Constraints on primary and secondary particulate carbon sources using chemical tracer and 14C methods during CalNex-Bakersfield. (October 2017)

• Record Type: Journal Article
• Authors: Sheesley, Rebecca J.; Nallathamby, Punith Dev; Surratt, Jason D.; Lee, Anita; Lewandowski, Michael; Offenberg, John H.; Jaoui, Mohammed; Kleindienst, Tadeusz E.
• Is Part Of: Atmospheric environment. Volume 166(2017)
• Page Start: 204
• Page End: 214
• Publication Date: 2017-10
• Subjects: Primary organic aerosol -- Chemical mass balance -- Radiocarbon -- Secondary organic aerosol -- CalNex; Air -- Pollution -- Periodicals; Air -- Pollution -- Meteorological aspects -- Periodicals; 551.51
• DOI: 10.1016/j.atmosenv.2017.07.025
• Languages: English
• ISSNs: 1352-2310

Abstract

Abstract: The present study investigates primary and secondary sources of organic carbon for Bakersfield, CA, USA as part of the 2010 CalNex study. The method used here involves integrated sampling that is designed to allow for detailed and specific chemical analysis of particulate matter (PM) in the Bakersfield airshed. To achieve this objective, filter samples were taken during thirty-four 23-hr periods between 19 May and 26 June 2010 and analyzed for organic tracers by gas chromatography – mass spectrometry (GC-MS). Contributions to organic carbon (OC) were determined by two organic tracer-based techniques: primary OC by chemical mass balance and secondary OC by a mass fraction method. Radiocarbon ( 14 C) measurements of the total organic carbon were also made to determine the split between the modern and fossil carbon and thereby constrain unknown sources of OC not accounted for by either tracer-based attribution technique. From the analysis, OC contributions from four primary sources and four secondary sources were determined, which comprised three sources of modern carbon and five sources of fossil carbon. The major primary sources of OC were from vegetative detritus (9.8%), diesel (2.3%), gasoline (<1.0%), and lubricating oil impacted motor vehicle exhaust (30%); measured secondary sources resulted from isoprene (1.5%), α-pinene (<1.0%), toluene (<1.0%), and naphthalene (<1.0%, as an upper limit) contributions. The average observed organic carbon (OC) was 6.42 ± 2.33 μgC m −3 . The 14 C derived apportionment indicated that modern and fossil components were nearly equivalent on average; however, the fossil contribution ranged from 32 to 66% over the five week campaign. With the fossil primary and secondary sources aggregated, only 25% of the fossil organic carbon could not be attributed. Whereas, nearly 80% of the modern carbon could not be attributed to primary and secondary sources accessible to this analysis, which included tracers of biomass burning, vegetative detritus and secondary biogenic carbon. The results of the current study contributes source-based evaluation of the carbonaceous aerosol at CalNex Bakersfield. Highlights: Primary sources of OC were motor vehicle exhaust ∼33% and vegetative detritus ∼10%. Secondary sources of OC from tracer were underestimated at <5%. Radiocarbon of total organic carbon was roughly 50:50 fossil:contemporary. Tracers could apportion only 20% of the contemporary OC. Additional chemical tracers are needed for contemporary sources like agriculture.