Implementation of the Phoenix Visibility Monitoring Network

Transcription

1 Implementation of the Phoenix Visibility Monitoring Network Paper # Joe Adlhoch Air Resource Specialists, Inc., 1901 Sharp Point Dr., Suite E, Fort Collins, CO D. Scott Cismoski Air Resource Specialists, Inc., 1901 Sharp Point Dr., Suite E, Fort Collins, CO Kristi Savig Air Resource Specialists, Inc., 1901 Sharp Point Dr., Suite E, Fort Collins, CO Michael Sundblom Arizona Department of Environmental Quality, 1110 W. Washington St., Phoenix, AZ, Darcy Anderson Arizona Department of Environmental Quality, 1110 W. Washington St., Phoenix, AZ, Michael George Arizona Department of Environmental Quality, 1110 W. Washington St., Phoenix, AZ, ABSTRACT The Arizona Department of Environmental Quality (ADEQ) implemented a long-term urban visibility monitoring network in 1992, based on the recommendations from urban haze studies in Phoenix ( ) and Tucson ( ). The Phoenix component of the network consisted of a transmissometer, nephelometer, and an automatic 35mm camera system. In 2000, Governor Hull of Arizona established the Brown Cloud Summit, which was charged with developing recommendations for improving visibility in the Phoenix metropolitan area. Among the recommendations were: enhancement of the visibility network, both spatially and technologically; and development of a Visibility Index. The expanded visibility network consists of 7 optical instruments (2 transmissometers and 5 ambient nephelometers), and 5 digital web camera systems located across the metropolitan area. The optical instruments operate continuously, measuring either total light extinction or particle light scattering. High resolution digital images (with views that include the optical monitoring sites) are captured every 15 minutes. All data and images captured by these and supplemental meteorological instruments are displayed on the Phoenix Visibility Network Web Site ( in real time, accessible to the public. Important components of the project include interpretation of the displayed images and data, reporting of the Phoenix Visibility Index, and education of the public on regional visibility issues.

2 The Blue Sky Index (the annual number of days with at least 25-mile visual range) was developed by the Brown Cloud Summit participants as in interim reporting mechanism until the Visibility Index is developed. The Visibility Index development utilized a survey program, in which Phoenix area residents were asked to rank and comment on a series of images of Phoenix under simulated levels of haze. The Visibility Index Oversight Committee, a successor group to the Brown Cloud Summit, has assisted ADEQ with formation and implementation of the index. INTRODUCTION The Arizona Department of Environmental Quality (ADEQ), as recommended by the Brown Cloud Summit and mandated by the state legislature in 2001, has expanded its existing visibility monitoring network in the Phoenix metropolitan area. The underlying goal is to better track visibility improvement in the region and present that information to the public in a meaningful way. The network enhancements include a significant increase in monitoring sites for better regional coverage, and the addition of new technologies to collect and disseminate visibilityrelated data. Background Long-term monitoring of the optical characteristics of haze in Phoenix began in 1993 with the installation of an Optec LPV-2 long-path transmissometer and an automatic 35mm camera system. An Optec NGN-2 ambient nephelometer was added to the network within the transmissometer sight path in Data from an Anderson dichotomous particulate sampler collocated with the nephelometer is used to better understand and validate the optical data. The LPV-2 transmissometer measures the ability of the atmosphere to transmit light of a specific wavelength (550 nm) by continuously measuring the loss in light received from a light source of known intensity across a known distance. Total light extinction can be calculated from the measured transmittance. Data are reported hourly. Various data screening algorithms are used to identify period in which the collected data may not be representative of light extinction due to pollution. For example, rain or fog will decrease transmittance and impede visibility, but these phenomena are not directly associated with particulate levels in the atmosphere. An ambient temperature and relative humidity sensor is collocated with the transmissometer receiver. In Phoenix the transmitter and receiver components of the transmissometer are located near downtown on multi-story rooftops approximately 4.7 km apart. The 35mm camera system automatically photographed downtown Phoenix three times per day (0900, 1200, and 1500). The photographs included most of the transmissometer sight path and the nephelometer and dichotomous sampler monitoring site. Used to document visual conditions, the photographs helped to better understand and validate the optical data. They also provide a long-term visual record of pollution conditions and specific events. The 35mm camera system was located in north Phoenix and viewed south west across downtown until it was removed in The NGN-2 nephelometer measures light scattered by aerosol particles integrated over a wide range of scattering angles (5 175 degrees) at a single point. The nephelometer can be directly

