Evaluating IMPROVE PM_2.5 element measurements

ABSTRACT

The Interagency Monitoring of PROtected Visual Environments (IMPROVE) network has collected airborne particulate matter (PM) samples at locations throughout the United States since 1988 and provided chemical speciation measurements on the samples using several techniques including X-ray fluorescence (XRF). New XRF instruments for measuring PM elemental content of IMPROVE samples were introduced in 2011. To evaluate the performance of these new instruments relative to the old instruments, archived sample from three IMPROVE monitoring sites were retrieved and analyzed on the new instruments. The agreement between the two instruments varied by element. Comparisons of the results were very good (slopes within 10% of unity) for most elements regularly measured well above the detection limits (sulfur, chlorine, potassium, titanium, vanadium, manganese, iron, copper, zinc, selenium, lead). Different particle compositions at the three sites highlighted different measurement interferences. High sea salt concentrations at the coastal site emphasized corrections applied in the old systems to light elements – sodium and magnesium – and resulted in poor agreement for these elements. Comparisons of the XRF measurements with collocated sulfate measurements by ion chromatography suggest that sulfur measurements from the new instruments are more precise but slight underestimates. Comparing elemental ratios to expected ratios for soil-derived PM demonstrate the new instruments are better at resolving the aluminum and silicon peaks.

Implications: The presented work represents a comprehensive analysis of the method change enacted within the Interagency Monitoring of PROtected Visual Environments (IMPROVE) air monitoring network. This work describes the implications of the last change in elemental quantification methodology. The most important point for data users performing longitudinal analyses is that light elements (e.g., sodium – sulfur) were affected; the old instrumentation overestimated these elements while the current measurements are slightly underestimated. The authors recommend these results to be taken into consideration when interpreting sea salt and crustal sources of atmospheric dust.

Acknowledgment

The authors thank Warren White for informative discussions and suggestions.

Disclosure statement

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

Data availability statement

All IMPROVE data is publicly available through the US EPA Air Quality System (https://www.epa.gov/aqs) as well as through the US Federal Land Manager Environmental Database (http://vista.cira.colostate.edu/Improve/improve-data/). Reanalysis data is available upon request.

Supplementary material

Supplemental data for this paper can be accessed online at https://doi.org/10.1080/10962247.2023.2262417

Additional information

Funding

The work was supported by the United States National Park Service [P11ATW0802].

Notes on contributors

Nicholas J. Spada

Nicholas J. Spada is a scientist in the Air Quality Research Center at the University of California at Davis. Dr. Spada conducts research on elemental profilings in mixed urban/industrial and remote environments. He also provides support on air monitoring strategies and technology to citizen scientists. He is a co-director of the Citizen Air Monitoring Network, based in the Bay Area of California.

Sinan Yatkin

Sinan Yatkin was an Assistant Project Scientist for the Air Quality Research Center at the University of California Davis when this work was performed. He was involved in the research of XRF method development and generation of reference materials.

Jason Giacomo

Jason Giacomo is the Laboratory Operations Manager for the Air Quality Research Center at the University of California Davis. Prior to this role, Dr. Giacomo, was the AQRC Spectroscopist specializing in elemental analysis by X-ray Fluorescence and optical absorption analysis using the AQRC hybrid integrating plate/sphere instrument. Since joining AQRC, Dr. Giacomo has worked to improve the quality control tools available to the lab and to ensure consistent and reliable operation of the analytical instruments in support of atmospheric particulate matter analysis.

Krystyna Trzepla

Krystyna Trzepla was the Laboratory Manager for the Air Quality Research Center at the University of California Davis until her retirement in 2020. Ms. Trzepla provided support for all research studies involving monitoring particles in the atmosphere, with special emphasis on the application of elastic lidar system for monitoring spatial distribution and elemental analyses by X-Ray Fluorescence and Proton Elastic Scattering.

Nicole P. Hyslop

Nicole P. Hyslop is the Associate Director for Quality Research in the Air Quality Research Center at the University of California Davis. Dr. Hyslop conducts research to characterize data quality to gain a better understanding of the sources of error in the measurements and improve quality assurance protocols to identify and reduce errors.