Synergy of satellite-based aerosol optical thickness analysis and trajectory statistics for determination of aerosol source regions

ABSTRACT

Over 10 years of satellite-based remote sensing data with trajectory statistics are used to determine sources of air mass related to different aerosol types. Aerosol typing is based on analysis of sun-photometer data and then extended in time with the use of satellite data. Supplemental analysis of Gaussian distributions of aerosol optical thickness changes during transport, based on Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data, is performed. It allows for differentiating between primary and secondary aerosol sources as well as to prove air mass source as a source of aerosol. It appears that source regions of air mass and aerosols’ sources are collocated in most cases. For western advection from Germany, the most probable aerosol sources are located between air mass source regions and the receptors. These are mostly associated with the industrial/urbanized aerosol type. Additionally, aerosols from intermittent and strong episodes of biomass burning to the east of the Polish border are found to originate from sources located closer to the receptors than backward trajectory analysis alone suggested.     

Analysis of Clear-Sky Aerosol Optical Properties and Source Characteristics in Guangzhou

The basic optical properties of clear-sky aerosol of Guangzhou in 2015 were retrieved using CE318 sun photometer data,and their temporal variation characteristics were analyzed and local pollution sources were explored.based on the HYSPLIT backward-trajectory model,the characteristics of external transport sources of air pollution in Guangzhou were studied.The results show that：（1) in 2015,the annual average AOD in Guangzhou is 0.625,which is at a relatively high level.Among them,AOD is the largest in spring,followed by autumn,winter,and summer,with obvious seasonal variations;（2) the daily variation of aerosol basic optical properties are closely related to human activities,and road traffic pollution is the main source of atmospheric aerosol;（3)Air pollution affected by external transport has obvious seasonal variation characteristics,which is superimposed with local emissions,causing air pollution in Guangzhou to be worse,and marine particles transport occurs all year round;（4) the wavelength exponent of all seasons is greater than 1,and is mainly distributed within the interval of 0.8 to 1.4.The aerosol components are stable throughout the year,mainly with smaller particle size aerosols.In general,the aerosol type in the Guangzhou area is mainly a mix of urban-industrial and marine aerosols.     

Airflow in a slot-ventilated enclosure partially filled with porous boxes: Part II - Measurements and simulations within porous boxes

The present study will give rise to better understanding of the airflow behaviour in a ceiling-slot ventilated enclosure partially filled with slotted porous boxes under isothermal conditions. Boxes were filled randomly with spheres of the same diameter. Laser Doppler velocimetry (LDV) measurements and computational fluid dynamics (CFD) predictions were carried out to characterize air velocity inside packed vented boxes. An original approach was also developed to evaluate the internal macroscopic velocities within the boxes by means of thermal sphere-shaped probes. LDV measurements and CFD predictions related to the main turbulent flow developed by the jet above the boxes were presented in the part I.Special attention was paid to the strong aerodynamic interactions observed on the top faces of the slotted boxes, between the external main flow and the return flow which predominate inside the boxes. Numerical and experimental data make it possible to evaluate the air ventilation levels and their heterogeneity for the different boxes. The RSM turbulence model gives reasonable agreement with experiments.     

Airflow patterns inside slotted obstacles in a ventilated enclosure

Laser Doppler measurements and CFD predictions were carried out to characterize air flow pattern, mean velocities and turbulence structure inside slotted boxes stacked within a slot ventilated enclosure. Special attention was paid to the strong aerodynamic interactions observed on the top faces of the slotted boxes, between the external main flow and the return flow which predominate inside the boxes. Numerical and experimental data make it possible to evaluate the air ventilation levels and their heterogeneity for the different boxes. The two turbulence models used, RSM and k-ε, give quite similar results for the velocity levels in the load and show qualitative agreement with experiments.     

Application of ADIFOR for air pollution model sensitivity studies

Typical computational methods of sensitivity analysis are discussed. Automatic differentiation addresses the need for computing derivatives of large codes accurately, regardless of the complexity of the model. Automatic differentiation in FORTRAN (ADIFOR) is a source transformation technique that accepts FORTRAN coded program for the computation of a function and generates portable FORTRAN code for the computation of the derivatives of that function. ADIFOR is introduced and applied to a comprehensive atmospheric chemistry/transport/radiative-transfer model to study the sensitivity of photochemical ozone production with respect to aerosol. The modeling results indicate that aerosol interaction with ozone may be as important as NO_x and non-methane hydrocarbon (NMHC) emissions in determining ozone production. The presence of scattering and/or absorbing aerosols in the atmosphere can cause significant differences in calculated ozone levels. Normalized sensitivity coefficients show that ozone and other photochemical oxidants are most sensitive to the aerosol single scattering albedo, which determines the scattering efficiency of the aerosol. ADIFOR is demonstrated to be an effective tool for sensitivity analysis in air pollution modeling.     

