Spring 2020 Air Quality Research Newsletter

2019-20 Winter Season Ends with No Ozone Exceedance Days

While there was plenty of snow throughout the Uinta Basin through the first half of February, persistent storms kept inversion episodes relatively short and weak, and widespread clouds and fog reduced solar radiation, so ozone didn’t have time to climb above EPA standards.  Ozone precursor concentrations in the Basin have been decreasing over the past several years, and evidence suggests this also helped to keep ozone lower (see Sections 4 and 12 of our 2019 Annual Report).  The figure at right is a time series of ozone and other parameters measured in the Basin during winter 2019-20.  The figure shows that ozone increased when periods with adequate snow depth and inversion conditions coincided, but daily maximum 8-hour average ozone stayed near or below about 60 ppb .

Ozone Forecasts:  With funding from UCAIR and the Utah Legislature, we have developed and are operating an ozone alert and forecast website, ozonealert.usu.edu. Recent updates made to the website this past winter include a quantitative 72-hour ozone forecast for the Ouray monitoring station. Our forecast ozone agreed well with observed ozone during periods with snow cover and inversion conditions. This ozone alert and forecast website, along with our email program, will serve as our front end for disseminating air quality information to industry and the public.

Ouray 8-hour average ozone, along with snow depth and total daytime UV radiation (incoming + outgoing UV-A and UV-B) measured at Horsepool. Inversion periods (calculated as days when daytime temperature at Ouray was at least 5°C colder than daytime temperature at Fruitland) are shown as blue shading.

• Seth Lyman and Huy Tran receive NSF award to study atmospheric mercury: In February Seth Lyman and Huy Tran received a $480,000, 3-year award from the National Science Foundation.  The award is part of a collaborative project with Colorado College, the University of Colorado, and the University of Utah to improve scientific understanding of atmospheric mercury chemistry.  Seth has developed new instrumentation that allows for accurate measurements of oxidized mercury in the ambient atmosphere at levels in the low parts-per-quadrillion range.  Seth, Trevor O'Neil, and student Tyler Elgiar will deploy these instruments at Storm Peak, a measurement station atop the Steamboat Springs ski resort, and Huy will develop a photochemical model to better understand mercury transport and chemistry.  Mercury in the atmosphere is not a unique problem to our region, and oil and gas production is not a significant source of mercury.  Global anthropogenic and natural sources emit mercury, and it can be transported across continents before depositing to ecosystems and impacting health and the environment.  
• New website for Uinta Basin Ozone Working Group: The Uinta Basin Ozone Working Group has a new website, https://basinozonegroup.usu.edu.  Visit the website for meeting dates and times, agendas, and other critical information.

Ambient Organic Compound Measurements will be Used to Improve Emissions Inventories and Model Performance

During fall 2019, we built 17 tripods (pictured at right) that can be programmed to collect simultaneous air samples with funding from Utah DAQ, the Utah Legislature, and UIMSSD.  We deployed these tripods in configurations across the Basin during winter 2020 and analyzed the samples in our lab for concentrations of a suite of 70 non-methane hydrocarbons, alcohols, and carbonyls (e.g., formaldehyde, acetaldehyde, etc.).  We completed wintertime data collection in February and have made all collected data available on our website.

Similar to preliminary deployments we conducted during winter 2019, alkene concentrations were higher in the western Uinta Basin during winter 2020 (see figure below).  Alkenes are extremely reactive, and large alkene sources can be expected to be important contributors to wintertime ozone production.  As detailed in Section 5 of our 2019 Annual Report, we believe natural gas-fueled engines are a large source of these alkenes.  Also, some of the samples we collected in February 2020, when no inversion was present, had high concentrations of methanol (greater than 50% of total non-methane organics in a few cases), and we are working to understand the sources of methanol in these samples.  We didn’t find a clear difference in the organic compound composition in areas with well-site glycol dehydrators versus areas without dehydrators. 

In a related project, we measured concentrations of glycols (ethylene glycol, propylene glycol, etc.) at our Seven Sisters monitoring station, which is near a large number of glycol dehydrators.  Glycols are relatively reactive ozone precursors, and we suspected that high concentrations of glycols may exist in the area (no one had attempted to measure them in the Basin atmosphere before).  In all of our measurements, however, glycol concentrations were below detection limits (2-8 ppb), showing that the are not important ozone precursors in the Uinta Basin.

The next step in this work is to compare these ambient measurements to inventory-based model results to see how well the model predicts measured concentrations, and to explore ways to improve model performance.

Map showing locations of organic compounds sampled on 10 January 2020 (22:00 start time; six-hour sample). Pie charts show the percent-by-volume of the different compound groups indicated. Pink dots in the figure are gas wells, and the faint orange dots are oil wells. the dotted black lines are roads. The red circle at right is an error.

Incorporation of Satellite Data Improves Air Quality Model Performance

With funding from Utah DAQ and the Utah Legislature, we are investigating methods to assimilate Moderate Resolution Imaging Spectroradiometer (MODIS) land surface data products (surface albedo, snow cover, and vegetation fraction) into meteorology and photochemistry models (we use the WRF model for meteorology and the CAMx model for chemistry and transport). These land surface characteristics ultimately drive the energy balances and transfers and air pollutant deposition in models. The traditional WRF and CAMx models apply long-term average climatological values of land surface characteristics, and these are often outdated and inaccurately estimated due WRF’s underperformance with respect to other quantities, including snow depth. In contrast, satellite data assimilation techniques provide instant and realistic observations of these characteristics. In earlier air quality modeling exercises for winter episodes, we had to manually correct the simulated snow depth of the entire Uinta Basin based on limited point observations in order to obtain adequate surface albedo, which is important for ozone formation. To overcome this limitation and accommodate MODIS data assimilation, we modified several WRF and CAMx source codes.

Our preliminary results show that, while assimilating MODIS data into our models provides an accurate representation of surface albedo and vegetation cover (see figure below), this does not necessarily translate to better ozone performance in comparison to earlier modeling exercises. This is because ozone performance is far more sensitive to emissions than to meteorological inputs. Furthermore, prior to MODIS data assimilation, we also applied other observational data assimilation techniques which have greatly improved WRF model performance. Regardless, we consider MODIS data assimilation as a significant step up from earlier manual and arbitrary corrections that had to be made to the model.

Comparison of surface albedo as simulated by WRF where no correction was applied (left) and with MODIS data assimilation (right) for an episode during winter 2011.

In future work, we will examine methane and nitrogen dioxide data from the TROPOspheric Monitoring Instrument (TROPOMI) satellite, in cooperation with ground-based measurements, for the purpose of developing a top-down emissions inventory for organic compounds and oxides of nitrogen in the Uintah Basin. This top-down emissions inventory will serve as a way to "ground-truth" regulatory oil and gas emission inventories.