Wintertime haze and ozone at Dinosaur National Monument

ABSTRACT

Dinosaur National Monument (DINO) is located near the northeastern edge of the Uinta Basin and often experiences elevated levels of wintertime ground-level ozone. Previous studies have shown that high ozone mixing ratios in the Uinta Basin are driven by elevated levels of volatile organic compounds (VOCs) and nitrogen oxides (NO_x) from regional oil and gas development coupled with temperature inversions and enhanced photochemistry from persistent snow cover. Here, we show that persistent snow cover and temperature inversions, along with abundant ammonia, also lead to wintertime haze in this region. A study was conducted at DINO from November 2018 through May 2020 where ozone, speciated fine and coarse aerosols, inorganic gases, and VOCs were measured. Three National Ambient Air Quality Standards (NAAQS) ozone exceedances were observed in the first winter, and no exceedances were observed in the second winter. In contrast, elevated levels of particulate matter were observed both winters, with 24-h averaged particle light extinction exceeding 100 Mm⁻¹. These haze events were dominated by ammonium nitrate, and particulate organics were highly correlated with ammonium nitrate. Ammonium nitrate formation was limited by nitric acid in winter. As such, reductions in regional NO_x emissions should reduce haze levels and improve visibility at DINO in winter. Long-term measurements of particulate matter from nearby Vernal, Utah, suggest that visibility impairment is a persistent issue in the Uinta Basin in winter. From April through October 2019, relatively clean conditions occurred, with average particle extinction of ~10 Mm⁻¹. During this period, ammonium nitrate concentrations were lower by more than an order of magnitude, and contributions from coarse mass and soil to haze levels increased. VOC markers indicated that the high levels of observed pollutants in winter were likely from local sources related to oil and gas extraction activities.

Implications: Elevated ground-level ozone and haze levels were observed at Dinosaur National Monument in winter. Haze episodes were dominated by ammonium nitrate, with 24-h averaged particle light extinction exceeding 100 Mm⁻¹, reducing visual range near the surface to ~35 km. Despite elevated ammonium nitrate concentrations, additional gas-phase ammonia was available, such that any increase in NO_x emissions in the region is likely to lead to even greater haze levels.

Acknowledgment

This work was funded by the National Park Service. The CSU portion of the work was funded by Cooperative Agreement P17AC00971, Task Agreements P18AC01188 and P20AC00679. The authors wish to thank the staff at Dinosaur National Monument for site access and support throughout the study. IMPROVE is a collaborative association of state, tribal, and federal agencies, and international partners. The US Environmental Protection Agency is the primary funding source, with contracting and research support from the National Park Service. The Air Quality Group at the University of California, Davis, is the central analytical laboratory, with ion analysis provided by Research Triangle Institute, and carbon analysis provided by Desert Research Institute. Ozone data are collected through the National Park Service Gaseous Pollutant Monitoring Program. The assumptions, findings, conclusions, judgments, and views presented herein are those of the authors and should not be interpreted as necessarily representing the National Park Service.

Data availability statement

Much of the data that support the findings of this study are openly available at

• http://views.cira.colostate.edu/fed/

• https://ard-request.air-resource.com/data.aspx

• https://www.nps.gov/subjects/air/webcams.htm

• https://www.epa.gov/outdoor-air-quality-data/download-daily-data

The data that support the findings of this study that are not publicly available are available from the corresponding author, AJP, upon reasonable request.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the National Park Service [P17AC00971/P18AC01188,P17AC00971/P20AC00679].

Notes on contributors

Anthony J. Prenni

Anthony J. Prenni is a chemist in the Air Resources Division of the National Park Service.

Katherine B. Benedict

Katherine B. Benedict is research scientist at Los Alamos National Laboratory.

Derek E. Day

Derek E. Day is a research associate at the Cooperative Institute for Research in the Atmosphere at Colorado State University.

Barkley C. Sive

Barkley C. Sive is a chemist in the Air Resources Division of the National Park Service.

Yong Zhou

Yong Zhou is a research scientist in the Department of Atmospheric Science at Colorado State University.

Lilly Naimie

Lilly Naimie is a graduate student in the Department of Atmospheric Science at Colorado State University.

Kristi A. Gebhart

Kristi A. Gebhart is a senior research associate at the Cooperative Institute for Research in the Atmosphere at Colorado State University.

Tracy Dombek

Tracy Dombek is a research chemist in the Analytical Sciences Division of RTI, International.

Miranda De Boskey

Miranda De Boskey is a chemist in the Analytical Sciences Division of RTI, International.

Nicole P. Hyslop

Nicole P. Hyslop is a principal investigator and operations manager in the Air Quality Research Center at the University of California, Davis.

Emily Spencer

Emily Spencer is a natural resource specialist at Dinosaur National Monument.

Quayle M. Chew

Quayle M. Chew is an air quality monitoring site operator at Dinosaur National Monument.

Jeffrey L. Collett

Jeffrey L. Collett, Jr. is a professor and department head of the Department of Atmospheric Science at Colorado State University.

Bret A. Schichtel

Bret A. Schichtel is a physical scientist in the Air Resources Division of the National Park Service.