3 calibrated with clean air and a span gas with known scattering characteristics. Data are reported hourly. Data screening algorithms, similar to those employed on transmissometer data, are used to identify period in which the collected data may not be representative of light scattering due to pollution. An ambient temperature and relative humidity sensor is collocated with the nephelometer. In Phoenix the nephelometer is located at the Phoenix Supersite on a 14 tower. Other instrumentation at the Supersite includes monitors for particulate, speciated particulate, gaseous, and meteorological parameters. The dichotomous sampler draws air through a 10 micron size selection device, and then utilizes a virtual impactor to further size select PM 2.5 particles. A dual filter system allows for the measurement of both PM 2.5 and PM coarse (particles with aerodynamic diameters greater than 2.5 microns but less than 10 microns). In Phoenix two dichotomous samplers operate at the Phoenix Supersite. Both instruments sample on the EPA 6-day schedule, the first collecting 24-hr samples, and the second collecting 6-hr morning (5:00 am 11:00 am) samples. Figure 1 presents a summary of annual transmissometer, nephelometer, PM 2.5 and PM coarse measurements from 1994 through , 2 These data are from the original visibility network, in which the nephelometer and dichotomous sampler are collocated, and both within the transmissometer sight path. PM 2.5 is a much larger contributor per unit mass to measured extinction or scattering then PM coarse due to its size. While PM coarse contributes more to total mass than PM 2.5, it does not scatter light as effectively. The difference between light extinction and light scattering measurements is attributed in part to Rayleigh scattering (approximately 11 Mm -1 for Phoenix), in part to contributions from particulate (elemental carbon) and gaseous (nitrogen dioxide) light absorption, and in part to the differences in measurement techniques (point vs. path measurements, different heights above ground level). While no definitive substantial trends can be identified in the data record of these parameters, PM 2.5 and total light extinction show lower values in the most recent years than were measured during most of the mid-1990 s.

4 Figure 1: Summary of annual light extinction (transmissometer), light scattering (nephelometer), PM 2.5 and PM coarse measurements taken in Phoenix from 1994 through Summary of Annual PM and Optical Data Phoenix, PM Mass (ug/m3) Extinction and Scattering (Mm-1) PM2.5 PMcoarse Total Light Extinction Particle Scattering Brown Cloud Summit After nearly a decade of visibility-related data collection and analysis, Governor Hull of Arizona established the Brown Cloud Summit in 2000 to identify strategies to improve visibility in the Phoenix metropolitan area. 3 The Visibility Standards Subcommittee of the Brown Cloud Summit was charged with establishing options for a visibility standard or other method to track progress in improving visibility in the Phoenix area and to recommend the structure for a public process to determine the standard or other method. The subcommittee recommended the following: Select a number of days per year as interim annual blue sky visibility targets until a daily Visibility Index value is selected for the metropolitan area. The target values would be 250 days in 2001, 260 days in 2002, and 275 days in Define a process to adopt a daily Visibility Index, not a standard, for the metropolitan area by the end of Significant pollution control strategies to improve visibility could be in effect by that date.

5 Require that ADEQ conduct peer-reviewed periodic scientific assessments of visibility data collected in the metropolitan area (in 2003, 2006, and 2010), to understand the air quality benefits of control programs recommended by the Summit. To accomplish this: - Seek funding for an expanded metropolitan area visibility monitoring network, and - Assign responsibility for operation of the network and the assessments to ADEQ. These recommendations were included in the Brown Cloud Summit final report, 4 and, subsequently, in Arizona House Bill 2538 of Both the state legislature and the Governor approved the bill later that year. Interim Blue Sky Index In accordance with this legislation, ADEQ created the Blue Sky Index as an interim reporting mechanism until the Visibility Index could be developed. The Blue Sky Index is a 12 month rolling list of the number of Blue Sky Days in the Phoenix metropolitan area. A Blue Sky Day is defined as a day during which a daytime (6:00 am 6:00 pm) six-hour average visual range, as measured by the downtown Phoenix transmissometer, is 25 miles (40 km) or more. 4 This visual range corresponds to an extinction value of approximately 100 Mm -1, or a deciview value of 23. ADEQ selected numerical targets for the number of Blue Sky Days in each year from 2001 through A table of those targets and the actual number of observed Blue Sky Days, by annual and quarterly periods, is presented in Table 1. The number of target Blue Sky Days increases with subsequent years based on the expectation that recent EPA and state regulations will result in visibility improvement in the near future. The quarterly number of Blue Sky Days is highest during 2 nd and 3 rd quarters, following the general pattern of historical visibility data in Phoenix, with best visibility in Spring and Summer, and worst visibility in Fall and Winter. When developing the definition of a Blue Sky Day, historical Phoenix transmissometer data were analyzed for the frequency of Blue Sky occurrences. Figure 2 presents a graph of the annual number of Blue Sky Days that have occurred in Phoenix since The general trend is seen to be increasing. Table 1. Target and Measured No. of Blue Sky Days, Based on Phoenix Transmissometer Days. Target Blue Measured No. of Blue Sky Days Year Sky Days Annual 1 st Quarter 2 nd Quarter 3 rd Quarter 4 th Quarter * * * 4 th Quarter and Annual Blue Sky Days for 2002 will be reported in early 2003.

