Neighbourhood-Scale Flow Regimes and Pollution Transport in Cities

Bannister, Edward J.; Cai, Xiaoming; Zhong, Jian; MacKenzie, A. Rob

doi:10.1007/s10546-020-00593-y

Cited by 12 publications

(4 citation statements)

References 98 publications

(132 reference statements)

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“…The data can be used to model and assess local or city-scale system interventions (an urban digital twin per se), ultimately providing evidence to shape local policy. For example, the implementation of the Birmingham Clean Air Zone in June 2021 (BCC, 2021b) demanded extensive 'before and after' monitoring coupled with modelling which required a range of disparate datasets including meteorology and traffic data (Bannister et al, 2020).…”

Section: Ukcric Birmingham Urban Observatorymentioning

confidence: 99%

Delivering sustainable, resilient and liveable cities via transformed governance

Rogers,

Grayson,

Sadler

et al. 2023

Front. Sustain. Cities

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In the context of steadily declining Natural Capital and universal recognition of the imperative to reverse this trend before we get to the point that nature is not able to restore itself, cities have a crucial role to play. The UK Government commissioned a comprehensive study into the value of biodiversity, and by extension nature, reinforcing “why we should change our ways”—yet what is missing is the “how?”. This paper uniquely describes both the “how?” and a conclusive demonstration of the remarkable benefits of implementing it in a city. Critical to this process, it took a UK Parliamentary Inquiry to reveal that nature has become invisible within the economy, yet the ecological ecosystem services nature provides have enormous benefits to both people and the economy. Therefore integration—or seamless weaving—of urban greenspace and nature into people's lives and the places where they live, work, and spend their leisure time is vital. Moreover, what nature does not provide must be provided by engineered systems, and these have an economic cost; put another way, there are enormous cost savings to be made by taking advantage of what nature provides. In addressing these issues, this paper is the definitive paper from a 20-year portfolio of research on how to bring about transformative change in the complex system-of-systems that make up our cities, providing as it does the crucial in-depth research into the many diverse strands of governance—the last link in a chain of the creation, testing and proof of efficacy of methodologies underpinning a theory and practice of change for infrastructure and cities. The impact of this portfolio of research on Birmingham is two-fold: the Star Framework that placed natural environment considerations at the heart of all decision-making in the city, and the successful bid for the largest of the UK Future Parks Accelerator awards. While both are transformative in their different ways, yet mutually supportive, the latter enabled the design of a suite of system interventions from which the value of Birmingham's greenspaces is estimated to rise from £11.0 billion to £14.4 billion—a remarkable return on investment from the research's conceptualization of Birmingham's urban greenspace as a “business” (with its associated business models). In achieving this, the necessary enablers of thinking and practicing systemically, seamlessly working across disciplinary boundaries, an unusually strong focus on both the aspirations of all stakeholders and the context in question to define “the problem,” and the testing of proposed system intervention(s) both now and in the future have been iteratively combined. However, it is the critical enabling steps of identifying the complete range of value-generating opportunities that the interventions offer, formulating them into alternative business models to underpin the case for change and ensuring that they are synergistic with all the dimensions of governance that yielded the profound outcomes sought.

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Section: Ukcric Birmingham Urban Observatorymentioning

confidence: 99%

Delivering sustainable, resilient and liveable cities via transformed governance

Rogers,

Grayson,

Sadler

et al. 2023

Front. Sustain. Cities

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“…In this section we focus on the numerical modeling of species that can be approximated as being passive and massless at the ecosystem scale. These include CO 2 , as well as other gases and UFPs whose lifetimes are longer than the longest air parcel residence times (Bannister et al, 2021;Janhäll, 2015;Kanani-Sühring & Raasch, 2015;Petroff et al, 2008). Other scalars, such as litter, animal detritus, and certain pollens, are much larger and must be treated differently (Section 6 below).…”

Section: Scalar Quantities In Realistic Landscapesmentioning

confidence: 99%

“…The relative size of sparse and dense patches of heterogeneity in forests may also affect scalar concentrations. For example, for flow through idealized porous media, maximum scalar concentrations occur in sparse patches where the patch size is less than the adjustment distance x A , but in the dense patches where the patch size is greater than x A (Bannister et al, 2021). The patterns in scalar transport are likely to be ecologically significant.…”

