Preface

Chapter 8 **Aerosol–Cloud Interaction: A Case Study 169**

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**VI** Contents

Sandeep R. Varpe, Gajanan R. Aher, Amol R. Kolhe and Sanjay D.

An aerosol is a type of two-phase mixture containing fine (nano- or micro-scale) solid parti‐ cles or liquid droplets in the air. Aerosols can be natural or artificial. Typical example of natural aerosols is fog, and examples of artificial aerosols include dust, particulate air pollu‐ tants and smoke. Aerosols are often produced through a complex interaction of sunlight; volatile organic compounds from trees, plants and cars or industrial emissions; and other airborne chemicals.

Aerosol particles and droplets have a significant impact on technological processes and hu‐ man activities. The role of particles and droplets in environmental and industrial applica‐ tions is twofold. On the one hand, particles and droplets are successfully used in engineering solutions. On the other hand, particles and droplets may pose potential hazard. In many cases, aerosols are at the core of human health, environmental and technological problems (climate change and air quality). However, aerosols can be successfully used in industry and technology (new materials, fire suppression and fuel delivery). Processes that control transport and dynamics of aerosol particles and droplets remain unresolved and in‐ troduce significant uncertainties into modelling and simulation.

The current scientific status of aerosol modelling and simulation and measurements and some advances in computational techniques, particle measurement technologies and practi‐ cal applications of aerosols are reviewed and considered in this book. This book also in‐ cludes a number of case studies focused on analysis of optical thickness and air quality in various regions.

The book contains eight chapters written by specialists from various countries who are working in various fields related to predictions of aerosol properties and their impact on human health or use of aerosols in industry.

#### **Operator Splitting Monte Carlo Method for Aerosol Dynamics**

Different methods are used in practice to solve the population balance equation describing aerosol dynamics, in particular direct discretization, method of moments and stochastic method. Being the most flexible among other methods, the stochastic method is time-con‐ suming and expensive from computational point of view. An operator splitting Monte Carlo (OSMC) method was developed to improve the numerical efficiency while preserving the flexibility of the stochastic method. Nucleation and surface growth are handled with deter‐ ministic means, while coagulation is simulated with a stochastic method (Marcus-Lushnikov stochastic process). The operator splitting errors of various schemes are analysed, and some numerical examples are provided.

#### **Methods of Moments for Resolving Aerosol Dynamics**

The solution of the population balance equation describing the formation of nano- and mi‐ cro-scale aerosol particles and their subsequent growth in quiescent or evolving flows has received significant attention from chemical engineers and atmospheric environment com‐ munity for the past years. Development of the method of moments to solve the population balance equation is presented. Three main methods of moments, including the Taylor-series expansion method, log-normal method and quadrature method, are discussed and ana‐ lysed.

#### **Computational Fluid-Particle Dynamics Modelling for Unconventional Inhaled Aerosols in Human Respiratory Systems**

Nano- and micro-scale aerosol particles which are mostly non-spherical and hygroscopic are used in medicine and pharmaceutical industry. Fundamentals and future trends of compu‐ tational fluid-particle dynamics models for lung aerosol dynamics are reviewed and dis‐ cussed with emphasis on physics of unconventional inhaled aerosols. Reconstruction of the human respiratory system, numerical model formulation and mesh generation are descri‐ bed. The case studies for fibre and droplet transport and deposition in the lung are also pro‐ vided. The study contributes to development of multi-scale numerical model allowing to simulate complex airflow-vapour-particle-structure dynamics of the entire human respirato‐ ry system in detail.

