat County PUD No. 1 (KPUD, or the District) is located in the southcentral portion of Washington, along the Oregon border. The District's native load is small, but growing, with a retail base of 12,377 electric customers, 82% of which are residential. It is a combined utility system consisting of electric, water and wastewater services. The electric system accounts for the vast majority of consolidated system revenues, at 96.7% of 2014 total operating revenues. Each of the systems is financed and accounted for separately; and is individually self-supporting. The District meets the majority of its electric retail load requirements with power purchases from: Bonneville Power Administration ([BPA]; 88% of load); and the rest from its 50% ownership share in the McNary Dam hydroelectric project (5MW)and 3% share of the Packwood Lake hydroelectric project (1MW). The district's also maintains additional renewable resources that are surplus to its needs, including a prepaid energy purchase equal to 13% of the energy and associated renewable energy credits from a local wind development (White Creek Wind 1, 204.7 MW project); and an investment in a local Landfill Gas-to-Energy (LGTE) facility (total capacity of 26 aMW). The output from the LGTE project is presently fully hedged through 2016. The wind output is sold into the region's wholesale energy markets. Any unhedged wind and LGTE generation provide a physical hedge for the district's load in the event wholesale market prices were to escalate. Off-system renewable power and contracted transmission sales accounted for 23.0% and 11.9%, respectively, of consolidated 2014 system revenues. Wholesale power related revenues are variable as they entail near term contracts and more volatile spot electricity market sales. The transmission revenues are more stable as they are based upon long-term, take-or-pay transmission sales agreements. Over the past few years, the district has taken steps (rate increases, cost cutting, hedging strategy, higher DSC target) to bolster its operations and finances, given the reliance on more variable wholesale electricity sales. Management projects coverage to improve to more than 1.50x by 2016, including contributions in aid of construction and the Build America Bonds federal subsidy as available cash flow for debt service coverage. Fitch-calculated debt service coverage, which excludes non-operating earnings, should approximate 1.25x. The District's financial metrics are adequate for the rating level. While recent rate increases are helping to mitigate low wholesale electricity sales and margins, leverage remains high, as measured by debt-to-FADS of 10.8x for fiscal 2014, compared with Fitch retail median of 8.7x for 2014. Liquidity remains solid and supported by an external bank line, in aggregate providing 155 days operating liquidity for fiscal 2014. The district's financial projections appear reasonable, with a 1.50x debt service coverage target. As noted, the district's calculation of debt service coverage is more liberal than the Fitch computation. Fitch calculated debt service coverage is projected at approximately 1.25x - 1.47x through 2019, sufficient for the 'A-' rating category. Most of KPUD's 2015 debt offering includes a partial debt restructuring and extension. KPUD's existing annual debt service ($10.5 million) escalates in 2017 (to roughly $11.9 million) and again in 2020 ($12.5 million). This added cost equates to roughly a 3-4% rise in the retail revenue requirement, assuming wholesale electricity prices slightly improve but remain relatively low through 2019. KPUD is additionally anticipating wholesale rate increases from its main source of power supply, BPA. The proposed debt restructuring plan will provide some rate relief over the next ten years in exchange for slightly higher rates towards the end of the debt life. Favorably, the agency's debt will be fully retired by 2036, in line with the expected operating life of the generating asset. Additional information is available at 'www.fitchratings.com'. ALL FITCH CREDIT RATINGS ARE SUBJECT TO CERTAIN LIMITATIONS AND DISCLAIMERS. PLEASE READ THESE LIMITATIONS AND DISCLAIMERS BY FOLLOWING THIS LINK: HTTP://FITCHRATINGS.COM/UNDERSTANDINGCREDITRATINGS. IN ADDITION, RATING DEFINITIONS AND THE TERMS OF USE OF SUCH RATINGS ARE AVAILABLE ON THE AGENCY'S PUBLIC WEBSITE 'WWW.FITCHRATINGS.COM'. PUBLISHED RATINGS, CRITERIA AND METHODOLOGIES ARE AVAILABLE FROM THIS SITE AT ALL TIMES. FITCH'S CODE OF CONDUCT, CONFIDENTIALITY, CONFLICTS OF INTEREST, AFFILIATE FIREWALL, COMPLIANCE AND OTHER RELEVANT POLICIES AND PROCEDURES ARE ALSO AVAILABLE FROM THE 'CODE OF CONDUCT' SECTION OF THIS SITE. FITCH MAY HAVE PROVIDED ANOTHER PERMISSIBLE SERVICE TO THE RATED ENTITY OR ITS RELATED THIRD PARTIES. DETAILS OF THIS SERVICE FOR RATINGS FOR WHICH THE LEAD ANALYST IS BASED IN AN EU-REGISTERED ENTITY CAN BE FOUND ON THE ENTITY SUMMARY PAGE FOR THIS ISSUER ON THE FITCH WEBSITE.