Section: Scalar Transport At the Upstream Edges Of Forestsmentioning

confidence: 99%

Realistic Forests and the Modeling of Forest‐Atmosphere Exchange

Bannister

MacKenzie

Cai

2022

Reviews of Geophysics

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Forests cover nearly a third of the Earth's land area and exchange mass, momentum, and energy with the atmosphere. Most studies of these exchanges, particularly using numerical models, consider forests whose structure has been heavily simplified. In many landscapes, these simplifications are unrealistic. Inhomogeneous landscapes and unsteady weather conditions generate fluid dynamical features that cause observations to be inaccurately interpreted, biased, or over‐generalized. In Part I, we discuss experimental, theoretical, and numerical progress in the understanding of turbulent exchange over realistic forests. Scalar transport does not necessarily follow the flow in realistic settings, meaning scalar quantities are rarely at equilibrium around patchy forests, and significant scalar fluxes may form in the lee of forested hills. Gaps and patchiness generate significant spatial fluxes that current models and observations neglect. Atmospheric instability increases the distance over which fluxes adjust at forest edges. In deciduous forests, the effects of patchiness differ between seasons; counter intuitively, eddies reach further into leafy canopies (because they are rougher aerodynamically). Air parcel residence times are likely much lower in patchy forests than homogeneous ones, especially around edges. In Part II, we set out practical ways to make numerical models of forest‐atmosphere more realistic, including by accounting for reconfiguration and realistic canopy structure and beginning to include more chemical and physical processes in turbulence resolving models. Future challenges include: (a) customizing numerical models to real study sites, (b) connecting space and time scales, and (c) incorporating a greater range of weather conditions in numerical models.

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“…The leaf area index (LAI: the total projected leaf area per unit ground area) and leaf area density (LAD: the distribution of leaf area with height) are important measures of the density and morphology of canopy structure (Bréda, 2003), along with their whole-plant equivalents plant area index (PAI) and plant area density (PAD). Leaf and plant area indices affect the permeability of air through the canopy (Bannister et al, 2021) and therefore the value of residence times. In their idealised forest canopy, GCF17 show that the values of τ increase with the forest's LAI, other than for air parcels released high in the canopy.…”

Section: Introductionmentioning

confidence: 99%

Air-parcel residence times in a mature forest: observational evidence from a free-air CO₂ enrichment experiment

Bannister

Jesson

Harper

et al. 2022

Preprint

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Abstract. In forests, air-parcel residence times – the inverse of first-order exchange rates – influence in-canopy chemistry and the exchanges of momentum, energy, and mass with the surrounding atmosphere. Accurate estimates are needed for chemical investigations of reactive trace species, such as volatile organic compounds, some of whose chemical lifetimes are in the order of average residence times. However, very few observational residence-time estimates have been reported. Little is known about even the basic statistics of real-world residence times or how they are influenced by meteorological variables such as turbulence or atmospheric stability. Here, we report opportunistic investigations of air-parcel residence times in a free-air carbon dioxide enrichment (FACE) facility in a mature, broadleaf deciduous forest with canopy height hc ≈ 25 m. Using nearly 50 million FACE observations, we find that median daytime residence times in the tree crowns range from around 70 s when the trees are in leaf to just over 34 s when they are not. Air-parcel residence times increase with increasing atmospheric stability, as does the dispersion around their central value. Residence times scale approximately with the reciprocal of the friction velocity, u*. During some calm evenings in the growing season, we observe distinctly different behaviour: pooled air being sporadically and unpredictably vented – evidenced by sustained increases in CO2 concentration – when intermittent turbulence penetrates the canopy. In these conditions, the concept of a residence time is less clearly defined. Parameterisations available in the literature underestimate turbulent exchange in the upper half of forest crowns and overestimate the frequency of long residence times. Robust parametrisations of air-parcel residence times (or, equivalently, fractions of emissions escaping the canopy) may be generated from inverse gamma distributions, with the parameters 1.4 ≤ α ≤ 1.8 and β = hc / u* estimated from widely measured flow variables. In this case, the mean value for τ becomes formally defined as 𝜏̅ = β / (α−1). For species released in the canopy during the daytime, chemical transformations are unlikely unless the reaction time scale is in the order of a few minutes or less.

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Neighbourhood-Scale Flow Regimes and Pollution Transport in Cities

Cited by 12 publications

References 98 publications

Delivering sustainable, resilient and liveable cities via transformed governance

Delivering sustainable, resilient and liveable cities via transformed governance

Realistic Forests and the Modeling of Forest‐Atmosphere Exchange

Air-parcel residence times in a mature forest: observational evidence from a free-air CO₂ enrichment experiment

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Neighbourhood-Scale Flow Regimes and Pollution Transport in Cities

Cited by 12 publications

References 98 publications

Delivering sustainable, resilient and liveable cities via transformed governance

Delivering sustainable, resilient and liveable cities via transformed governance

Realistic Forests and the Modeling of Forest‐Atmosphere Exchange

Air-parcel residence times in a mature forest: observational evidence from a free-air CO2 enrichment experiment

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Product

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Air-parcel residence times in a mature forest: observational evidence from a free-air CO₂ enrichment experiment