Elemental carbon is often found in ambient particulate matter (PM), and it contributes to the PM's oxidative potential (OP) and thus poses great health concerns. Previous review articles mainly focused on the methodologies in evaluating OP in PM and its relationship with selected chemical constituents, including metal ions, PAHs, and inorganic species. In recent years, growing attention has been paid to the effect of atmospheric aging processes on the OP of EC-containing airborne particles (ECCAPs). This review investigates more than 150 studies concerning the OP measurements and physico-chemical properties of both fresh and aged ECCAPs such as laboratory-generated elemental carbon (LGEC), carbon black (CB), soot (black carbon), and engineered carbon-containing nanomaterials (ECCBNs). Specifically, we summarize the characteristics of water-soluble and insoluble organic species, PAHs, quinone, and oxygen-containing functional groups (OFGs), and EC crystallinity. Both water-soluble organic carbon (WSOC) and water-insoluble organic carbon (WIOC) contribute to the OP. Low molecular weight (MW) PAHs show a higher correlation with OP than high MW PAHs. Furthermore, oxidative aging processes introduce OFGs, where quinone (CO) and epoxide (O–C–O) increase the OP of ECCAPs. In contrast, carboxyl (–COOH) and hydroxyl (–OH) slightly change the OP. The low crystallinity of EC favors the oxygen addition and forms active OFG quinone, thus increasing the OP. More detailed analyses for the EC microstructures and the organic coatings are needed to predict the OP of ECCAPs.
Ke Min,Shenxi Deng,Zhao Shu,Yong Li,Bo Chen,Ming Ma,Qian Liu,Guibin Jiang
Elemental carbon (EC) and organic carbon (OC) exist ubiquitously and interact mutually in the environment. Simultaneous analysis of EC and OC will greatly advance our understanding of the behavior and fate of EC and OC, but is however still a great challenge due to the lack of suitable analytical tools. Here, we report a matrix-free laser desorption/ionization mass spectrometry (LDI-MS) method capable of simultaneous analysis of EC and OC by monitoring two independent groups of specific MS fingerprint peaks. We found that EC itself can generate carbon cluster peaks in the low mass range under laser excitation, and meanwhile it can also serve as a matrix to assist the ionization of OC in LDI-MS. By using per- and polyfluoroalkyl substances (PFASs) as a typical set of OC and carbon black (CB) as a model EC, we successfully monitored the adsorption process of PFASs on CB enabled by LDI-MS. We show that hydrophobic interaction dominates the sorption of PFASs to CB, which was affected by the functional groups and carbon chain length of PFASs. Furthermore, environmental substances in water such as humic acid (HA) and surfactants can significantly affect the adsorption of PFASs on CB probably by changing the adsorption sites of CB. Overall, we demonstrate that LDI-MS offers a versatile and high-throughput tool for simultaneous analysis of EC and OC species in real environmental samples, which makes it promising for investigating the environmental behaviors and ecological risks of pollutants.
Yue Liu,Junjie Liu,Ji Xiao,Jing Ye,Lixu Guo,Caiqing Yan
Carbonaceous aerosol, including organic carbon (OC) and elemental carbon (EC), has significant influence on human health, air quality and climate change. Accurate measurement of carbonaceous aerosol is essential to reduce the uncertainty of radiative forcing estimation and source apportionment. The accurate separation of OC and EC is controversial due to the charring of OC. Therefore, the development of reference materials (RM) for the validation of OC/EC separation is an important basis for further study. Previous RMs were mainly based on ambient air sampling, which could not provide traceability of OC and EC concentration. To develop traceable RMs with known OC/EC contents, our study applied an improved aerosol generation and mixing technique, providing uniform deposition of particles on quartz filters. To generate OC aerosol with similar pyrolytic property of ambient aerosol, both water soluble organic carbon (WSOC) and water insoluble organic carbon (WIOC) were used, and amorphous carbon was selected for EC surrogate. The RMs were analyzed using different protocols. The homogeneity within the filter was validated, reaching below 2 %. The long-term stability of RMs has been validated with RSD ranged from 1.7–3.2 %. Good correlation was observed between nominal concentration of RMs with measured concentration by two protocols, while the difference of EC concentration was within 20 %. The results indicated that the newly developed RMs were acceptable for the calibration of OC and EC, which could improve the accuracy of carbonaceous aerosol measurement. Moreover, the laboratory-generated EC-RMs could be suitable for the calibration of equivalent BC concentration by Aethalometers.
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