SummaryA capillary zone electrophoresis method for identification and determination of aesculin and aesculetin has been established using borate-phosphate buffer containing 30 % ethanol with on-column UV detection. A detailed investigation of the influence of changes in borate concentration, pH, applied voltage, temperature and organic modifier was then carried out. For both aesculin and aesculetin, a linear plot of migration time (MT) against borate concentration was obtained, and In[measured peak area (MA)] and lnMT both gave linear plots against In(applied voltage) with correlation coefficient r > 0.999, which also resulted in a linear correlation between MA and MT(r >_0.9998) under varied voltage. Ethanol as organic modifier to the background electrolytes helped in separating aesculin and aesculetin from other components in ash barks. The reproducibility with relative standard deviation in MT and in normalized peak area(NA) and linearity based on NA against concentration were evaluated. Finally, the method was successfully applied to monitor the quality of different ash barks and to compare the effect of sample preparation on content of bioactive components in ash bark. Results indicate that CZE promises to be applicable to quality control of traditional Chinese medicines containing aesculin and aesculetin.

Mineral dust is a dominant aerosol type in northwestern China and can mix with other air pollutants during its long‐range transport, playing an important role in Earth's energy budget and hydrological cycle on both regional and global scales. In this study, the optical properties of pure dust and polluted dust were compared by using ground‐based lidar and sun photometer data at SACOL (Semi‐Arid Climate and Environment Observatory of Lanzhou University) from August 2009 to August 2012. The total attenuated backscattering coefficient at 532 nm, the volume depolarization ratio (VDR) and the color ratio (CR) derived from the L2S‐SM‐II dual‐band polarization lidar and aerosol optical depth (AOD) and Angstrom exponent from sun photometer data were used to identify pure dust and polluted dust. The results showed that AOD at 440 nm of pure dust was widely distributed within the range of 0.4–1.1 but the AOD of polluted dust was generally less than 0.6. The frequency distribution of VDR showed that the mean value of pure dust was greater than that of polluted dust and the peak values were 0.31 and 0.21, respectively. The frequency distribution of CR showed that the mean value of pure dust was larger than that of polluted dust, and it was mostly pure dust aerosol when color ratio was greater than 0.8. The VDR showed a positive correlation with CR. Using the frequency distribution of VDR, a threshold value of 0.25 was proposed to differentiate pure dust from polluted dust. The rates of misclassification were 20.7% and 18.6% for pure dust and polluted dust, respectively. This work will be helpful for the classification of aerosol types in satellite observations and numerical modeling.

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The present study investigates the influences of stratospheric quasi-biennial oscillation (QBO) and El Niño–Southern Oscillation (ENSO) on the intensity of stratospheric isentropic mixing based on ERA-Interim and MERRA-2 reanalysis products. It is found that isentropic mixing in the stratosphere is modulated by QBO and ENSO. An analysis of the QBO basis function in the multiple regression model reveals that isentropic mixing in the lower stratosphere is suppressed in the equatorial region in the WQBO phase, while the mixing enhances in the subtropical and mid-latitude regions. This result is not consistent with the Holton–Tan mechanism. However, isentropic mixing in the mid-latitudes becomes stronger in the middle stratosphere in the EQBO phase, which agrees well with the Holton–Tan effect. Composite analysis indicates that QBO-induced changes in the direction and speed of the stratospheric zonal wind can affect wave propagation and wave breaking. In the WQBO phase, zonal wind weakens, and a planetary wave is anomalously converging near 30°N, which leads to an increase in isentropic mixing; on the contrary, wind speed becomes large, and the upward propagation of planetary wave divergence, which lead to the isentropic mixing, becomes weak near 60°N. In the EQBO phase, the wind is relatively weak around 60°N, and the isentropic mixing is strong. Multiple regression analysis reveals the ENSO impact on the intensity of isentropic mixing, which shows weak mixing in the middle and high latitudes and strong mixing in the low latitudes of the lower stratosphere in the El Niño years. In the middle stratosphere, isentropic mixing enhances in the mid-latitude region due to intensified upward propagation of planetary waves but weakens in the polar region. Composite analysis reveals a clear relationship between the mixing strength zones of the El Niño and La Niña years with the position of the polar jet and changes in zonal wind speed.