Xingna Yu

Measurement and analysis of surface aerosol optical properties over urban Nanjing in the Chinese Yangtze River Delta

Aerosol optical properties including aerosol scattering coefficient (σsp), absorption coefficient (σap), single scattering albedo (SSA), PM2.5 mass concentration and their relationship with meteorological factors were measured and analyzed from 1st March to 30th April 2011. The observations were conducted at an urban-industrial site in Nanjing located in the Yangtze River Delta (YRD) region, China. The averaged σsp at 550 nm is found to be 329.3±321.6 Mm(-1) and occurred most frequently within the range of 100-200 Mm(-1). σap at 532 nm is measured to be 28.1±17.6 Mm(-1), which is remarkably smaller than most of the measurements made over megacities in China and nearly equivalent to the observations made at rural sites in the YRD. The mean SSA at 532 nm is 0.89±0.08 with the occurrence frequency of higher SSA (>0.9) accounting for about 60%, indicating that scattering-related aerosols are dominant over Nanjing during the study period. A bi-peak diurnal variation of σap and σsp is found with the maximum during late at night and early morning and the minimum in the afternoon, but the diurnal pattern of SSA is just the opposite to this. Significant correlation coefficients are noticed between different aerosol optical properties. σsp and σap showed a clear negative correlation with wind speed, temperature, and visibility. During the study period, the lower northwesterly and southeasterly winds are attributed to an increase in the aerosol optical properties. The σsp and σap increased significantly during severe haze and dust episodes caused by the accumulation of pollutants from both local and regional sources under favorable weather conditions.

Analysis of water vapor effects on aerosol properties and direct radiative forcing in China

The effects of column water vapor (CWV) on aerosol optical properties, radiative effects and classification are studied by using aerosol and CWV data from eight Aerosol Robotic Network (AERONET) sites in China: Beijing, XiangHe, Shouxian, Taihu, Hong_Kong, Zhongshan_Univ, SACOL, and Mt_WLG, which represents 5 distinct aerosol climatologies in China. Contrast in correlations between aerosol optical depth (AOD) and CWV is found. High correlation coefficient (R) ranging from 0.63-0.94 is observed at Beijing and XiangHe (North China Plain), SACOL (Northwest China) and Mt_WLG (the Tibetan Plateau). R values at stations in the Middle-East China (Shouxian and Taihu) are within 0.32-0.45. AOD shows poor correlation to CWV in Southeast China (R at Hong_Kong and Zhongshan_Univ of 0.15 and 0.27). At most sites, the asymmetry (ASYM) of fine-mode aerosol increases with CWV with R larger than ~0.4. Aerosol direct radiative forcing efficiency (ADRFE) at the bottom of the atmosphere (BOA) is affected by CWV, with R >~0.5 over the north and Middle-East China sites. The statistic results show that an increase of CWV by 0.1 cm could result in enhancements of ADREF at the BOA by about 1.1-2.8 W m-2 at all the sites except Mt_WLG. The aerosol classification shows that the mix-small aerosol type is always dominated under the high CWV air. The clusters of back-trajectories with relative humidity (RH) from Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model indicate that the air mass with high RH is often from south and east directions. The influence of CWV on aerosol properties is mainly shown in the properties of fine mode aerosol, which needs to be considered in the study of aerosol radiative forcing and climate effects.

The Influences of Heterogeneous Reaction on Particle Optical Properties: A Laboratory Case of SO2 on Hematite and Hematite-NaCl Mixture

The particle optical property variation for heterogeneous reaction of SO2 on hematite and hematite-NaCl mixture was investigated in a static reaction chamber at 298 K using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The increases of absorption and backward scattering coefficients are commonly higher in mixture with 50-70% NaCl than pure hematite and other mixtures. For both pure hematite and mixture, under reactions of 1-10% O2 concentrations, the absorption and backward scattering coefficients are in a higher increment than those of 20-30% O2 concentrations. The absorption and backward scattering coefficients rise by commonly larger magnitudes at high SO2 concentration than low SO2 concentration, in a quicker approach to equilibrium.