#### **Lidar Mapping of Near-Surface Aerosol Fields**

Aerosol pollutions in the low troposphere have a significant impact on human health. Nearsurface atmospheric measurements over urban or industrial areas and monitoring of air quality become important problems. The experimental results on lidar mapping of aerosol fields over the Sofia city (Bulgaria) obtained during seven-month experimental campaign in 2015 are presented. The measurements are conducted by scanning observation zones in hor‐ izontal and vertical directions. Two-dimensional colour-coded sector maps of the near-sur‐ face aerosol density are obtained using the aerosol backscattering profiles retrieved at different azimuth or elevation angles. The analysis of the lidar maps shows a good correla‐ tion between the aerosol density distribution and the locations of important sources of aero‐ sol pollutions (city streets with intensive traffic, industrial facilities and densely populated residential districts). The results reported demonstrate that aerosol lidar mapping could be regarded as an effective approach for accurate and reliable determination of the density, spatial distribution and temporal dynamics of close-to-ground aerosols, covering broad ur‐ ban areas.

#### **Aerosols Monitored by Satellite Remote Sensing**

Aerosol particles suspended in atmosphere affect air quality and climate change. Global dis‐ tribution of aerosol particles is monitored by satellite remote sensing. The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite provides global, vertically resolved measurements of aerosol distribution and aerosol extinction coefficients. This allows to perform height-resolved discrimination of aerosol into several types provid‐ ing a new insight into the role that atmospheric aerosols play in regulating the Earth's weather, climate and air quality.

#### **The Image-Based Integrated Method for Determining and Mapping Aerosol Optical Thickness**

An image-based integrated method for determining and mapping aerosol optical thickness is developed. The methodology proposed uses the radiative transfer equation and non-var‐ iant targets with the revised darkest pixel method to improve the accuracy of predictions of optical thickness in urban areas. The method developed is applied to Landsat TM/ETM+ sat‐ ellite images of Limassol (Cyprus) over a period of time. An accuracy assessment of the method shows a strong correlation between the values from the sun photometers and the values derived from the image-based integrated method.

#### **Spatial Distribution of Aerosol Optical Thickness Retrieved from SeaWiFS Images by a Neural Network Inversion over the West African Coast**

The desert aerosol plumes characterized by high optical thicknesses often crossing West Af‐ rican coast affect accuracy of optical thickness predictions. Aerosol optical thickness predic‐ tions from December 1997 to November 2009 by using neural networks inversion make possible a better understanding of climate change in a specific region.

#### **Aerosol-Cloud Interaction: A Case Study**

received significant attention from chemical engineers and atmospheric environment com‐ munity for the past years. Development of the method of moments to solve the population balance equation is presented. Three main methods of moments, including the Taylor-series expansion method, log-normal method and quadrature method, are discussed and ana‐

**Computational Fluid-Particle Dynamics Modelling for Unconventional Inhaled Aerosols**

Nano- and micro-scale aerosol particles which are mostly non-spherical and hygroscopic are used in medicine and pharmaceutical industry. Fundamentals and future trends of compu‐ tational fluid-particle dynamics models for lung aerosol dynamics are reviewed and dis‐ cussed with emphasis on physics of unconventional inhaled aerosols. Reconstruction of the human respiratory system, numerical model formulation and mesh generation are descri‐ bed. The case studies for fibre and droplet transport and deposition in the lung are also pro‐ vided. The study contributes to development of multi-scale numerical model allowing to simulate complex airflow-vapour-particle-structure dynamics of the entire human respirato‐

Aerosol pollutions in the low troposphere have a significant impact on human health. Nearsurface atmospheric measurements over urban or industrial areas and monitoring of air quality become important problems. The experimental results on lidar mapping of aerosol fields over the Sofia city (Bulgaria) obtained during seven-month experimental campaign in 2015 are presented. The measurements are conducted by scanning observation zones in hor‐ izontal and vertical directions. Two-dimensional colour-coded sector maps of the near-sur‐ face aerosol density are obtained using the aerosol backscattering profiles retrieved at different azimuth or elevation angles. The analysis of the lidar maps shows a good correla‐ tion between the aerosol density distribution and the locations of important sources of aero‐ sol pollutions (city streets with intensive traffic, industrial facilities and densely populated residential districts). The results reported demonstrate that aerosol lidar mapping could be regarded as an effective approach for accurate and reliable determination of the density, spatial distribution and temporal dynamics of close-to-ground aerosols, covering broad ur‐

