The “Zero-order Model” revisited: Paul Schindler's influence on the development of trace metal scavenging models

In 1975 Paul Schindler produced the first oceanic trace metal scavenging model to explicitly include the role of surface chemistry as a control on trace metal water column residence times. The eighteen years that have elapsed since the publication of Schindler's seminal paper have seen the development of a variety of oceanic scavenging models; yet, the fundamental insight of his Zero-order Model remains the benchmark. This paper describes the role of Paul Schindler's work on surface chemistry in providing a framework for the current generation of trace element scavenging models.     

Characteristics, threats and opportunities of landfill scavenging: The case of Gaborone-Botswana

In Gaborone, as in other large cities in the developing world, individuals try to make a living by engaging in novel occupations such as landfill scavenging. This paper reports on a research conducted in the Gaborone landfill, the largest in Botswana. The study content-analyzed available literature from other countries. It also relied mainly on direct field observations. The discussions on and answers to closed and interview schedules by stakeholders, affected- and- interested – persons, provided the information on the threats and opportunities related to the landfill site and its informal management activities. This on-going case study lends credence to the potential of scavenging in sustaining livelihoods among those who cannot secure employment in the formal urban market. Scavenging tends to be useful although it may hazardous to the informal entrepreneurs. Taking all the threats into consideration, the decommissioning and closure of the landfill seems inevitable, in spite of the apparent short-term livelihood opportunities it provides to the informal sector.     

Crater formation in soils by raindrop impact

The process of crater formation by the impact of water drops on soil, sand and various other target material was studied. Craters of various shapes and sizes were observed on different target materials or conditions, ranging from circumferential depression to completely hemispherical shape. Crater shape was dependent upon target material, its ?ow stress or shear strength and the presence and thickness of water on the surface. Between 5 and 22 per cent of impact energy was spent on cratering, but the relationship between crater volume and kinetic energy of a raindrop was curvilinear, indicating a lower ef?ciency of impact energy in removing target material as the energy increases. Impact impulse, on the other hand, showed a more linear relationship with crater volume, and the ratio of impulse over crater volume (I/V) remained constant for the entire range of drop sizes, impact velocities, and surface conditions used in this study. Surface shear strength, represented by the penetration depth of fall‐cone penetrometer, appeared to be a key factor involved in this process. An equation was developed which related crater volume to cone penetration depth and impact impulse. Crater volume, which appeared to be a better indicator of the total amount of material dislodged by a raindrop than splash amount, can thus be predicted using this equation. Copyright © 2004 John Wiley & Sons, Ltd.     

无锡梅雨期湿沉降综合分析

利用2008—2014年梅雨期间酸雨观测资料及2014年6月16—27日降水个例加密采样资料,结合大气污染物资料分析了近7 a无锡梅雨期酸雨特征,研究降水过程中空气污染物、p H值、电导率的变化及降水对污染物的清除作用。结果表明:无锡市梅雨期酸雨年平均p H值呈现逐年递增趋势。降水过程中,颗粒物质量浓度显著降低;气体浓度变化受其自身日变化及排放源影响大于雨水的清除作用;样品的p H值、K值每个过程变化并不一致,K值变化与颗粒物质量浓度变化大致保持一致。降水、风对颗粒物质量浓度影响大于对气体浓度的影响。长时间连续降水时,降水对颗粒污染物的清除存在极限。小时雨量在0~0.5 mm时,降水对颗粒物浓度做负清除,其值反而略有增加;小时雨量在0.6~5.0 mm时,降水对颗粒物质量浓度做正清除;小时雨量达到5.1 mm及以上时,对PM_(2.5)和PM_(2.5-10)做正清除,对PM_(10)做负清除。降水对SO_2有稀释清除作用;对NO_2的稀释作用取决于其开始浓度值;对CO、O_3的清除作用不显著。     

两次强降水过程雨滴谱特征及差异

利用寿县观测站内的Parsivel激光雨滴谱仪结合观测站雨量数据及雷达基数据,分析了发生在2015年6月26—30日梅雨期间和2015年8月7—10日超强台风"苏迪罗"影响期间2次强降水过程的雨滴谱结构特征及其差异,拟合了雨强与雷达反射率因子之间的关系。结果表明:雨强的大小直接影响雨滴谱的特征参量,且随着雨强增大而增大;梅雨锋暴雨中1.0mm直径≤1.5mm的粒子所占比例最多,雨强贡献率最大;台风雨中0.75mm直径≤1.0mm的粒子所占比例最多,但1.0mm直径≤1.25mm的粒子对雨强的贡献最大,说明较大粒子对强降水的贡献较大。     

