ABSTRACT

The study will comprise three tasks, described in the remainder of this extended abstract:

Task 1 - Characterize Historical Pollution Episodes and Create Pollution Climatologies

In this task we will assemble available air quality and meteorological data along the Wasatch Front for a five-year period (1994-1998) into a Microsoft Access relational database that can be queried for detailed analysis. This database will be made available to project planners as well as analyzed as part of this task. Available meteorological data is currently available for surface sites primarily, but several of these are located in canyons and ridgetops in complex terrain around the Salt Lake Basin. Meteorological data will be merged with historical air quality measurements of CO, NO_x, SO₂, and suspended particulates (PM₁₀ and PM_2.5) from the EPA AIRS and IMPROVE databases, and others. Similar data will be acquired after the intensive study period and merged with measurements acquired by other investigators during the study period. We plan to make the resulting data base available over the internet and on CD ROM.

This task will also include analyses of historical data. Statistical summaries of air quality measurements will be compiled to determine where and when the highest concentrations occur and the meteorological conditions associated with those occurrences. Analyses will also address the extent to which meteorology during October represents meteorology during other seasons, and the year-to-year variation in meteorology for Octobers during different years. Other specific analyses will include 1) comparison of temperatures by hour from different elevations (including those on ridgetops, passes, and valley floors) to evaluate the timing and intensity of surface layers; 2) comparison of surface, 750 mb, and 500 mb temperatures to evaluate the presence and intensity of subsidence inversions; 3) hourly wind speeds and directions in passes, especially the pass between the Salt Lake and Utah Valleys, to determine the timing and intensity of transport; and 4) examination of morning and afternoon soundings for heights and intensities of the surface and boundary layer.

Terrain maps of ground-level and elevated emissions sources and intensities will be prepared to compare their locations with those of air quality monitors. These will be used with the meteorological analysis to determine where continuous light scattering and CO monitors should be located during the October 2000 (Task 2 of this study, described below). Gaps in the existing meteorological network will be identified that might be filled as part of the Task 2 experimental design.

Conclusions from this task will be used to identify unique aspects of pollution episodes during stagnant and stable periods, such as locations of local hot spots and areas of highest concentrations, and local transport corridors associated with downslope flows. Our intention is to provide information that will enhance field study design by allowing researchers to focus on areas of highest pollutant concentrations that may be expected during the intensive measurement period, and that will ultimately enable a positive link of field study results to simultaneously observed air pollution episodes.

Task 2 - Air Quality Monitoring During Intensive Studies

This task will consist of CO and particulate measurements during the intensive field study period. Some of the hypotheses we want to test as a result of these measurements include:

1. Most particle and CO emissions accumulate overnight and during the morning within the surface radiation layer.
2. Interchange of pollutants between the Salt Lake and Utah Valleys does not take place until after breakup of the morning surface layer. This transfer ends soon after sunset when the surface layer reforms.
3. Mixing of surface emissions aloft is an effective removal mechanism for the Salt Lake Valley. There is little carryover of pollutants from one day to the next.

We will select and instrument at least eight locations for monitoring of particle light scattering (b_scat) and carbon monoxide concentrations. B_scat is a surrogate for PM_2.5 concentrations in the atmosphere. These measurements will be acquired using battery-powered units that can be located anywhere without extensive logistical support.

DRI currently has 16 portable CO sensors and 8 to 10 portable particulate sensors available for deployment. Ambient CO will be monitored with a Dräger Pac III personal gas detectors. These menu-driven instruments operate on an electrochemical principal. They are compact and self-contained and will log average CO concentrations on for programmable averaging periods. Continuous PM_2.5 measurements will be made with DustTrak Aerosol Monitors (TSI Corporation). These instruments measure the light scattered by particles and can also be used to measure particulate concentrations over different averaging periods. They will acquire values over 5 minute averaging intervals so that short spikes from nearby emitters can be separated from more smoothly varying diurnal cycles that result from a mixture of pollutants. They are also lightweight and portable. We have used both of these instruments successfully in numerous air quality studies. This task will also test the effectiveness of these measurement methods for use in intensive field studies such as the VTMX study.

We will finalize locations for these monitors after hypotheses have been refined by historical data analysis and after a survey of the area. In general, they will be located near and away from sources, at the base of and atop tall buildings, in canyons or on hillsides that experience specific flows, in mountain passes, and on one or more islands in the Great Salt Lake. Wherever possible and practical the instruments will be located in the vertical: 1) within the nighttime radiation layer; 2) above the nighttime radiation layer but below the pollutant mixed layer, and 3) above the pollutant mixed layer (possibly on an accessible mountaintop).

This task will include quality assurance measures to provide the resulting data set with quantified precision and accuracy. QA measures will include laboratory calibrations prior to deployment, field calibrations at the time of deployment, documentation of all field activities, and laboratory calibration checks after instrument takedown. Documentation of QA procedures employed and evaluation of the final data set will be included along with final data files. Data from these measurements will be integrated into the project database (Task 1) in a common structure.

Task 3 - Data Analysis

In this task we will analyze the Task 2 measurements to evaluate the hypotheses about the effects of vertical mixing on pollutant concentrations in the Salt Lake Valley, in the neighboring Utah Valley, and in pristine regions beyond the Wasatch Front. Data analysis will include descriptions of the onset and evolution of air pollution episodes in the Salt Lake Basin during the intensive study period, and of VTMX processes inferred from short term patterns. Concurrent meteorological data will be acquired and used to prepare urban scale flow field analyses for the study period. Finally, an assessment will be made of how well conditions encountered during the intensive study period represent actual historical episodes for the same time of year. Data analysis results will be detailed in a report that will accompany the resulting data files for dissemination to all interested parties. Journal articles will be prepared that describe the results of these analyses.

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