Positive sampling artifact of carbonaceous aerosols and its influence on the thermal-optical split of OC/EC 1Department of Environmental Science and Engineering, Tsinghua University, Beijing, China
2School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
Received: 07 Jun 2009 – Published in Atmos. Chem. Phys. Discuss.: 22 Jun 2009 Abstract. Accurate measurement of carbonaceous aerosols is challenging, due to the
sampling artifact and the problems of the split of OC/EC. Two approaches have
been used to account for the positive artifact: backup quartz approach in
which a backup quartz filter is placed either behind a front quartz filter
(QBQ) or in a parallel port behind a Teflon filter (QBT), and organic denuder
approach in which an organic denuder is placed upstream of the quartz filter.
Both approaches were evaluated in Beijing, China, from January to February
2009. 10% of the OC captured by the bare quartz filter was from the positive
artifact. The origin of backup OC was quantitatively evaluated by the
denuder-based method. All of the QBQ OC was from gaseous organics passing
through the front filter, but the QBQ had not reached equilibrium with gas
phase due to the relative small sampling volume resulting in an
undercorrection of the positive artifact by 3.7%. QBT OC was from both
gaseous organics passing through the front filter (82%) and the evaporated
organic carbon (18%), thus overcorrecting the positive artifact by 6.3%.
Even the positive artifact-contributed QBT OC was found to overestimate the
positive artifact, perhaps due to the difference in the adsorption properties
of the loaded filter and the filter without particle loading. Re-partitioning
of PC and EC was performed by the multiple linear regression approach. The
attenuation coefficient of PC was twofold higher than that of EC, indicating
PC was darker than EC, resulting in the underestimation of native EC by
TOT-split-EC. It was also found that PC formed on the bare quartz filter
(45.56 m2/g) was darker than that formed on the denuded filter
(38.64 m2/g), indicating that the underestimation for the bare quartz
filter was more significant.
Revised: 28 Aug 2009 – Accepted: 01 Sep 2009 – Published: 29 Sep 2009
Citation: Cheng, Y., He, K. B., Duan, F. K., Zheng, M., Ma, Y. L., and Tan, J. H.: Positive sampling artifact of carbonaceous aerosols and its influence on the thermal-optical split of OC/EC, Atmos. Chem. Phys., 9, 7243-7256, doi:10.5194/acp-9-7243-2009, 2009.