NEW YORK--(BUSINESS WIRE)--Fitch Ratings has affirmed the 'AA-' rating on the following bonds, issued by the city of Tacoma, WA (the city) on behalf of Tacoma Power, a department of the city: The bonds are secured by and payable solely from electric system net revenues. SOLID POWER SUPPLY RESOURCES: Tacoma Power is a vertically integrated electric system that draws on a resource mix balanced between low-cost owned hydro resources and purchased power mainly from Bonneville Power Administration (BPA). Capacity is sufficient to meet projected load growth through at least 2025. FUTURE METRICS REFLECT REPAYMENT: Financial metrics have generally strengthened in recent years, as rate increases bolstered cash flow and increased the utility's very strong liquidity position. Tacoma Power plans to draw on reserves to repay a portion of its outstanding debt, which will reduce cash on hand but the resulting decrease in annual debt service should improve coverage. Overall, metrics should remain sufficient for the rating category. COMPETITIVE RETAIL ELECTRIC RATES: Rates are inline with regional municipal utilities and below those of neighboring investor owned utilities. Competitive rates, combined with a history of timely rate approvals, indicate some rate flexibility. Favorably, the utility established a rate stabilization fund (RSF), which can be used to smooth future rate increases, if needed. DIVERSE CUSTOMERS, SOFT ECONOMY: The service area has a diverse economy supported by a range of industry sectors. Residential sales make up a healthy 38% of retail revenue and there is minimal customer concentration. However, the city was noticeably affected by the recession and recovery has been sluggish, with economic indicators persistently lagging both the state and nation. WHOLESALE SALES VARIABILITY: Tacoma Power is a net seller into the wholesale power market in most years. These nonfirm, short-term sales are subject to hydrological conditions and market prices, which creates variability in revenues. Favorably, implemented and anticipated retail rate increases help to insulate Tacoma Power from future wholesale sales fluctuations. MANAGEMENT OF REVENUE STREAMS: Given Tacoma Power's reliance on more volatile wholesale sales and uncertain telecommunication revenues, it is important for the utility to manage these operations together with electric rates in a way that maintains stable financial performance. Increasing financial support of the telecommunications division by the electric system, to the detriment of financial metrics, could pressure the rating. Tacoma Power is a division of the city's Department of Public Utilities. The utility operates the city's vertically integrated electrical generation and distribution facilities and its telecommunications division, the Click! Network (Click). Tacoma Power is one of the largest publicly owned utilities in the Pacific Northwest, serving approximately 172,531 customers in a service area that is approximately 180 square miles and serves the greater Tacoma area The city is located approximately 30 miles south of Seattle in the Puget Sound region. The area has a diverse economy, with industry sectors that include the military, healthcare, manufacturing and wholesale distribution, along with the Port of Tacoma, which is considered an economic engine for the region. Fitch notes that the city was perceptibly affected by the national economic downturn, as evidenced by service area economic indicators that persistently lag both the state and the nation. Favorably, there has been a positive trend in employment since mid-2014 indicating regional job creation. The utility has not seen an increase in bad debt expense or a lag in collections. Tacoma Power's reasonably well-diversified customer base somewhat mitigates its service area. The city's GO debt rating was downgraded in July 2012 from 'AA' Stable Outlook to 'A+' with a Negative Outlook and revised to a Positive Outlook in June 2013. Tacoma Power is somewhat insulated from the city's fiscal difficulties, as the utility is not required to make transfers to the city's general