title: Thermal/optical methods for elemental carbon quantification in soils and urban dusts: equivalence of different analysis protocols.
abstract: Quantifying elemental carbon (EC) content in geological samples is challenging due to interferences of crustal, salt, and organic material. Thermal/optical analysis, combined with acid pretreatment, represents a feasible approach. However, the consistency of various thermal/optical analysis protocols for this type of samples has never been examined. In this study, urban street dust and soil samples from Baoji, China were pretreated with acids and analyzed with four thermal/optical protocols to investigate how analytical conditions and optical correction affect EC measurement. The EC values measured with reflectance correction (ECR) were found always higher and less sensitive to temperature program than the EC values measured with transmittance correction (ECT). A high-temperature method with extended heating times (STN120) showed the highest ECT/ECR ratio (0.86) while a low-temperature protocol (IMPROVE-550), with heating time adjusted for sample loading, showed the lowest (0.53). STN ECT was higher than IMPROVE ECT, in contrast to results from aerosol samples. A higher peak inert-mode temperature and extended heating times can elevate ECT/ECR ratios for pretreated geological samples by promoting pyrolyzed organic carbon (PyOC) removal over EC under trace levels of oxygen. Considering that PyOC within filter increases ECR while decreases ECT from the actual EC levels, simultaneous ECR and ECT measurements would constrain the range of EC loading and provide information on method performance. Further testing with standard reference materials of common environmental matrices supports the findings. Char and soot fractions of EC can be further separated using the IMPROVE protocol. The char/soot ratio was lower in street dusts (2.2 on average) than in soils (5.2 on average), most likely reflecting motor vehicle emissions. The soot concentrations agreed with EC from CTO-375, a pure thermal method.
authors.affiliation: Key Laboratory of Aerosol Science & Technology, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China ; Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, United States of America.
authors.forename: Yongming
authors.initials: Y
authors.lastname: Han
authors.affiliation: Key Laboratory of Aerosol Science & Technology, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China ; Desert Research Institute, Reno, Nevada, United States of America.
authors.forename: Antony
authors.initials: A
authors.lastname: Chen
authors.affiliation: Key Laboratory of Aerosol Science & Technology, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China.
authors.forename: Junji
authors.initials: J
authors.lastname: Cao
authors.affiliation: AtmAA Inc., Calabasas, California, United States of America.
authors.forename: Kochy
authors.initials: K
authors.lastname: Fung
authors.affiliation: Key Laboratory of Aerosol Science & Technology, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China ; School of Public Health and Primary Care, The Chinese University of Hong Kong, Shatin, Hong Kong, China.
authors.forename: Fai
authors.initials: F
authors.lastname: Ho
authors.affiliation: Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, United States of America.
authors.forename: Beizhan
authors.initials: B
authors.lastname: Yan
authors.affiliation: Key Laboratory of Aerosol Science & Technology, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China.
authors.forename: Changlin
authors.initials: C
authors.lastname: Zhan
authors.affiliation: Key Laboratory of Aerosol Science & Technology, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China.
authors.forename: Suixin
authors.initials: S
authors.lastname: Liu
authors.affiliation: Key Laboratory of Aerosol Science & Technology, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China.
authors.forename: Chong
authors.initials: C
authors.lastname: Wei
authors.affiliation: Key Laboratory of Aerosol Science & Technology, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China.
authors.forename: Zhisheng
authors.initials: Z
authors.lastname: An
mesh_terms: D002244:Carbon / Q000032:analysis*; D002681:China; D002947:Cities; D004391:Dust / Q000032:analysis*; D004784:Environmental Monitoring / Q000379:methods*; D006801:Humans; D055095:Optics and Photonics / Q000379:methods*; D012987:Soil / Q000737:chemistry*; D053260:Soot / Q000032:analysis; D013696:Temperature
chemical_list: D004391:Dust; D012987:Soil; D053260:Soot; D002244:Carbon