北京2019年冬季一次典型霾污染特征与成因分析

为研究北京冬季霾污染过程的污染特征和成因,以北京2019年12月一次典型PM_2.5污染过程为分析对象,利用气溶胶垂直探测资料、边界层气象场和近地湍流资料,对霾不同污染阶段的特征与边界层理化特性的演变进行综合分析.结果表明：①观测期间北京共经历两次污染生消,历时5 d,PM_2.5小时浓度最高220 μg·m^-3,超过重度污染标准的时次占比53%.②高空稳定形势和地面均压场配置下,来自北京西南城市群地表的气溶胶和水汽传输（占比48%）,在近地层偏南弱风（风速1~2 m·s^-1）,贴地强逆温［0.8 K·（100 m）^-1］和高湿（相对湿度80%以上）等不利扩散的气象条件下不断吸湿增长,加之本地污染排放,成为霾日维持的主要原因.且随污染加重,气溶胶球形特征逐步显著（退偏比从0.05降至0.02）.③各湍流统计量（湍流强度、摩擦速度和湍流动能）在重污染发生与结束前提前出现规律性异常突降（小时波动率77%）与激增（超过一个量级的峰值）现象,表明湍流统计量可作为重污染过程发生和结束的预报指标,其中湍流强度响应提前的时长与其峰值后的持续湍流强弱有关.污染累积阶段摩擦速度（0.04~0.21 m·s^-1）、湍流强度（均值0.678）和湍流动能（均值0.643 m²·s^-2）等均维持在较低水平,底层大气混合扩散能力较差,对污染持续累积起重要作用.另外晴天和霾天感热通量均由地面向大气输送,且呈明显的日单峰变化特征,霾天感热通量（20W·m^-2）较晴天小（60W·m^-2）;潜热通量则全程在0值附近.     

北京平原和延庆地区山谷风异同及对污染的影响

在一定的地形与天气条件下,山谷风环流是影响山地和平原气溶胶污染的主要气象因素之一.本研究基于2015~2019年京津冀地区生态环境监测数据和多源气象数据,对比分析了北京平原和延庆地区山谷风异同,结合典型污染事件揭示了山谷风不同阶段对PM_2.5浓度的影响机制.经分析发现,观象台山谷风为偏西南风转偏东北风,延庆站为偏东南风转偏东北风,随着污染等级加重,山谷风强度减弱17.7%~32.4%;观象台风速2~6 m·s^-1时,最大为SE风向PM_2.5浓度83μg·m^-3,东南风浓度高于西南;延庆站风速2~6 m·s^-1时,偏东南方向浓度高于其他风向20~40μg·m^-3,谷风阶段PM_2.5浓度高于近5年均值10~12μg·m^-3.以2015年3月5~8日重污染事件为例,山谷风的影响作用主要体现在谷风时段东南风的高湿性及区域传输作用,延庆站3月6~7日谷风阶段PM_2.5浓度上升100~130μg·m^-3;山风时段逆温发展至1000 m,观象台和延庆站露点先后抬升18℃左右,延庆站露点峰值滞后观象台2 h,高湿环境下PM_2.5浓度小幅上升.同时,3月6~7日延庆站400 m高度和玉渡山站热力梯度逐渐减小,山谷风分别减小8%和6%,局地环流减弱可能与边界层和高浓度气溶胶双向反馈机制有关.     

一次低纬高原暖区暴雨对流系统演变及边界层触发

利用高空和地面区域站、FY2G卫星TBB、昆明C波段多普勒雷达、闪电观测资料和NCEP/NCAR1° ×1°再分析资料,分析了2017年7月12-13日云南副高外围暖区暴雨对流系统演变特征及边界层触发成因.结果表明,滇东中部和滇中中部暴雨,12日08:00以锋面降水为主,14:00后以暖区降水为主;环境场具有弱垂直风切...     

天津大气PM_(2.5)垂直特征及边界层影响

利用2006年12月17日至2007年1月1日天津250 m气象铁塔40 m、120 m、220 m高度PM2.5浓度监测资料及铁塔边界层气象资料,分析了不同天气背景下PM2.5随时间、高度变化的分布特征,研究了铁塔边界层气象条件包括逆温、特征摩擦速度、湍流动量和热量对PM2.5的影响,发现垂直PM2.5细粒子的浓度高低与天气背景及边界层气象条件是密切相关。边界层垂直动力和热力变化影响着PM2.5浓度的变化,冷空气过境时刻,PM2.5浓度达到最高峰值。40 m高度出现一个临界摩擦速度0.4 m/s,高浓度PM2.5比较集中在摩擦速度小于0.4 m/s的区域内,大于0.4 m/s这个摩擦速度,边界层的垂直湍流动量及水平和垂直方向的热量输送通量就会明显的变化,因而促使PM2.5在空中的扩散或沉降。也就是说,当摩擦速度小于0.4 m/s时,有利于PM2.5在空中的累积,PM2.5浓度趋于增高的趋势;反之,有利于PM2.5扩散,PM2.5浓度趋于减小的趋势。     