一次拖曳型飑线过程雨滴谱演变特征研究

利用Thies激光雨滴谱仪观测资料和CINRAD/SA多普勒雷达观测资料,分析了2017年7月18日一次典型中纬度拖曳型飑线过程不同发展阶段雨滴谱和积分参数的演变特征,主要结果为：1）成熟飑线回波包括对流带、过渡区和拖曳层状云区三部分,对流带前侧不断有对流带生成并合并到主对流带中,使得对流带的前沿具有强的反射率因子,并且有多个雨强大值中心。2）垂直穿过飑线对流带,雨强增加阶段有较少的小粒子（直径小于1 mm）和特大粒子（直径大于5 mm）,以及较低的雨滴浓度和反射率因子,而雨强减弱阶段有较多的小粒子和特大粒子,以及较高的雨滴浓度和反射率因子;飑线加强阶段,雨滴谱有较大的峰值直径（0.44 mm）、较多的大（直径大于3 mm）和特大粒子,而飑线减弱阶段,雨滴谱有较小的峰值直径（0.19 mm）、较少的大粒子。3）对流带、过渡区和层状云降水雨滴谱的Gamma谱三参数N0、μ、λ随雨强增大有明显的分层特征,相同雨强时,对流云和过渡区降水的三参数比层状云降水的数值大;而飑线不同发展阶段、不同降水类型的λ-μ关系具有一致性,二次多项式可以很好地拟合λ-μ关系。4）归一化雨滴谱参数NW和D0的分布可以用来区分对流云和层状云降水,并给出了新的分离线方程;另外,飑线在发展和减弱阶段的雨滴谱特征有明显差异,表明飑线演变过程降水形成的微物理机制发生变化,前期冷云过程有重要影响,而后期暖云过程起主导作用。     

降水现象仪观测应用评估

利用2017年9月至2018年8月北京20个站降水现象仪采集数据与人工平行观测数据,对降水现象仪进行了对比评估。结果表明:降水现象仪的缺测率为0.01%,空报率为0.6%,捕获率为93.5%,漏报率为27.9%,错报率为10.0%。从统计结果可知,降水现象仪的缺测率、空报率较低,捕获率较高,体现出设备性能良好的一面,漏报率和错报率偏高,表明设备漏识别和错误识别的情况较多,漏报主要发生在弱降水过程中,错报主要出现在毛毛雨的识别上。设备测量和人工观测降水开始时间一致性较好,终止时间一致性偏差;降水现象仪现存问题:在大雨强时易出现雨滴叠加误识别,在小雨强时识别率会降低,在无降水错误输出降水现象方面缺少质控。     

基于旋翼无人机观测的雾天和霾天VOCs垂直分布特征研究

为研究雾和霾天气下VOCs时空变化特征,于2020年11月19日—2021年1月15日在江苏省东海国家气象观测站进行为期58 d的外场观测试验。利用自主研发的多旋翼无人机捕获2次辐射雾和2次霾天气过程,获得气温、气压、相对湿度、风向、风速、VOCs、O₃等7种要素100多条垂直廓线。结果表明：时间上,霾过程夜间VOCs体积浓度(0.225～0.253 ppm(parts per million, 1 ppm=10^-6))明显高于白天(0.191～0.205 ppm),雾形成前体积浓度(0.121～0.239 ppm)显著高于雾过程(0.056～0.209 ppm)。雾过程中VOCs体积浓度与雾强度变化相反,雾层高度与VOCs体积浓度剧烈变化高度一致,雾层(<200 m)中VOCs体积浓度(0.172～0.178 ppm)明显减小,显著低于雾形成前(0.195～0.240 ppm),雾层以上浓度变化大,雾结束后1 h内保持雾过程中分布特点。雾对逆温层中的水溶性污染物有清除作用,VOCs体积浓度和O₃质量浓度均下降。     

基于双偏振雷达和降水现象仪的郑州“7·20”极端强降水微物理特征分析

利用降水现象仪、双偏振雷达、常规气象观测资料和再分析数据,分析了郑州“7·20”极端强降水过程的微物理特征。此次过程受多尺度天气系统的共同影响,为复杂多变的降水微物理特征提供了有利的环境条件。结果表明,此次过程地面雨滴谱分布随时间存在明显变化,雨滴谱参数分布较广,覆盖了从大陆性对流降水至海洋性对流降水的分布区域。20日16—17时最强降水时段,小粒子数密度显著高于东亚地区普通对流性降水的统计结果和华南地区夏季平均值,且存在大量大粒子,保证了极高的降水效率。双偏振雷达参量的垂直结构反演结果显示,对流系统质心低,具有典型的暖云特征;0 ℃层以上冰相过程相对活跃,0 ℃层以下强烈的暖雨过程,大量的冰相粒子落下并融化和低层高效率的雨滴碰并增长过程,导致各尺度高浓度雨滴的生成,最终形成地面的极端强降水。     

A simulation study of the role of raindrop erosion in the formation of desert pavements

A simple model of raindrop erosion—the combined effects of the detachment of sediment by raindrops and its transport by splash or by overland flow—is developed to examine the role of this process in the formation of desert pavements. Application of the model to soils in areas of existing pavement initially simulates the formation of pavements, but the changing sediment size distributions lead to the subsequent destruction of these modelled surfaces. An improved model that accounts for the feedback effects of the changing size distributions on infiltration and microtopography is then developed. Incorporating these effects allows simulated pavements to be maintained over longer periods. The model yields desert pavements whose particle size compositions differ in response to differences in initial soil characteristics, slope and rainfall intensity. This model is tested against empirical data from a site where there is intershrub pavement and associated mounds of fines beneath desert shrubs. The results successfully predict the accumulation of fines under shrubs but underestimate the development of the pavement between shrubs. These findings suggest that the raindrop erosion mechanism on its own cannot account for the development of the pavement and that some other mechanism leading to the surface concentration of coarse particles must also be operating.