PM_2.5 in Carlsbad Caverns National Park: Composition, sources, and visibility impacts

ABSTRACT

Carlsbad Caverns National Park in southeastern New Mexico is adjacent to the Permian Basin, one of the most productive oil and gas regions in the country. The 2019 Carlsbad Caverns Air Quality Study (CarCavAQS) was designed to examine the influence of regional sources, including urban emissions, oil and gas development, wildfires, and soil dust on air quality in the park. Field measurements of aerosols, trace gases, and deposition were conducted from 25 July through 5 September 2019. Here, we focus on observations of fine particles and key trace gas precursors to understand the important contributing species and their sources and associated impacts on haze. Key gases measured included aerosol precursors, nitric acid and ammonia, and oil and gas tracer, methane. High-time resolution (6-min) PM_2.5 mass ranged up to 31.8 µg m⁻³, with an average of 7.67 µg m⁻³. The main inorganic ion contributors were sulfate (avg 1.3 µg m⁻³), ammonium (0.30 µg m⁻³), calcium (Ca²⁺) (0.22 µg m⁻³), nitrate (0.16 µg m⁻³), and sodium (0.057 µg m⁻³). The WSOC concentration averaged 1.2 µg C m⁻³. Sharp spikes were observed in Ca²⁺, consistent with local dust generation and transport. Ion balance analysis and abundant nitric acid suggest PM_2.5 nitrate often reflected reaction between nitric acid and sea salt, forming sodium nitrate, and between nitric acid and soil dust containing calcium carbonate, forming calcium nitrate. Sulfate and soil dust are the major contributors to modeled light extinction in the 24-hr average daily IMPROVE observations. Higher time resolution data revealed a maximum 1-hr extinction value of 90 Mm⁻¹ (excluding coarse aerosol) and included periods of significant light extinction from BC as well as sulfate and soil dust. Residence time analysis indicated enrichment of sulfate, BC, and methane during periods of transport from the southeast, the direction of greatest abundance of oil and gas development.

Implications: Rapid development of U.S. oil and gas resources raises concerns about potential impacts on air quality in National Parks. Measurements in Carlsbad Caverns National Park provide new insight into impacts of unconventional oil and gas development and other sources on visual air quality in the park. Major contributors to visibility impairment include sulfate, soil dust (often reacted with nitric acid), and black carbon. The worst periods of visibility and highest concentrations of many aerosol components were observed during transport from the southeast, a region of dense Permian Basin oil and gas development.

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Acknowledgment

The authors thank officials at Carlsbad Caverns National Park for providing study access and logistical support. This work was supported by the National Park Service under Agreement Number P20AC00679 with Colorado State University.

Disclosure statement

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

Data availability statement

The data that support the findings of this study are available from the corresponding author, Jeffrey L. Collett, upon reasonable request. https://doi.org/10.25675/10217/235481.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/10962247.2022.2081634

Additional information

Funding

This work was supported by the National Park Service [P20AC00679].

Notes on contributors

Lillian E. Naimie

Lillian E. Naimie received a B.A. in Chemistry from Colby College. She is currently a Ph.D. student at Colorado State University in Atmospheric Science.

Amy P. Sullivan

Amy P. Sullivan is a Research Scientist III in Atmospheric Science at Colorado State University.

K.B. Benedict

K.B. Benedict is a Research Scientist at Los Alamos National Laboratory. During the data collection of this work, she was a Research Scientist in Atmospheric Science at Colorado State University.

Anthony J. Prenni

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

B.C. Sive

B.C. Sive is an atmospheric chemist in the Air Resources Division of the National Park Service where he serves as the Program Manager for the Gaseous Pollutant Monitoring Program (GPMP).

Bret A. Schichtel

Bret A. Schichtel is a physical scientist in the Air Resource Division of the National Park Service and an affiliate Research Scientist at the CSU-Cooperative Institute for Research in the Atmosphere.

Emily V. Fischer

Emily V. Fischer is an Associate Professor of Atmospheric Science at Colorado State University.

Ilana Pollack

Ilana Pollack is a Research Scientist III in Atmospheric Science at Colorado State University.

Jeffrey Collett

Jeffrey Collett, Jr. is a Professor and Department Head for Atmospheric Science at Colorado State University.