Urban Transportation and Air Pollution

Akula Venkatram, Nico Schulte

• Publisher: Elsevier
• Year: 2018
• ISBN:
  9780128115077
• Topic: Technology & Engineering
• Subtopic: Transportation & Navigation
• Index: Technology & Engineering

Urban Transportation and Air Pollution synthesizes state-of-the-art methods on estimating near-road concentrations of roadway emissions. The book provides the information needed to make estimates using methods based on a minimal set of model inputs that can be applied by a wide range of users in many situations. Discussions include methods to estimate traffic emission under numerous urban driving conditions, the uncertainty of emission models, and the effects of road configurations, such as near-road solid barriers. Final sections present dispersion models that link traffic emissions with near road concentrations in urban environments.

Addressing transportation-related environmental issues is extremely important as urban areas are constantly searching for ways to mitigate impacts from transportation sources. This book helps to explain dispersion models, a critical tool for estimating the impact of roadway emissions in cities.

• Compiles and synthesizes the state-of-the-science methods for estimating roadway emissions
• Demonstrates, with clear examples, how modeling methods reduce uncertainties in real-world problems
• Emphasizes how local-scale, semi-empirical, steady-state modeling can be applied using only a small set of inputs
• Offers an overview of the meteorology that governs air pollution dispersion in cities

Chapter One

Introduction

Abstract

This book summarizes some of the research conducted during the last 15 years on estimating the impact of vehicle-related emissions on near-road air quality. This book focuses on plume-based transport and dispersion models applicable to source–receptor distances of a few kilometers. The models described in this book are applicable to urban areas. Chapter 2 discusses terminology and concepts used to characterize air pollutants and meteorological processes. Chapter 3 presents fundamental concepts of micrometeorology and dispersion in the surface layer. Chapter 4 presents models that predict concentrations next to roads in urban areas. These models account for the presence of solid and vegetative barriers next to the roads and for depression of the roadway. Chapter 5 discusses the effect of buildings next to the road on concentrations of traffic emissions. Chapter 6 summarizes the models presented in this book and provides a description of methods used to estimate micrometeorological inputs required for the models.

Keywords

Turbulence; traffic-related air pollution; dispersion model; urban roadway

Contents

• Scope of the Book 1
• Models Treated in this Book 2
• Modeling Emissions for Transport Applications 4
• Organization of this Book 8
• References 10

Scope of the Book

This book summarizes some of the research conducted during the last 15 years on estimating the impact of vehicle-related emissions on near road air quality. Although the impact of roadway emissions on air quality has been studied since the 1970s, it has become prominent more recently in the light of a number of epidemiological studies reporting associations between living within a few hundred meters of high-traffic roadways and adverse health effects such as asthma and other respiratory impacts, birth and developmental effects, premature mortality, cardiovascular effects, and cancer (e.g., Harrison et al., 1999; Brauer et al., 2002; Hoek et al., 2002; Finkelstein et al., 2004).

Air quality monitoring studies conducted near major roadways indicate that these health effects are associated with elevated concentrations, compared with overall urban background levels, of motor-vehicle-emitted compounds, which include carbon monoxide (CO); nitrogen oxides (NO_x); coarse (PM_10–2.5), fine (PM_2.5), and ultrafine (PM_0.1) particle mass; particle number; black carbon, polycyclic aromatic hydrocarbons, and benzene (Kim et al., 2002; Hutchins et al., 2000; Kittelson et al., 2004).

This book describes models that describe the transport and dispersion of pollutants emitted from vehicles traveling on urban roads. It does not deal with the chemistry of pollutant formation or the factors that determine the emissions rate from vehicles. This is a subject with an extensive literature that can be readily consulted by the reader. We confine ourselves to the modeling of the processes that connect emissions to the corresponding concentrations at a receptor. We first review the types of models that are generally used to estimate concentrations as a backdrop to the models that we discuss in this book.

Models Treated in this Book

An air quality model is a mathematical description of the system that governs the fate of air pollutants emitted into the atmosphere. The air quality system consists of a large number of processes, which include transport by the mean wind, dispersion through turbulence, scavenging through dry and wet deposition, and chemistry involving the chemical species in the atmosphere. The relative importance of these processes depends on the source-receptor distance of concern. For example, at distances of a few tens of kilometers from a source, transport and dispersion are the dominant processes although this is not always true.

It is convenient to use different approaches to modeling air pollution depending on source-receptor distances. For distances of tens of kilometers from the source, a continuously emitted pollutant is treated as a plume governed by meteorology in the vicinity of the source. For larger distances, when meteorological variables show significant spatial and temporal variations, it is more convenient to model the fate of emissions using puff models or Eulerian grid models. In puff models, an emission over a short period of time is embedded in a puff or air parcel, which is then tracked as it follows the varying wind field. The puff grows in response to turbulent dispersion, and the chemical species inside the puff undergo scavenging and chemical reactions. Puff models require a great deal of bookkeeping because one needs to keep track of the large number of puffs that correspond to each hour of emission. Some of this bookkeeping can be avoided through receptor-oriented puff models. In this approach, the concentration of the species at a receptor is governed only by the puff that arrives at the time and location of interest. The final state of this puff is determined by calculating the history of puff before it arrives at the receptor. This involves tracing the path of the puff as it passes over emissions and is subject to scavenging and chemical reactions.

The Eulerian grid model solves the mass conservation equations using a grid of boxes. In essence, a mass balance is performed for each box for a short period of time. This mass balance involves inflow and outflow of material in the box through transport and dispersion, scavenging through wet and dry processes, and chemical reactions among the species in the box. The boxes within the domain of interest are interconnected through transport between the boxes. The computational requirements of a grid model are proportional to the number of grid boxes used to describe the domain; a change in grid size by a factor of 2 increases the number of boxes by a factor of 8. Therefore grid resolution has to be relatively coarse, about 1 km, to keep the computational require...