fund. Instead, the utility is charged a gross earnings tax by the city, which is legally restricted to 6% of electric revenues and 8% of telecommunications revenues. Fitch views Tacoma Power's resource mix as a predominant credit strength. All of Tacoma Power's resources are carbon free and the utility has a healthy balance of purchased power and owned generation. The majority of Tacoma Power's resources are hydroelectric based, with 43% of its 2014 resource portfolio provided by its four hydroelectric generating projects and 53% provided by a long-term power purchase contract with BPA, the regional federal power marketing agency. Tacoma Power is a net seller into the wholesale electricity market under most water conditions. Wholesale revenues for any year are based on market prices, loads and water availability for generation, which creates volatility in the utility's overall revenues. Tacoma Power has implemented a series of rate increases to make the utility less dependent on its wholesale sales and strengthen its retail revenue base. Fitch views Click as increasing the business risk profile of Tacoma Power due to the competitive nature of the telecommunications industry. Click is not self-supporting and requires upwards of $6 million annually from the electric system. Competition from larger telecommunication companies could continue to erode the Click customer base and revenues. Management has presented a proposal to its board and city council to enter into a lease agreement with Wave Broadband for 40 years. The agreement would give Wave Broadband control of running the Click network, while allowing Tacoma Power to continue owning the assets. Approval (or denial) of the proposal is expected in the coming months. The ability to make Click self-supporting without electric system intervention, be it through a lease agreement or other means, would be viewed positively. Financial metrics have been strong and stable, after recovering from a low point in 2010. Debt service coverage (DSC) increased from 2.08x in 2010 to 2.40x in 2014, which compares favorably to the 'AA-' median of 2.38x. Management's implementation of a series of rate increases has helped to insulate metrics from wholesale sale fluctuations and also allowed the utility to bolster its liquidity position. Liquidity is very strong, with unrestricted funds equal to 335 days cash on hand (DCOH). Tacoma Power is planning to repay its 2005B bonds this year with a mix of cash and excess bond reserves. The refunding should substantially decrease debt service in 2015 through 2020, from an average of $55 million per annum to $30 million per annum. The utility's most recent financial forecast suggests stronger DSC than past projections, given the decrease in debt service. DSC is projected to be above 3.0x starting in 2016 through the forecast period. DCOH will decrease to an average of 166 DCOH as funds are used to repay debt, but should remain acceptable for the rating category. Liquidity will be enhanced by a revolving line of credit for working capital needs. Additional information is available at 'www.fitchratings.com'. 2015 Outlook: U.S. Public Power and Electric Cooperative Sector (Steady as She Goes) ALL FITCH CREDIT RATINGS ARE SUBJECT TO CERTAIN LIMITATIONS AND DISCLAIMERS. PLEASE READ THESE LIMITATIONS AND DISCLAIMERS BY FOLLOWING THIS LINK: HTTP://FITCHRATINGS.COM/UNDERSTANDINGCREDITRATINGS. IN ADDITION, RATING DEFINITIONS AND THE TERMS OF USE OF SUCH RATINGS ARE AVAILABLE ON THE AGENCY'S PUBLIC WEBSITE 'WWW.FITCHRATINGS.COM'. PUBLISHED RATINGS, CRITERIA AND METHODOLOGIES ARE AVAILABLE FROM THIS SITE AT ALL TIMES. FITCH'S CODE OF CONDUCT, CONFIDENTIALITY, CONFLICTS OF INTEREST, AFFILIATE FIREWALL, COMPLIANCE AND OTHER RELEVANT POLICIES AND PROCEDURES ARE ALSO AVAILABLE FROM THE 'CODE OF CONDUCT' SECTION OF THIS SITE. FITCH MAY HAVE PROVIDED ANOTHER PERMISSIBLE SERVICE TO THE RATED ENTITY OR ITS RELATED THIRD PARTIES. DETAILS OF THIS SERVICE FOR RATINGS FOR WHICH THE LEAD ANALYST IS BASED IN AN EU-REGISTERED ENTITY CAN BE FOUND ON THE ENTITY SUMMARY PAGE FOR THIS ISSUER ON THE FITCH WEBSITE.

