IMPROVE Research

Characterization of IMPROVE data quality
Contact—Nicole Hyslop (530-754-8979) and Warren White (530-752-1213)

One method that Crocker researchers use to identify sources of uncertainty in the data measurement process is by studying and comparing output from IMPROVE aerosol samplers located side by side. These samplers are located on the roof of Gausi Hallat UC Davis. Credit: Liese Greensfelder

Each year Crocker Nuclear Laboratory delivers nearly one million new measurement values for the IMPROVE network. A large community of researchers and analysts use these data to address a wide range of scientific and regulatory issues. All data pass through multiple layers of review and quality assurance before publication, but all carry some uncertainty from the irreducible error that is present in any measurement. An ongoing program of research works to:

  • characterize various dimensions of this uncertainty; 
  • supply clear guidance on the strengths and limitations of IMPROVE data in the diverse analyses to which they are subjected;
  • identify the sources of uncertainty in the measurement process, and
  • reduce the uncertainty in the measurement through new quality assurance measures.

Hyslop N.P and White W.H. (2008) An empirical approach to estimating detection limits using collocated data, Environmental Science & Technology 42, 5235-5240.

Hyslop N.P and White W.H. (2008) An evaluation of Interagency Monitoring of PROtected Visual Environments (IMPROVE) collocated precision and uncertainty estimates, Atmospheric Environment 42, 2691-2705.

Hyslop N.P and White W.H. (2009) Estimating precision using duplicate measurements, Journal of the Air & Waste Management Association 59, 1032-1039.

Hyslop N.P and White W.H. (2011) Identifying sources of uncertainty from the inter-species covariance of measurement errors, Environmental Science & Technology 45, 4030-4037.

Hyslop N.P, Trzepla K and White W.H. (2012) Reanalysis of archived IMPROVE PM2.5 samples previously analyzed over a 15-year period, Environmental Science & Technology 46, 10106-10113.

Trzepla-Nabaglo K, Wakabayashi P.H. and White W.H. (2009) Toward establishing the stability of multi-year monitoring of elements in airborne particles, Journal of the Air & Waste Management Association 59, 1040-1044.

White W.H. (2008) Chemical markers for sea salt in IMPROVE aerosol data, Atmospheric Environment 42, 261-274.

Miscellaneous on-line advisories on specific data issues are collected at

FT-IR OM, OC, EC and functional groups
Contact—Ann Dillner (530-752-0509)


Crocker researchers are developing methods of using FT-IR spectroscopy to help quantify the composition of airborne particles. The graph above shows the characteristic FT-IR spectroscopic absorbance of adipic acid, (CH2)4(COOH)2, an atmospherically relevant carbon molecule. Image: Ann Dillner

Crocker Nuclear Laboratory is conducting an ongoing research program to develop FT-IR (Fourier transform-infrared spectroscopy) methods to measure functional groups, organic matter (OM), organic carbon (OC) and elemental carbon (EC) in particles collected on Teflon© filters.  Direct measurement of OM is useful because current methods require using an estimated organic mass/organic carbon ratio—OM/OC—to convert measured OC to OM. Organic functional groups are summed to determine OM and they provide information for identifying sources and understanding atmospheric processes of organic aerosols.  FT-IR calibrated to thermal/optical reflectance (TOR) OC and EC using partial least squares regression is a cost effect method for obtaining TOR data for intensive sampling campaigns and major monitoring networks.

Reggente, M., Dillner, A. M., Takahama, S., Predicting ambient aerosol thermal-optical reflectance (TOR) measurements from infrared spectra: extending the predictions to different years and different sites. Atmospheric Measurement Techniques Discussions, 2016, in revision.

Dillner, A. M., Takahama, S., Predicting Ambient Aerosol Thermal Optical Reflectance (TOR) Measurements from Infrared Spectra:  Elemental Carbon.Atmospheric Measurement Techniques, 8, 4013-4023, 2015.

Dillner, A. M., Takahama, S., Predicting Ambient Aerosol Thermal Optical Reflectance (TOR) Measurements from Infrared Spectra:  Organic Carbon.Atmospheric Measurement Techniques, 8, 1097-1109, 2015.

Takahama, S., Dillner, A. M., Model selection for partial least squares calibration and implications for analysis of atmospheric organic aerosol samples with mid-infrared spectroscopy. Journal of Chemometrics, DOI: 10.1002/cem.2761, 2015.

George, K. M., Ruthenburg, T.C., Smith, J., Yu, L., Zhang, Q., Anastasio, C., Dillner, A. M., FT-IR quantification of the carbonyl functional group in aqueous-phase secondary organic aerosol from phenols. Atmospheric Environment 100 (2015) 230-237.