Vectorized simulation of groundwater flow and streamline transport

We describe a modeling suite of Matlab functions for simulating nonpoint source (NPS) pollution in groundwater aquifers. The NPS model simulates groundwater flow and contaminant transport from a large array (order of 10² – 10⁷) of spatially distributed sources with time-varying pollution strength to a similarly large array of spatially distributed production wells (receptors) using the streamline transport approach. The code solves three equations: steady-state groundwater flow, particle tracking, and transient advection dispersion contaminant transport. The code performs convolution integration in its predictive step. Written in highly efficient vectorized form to avoid time consuming “for/while” loops, the code is also suitable for other groundwater flow and transport problems. The code is verified against analytical solutions and finite element software Comsol. An application illustrates 200 years of transient nitrate transport in the 2000 km² Tule River aquifer sub-basin of the Central Valley, California, with 9000 individual nitrate sources and 1920 wells.     

High-order discontinuous Galerkin computation of axisymmetric transonic flows in safety relief valves

This paper presents a discontinuous Galerkin (DG) discretization of the compressible RANS and k–ω turbulence model equations for two-dimensional axisymmetric flows. The developed code has been applied to investigate the transonic flow in safety relief valves.This new DG implementation has evolved from the DG method presented in [1]. An “exact” Riemann solver is used to compute the interface numerical inviscid flux while the viscous flux discterization relies on the BRMPS scheme [2] and [3]. Control of oscillations of high-order solutions around shocks is obtained by means of a shock-capturing technique developed and assessed within the EU ADIGMA project [4].The code has been applied to compute the flow in a spring loaded safety valve at several back pressures and different disk lifts. The predicted device flow capacity and the pressure inside its bonnet have been checked against experimental data. The CFD simulations allow to clarify the complex flow patterns occurring and to explain the measured trends.     

Computational analysis of wind interactions for comparing different buildings sites in terms of natural ventilation

Nowadays building designers have to face up to new strategies to achieve the best sustainable building designs. Well planned natural ventilation strategies in building design may contribute to a significant reduction on building’s energy consumption. Natural ventilation strategies are conditioned to the particular location of each building. To improve natural ventilation performance of a building, the analysis of the influence of the location and the surrounding buildings on wind flow paths around the design building is a must. New computational tools such as Computational Fluid Dynamics (CFD) are particularly suited for modelling outdoor wind conditions and the influence on indoor air conditions prior to building construction. Hence, reliable methodologies are necessary to support building design decisions related to naturally ventilated buildings prior to construction.This paper presents a case study for the selection of the best future building location attending to natural ventilation behaviour inside the building, conditioned by different evolving environment. A validated CFD model is used to represent outdoor and indoor spaces. The methodology explains how to qualitatively and quantitatively analyze wind paths around and through a building to quantify the natural ventilation performance. The best location, from two real possible solutions, is then selected.     

考虑不同服装热阻的层式通风供暖运行优化研究

为满足室内人员在不同着装时的热舒适需求,以某层式通风供暖办公室为研究对象,在考虑不同服装热阻的前提下,通过改进TOPSIS法优化了送风参数(即送风角度、送风速度和送风温度)；在优化过程中,将PMV/PPD、垂直温差、空气龄和能量利用效率作为通风性能评价指标,以送风温度、送风速度、送风角度和服装热阻为设计变量,通过CFD模拟分析,采用中心复合设计响应面法得到通风性能与设计变量间的函数关系,然后用于改进TOPSIS法评估所有可能方案的通风性能以达到提高计算效率的目的；结果表明：基于改进TOPSIS法优化层式通风供暖送风参数可以显著改善通风性能,PPD、空气龄和垂直温差分别平均降低了37.08%、22.46%和48.17%,能量利用效率平均提高了20.42%。     

Seasonal variation of columnar aerosol optical properties over Athens, Greece, based on MODIS data