News Article | November 2, 2015
Site: www.greentechmedia.com

Seattle-based startup 1Energy has been a small but spirited contender in the emerging energy storage management software field, with a decided emphasis on an open-standards-based approach to linking batteries and other grid-connected assets at scale. For the past few years, it has deployed its software in the form of an intelligent controller, integrating with individual battery-inverter systems in a showcase set of Pacific Northwest utility pilot projects, while promising a fleet management platform to tie them all together. Last month's launch of 1Energy's Distributed Energy Resource Optimizer, or DERO, platform marks the delivery on that promise, with some extras to boot. First, 1Energy disclosed a set of partners that have been using its software for a broad set of applications, from AES Energy Storage to Duke Energy. Second, it has expanded the range of distributed energy resources (DERs) it can manage beyond batteries. Snohomish Public Utility District is the first customer for 1Energy’s DERO platform, which makes sense, since it’s the first utility to deploy multiple batteries, of different chemistries and serving different needs, using the startup’s software. “We really believe that, while DERO is initially managing a fleet of storage assets for Snohomish, it will manage not just storage, but other distributed resources like solar in the near future,” Rogers Weed, 1Energy’s vice president of product management, said in a Thursday interview. In fact, “the second customer for DERO wants us to use it to manage more than storage,” he said. While he didn’t name the customer, he did say that “they’re interested in DERO optimizing grid-connected solar [and] behind-the-meter solar.” That makes 1Energy’s new platform less of a standard energy storage management system, he said, and more of a distributed energy resource management system, or DERMS, in GTM Research parlance. In fact, “we think it’s a better DERMS product, first of all, because it relies on local intelligence with local assets, and then focuses on the fleet-level stuff.” The local level comes from 1Energy’s intelligent controller software, which runs battery systems being deployed by home-state partners Snohomish PUD and Puget Sound Energy. It’s installed on a server at the site, and keeps the entire thing running, according to a set of operating parameters that can be preset to engage when certain local grid conditions are met, or when ordered to do so by central control. DERO, by contrast, works at the fleet or utility level, with each individual end-node as a partner, so to speak. “It integrates with transmission and operations platforms and energy-trading platforms, and it will execute and optimize fleet-level applications,” he said. “We’re delivering optimization, not just aggregation -- and we started with storage, the super-set asset,” he said. That’s not just another way to say "holy grail," by the way. It’s referring to the full-spectrum value available to storage systems that can switch from charge to discharge, and from active to reactive power, at the drop of a hat. That’s only if the software that’s running them is flexible and reliable enough to take advantage of the money-making reasons to do so, of course. In the case of Snohomish PUD, 1Energy will be putting together a stack of imperatives, ranging from responses to local grid conditions to energy market imbalances driven by changes in wind farm production a thousand miles away. Snohomish PUD’s batteries -- two 1.5-megawatt, 500-kilowatt-hour lithium-ion batteries from LG Chem and Mitsubishi-Yuasa, and a 2-megawatt vanadium redox flow battery system from UniEnergy Technologies  -- have as their first priority relieving any local distribution grid constraints that could overload circuits or transformers, as part of their value in delaying the replacement of these assets. That’s managed by local control, which can also override commands that would push the system into unsafe operating zones and the like. With DERO, Snohomish PUD will be adding a list of value propositions to each system’s