title: Positive sampling artifacts in particulate organic carbon measurements in roadside environment.
abstract: The positive artifacts in particulate organic carbon measurements in a roadside environment were characterized using two filters in tandem. The experiments were performed for PM(1.0), PM(2.5), and PM(10) at 24-h interval using a URG sampler, followed by organic carbon (OC)/elemental carbon (EC) analysis by the Interagency Monitoring of Protected Visual Environments thermal/optical reflectance carbon analysis protocol. The OC concentrations, derived from the quartz filter behind a front quartz filter, were quite similar for PM(1.0), PM(2.5), and PM(10), ranging from 0.6 to 2.7 microg C m(-3) for PM(1.0), from 0.7 to 2.7 microg C m(-3) for PM(2.5), and from 1.1 to 2.7 microg C m(-3) for PM(10). They were respectively approximately 2.8%, approximately 2.4%, and approximately 1.6% of the particulate mass. The most abundant species on the backup quartz filters were OC2 (250 degrees C) and OC3 (450 degrees C), accounting for approximately 80% of measured organic carbon on the backup quartz filters. It indicates the filter artifacts are mainly composed of adsorbed semi-volatile organics (below the analysis temperature of 450 degrees C) including gaseous and particulate phase; the loading of artifacts depends on the nature of vapor and its interaction with filter substrate, rather than particle sizes. The uncorrected OC/EC ratios on the front quartz filters were approximately 10% higher than the corrected OC/EC ratios by positive organic artifacts in winter, and it is approximately 20% higher in summer. Another finding is that the separation distance of the front and backup filters influence the level of artifacts assessed by the backup filter.
authors.affiliation: Department of Environmental Science and Technology, School of Human Settlements and Civil Engineering, Xi'an Jiaotong University, Xi'an, China. chengyan6@gmail.com
authors.forename: Yan
authors.initials: Y
authors.lastname: Cheng
authors.forename: Shun Cheng
authors.initials: SC
authors.lastname: Lee
authors.forename: Kin Fai
authors.initials: KF
authors.lastname: Ho
authors.forename: Kochy
authors.initials: K
authors.lastname: Fung
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D016477:Artifacts; D002244:Carbon / Q000032:analysis*; D004784:Environmental Monitoring; D010316:Particle Size; D052638:Particulate Matter / Q000032:analysis*; D014186:Transportation
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter; D002244:Carbon