Ruthenburg, T.C., Perlin, P. C., Liu, V., , McDade, C. E., Dillner, A. M.,  Determination of Organic Mass and Organic Mass to Organic Carbon Ratios by Infrared Spectroscopy with Application to Selected Sites in the IMPROVE Network. Atmospheric Environment, 86, 47-57, 10.1016/j.atmosenv.2013.12.034, 2014.

Coury, C. Dillner, A.M., ATR-FTIR Characterization of Organic Functional Groups and Inorganic Ions in Ambient Aerosols at a Rural Site, Atmospheric Environment, 43, 940–948, 2009.


Multi-wavelength analysis of particle light absorption
Contact—Chuck McDade (530-752-7119)

Crocker Nuclear Laboratory scientists have designed and built a new broad-band light source instrument to adapt the Hybrid Integrating Plate/Sphere Analysis (HIPS) light absorption measurement for a full spectrum of wavelengths throughout the visible and including the near IR and UV. Work is underway to develop approaches for calibration and for analysis of the data from this new spectrometer.

The spectrometer’s broadband light source has an output spanning 190 to 1700 nm. Light from the source is directed through a collimating and focusing assembly and then onto each sampled filter. An integrating sphere captures light reflected from the filter, and there are detectors for both the reflected light and the light transmitted through the filter. The light absorbance for each filter is calculated from these reflected and transmitted light values. Light from the reflectance and transmittance detectors is directed through fiber optic bundles to an ultraviolet/visible/near-infrared spectrometer. The spectrometer separates the signals by wavelength and thus allows the calculation of light absorption at multiple regions of the spectrum.

X-ray fluorescence (XRF) measurement and calibration
Contact— Krystyna Trzepla (530-752-4232), Nicole Hyslop (530-754-8979) or Ann Dillner (530-752-0509)

This aerosol generation and sampling system developed at Crocker Nuclear Laboratory can produce standard reference materials for improved XRF calibration. Credit: Crocker Nuclear Lab staff

Crocker Nuclear Laboratory (CNL) has developed an aerosol generation and sampling system that provides the capability to produce standard reference materials for improved XRF calibration. We have demonstrated this capability by successful calibrations of various XRF systems for sulfur, sodium and chloride and have extended this capability to other elements including lead standards to support health effects studies. Analytical interferences observed in XRF analysis of particulate matter samples have also been quantified using the aerosol generation and sampling system.

More information on XRF reference materials can be found on the Crocker Nuclear Laboratory's Analytical Services website

Yatkin, S., Amin, H. S., Trzepla, K., Dillner, A. M. (2016).  Preparation of Lead (Pb) X-ray Fluorescence Reference Materials for the EPA Pb Monitoring Program and the IMPROVE Network Using an Aerosol Deposition Method, Aerosol Science and Technology.

Indresand H, White W. H, Trzepla K and Dillner A. M. (2013) Preparation of sulfur reference materials that reproduce atmospheric particulate matter sample characteristics for XRF calibration, X-Ray Spectroscopy, DOI 10.1002/xrs.2456.

Indresand H and Dillner A.M. (2012) Experimental characterization of sulfur interference in IMPROVE aluminum and silicon XRF data, Atmospheric Environment, 61, 140-147.

Evaluation of organic carbon measurements in the IMPROVE and CSN networks
Contact—Ann Dillner (530-752-0509)

The gain and loss of gaseous carbonaceous material from quartz filters can bias the measurement of organic particulate matter. Crocker Nuclear Laboratory scientists have worked with others in the IMPROVE and Chemical Speciation Network (CSN) communities to investigate organic carbon measurement uncertainty related to determining a consistent method for estimating sampling artifacts and evaluating post-sampling losses during field latency and transport

Ann M. Dillner, Mark C. Green, Marc Pitchford, Bret Schichtel, Bill Malm, Warren H. White, Joann Rice, Neil Frank, Judy Chow and Scott Copeland (2013) Recommendation of the IMPROVE/CSN Organic Carbon Artifact Adjustment Committee, Report to the IMPROVE Steering Committee and CSN, March 26.

Dillner A. M, Phuah C. H and Turner J. R. (2009) Effects of Post-Sampling Conditions on Ambient Carbon Aerosol Filter Measurements, Atmospheric Environment, 43 (37) 5937–5943.

Phuah C. H, Peterson M. R, Richards M. H, Turner J. R and Dillner A.M. (2009) A Temperature Calibration Procedure for the Sunset Laboratory Carbon Aerosol Analysis Lab Instrument, Aerosol Science and Technology, 43 (10) 1013-1021.