Ground-based observation of aerosol optical properties in Lanzhou, China

Aerosol optical properties from August 2006 to July 2007 were obtained from ground-based and sky radiance measurements in Semi- Arid Climate and Environment Observatory of Lanzhou University （SACOL）, China. High aerosol optical thickness （AOT） associated with low .Angstrom exponent （α） was mainly observed in spring, which was consistent with the seasonal dust production from Hexi Corridor. The maximum monthly average value of AOT 0.56 occurred in March of 2007, which was two times larger than the minimum value of 0.28 in October of 2006. Approximately 60% of the AOT ranged between 0.3 and 0.5, and nearly 93% ofα value varied from 0.1 to 0.8, which occurred in spring. The significant correlation between aerosol properties and water vapor content was not observed. The aerosol volume size distribution can be characterized by the bimodal logarithm normal structure： fine mode （r 〈 0.6 μm） and coarse mode （r 〉 0.6 μm）. Aerosols in spring of SACOL were dominated by large particles with the volume concentration ratio of coarse to fine modes being 7.85. The average values of asymmetry factor （g） in the wavelength range 440-1020 nm were found to be 0.71, 0.67, 0.67 and 0.69 in spring, summer, autumn and winter, respectively.

Seasonal Variation of Columnar Aerosol Optical Properties in Yangtze River Delta in China

In order to understand the seasonal variation of aerosol optical properties in the Yangtze River Delta,5 years of measurements were conducted during September 2005 to December 2009 at Taihu,China.The monthly averages of aerosol optical depth were commonly 0.6;the maximum seasonal average（0.93） occurred in summer.The magnitude of the Angstr¨om exponent was found to be high throughout the year;the highest values occurred in autumn（1.33） and were the lowest in spring（1.08）.The fine modes of volume size distribution showed the maxima（peaks） at a radius of ～0.15 μm in spring,autumn,and winter;at a radius of ～0.22 μm in summer.The coarse modes showed the maxima（peaks） at a radius of 2.9 μm in spring,summer,and autumn and at a radius of 3.8 μm in winter.The averages of single-scattering albedo were 0.92（spring）,0.92（summer）,0.91（autumn）,and 0.88（winter）.The averages of asymmetry factor were found to be larger in summer than during other seasons;they were taken as 0.66 at 440-1020 nm over Taihu.The real part of the refractive index showed a weak seasonal variation,with averages of 1.48（spring）,1.43（summer）,1.45（autumn）,and 1.48（winter）.The imaginary parts of the refractive index were higher in winter（0.013） than in spring（0.0076）,summer（0.0092）,and autumn（0.0091）,indicating that the atmosphere in the winter had higher absorbtivity.

Effects of Sand-Harvesting on River Water Quality and Riparian Soil Physico-Chemical Properties

The widespread distribution of river sand-harvesting activities continues to degrade river water quality and the surrounding riverine environments. This study determined practical effects of sand-harvesting on two rivers in Kakamega County Kenya. Water samples were tested for turbidity and total suspended solids (TSS). For riparian soils, nitrogen (N), phosphorus (P), pH, organic carbon (OC), moisture content and textural class were determined on composite samples obtained from the field. Two control sites not affected by sand-harvesting were also used for comparison. Results indicate TSS concentrations increased during the rainy season when sand-harvesting was occurring, with significant differences between the control and sand-harvesting sample groups. Between seasons—dry and wet—in natural circumstances, the riparian soil moisture and phosphorus contents increased significantly. The study shows that river sand-harvesting degrades the aesthetic value of riparian areas, and makes rivers prone to bank erosion, and silt. This increases river water turbidity. The study concludes that sand-harvesting does not directly affect the riparian soil moisture content, total N, P, pH, OC or textural class, but reduces productivity of riparian land and puts the riverine ecosystems at risk.

北京地区2013–2017年细颗粒物爆发增长事件的演变特征及气象成因分析

本文详细分析了2013–2017年北京地区细颗粒物爆发增长事件的演变特征,并结合气态前体物和常规气象要素对3种事件类型(3h, 6h和9h事件)的污染来源及其气象成因进行了探讨。北京地区细颗粒物爆发增长事件呈逐年下降趋势,且多发生在秋冬季;事件的生消过程中NO2的增长速率远高于SO2,表明移动源的贡献要高于固定源。风向-风速-PM2.5的polar Plot结果表明,来自北京东南方向气团的污染物输送对于3h事件有较大影响, 9h事件受主要受局地排放及二次转化的影响, 6h事件则源于局地排放和区域传输的共同贡献。

Particle size distribution and characteristics of polycyclic aromatic hydrocarbons during a heavy haze episode in Nanjing,China

A heavy haze episode caused by agricultural burning occurred in Nanjing from November 7 to November 8, 2009. PM10 samples were collected on normal and hazy days from November I to November 14, 2009 at both city and suburban sites of Nanjing. Sixteen PAHs were measured during the day and at night. The results show that the concentrations of the particles were as high as 579.55 and 573.43 μg/m^3 during the haze episode at the city and suburban sites, respectively, 3-4 times higher than those on a normal day. The proportions of fine particles during the haze episode were also higher than those on a normal day. The changes in the concentrations of PAHs were in accordance with the concentrations of the particles. High- molecular-weight PAHs composed approximately 80% of the total PAHs on normal days and during the haze episode. The concentration of PAHs in fine fractions significantly increased during the haze episode, and this increase was most obvious at night at the city site, The proportion of total carcinogenic PAHs in fine particles was relatively high during the haze episode at both sampling sites, particularly at night at the city site.

Characteristics of different charge transfer modes in upward flashes inferred from simultaneously measured currents and fields

The authors present an analysis of different charge transfer modes during upward negative flashes.The analysis includes a total number of 94 pulses that occurred during two upward negative flashes recorded at the Säntis Tower.The pulses included 59 mixed-mode(MM)initial continuous current(ICC)pulses,17 M-component-type ICC(M-ICC)pulses,8 returnstroke pulses,and 10 classical M-component(MC)pulses.It is found that the initial stage of the flash is responsible for the largest share of the total charge transferred to the ground.Simulation results for the electric fields associated with the considered charge transfer modes are presented and discussed.Return stroke(RS)and MM pulses were simulated adopting the MTLE model,while MCs and M-ICC pulses were simulated using the guided wave model of Rakov et al.The simulated results are shown to be in good agreement with simultaneous records of electric fields measured at a distance of 15 km from the Säntis Tower.The inferred velocities for MCs and M-ICC pulses range from 2.0×10^(7) to 9.0×10^(7) m/s,and the corresponding junction point heights range from 1.0 to 2.0 km.The inferred pulse velocities for RSs and MM pulses range from 1.3×10^(8) to 1.65×10^(8) m/s.The inferred current attenuation constants of the MTLE model obtained in this study range from 0.3 to 0.8 km,lower than the value of 2 km previously suggested for RSs in downward flashes.The obtained results support the assumption that the mode of charge transfer to the ground giving rise to MM pulses is similar to that of RSs.The results are also in support of the generally assumed similarity between M-ICC pulses and classical MCs.