A long-term (2000–2005) data set of aerosol optical properties obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) is analyzed focusing on the Greater Athens Area in the Eastern Mediterranean region. The MODIS aerosol optical depth standard product (AOD at 550 nm) and its respective ratio attributed to fine-mode particles (FM) are employed to evaluate the inter-annual and seasonal variability of the aerosol properties over Athens. Based on AOD₅₅₀ and FM values three specific aerosol types are discriminated corresponding to different aerosol load and optical properties. The aerosol types considered correspond to urban/industrial aerosols, coarse-mode particles and clean maritime conditions. This study focuses on the seasonal and year-to-year fluctuation of the number of occurrences as well as the AOD₅₅₀ and FM values of each aerosol type. The coarse-mode particles are observed mainly in the summer, while spring is the most favorable season for the occurrence of urban/industrial aerosols. On the other hand, clean maritime conditions occur mainly in the winter. The AOD₅₅₀ values for the coarse-mode particles are higher in spring, while the urban/industrial and clean maritime aerosols exhibit slightly higher values in the summer. The seasonal distribution of the aerosol properties is related to anthropogenic and dust emissions in the spring/summer period, but is modified by atmospheric dispersion and precipitation in late autumn/winter. The main conclusion of the study is that the coarse-mode particles exhibit much stronger inter-annual and seasonal variability compared to the urban/industrial aerosols. Finally, three cases corresponding to each aerosol type are analyzed with the aid of synoptic weather maps, air mass trajectories and MODIS data.     

Distribution and transport of aerosols in the south Indian region and surroundings

The weather/climate of south India is entirely different from that of north India. So the aerosol loading and variability in the regions also show considerable difference. The present study investigates the aerosol distribution over the south Indian region. The transport of aerosols over the region is studied in detail and climate features of the region are investigated to understand the aerosol distribution of the region. In situ observations available in two stations in the west coast and equatorial Indian region and satellite data available for the region are used for the analysis. Aerosol concentration is less in south India compared to that in north India with AOD (aerosol optical depth) values above 0.5 in north India and below 0.4 in south India. The studies reveal the seasonal variability in aerosol loading with high aerosol concentration during summer (>0.4) and less loading during winter season (<0.3) in south India. In situ aerosol observations taken for the first time in Cochin station implies variability in coarse mode aerosols with AOD near 0.3 in summer and near 0.2 in winter. The seas surrounding south India have significant impact in the aerosol loading as they are the sources of marine aerosols such as sea-salt, sulphates etc. Exchange of aerosols takes place from the marine environment and land regions over south India and surroundings. The coastal region of south India experiences high aerosol loading during June to August period. Different climate pattern of the region and the presence of adjoining seas lead to a mixed aerosol content, which includes aerosols of marine and continental origin. In north India, anthropogenic and natural aerosols such as dust, black carbon etc. are dominant in the atmosphere.     

Aerosol optical and microphysical properties observed by the lidar technique from a forest-fire smoke event over Madrid

On 27 August 2012, a wildfire occurred in the western zone of the Madrid region. Consequently, a significant release of smoke and aerosols was injected into the free troposphere and advected by the synoptic circulation in trajectories that passed over the capital. This event was detected by the Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT; Research Centre for Energy, Environment and Technology), Madrid lidar station at about 5 km height. While the main aerosol plume did not pass over the lidar station, the eastern portion of the dispersed emissions did. No aerosol layers were detected by lidar in the free-troposphere for the next few days. Since few observations of fresh biomass burning aerosol have been carried out by lidar so far, this study contributes to previous studies on biomass burning aerosols, in particular regarding the first stages of the smoke transport.

This article studies the optical and microphysical properties of the smoke aerosols retrieved by the lidar technique along with the recently developed Lidar/Radiometer Inversion Code (LiRIC), which combines both lidar and sun–sky photometer data. The sun–sky photometer data are provided by the Agencia Estatal de Meteorología (AEMET; Spanish Meteorological Agency) station close to the CIEMAT site. We suggest that the aerosol properties retrieved might be linked to the water uptake phenomenon in view of the fact that simultaneous water vapour lidar measurements exhibited a close relationship with backscatter coefficient profiles. This article is concerned not only with showing the capability of combining different remote-sensing techniques and the LiRIC code to provide aerosol vertical distribution for fine and coarse modes, but also with providing signs about the plausible interaction between aerosols and humidity that leads fresh biomass burning aerosols to act as cloud condensation nuclei. This key role, known as the indirect effect, remains the major source of uncertainty when the global radiation budget is assessed.     