6 Figure 2: Annual number of Blue Sky Days in Phoenix from 1994 through 2001, based on Phoenix transmissometer data. Annual No. Blue Sky Days Based on Phoenix Transmissometer Data No. of Occurrences Final Visibility Index Executive Order (46 KB) directed the Governor's Brown Cloud Summit to establish options for a visibility standard or other method to track progress in improving visibility in the Phoenix area. 3 The Summit concluded a daily Visibility Index for the metropolitan area should have its characteristics defined through a public survey process. This process called for a representative cross-section of residents of Area A (as described in House Bill 2538, roughly the Phoenix metropolitan area), to determine what visual air qualities are desirable, what visual range is acceptable, and how often the combination of acceptable visual range and air quality is preferred. The Visibility Oversight Committee s charge is to advise ADEQ in the following ways: Advise consultant prior to conducting public visibility survey. Meet with the selected contractor after the actual survey is complete to discuss likely success and whether additional surveying may be required. Review the draft analysis report from the contractor, release it for public comment. Present the index to the public jointly with ADEQ at a media event.

7 Provide the Visibility Index to the Cap and Trade Oversight Committee for their consideration as the target for improving visibility. Through a series of meetings in 2002, ADEQ and the Visibility Index Oversight Committee designed the visibility survey, selected a contractor to conduct the survey, and oversaw the completion of the field portion of the survey. In late 2002, the contractor, BBC Research and Consulting, presented the draft survey results to ADEQ and the Committee. A final report was issued in early 2003 which included comments received from ADEQ and the Committee. 6 After reviewing the survey results the Committee discussed several components that would form the index. Each component, documented in the Committee s Final report, 7 is summarized below: Methodology to best represent daylight hours The Committee concluded that using actual daylight hours was preferred over fixed clock hours (e.g., 6:00 a.m. to 6:00 p.m.). Members noted that actual daylight hours would range from 11 to 15 hours per day depending on the season and should be updated on a monthly basis. A fixed clock method would have utilized pre-dawn and post-sunset hours in the winter, and neglected early morning and early evening daylight hours during summer. Rolling average vs. block average The Committee concluded that rolling averages rather than block averages would be most feasible given the selection of actual daylight hours. Approach for the Visibility Index The Committee selected to use index categories (e.g., excellent to very poor) rather than a bright line approach. The members reasoned that an index category approach using excellent, good, fair, poor, and very poor categories is much easier for the general public to understand. It includes categories, which reflect what people actually see, and is a more intuitive method. Averaging period The Committee selected 4-hour averaging for the Visibility Index in order to provide timely information to the public and also provide a measurement period that can be most useful in longer term trend analysis. Members also came to general agreement that ADEQ should proceed with data analysis and reporting as appropriate and feasible, but that the daily value used for comparison to the long term trend should be based upon the worst 4-hour average. Category thresholds Based upon the technical analysis of the survey results conducted by Air Pollution Evaluations and Solutions, the Committee selected the following category thresholds for the Visibility Index: 1-14 deciviews - excellent; deciviews - good; deciviews - fair; deciviews - poor; and 29 or more deciviews - very poor.

