Atmos. Chem. Phys. Discuss., 9, 27359-27400, 2009
© Author(s) 2009. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Quantification of organic carbon sampling artifacts in US non-urban and urban networks
J. C. Chow1,2, J. G. Watson1,2, L.-W. A. Chen1, J. Rice3, and N. H. Frank3
1Division of Atmospheric Sciences, Desert Research Institute, 2215 Raggio Parkway, Reno, NV, USA
2Institute of Earth Environment, Chinese Academy of Sciences, No. 10, Fenghui South Road, High-tech Zone, P.O. Box 17, Xian 710075, China
3Office of Air Quality Planning & Standards, US Environmental Protection Agency, 109 TW Alexander Dr., Research Triangle Park, NC, USA

Abstract. Different approaches to estimate organic sampling artifacts have been adopted by US long-term air quality monitoring networks. This study documents field blank (bQF) and backup filter (quartz-fiber behind quartz-fiber filter; QBQ) carbon levels for the: 1) Interagency Monitoring of Protected Visual Environments (IMPROVE); 2) Speciation Trends Network (STN; part of the Chemical Speciation Network [CSN]; and 3) Southeastern Aerosol Research and Characterization (SEARCH) networks. Filter pack sample handling procedures and blank correction methods are examined. Due to a relatively short (1–15 min) passive exposure period, STN/CSN and SEARCH network bQF organic carbon (OC; 0.8–1 μg/cm2) may underestimate positive and negative OC artifacts, respectively, resulting from passive adsorption or volatilization of volatile or semi-volatile organic compounds on quartz-fiber filters while they are in the sampler. This is evidenced by a lack of temporal or spatial variability and low bQF levels. With ~7 d of ambient passive exposure, average IMPROVE bQF and QBQ OC are comparable (2.4±0.5 and 3.1±0.8 μg/cm2) and more than twice those found in the STN/CSN and SEARCH networks. Lower STN/CSN flow rates and larger filter deposit areas result in 9–20% of the areal density (μg/cm2) compared to IMPROVE areal deposits. STN/CSN bQF values are 11–34% lower than linear regression intercepts derived from collocated IMPROVE-STN/CSN data pairs. Using a preceding organic denuder in the SEARCH network reduces the organic vapor adsorption on QBQ, though the longer QBQ period in the sampler may result from passive organic vapor adsorption as well as evaporated OC from the front filter deposits.

Citation: Chow, J. C., Watson, J. G., Chen, L.-W. A., Rice, J., and Frank, N. H.: Quantification of organic carbon sampling artifacts in US non-urban and urban networks, Atmos. Chem. Phys. Discuss., 9, 27359-27400, doi:10.5194/acpd-9-27359-2009, 2009.
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