Chemistry and aerosols in the marine boundary layer: 1-D modelling of the three ACE-2 Lagrangian experiments

Three Lagrangian experiments were conducted during IGAC's second aerosol characterization experiment (ACE-2) in the area between Portugal, Tenerife and Madeira in June/July 1997. During each Lagrangian experiment, a boundary layer air mass was followed for about 30 h, and the temporal evolution of its chemical and aerosol composition was documented by a series of vertical profiles and horizontal box pattern flown by the Meteorological Research Flight research aircraft Hercules C130. The wealth of observational data that has been collected during these three Lagrangian experiments is the basis for the development and testing of a one-dimensional Lagrangian boundary layer model with coupled gas, aqueous, and aerosol phase chemistry. The focus of this paper is on current model limitations and strengths. We show that the model is able to represent the dynamical and chemical evolution of the marine boundary layer, in some cases requiring adjustments of the subsidence velocity and of the surface heat fluxes. Entrainment of a layer rich in ozone and carbon monoxide from a residual continental boundary layer into the marine boundary layer as well as in-cloud oxidation of sulphur dioxide by hydrogen peroxide are simulated, and coherent results are obtained, concerning the evolution of the small, presumably sulphate–ammonia aerosol mode.     

Removal of 2, 4‐D from aqueous solution by the adsorbents from spent bleaching earth

Abstract

The removal of 2, 4‐D (2, 4‐ dichlorophenoxyacetic acid) from aqueous solutions by activated spent bleaching earths (SBE) was studied at 20 °C. Experiments were performed as a function of time, initial concentration, dose and particle size of the adsorbent. The Langmuir and Freundlich adsorption equations were fitted by the adsorption data obtained. The values of Langmuir and Freundlich constants were determined. The adsorption kinetic was found to follow Lagergren equation. Both the boundary layer and intraparticle diffusion played important roles in the adsorption rate of 2, 4‐D. As the size of the adsorbent increased, the time to reach equilibrium increased but adsorption capacity decreased.     

强震作用下地埋结构的数值模型

应用时域边界元法研究了结构 介质动力相互作用问题。假设摩擦遵守库仑定理 ,当入射波足够强时界面会出现局部滑移、分离。由于边界上的区域 (滑移、分离和粘着 )是未知的 ,所以 ,笔者研究的实际上是个复杂的边界非线性问题。该模型对评估和预测地埋结构在动荷载下的安全具有重要的理论价值     

Implications of Heterogeneous Chemistry of Nitric Acid for Nitrogen Deposition to Marine Ecosystems: Observations and Modeling

Size resolved particle composition and nitric acid (HNO₃)measurements from the ASEPS'98 experiment conducted in the BalticSea are used to provide observational evidence of substantialgas-particle transfer of oxidized nitrogen (N) compounds in themarine boundary layer. We then focus on the importance ofHNO₃ reactions on sea salt particles in determining spatio-temporal patterns of N dry deposition to marine ecosystems.Modelling results obtained assuming no kinetic or chemical limiton HNO₃ uptake and horizontally homogeneous conditions withnear-neutral stability, indicate that for wind speeds 3.5 – 10 ms^-1 transfer of HNO₃ to the particle phase to formparticle nitrate (NO₃ ^-) may decrease the N depositionvelocity by 50%. We extend this research using the CHEM-COASTmodel to demonstrate that, in a sulphur poor environment undermoderate wind speeds with HNO₃ concentrations representativeof those found in the marine boundary layer, inclusion ofheterogeneous reactions on sea spray significantly reducesmodelled NO₃ ^- deposition in the near coastal zone.     

输水隧道的减震措施研究

隔震技术是近几十年发展起来的新技术,对地面结构减震效果显著。本文运用Newmark隐式时间积分有限元法并采用粘-弹性人工边界,分析了在输水隧道施工中设置减震层和注浆加固一定范围内围岩这2种方法的减震效果、适用条件及其减震机理。计算结果表明:减震层或加固层的设置均使隧道衬砌应力减小,起到保护隧道衬砌的作用;在较大的范围内注浆加固围岩的办法,对软土中的输水隧道的减震更加有效,它能充分发挥围岩的承载能力;而在围岩与衬砌间设置减震层的办法,对稳定性极好的坚硬围岩中的输水隧道的减震效果更加有效。计算结果可为地震区的输水隧道抗震设计提供依据。