8 Environmental goal The Committee recommended that the environmental goal of the index will be to show continued progress through 2018 by: 1) improving visibility to move days now in the poor/very poor categories up to the fair category; and 2) moving days classified as fair to the good/excellent categories. A progress assessment will be conducted every 5 years through The option provides a clear, long term method to track visibility trends in the Phoenix metropolitan area. Additionally, the Committee agreed that the index should not be used to affect short term actions because other programs, such as the High Pollution Advisory Program, are currently in place in the Phoenix Metropolitan area. Table 2 summarizes the recommended Visibility Index, which is scheduled to be implemented beginning January 1, Table 2. Recommended Visibility Index. Recommended Visibility Index for Area A 1. Index Categories 2. Averaging Category Excellent Deciview Range 14 or less Good 15 to 20 Fair 21 to 24 Poor 25 to 28 Very Poor 4-Hour Rolling Average 3. Statistic for Reporting Period 29 or greater Highest Daily Average Deciview Value, as measured during daylight hours (adjusted monthly) 4. Environmental Goal Show continued progress through 2018 Move days in the poor/very poor categories up to the fair category Move days in the fair category up to the good/excellent categories Progress assessment to be conducted every 5 years through 2018

9 Expanded Visibility Network The original visibility network monitored air in the downtown Phoenix area. During the Brown Cloud Summit it became apparent that this narrow focus would not serve the purpose of tracking visibility improvement throughout the metropolitan area. Visibility can be expected to vary across the region because: Phoenix and its suburbs cover over 9,000 square miles with varying population density Visibility events can be dominated by local sources and affected by local meteorology In addition to better monitoring coverage, ADEQ desired greater public awareness of visibility issues, which can be gained through a more regionally comprehensive network and publicly accessible results and information. To achieve this goal, ADEQ developed a web site to showcase real-time visibility data from the network. ADEQ designed the expanded network to include monitoring sites in several clusters in the east, central, and west regions of the Phoenix metropolitan area. An ideal monitoring cluster consists of a transmissometer with a nephelometer located within the sight path and a digital camera viewing the sight path. This ideal was not achievable at all locations. No satisfactory transmissometer path could be found in the west metro area, and additional nephelometer/camera pairs were added to optimize regional coverage. The approximate locations of new visibility instrumentation are displayed geographically in Figure 3 and summarized in Table 3. Table 4 lists and briefly describes the instrument models selected for use in the network.

10 Figure 3: Monitoring locations in the expanded visibility network. Transmissometer paths are red, nephelometer locations green, and digital camera locations and view angles yellow. Table 3. Number of Instrument Types in the Phoenix Expanded Visibility Monitoring Network. Location Transmissometer Nephelometer Digital Camera East Metro Area Central Phoenix West Metro Area 0* 2 2 * ADEQ may add a transmissometer in the west metro area at a later date if a satisfactory sight path can be found.

11 Table 4. Instrument Models Selected for Phoenix Expanded Visibility Monitoring Network. Instrument Model Description Transmissometer Optec LPV-3 This new model is based on the LPV-2, which is used in the IMPROVE, ADEQ urban, and other networks. Several new design features enhance the reliability of the LPV-3: a new lamp monitoring design helps to reduce the incidence of lamp brightening common to the LPV-2; and a positive locking mechanism is used to provide for optimal and repeatable lamp orientation when in use. An ambient temperature and relative humidity sensor is collocated with the transmissometer receiver. All data is collected by a Campbell 23X datalogger which can be Nephelometer Digital Camera Image Acquisition and Processing Optec NGN-2 Olympus C-2100 ARS HRDC-R interrogated via modem as required. This model is used by IMPROVE and IMPROVE protocol networks. It has been used in urban and wilderness networks in Arizona since An ambient temperature and relative humidity sensor is collocated with the nephelometer. All data is collected by a Campbell 23X datalogger which can be interrogated via modem as required. This model includes features necessary to capture high quality digital images suitable for qualitative (layered haze frequency) and quantitative (extraction of visibility information) analyses: 2.1 megapixel resolution, selectable white balance, control of all camera functions via custom PC software, high quality glass lens, and 10x optical zoom. This rugged single-board computer controls the Olympus camera, collects and processes images, gathers related visibility data from other dataloggers via modem, and submits data via FTP over the internet to the project web site for display. Network Web Site ADEQ developed the Phoenix Visibility Network Web Site ( to display and help interpret real-time visibility data. The web site was modeled after other successful regional digital camera network web sites (e.g., NESCAUM s CAMNet and MidWest RPO s MidWest HazeCam networks). Specific goals of the web site include: Educating the public regarding visibility-related issues in the Phoenix area. Providing a publicly accessible platform for tracking visibility improvement in the Phoenix area. Providing a potential resource for state and city staff to assess the effectiveness of existing and future regulations.