Role of sea-surface wind and transport on enhanced aerosol optical depth observed over the Arabian Sea

The objective of this study is to understand the reasons for the enhancement in aerosol optical depth (AOD) over the Arabian Sea observed during June, July and August. During these months, high values of AOD are found over the sea beyond 10° N and adjacent regions. The Arabian Sea is bounded by the lands of Asia and Africa on its three sides. So the region is influenced by transported aerosols from the surroundings as well as aerosols of local origin (marine aerosols). During the summer monsoon season in India, strong surface winds with velocities around 15 m s^?1 are experienced over most parts of the Arabian Sea. These winds are capable of increasing sea spray activity, thereby enhancing the production of marine aerosols. The strong winds increase the contribution of marine aerosols over the region to about 60% of the total aerosol content. The main components of marine aerosols include sea salt and sulphate particles. The remaining part of the aerosol particles comes from the western and northern land masses around the sea, of which the main component is transported dust particles. This transport is observed at higher altitudes starting from 600 m. At low levels, the transport occurs mainly from the Indian Ocean and the Arabian Sea itself, indicating the predominance of marine aerosols at these levels. The major portion of the total aerosol loading was contributed by coarse-mode particles during the period of study. But in the winter season, the concentration of coarse-mode aerosols is found to be less. From the analysis, it is concluded that the increase in marine aerosols and dust particles transported from nearby deserts results in an increase in aerosol content over the Arabian Sea during June, July and August.     

Three dimensional numerical simulations of long-span bridge aerodynamics, using block-iterative coupling and DES

The design of long-span bridges often depends on wind tunnel testing of sectional or full aeroelastic models. Some progress has been made to find a computational alternative to replace these physical tests. In this paper, an innovative computational fluid dynamics (CFD) method is presented, where the fluid-structure interaction (FSI) is solved through a self-developed code combined with an ANSYS-CFX solver. Then an improved CFD method based on block-iterative coupling is also proposed. This method can be readily used for two dimensional (2D) and three dimensional (3D) structure modelling. Detached-Eddy simulation for 3D viscous turbulent incompressible flow is applied to the 3D numerical analysis of bridge deck sections. Firstly, 2D numerical simulations of a thin airfoil demonstrate the accuracy of the present CFD method. Secondly, numerical simulations of a U-shape beam with both 2D and 3D modelling are conducted. The comparisons of aerodynamic force coefficients thus obtained with wind tunnel test results well meet the prediction that 3D CFD simulations are more accurate than 2D CFD simulations. Thirdly, 2D and 3D CFD simulations are performed for two generic bridge deck sections to produce their aerodynamic force coefficients and flutter derivatives. The computed values agree well with the available computational and wind tunnel test results. Once again, this demonstrates the accuracy of the proposed 3D CFD simulations. Finally, the 3D based wake flow vision is captured, which shows another advantage of 3D CFD simulations. All the simulation results demonstrate that the proposed 3D CFD method has good accuracy and significant benefits for aerodynamic analysis and computational FSI studies of long-span bridges and other slender structures.     

辐射传输LOWTRAN程序气溶胶模式分析评述(一):发展过程

详细介绍了LOWTRAN计算程序中的大气气溶胶模式结构，综述了气溶胶诸物理量的引入历史及其相应模式的逐步发展过程，分析了LOWTRAN在处理大气气溶胶方面的成功经验，这对今后建立符合中国地域和气候特征的大气气溶胶模式以及遥感图像的大气订正有参考价值。     

并列双U型通风方式下采空区瓦斯运移规律研究

为了更好地分析和掌握并列双U型通风方式下采空区瓦斯分布和运移规律,针对某矿综采工作面并列双U型通风系统的特点,建立了CFD模型,数值模拟了并列双U型通风方式下采空区瓦斯运移规律;分析结果表明,在综采工作面采用并列双U型通风方式,由于位于采空区上隅角附近联络巷的作用使采空区的大部分瓦斯可以随漏风进入辅助回风巷连续排出,使采空区和流经上隅角的瓦斯减少,有效解决了综采工作面瓦斯超限的问题。     

Modeling temperature and species fluctuations in turbulent,reacting flow

Assumed Gaussian and β probability density functions (PDFs) for temperature are used with series expansions of the reaction-rate coefficients to compute the mean reaction-rate coefficients in a turbulent, reacting flow. The series-expansion/assumed PDF approach does not require any numerical integration, which substantially reduces computational cost with little loss of accuracy. An assumed multivariate β PDF for species is investigated for use in modeling the interaction of species fluctuations and chemical combustion. The multivariate β PDF is initially evaluated through a parametric study. Results of the parametric study indicate that species fluctuations can increase or decrease the magnitude of the species production term, depending on the type of reaction. The models are then tested on a two-dimensional high-speed turbulent reacting hydrogen-air mixing layer. For the conditions tested the numerical simulations indicate that the net effect of species fluctuations is to reduce the mean species production rate.     

