Review of Sunset OC/EC Instrument Measurements During the EPA's Sunset Carbon Evaluation Project.

Steven Brown,Theresa O’Brien,Richard Tun,Hilary Minor,Brandon Feenstra,Dustin Kuebler,Elizabeth Landis,Yousaf Hameed,Robert Day,Joann Rice,Will Wetherell

doi:10.3390/atmos10050287

Abstract

To evaluate the feasibility of the Sunset semicontinuous organic and elemental carbon (OC/EC) monitor, the U.S. Environmental Protection Agency (EPA) sponsored the deployment of this monitor at Chemical Speciation Network (CSN) sites with OC and EC measurements via quartz fiber filter collection in Chicago, Illinois; Houston, Texas; Las Vegas, Nevada; St. Louis, Missouri; Rubidoux, California; and Washington, D.C. Houston, St. Louis, and Washington also had collocated Aethalometer black carbon (BC) measurements. Sunset OC generally compared well with the CSN OC (r2 = 0.73 across five sites); the Sunset/CSN OC ratio was, on average, 1.06, with a range among sites of 0.96 to 1.12. Sunset thermal EC and CSN EC did not compare as well, with an overall r2 of 0.22, in part because 26% of the hourly Sunset EC measurements were below the detection limit. Sunset optical EC had a much better correlation to CSN EC (r2 = 0.67 across all sites), with an average Sunset/CSN ratio of 0.90 (range of 0.7 to 1.08). There was also a high correlation of Sunset optical EC with Aethalometer BC (r2 = 0.77 across all sites), though with a larger bias (average Sunset/Aethalometer ratio of 0.56). When the Sunset instrument was working well, OC and OptEC data were comparable to CSN OC and EC.

Highlights

Carbonaceous aerosol is a significant, and often the largest, component of fine particulate matter less than 2.5 microns in diameter (PM2.5 ) in many areas of the United States
We report values when the two measurements we are comparing occurred on the same day; e.g., for Sunset and Chemical Speciation Network (CSN) OC, only those days with measurements of both, and for Sunset and Aethalometer, only those days with measurements of both
For coefficient of variation (CV), which is similar to the 8.8% CV across six collocated CSN OC thermal optical reflectance (TOR)

Summary

Introduction

Carbonaceous aerosol is a significant, and often the largest, component of fine particulate matter less than 2.5 microns in diameter (PM2.5 ) in many areas of the United States. It is composed of organic and elemental carbon (OC, EC) [1], but its composition, sources, and spatiotemporal variations are not well-characterized [2]. EC is directly emitted from combustion processes, such as from mobile sources or from biomass burning While it is well-established that elevated PM2.5 levels are associated with many health effects, such as respiratory and cardiac disease, the complex interaction of specific health effects from individual compounds or PM2.5 components, such as OC and EC, are less well understood.

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Conclusion