stack. “Energy arbitrage will be the default plan,” with each system taking a five-day forecast of expected prices to charge when they’re low and discharge when they’re high. But higher-value services await, starting with the Bonneville Power Administration (BPA), the federal agency that runs the region’s hydro-powered transmission network. “BPA will be sending them transmission constraint signals, along with a value for alleviating that for BPA. Snohomish will look at that every six hours ahead” to adjust its batteries’ charge-discharge plans. More pressing still is the utility’s exposure to the spot power market, driven by the variable nature of its share of wind power. “You only have a few hours' notice before you forecast that wind is going to under-deliver,” and the cost of making up for the difference depends on hard-to-predict spot prices that have to be integrated into the calculation. Finally, Snohomish has to pay BPA “energy-imbalance mitigation” costs when its hourly forecast of its energy needs falls out of a certain band of tolerance, in order to put a price on failing to meet one’s grid commitments. “The problem is, you don’t really know how you’re going to do on your hourly forecast until you’re into the hour itself,” he said, since the variable being measured is how reality is failing to perform to the best predictive models. That requires five- to ten-minute projections of whether the utility is going to end the hour in the penalty zone, what that penalty costs versus doing whatever else the battery had stacked up to do that hour, and deciding whether or not to act. All in all, it’s a complicated set of decisions being made at the fleet level. At the same time, these decisions rely on each distributed energy asset actually being on-line when it’s needed, and ready to respond to dispatch. It also relies on knowing each battery’s cost of charging and discharging at different power densities at different rates, and how well it stacks up to every other battery in the fleet. All of this complexity would be better managed through common standards, rather than by the one-off systems-integration methods used in most of today’s energy storage deployments. 1Energy has played a central role in one such standards effort, dubbed the Modular Energy Storage Architecture (MESA), which includes long-time partners such as Alstom Grid, Parker Hannifin and Pacific Northwest National Laboratory, and more recently, big utility Duke Energy. Duke also used 1Energy’s software in its 1.5-megawatt, 300-kilowatt-hour Rankin battery project, according to the project list the startup released last week. The project tested different approaches and algorithms for using batteries to balance the effects of lots of solar PV at the end of a stressed-out distribution grid circuit, indicating how solar might link up with storage for 1Energy’s mysterious DERO customer number two. 1Energy’s list of deployments also includes AES Energy Storage’s 20-megawatt, 5-megawatt-hour Cochrane project in Chile, which helps remote desert mining operations manage their extreme power needs. AES Energy Storage has built its own software to manage the energy-market-facing aspects of its hundreds of megawatts of grid battery systems, but it’s been partnering with project developers and other software vendors to manage other aspects of their operations. These projects, its home-state deployments, and a newly announced 1.5-megawatt, 3-megawatt-hour project for Texas utility Austin Energy using Tesla Energy's batteries, brings the startup’s total list to some 20 megawatts and 28 megawatt-hours of batteries that plan to use its software. It’s a figure that helps put 1Energy into clearer ranking with such energy storage management software heavyweights such as Younicos, Greensmith, or NEC Energy Solutions. Meanwhile, 1Energy isn’t alone in seeking to create software that can standardize how energy storage systems interact with the broader IT infrastructure. Rival startup Geli is working on similar concepts, although Geli tends to focus on building operations as its key user, while 1Energy has focused on utilities as its customers.