On the effect of wind direction and urban surroundings on natural ventilation of a large semi-enclosed stadium

Natural ventilation of buildings refers to the replacement of indoor air with outdoor air due to pressure differences caused by wind and/or buoyancy. It is often expressed in terms of the air change rate per hour (ACH). The pressure differences created by the wind depend - among others - on the wind speed, the wind direction, the configuration of surrounding buildings and the surrounding topography. Computational Fluid Dynamics (CFD) has been used extensively in natural ventilation research. However, most CFD studies were performed for only a limited number of wind directions and/or without considering the urban surroundings. This paper presents isothermal CFD simulations of coupled urban wind flow and indoor natural ventilation to assess the influence of wind direction and urban surroundings on the ACH of a large semi-enclosed stadium. Simulations are performed for eight wind directions and for a computational model with and without the surrounding buildings. CFD solution verification is conducted by performing a grid-sensitivity analysis. CFD validation is performed with on-site wind velocity measurements. The simulated differences in ACH between wind directions can go up to 75% (without surrounding buildings) and 152% (with surrounding buildings). Furthermore, comparing the simulations with and without surrounding buildings showed that neglecting the surroundings can lead to overestimations of the ACH with up to 96%.     

Effects of implementing satellite observed aerosols into a mesoscale atmosphere model

This study investigated the performance of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU-NCAR) Mesoscale Model (MM5) in calculating the aerosol forcing on cloud cover, incoming surface solar radiation, and near-surface air temperature via the implementation of aerosol optical depth in the shortwave radiation parameterization. MM5 simulations with and without aerosol data are performed in the periods of 6–7 August 2003 and 19–21 September 2003 during which strong aerosol forcing was observed with Moderate Resolution Imaging Spectroradiometer (MODIS) data in the mid-Atlantic region. Both periods clearly showed that aerosols had a direct negative effect on surface solar radiation through aerosol scattering. For example, every 0.1 change in MODIS aerosol optical thickness (AOT) results in 44 and 59?W?m^?2 decreases in surface solar radiation for the first and second periods, respectively. A magnitude of 0.1 increment in MODIS AOT reduces air temperature 0.36 and 0.56?K for the first and second periods, respectively. Comparisons with satellite-derived surface solar radiation retrievals showed that aerosol implementation in MM5 consistently showed better incoming surface solar radiation than that of the non-aerosol case. This helps to reduce uncertainties related to the radiation–cloud–aerosol interaction in numerical weather modelling systems.     

Simulation of remote sensing of sea surface temperature from space: influences of cirrus clouds and stratospheric aerosols on sea surface temperatures derived from the VISSR Atmospheric Sounder

This simulation study demonstrates that cirrus clouds and volcanic aerosols with atmospheric gases would greatly affect the transmission functions and brightness temperatures of infrared window channels in the VISSR Atmospheric Sounder (VAS), and VAS-derived sea surface temperature (SST) determinations. The ;clear air (CLR) retrieval equations should not be used in the presence of cirrus and high stratospheric aerosol loadings. An alternative five-window channel algorithm could be found that would work in arbitrary clear, cirrus or aerosol conditions, but the retrieval accuracy would decrease in comparison with the multi-channel SST (MCSST) algorithms for simply cirrus clouds, or aerosols only. In MCSST algorithms, channel 12 (3–94μ) is most important for CLR, or tenuous cirrus with any kind of aerosols, or moderate cirrus with weak aerosols, whereas for moderate cirrus combined with the strong aerosol, or dense cirrus with any kind of aerosols, channel 5 (13‐34μ) or channel 8 (11–22μ) becomes the most important. In addition, the effects of variations of water vapour profile, aerosol concentration, and sea surface reflection (SSR) on SST retrievals need to be considered.