NO_x instrument intercomparison for laboratory biomass burning source studies and urban ambient measurements in Albuquerque, New Mexico

ABSTRACT

Understanding nitrogen oxides (NO_x = NO + NO₂) measurement techniques is important as air-quality standards become more stringent, important sources change, and instrumentation develops. NO_x observations are compared in two environments: source testing from the combustion of Southwestern biomass fuels, and urban, ambient NO_x. The latter occurred in the urban core of Albuquerque, NM, at an EPA NCORE site during February–March 2017, a relatively clean photochemical environment with ozone (O₃) <60 ppb for all but 6 hr. We compare two techniques used to measure NO_x in biomass smoke during biomass burning source testing: light absorption at 405 nm and a traditional chemiluminescence monitor. Two additional oxides of nitrogen techniques were added in urban measurements: a cavity attenuated phase shift instrument for direct NO₂, and the NO_y chemiluminescence instrument (conversion of NO_y to NO by molybdenum catalyst). We find agreement similar to laboratory standards for NO_x, NO₂, and NO comparing all four instruments (R² > 0.97, slopes between 0.95 and 1.01, intercepts < 2 ppb for 1-hr averages) in the slowly varying ambient setting. Little evidence for significant interferences in NO₂ measurements was observed in comparing techniques in late-winter urban Albuquerque. This was also confirmed by negligible NO_z contributions as measured with an NO_y instrument. For the rapidly varying (1-min) higher NO_x concentrations in biomass smoke source testing, larger variability characterized chemiluminescence and absorption instruments. Differences between the two instruments were both positive and negative and occurred for total NO_x, NO, and NO₂. Nonetheless, integrating the NO_x signals over an entire burn experiment and comparing 95 combustion experiments, showed little evidence for large systematic influences of possible interfering species biasing the methods. For concentrations of <2 ppm, a comparison of burn integrated NOx, NO₂, and NO yielded slopes of 0.94 to 0.96, R² of 0.83 to 0.93, and intercepts of 8 to 25 ppb. We attribute the latter, at least in part, to significant noise particularly at low NO_x concentrations, resulting from short averaging times during highly dynamic lab burns. Discrepancies between instruments as indicated by the intercepts urge caution with oxides of nitrogen measurements at concentrations <50 ppb for rapidly changing conditions.

Implications: Multiple NO_x measurement methods were employed to measure NO_x concentrations at an EPA NCORE site in Albuquerque, NM, and in smoke produced by the combustion of Southwestern biomass fuels. Agreement shown during intercomparison of these NO_x techniques indicated little evidence of significant interfering species biasing the methods in these two environments. Instrument agreement is important to understand for accurately characterizing ambient NO_x conditions in a range of environments.

Acknowledgment

The authors acknowledge the constructive input of three anonymous reviewers to making this paper stronger.

Additional information

Funding

The Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists (WDTS) under the Visiting Faculty Program (VFP) supported this research. The New Mexico Consortium is gratefully acknowledged for financial support in this research. MKD acknowledges support from LANL and DOE Office of Science Biological and Environmental Research Atmospheric System Research Program.

Notes on contributors

Caroline Allen

Caroline Allen earned a B.S. in environmental engineering at the New Mexico Institute of Mining and Technology and is currently a J.D. student at University of Missouri–Kansas City.

Christian M. Carrico

Christian M. Carrico is an associate professor in the Department of Civil and Environmental Engineering the New Mexico Institute of Mining and Technology.Samantha L. Gomez is an M.S. student in the Department of Civil and Environmental Engineering of the New Mexico Institute of Mining and Technology and a scientist at Los Alamos National Laboratory.

Samantha L. Gomez

Christian M. Carrico is an associate professor in the Department of Civil and Environmental Engineering the New Mexico Institute of Mining and Technology.Samantha L. Gomez is an M.S. student in the Department of Civil and Environmental Engineering of the New Mexico Institute of Mining and Technology and a scientist at Los Alamos National Laboratory.

Peter C. Andersen

Peter C. Andersen, Andrew A. Turnipseed, Craig J. Williford, and John W. Birks are scientists at 2B Technologies, Inc.

Andrew A. Turnipseed

Peter C. Andersen, Andrew A. Turnipseed, Craig J. Williford, and John W. Birks are scientists at 2B Technologies, Inc.

Craig J. Williford

Peter C. Andersen, Andrew A. Turnipseed, Craig J. Williford, and John W. Birks are scientists at 2B Technologies, Inc.

John W. Birks

Peter C. Andersen, Andrew A. Turnipseed, Craig J. Williford, and John W. Birks are scientists at 2B Technologies, Inc.

Dwayne Salisbury

Dwayne Salisbury, Richard Carrion, Dan Gates, and Fabian Macias are air quality specialists for the City of Albuquerque, NM.

Richard Carrion

Dwayne Salisbury, Richard Carrion, Dan Gates, and Fabian Macias are air quality specialists for the City of Albuquerque, NM.

Dan Gates

Dwayne Salisbury, Richard Carrion, Dan Gates, and Fabian Macias are air quality specialists for the City of Albuquerque, NM.

Fabian Macias

Dwayne Salisbury, Richard Carrion, Dan Gates, and Fabian Macias are air quality specialists for the City of Albuquerque, NM.

Thom Rahn

Thom Rahn, Allison C. Aiken, and Manvendra K. Dubey are scientists at the Los Alamos National Laboratory.

Allison C. Aiken

Thom Rahn, Allison C. Aiken, and Manvendra K. Dubey are scientists at the Los Alamos National Laboratory.

Manvendra K. Dubey

Thom Rahn, Allison C. Aiken, and Manvendra K. Dubey are scientists at the Los Alamos National Laboratory.