12 These goals are met with a combination of image and data postings, instrument and data descriptions, educational materials, and relevant links to other visibility-related web sites. Selected web site pages are described briefly below. Figure 4 presents sample screens from the site. All images and visibility data collected in the network are archived and analyzed outside of the website environment. These data will be used to monitor long-term trends and short-term events. In-depth analyses that are not possible in real-time will still be performed and reported by more conventional means. PhoenixVis.net Home Page/All Sites Page The Home Page provides an introduction to PhoenixVis.net and to the visibility monitoring network, and links to all other information on the web site. Current thumbnail images from all 5 network cameras are displayed. Once the Visibility Index is implemented, the current value will be displayed on the Home Page. The Visibility Index will be based on data from the central Phoenix transmissometer. Each site s Real-Time Page can be accessed directly from the thumbnail images or the left-hand banner. Direct links to the Blue Sky Target Page (current, historical, and target counts), Visibility Index Page (current and historical values), and other municipal web sites are also available. Blue Sky Target Page The Blue Sky Target Page provides an introduction to this interim visibility reporting mechanism, a current and historical tabulation of Blue Sky Days in the Phoenix area, and whether or not the Blue Sky Targets have been met for particulate years. As on the Home Page, the left-hand banner provides direct access to individual Real-Time pages, the Visibility Index Page, and other municipal web sites.

13 Figure 4: Sample pages from PhoenixVis.net. Phoenix Visibility Home/All Sites Page Blue Sky Target Page April 10, 2003 April 11, 2003 Site-Specific Real-Time Page 48-hr Image Archive Page Real-Time Pages The Real-Time page provides a large current image for the site selected. Images are captured every 15 minutes around the clock. Commands on the page allow the user to zoom in or out, save a high resolution image, request identification of landmarks in the vista, and locate the site and vista on a map of the Phoenix area. Real-time visibility-related data are displayed below the image. The specific data displayed depends on what air quality parameters are collected nearby the camera site. Generally nephelometer scattering and meteorological data are included. It is important to remember that all visibility-related data reported in real-time is by definition preliminary and largely non-validated. Some minimal validation algorithms are employed (e.g., min/max data ranges, and instrument diagnostic flags), but final validated data cannot be reported by ADEQ on the web site in real-time. Selections on this page allow the user to view the 48-hr Image Archive Page and the 48-hr Data Record Page.

14 48-hr Image Archive Page The 48-hr Image Archive Page displays top of the hour thumbnail images for the current day and the previous day. This is designed to give the user a quick look at recent visibility conditions. Clicking on an hourly thumbnail image will make it appear larger at the top of the page, next to a static pristine image for comparison. Landmark and mapping functions are also available here. The 48-hr Data Record Page complements this image archive by providing data plots of preliminary hourly visibility-related data for the current and previous day. Conclusions The Arizona Department of Environmental Quality, as mandated by the state legislature, has developed a large visibility network in the Phoenix metropolitan area consisting of transmissometers, nephelometers, and digital cameras. The data and images collected with these instruments, as well as resources for understanding this information, are accessible to government officials, industry representatives, academic researchers, and the general public on ADEQ s visibility web site: It is believed that this visibility monitoring network will provide a satisfactory mechanism for tracking visibility improvement and reporting real-time data in the years to come. REFERENCES 1. ADEQ, Arizona Department of Environmental Quality Annual Report 2001, Air Resource Specialists, Inc., Phoenix and Tucson, Arizona, Visibility Monitoring Program, Transmissometer and Nephelometer Operations, Annual Quality Assurance Report, December 2001 through November 2002, September Governor Jane Dee Hull, Executive Order , Governor s Brown Cloud Summit, Brown Cloud Summit Visibility Standard Subcommittee, Final Report, Visibility Standard Recommendations Working Group, Visibility Standard Subcommittee, Governor s Brown Cloud Summit, July State of Arizona House of Representatives, Forty-fifth Legislature, First Regular Session, 2001, House Bill 2538, BBC Research and Consulting, Phoenix Area Visibility Survey, Final Report, February Visibility Index Oversight Committee, Final Report Recommendation for a Phoenix Area Visibility Index, March 2003.

15 KEYWORDS Digital Web Camera Phoenix PM 2.5 Monitoring Network Nephelometer Transmissometer Visibility Index