Study On The Sampling And Analysis Methods Of Carbonaceous Aerosol

Carbonaceous aerosol, consisting of organic carbon (OC) and elemental carbon(EC), has been the focus of extensive studies due to its complex effects on multiplegeographical scales, such as human health, visibility/haze, atmospheric brown clouds,radiative forcing/climate change; however, its sampling and analysis, which arefundamental to further studies, are still facing substantial challenges. In this work, thesampling and thermal-optical analysis methods of carbonaceous aerosol wereinvestigated based on a multi-channel sampler, an organic denuder, and multipleanalysis approaches. The results will be highly relevant in the improved measurement ofcarbonaceous aerosol and the establishment of standardized methods.With respect to the performance for removing VOCs, useful time and specificsurface area, an activated-carbon honeycomb denuder was selected for investigating thesampling methods. When using the denuder approach, it was demonstrated that thedenuder could effectively remove the positive artifact, and would not introduceadditional artifacts such as the particle loss due to diffusion and the contamination ofactivated-carbon material. When using the backup quartz approach, results from theapportionment of backup OC showed that all of the backup OC in the sequential-quartzmethod was from VOCs, however, it could reliably estimate the positive artifact onlywhen both the front and backup quartz filter reach equilibrium with VOCs; the backupOC in the Teflon-quartz in series method also included volatilized particulate OC, as aresult, would overestimate the positive artifact.The thermal-optical methods differ mainly with respect to temperature protocol andcharring correction method, which are investigated in this work. The discrepancybetween OC or EC concentrations defined by different temperature protocols werecaused by the systemic artifact and the early split, moreover, emissions from biomassburning would increase the discrepancy. Premature evolution of EC was found to begin when the peak inert mode temperature was increased from580℃(IMPROVE-Aprotocol), which would result in the overestimation of OC and the underestimation ofEC. The discrepancy between OC or EC concentrations defined by different charringcorrection method was mainly related to secondary organic aerosol (SOA). The OC toEC ratio calculated by results from tranmittance correction included importantinformation about the extent of SOA production, whereas the OC to EC ratio based onreflectance correction exhibited no correlation with SOA, indicating the transmittancecorrection method was more reliable.It was demonstrated that EC was also a complex aggregate of different species, andcould also evolve in the inert atmosphere, indicating that a specific boundary betweenOC and EC does not exist. Moreover, water-soluble organic carbon would alsocontribute to the light absorption, providing new evidence for the atmospheric presenceof brown carbon.