ABSTRACT
Brown carbon (BrC) refers to a group of organic compounds in fine atmospheric particles (PM2.5) that are able to absorb light in the ultraviolet and visible range. They have a significant impact on the visibility of air and on the earth's climate. In this study, we used a black carbon analyzer (Model AE33) to conduct field measurements in northern suburban Nanjing from March 2021 to February 2022. We measured the light absorption coefficients of BrC in PM2.5 and quantified the contributions of primary (BrCpri) and secondary brown carbon (BrCsec) in BrC by using the minimum correlation method (MRS), combined with the backward trajectories,potential source contribution function (PSCF) analysis, and diurnal patterns to analyze the seasonal characteristics of BrC. The results showed that the annual average light absorption of BrC was(7.76±7.17)Mm-1 (at 370 nm), and its contribution to the total aerosol light absorption was (22.0±8.8)%. BrC light absorption at different wavelengths all showed a U-shape seasonal variation of high in spring and winter and low in summer and fall. MRS analysis showed that the annual average contributions of BrCpri and BrCsec were (62.9±21.4)% and (37.1±21.4)% (at 370 nm), respectively; however, the contribution of BrCsec increased with the increase in wavelength, and it became dominant in longer wavelengths such as 660 nm. Backward trajectory and PSCF analysis showed that BrC was heavily influenced by air masses from the sea in spring, summer, and fall but was influenced greatly by local and regional continental emissions in winter. Traffic emissions in spring, summer, and fall were more intense to contribute to BrCpri than that in winter, whereas coal and biomass combustion had a greater impact on BrCpri in winter. Detailed analysis revealed that gas-phase photochemistry and aqueous chemistry had different influences on BrCsec formation in different seasons. It was mainly from gas-phase photochemistry in summer but was dominated by aqueous process in winter; both processes, however, were important pathways to BrCsec in spring and fall.
ABSTRACT
Bone marrow mesenchymal stromal cells (BMSCs) have potential applications in cell and gene therapies for cardiac disease. The cardiac-specific transcription factors GATA-binding protein 4 (GATA4) and T-Box protein 5 (TBX5) are considered to be pivotal in cardiogenesis. The aim of this study was to investigate the effects of GATA4 and TBX5 on cardiomyogenic differentiation of BMSCs. The BMSCs were initially isolated and identified. Vectors harboring cardiac transcription factor genes GATA4 and TBX5 or empty vectors were transferred into BMSCs. Cardiomyogenic cells differentiated from BMSCs were identified by expression of cardiac-specific markers including cardiac troponin T, connexin 43, ß-myosin heavy chain, and myosin light chain-2 using immunocytochemical staining, western blotting, and quantitative real-time PCR. The ultrastructures of the differentiated cells were examined by transmission electron microscopy, which were similar to those of fetal cardiomyocytes. The differentiated cells exhibited L-type calcium current activities reflective of the electrophysiological characteristics of cardiomyocytes. These findings indicate that exogenous expression of cardiac-specific transcription factors GATA4 and TBX5 enhance cardiomyogenic differentiation of BMSCs.