Positive sampling artifact of carbonaceous aerosols and its influence on the thermal-optical split of OC/EC

Abstract

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 m 2 /g) was darker than that formed on the denuded filter (38.64 m 2 /g), indicating that the underestimation for the bare quartz filter was more significant.

Determination of the biogenic secondary organic aerosol fraction in the boreal forest by NMR spectroscopy

“…In overall the amount of carbon fraction lost by evaporation was inversely correlated to the amount of WSOC per cm 2 , pointing to positive sampling artefacts. Indeed, adsorption artefacts are typically more significant at low carbon loadings (Cheng et al, 2009). Additional tests by using standard water-soluble semi-volatile compounds were also performed to establish their recovery after evaporation, and specifically with maleic acid, pinic acid, cis-pinonic acid and vanillin.…”

Quantifying black carbon light absorption enhancement with a novel statistical approach

“…A typical negative artifact of 10 % is expected and can be corrected by backup filters (Subramanian et al, 2004). There was evidence to show that SVOC could affect OC / EC split in thermal-optical analysis (Cheng et al, 2009). However, the bias in EC caused by the OC / EC split drift due to SVOC is systematic, making it fall into the scenario discussed in Test B.…”

Relative importance of black carbon, brown carbon, and absorption enhancement from clear coatings in biomass burning emissions

“…OC and EC were measured by thermal optical analysis (Sunset Laboratories, Forest Grove, OR, USA) following the IMPROVE-A protocol where the EC / OC split was determined by thermal optical transmittance. The effects of positive sampling artifacts due to carbonaceous gas adsorption were assessed using quartz filters behind Teflon (QBT; Cheng et al, 2009) for 14 of the 96 fires, including grass, rice straw, ponderosa pine, black spruce, and peat. For fires with QBT collected, the OC on the backup filter was subtracted directly.…”