Aerosol particles suspended in atmosphere affect air quality and climate change. Global dis‐ tribution of aerosol particles is monitored by satellite remote sensing. The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite provides global, vertically resolved measurements of aerosol distribution and aerosol extinction coefficients. This allows to perform height-resolved discrimination of aerosol into several types provid‐ ing a new insight into the role that atmospheric aerosols play in regulating the Earth's

**The Image-Based Integrated Method for Determining and Mapping Aerosol Optical**

An image-based integrated method for determining and mapping aerosol optical thickness is developed. The methodology proposed uses the radiative transfer equation and non-var‐ iant targets with the revised darkest pixel method to improve the accuracy of predictions of

lysed.

VIII Preface

**in Human Respiratory Systems**

**Lidar Mapping of Near-Surface Aerosol Fields**

**Aerosols Monitored by Satellite Remote Sensing**

weather, climate and air quality.

ry system in detail.

ban areas.

**Thickness**

Aerosol and cloud interactions are critical in understanding the climate change since clouds play an important role in controlling incoming and outgoing radiation. Extensive studies have been performed for the past years highlighting various mechanisms of cloud proper‐ ties through the interaction of atmospheric aerosol particles with cloud parameters. The study deals with the spatial and temporal variations of the MODIS retrieved aerosol and cloud products at the nine selected stations over Western Himalaya and Deccan Plateau re‐ gions. Western Himalaya is desert dust–dominated region, while Deccan Plateau is domi‐ nated by fossil fuel and biomass burning. The data obtained allow to investigate aerosolcloud interaction and to quantify the aerosol indirect effect over these regions.

This book covers many aspects of aerosol science representing the latest research of various groups of internationally recognized experts. This book is intended for engineers and tech‐ nical workers whose work is related to predictions of aerosol properties. It will be of interest to academics working in environmental engineering and to industrial practitioners in com‐ panies concerned with design and optimisation of systems with solid or liquid particles. The works presented in the book are easily extendible to be relevant in other areas in which aer‐ osols play an important role.

The open exchange of scientific data, results and ideas will hopefully lead to improved pre‐ dictions of aerosol impact on human activities and industrial processes. This book presents necessary data and helpful suggestions to advance understanding the formation, atmos‐ pheric fate and transport, health effects and climate change interactions of aerosols.

#### **Dr. Konstantin Volkov**

MEng, MSc, PhD, DSc, CEng, MIMechE, MInstP Department of Mechanical and Automotive Engineering School of Mechanical and Aerospace Engineering Faculty of Science, Engineering and Computing Kingston University London, United Kingdom

#### **Operator Splitting Monte Carlo Method for Aerosol Dynamics Operator Splitting Monte Carlo Method for Aerosol Dynamics**

Kun Zhou and Tat Leung Chan Kun Zhou and Tat Leung Chan

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/65140

#### **Abstract**

Aerosol dynamics are described by the population balance equation (PBE). In principle, three typical methods (i.e., direct discretization, method of moments, and stochastic method) have been widely used to solve the PBE. Stochastic method is the most flexible among the three methods. However, stochastic method is computationally expensive. Recently, an operator splitting Monte Carlo (OSMC) method has been developed so as to improve the numerical efficiency while preserving the flexibility of the stochastic method. Within the OSMC, nucleation and surface growth are handled with determin‐ istic means, while coagulation is simulated with a stochastic method (the Marcus‐ Lushnikov stochastic process). The stochastic and deterministic treatments of various aerosol dynamic processes are synthesized under the framework of operator splitting. Here, the operator splitting errors of various schemes are analyzed rigorously, combined with concrete numerical examples. The analyses not only provide sound theoretical bases for selecting the most efficient operator splitting scheme for the usage of the OSMC, but also shed lights on how to adopt operator splitting in other PBE solving methods, i.e., direct discretization, method of moments, etc.

**Keywords:** Monte Carlo simulation, aerosol dynamics, operator splitting