RESTON, Va.--(BUSINESS WIRE)--The Utility Variable-Generation Integration Group (UVIG) has released an updated version of a summary table detailing markets and market rules for variable generation (VG) in North America. Capturing the state of markets as of March 2015, the document is the third update of a table first issued in December 2004. This year, solar energy was added to the table in recognition of the significant growth in installed solar power capacity. The table was also reorganized and streamlined to improve readability and to enable comparison and contrast between the entities profiled in the table. UVIG appreciates the financial and technical support of the Lawrence Berkley National Laboratory (LBNL) and the U.S. Department of Energy’s Office of Electric Delivery and Reliability. Some of the major findings are that every Regional Transmission Organization, Independent System Operator (ISO), Transmission System Operator (TSO) and utility in North America that is integrating a large amount of wind power is using wind plant output forecasts to improve the reliable and economic operation of their system; solar power forecasts are not as prevalent, but some of these same entities are experimenting with solar power forecasting; wind generation is increasingly being required to follow dispatch signals at short time intervals; and a small but growing number of requirements for variable generation to provide or be capable of providing different types of grid support services, such as frequency response and inertial response, are being seen. The document was compiled by Kevin Porter and Kevin Starr of Exeter Associates with UVIG participation and LBNL support, based on a survey covering PJM Interconnection, the New York Independent System Operator, ISO New England, the Ontario Independent System Operator, Midwest ISO, Southwest Power Pool, the Electric Reliability Council of Texas, California Independent System Operator, Alberta Electric System Operator, Bonneville Power Administration, Public Service Company of Colorado (a subsidiary of Xcel Energy), Arizona Public Service, PacifiCorp, and Puget Sound Electric. The table presents responses to a number of questions, with the more important ones noted below: The document can be downloaded at http://uvig.org/resources/ Formerly known as the Utility Wind Integration Group, the Utility Variable-Generation Integration Group (UVIG) was established in 1989 to provide a forum for the critical analysis of wind technology for utility applications and to serve as a source of credible information on the status of wind technology and deployment. The group’s current mission is to accelerate the development and application of good engineering and operational practices supporting the appropriate integration of wind and solar power for utility applications through the coordinated efforts and actions of its members, in collaboration with the U.S. Department of Energy, its National Renewable Energy Laboratory and utility research organizations. UVIG is an international organization with over 180 members from the United States, Canada, Europe, and Asia, including investor-owned, public power, and rural electric cooperative utilities; transmission system operators, corporate members; and associate member government and academic organizations.

Secondary organic aerosol (SOA) formation in the atmosphere is currently often modeled using a multiple lumped "two-product" (N·2p) approach. The N·2p approach neglects: 1) variation of activity coefficient (¶i) values and mean molecular weight MW̄in the particulate matter (PM) phase; 2) water uptake into the PM; and 3) the possibility of phase separation in the PM. This study considers these effects by adopting an (N·2p)¶̄ approach (θ is a phase index). Specific chemical structures are assigned to 25 lumped SOA compounds and to 15 representative primary organic aerosol (POA) compounds to allow calculation of ¶ and MW̄values. The SOA structure assignments are based on chamber-derived 2p gas/particle partition coefficient values coupled with known effects of structure on vapor pressure pL̊i (atm). To facilitate adoption of the (N·2p)¶pMW̄θ approach in large-scale models, this study also develops CP-Wilson.1 (Chang-Pankow-Wilson.1), a group-contribution ¶-prediction method that is more computationally economical than the UNIFAC model of Fredenslund et al. (1975). Group parameter values required by CP-Wilson.1 are obtained by fitting ¶ values to predictions from UNIFAC. The (N·2p)¶pMW̄θ approach is applied (using CP-Wilson.1) to several real α-pinene/O3 chamber cases for high reacted hydrocarbon levels (δHC≈400 to 1000 μgm-3) when relative humidity (RH) ≈50%. Good agreement between the chamber and predicted results is obtained using both the (N·2p)¶MW̄θ̧ and N·2p approaches, indicating relatively small water effects under these conditions. However, for a hypothetical α-pinene/O3 case at ΔHC=30 μgm-3 and RH=50%, the (N·2p)¶MW̄θ̧ approach predicts that water uptake will lead to an organic PM level that is more double that predicted by the N·2p approach. Adoption of the (N·2p)¶MW̄θ approach using reasonable lumped structures for SOA and POA compounds is recommended for ambient PM modeling. © 2010 Author(s).

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