Marina K.-A. Neophytou

The rise of low-cost sensing for managing air pollution in cities.

Ever growing populations in cities are associated with a major increase in road vehicles and air pollution. The overall high levels of urban air pollution have been shown to be of a significant risk to city dwellers. However, the impacts of very high but temporally and spatially restricted pollution, and thus exposure, are still poorly understood. Conventional approaches to air quality monitoring are based on networks of static and sparse measurement stations. However, these are prohibitively expensive to capture tempo-spatial heterogeneity and identify pollution hotspots, which is required for the development of robust real-time strategies for exposure control. Current progress in developing low-cost micro-scale sensing technology is radically changing the conventional approach to allow real-time information in a capillary form. But the question remains whether there is value in the less accurate data they generate. This article illustrates the drivers behind current rises in the use of low-cost sensors for air pollution management in cities, while addressing the major challenges for their effective implementation.

DISPERSION EXPERIMENTS IN CENTRAL LONDON The 2007 Dapple Project

In the event of a release of toxic gas in the center of London, emergency services personnel would need to determine quickly the extent of the area contaminated. The transport of pollutants by turbulent flow within the complex streets and building architecture of London, United Kingdom, is not straightforward, and we might wonder whether it is at all possible to make a scientifically reasoned decision. Here, we describe recent progress from a major U.K. project, Dispersion of Air Pollution and its Penetration into the Local Environment (DAPPLE; information online at www.dapple.org.uk). In DAPPLE, we focus on the movement of airborne pollutants in cities by developing a greater understanding of atmospheric flow and dispersion within urban street networks. In particular, we carried out full-scale dispersion experiments in central London from 2003 through 2008 to address the extent of the dispersion of tracers following their release at street level. These measurements complemented previous studies because 1...

City breathability as quantified by the exchange velocity and its spatial variation in real inhomogeneous urban geometries: An example from central London urban area

The breathability capacity and its spatial variation within an inhomogeneous urban area is investigated by examining the air flow and the induced flow exchange processes inside a real neighbourhood area of central London. The variation of the exchange velocity (as an index of city breathability) is interpreted in association with the local urban geometrical parameters and hence geometrical inhomogeneity. Numerical studies addressing flow exchange processes in urban areas have addressed so far rather idealised homogeneous geometries (e.g. Hamlyn and Britter, 2005; Salizzoni et al., 2009; Buccolieri et al., 2010; Hang et al., 2009 and 2010). This work analyses the results obtained from a Computational Fluid Dynamics (CFD) simulation study using a Reynolds-Average-Navier-Stokes (RANS) solver to study the flow and induced exchange processes in the area around the Marylebone Road and Gloucester Place intersection modelled at a 1:200 scale, with the wind direction blowing in the direction of the Marylebone street axis. Flow visualisations from the numerical results confirm that the particular building shapes and street canyon geometries determine the shape and size of vortical structures that are present in the flow field and thereby the exchange processes with the flow above. By considering appropriate control volumes enclosing each building, the exchange velocities, U(E), were deduced and found to range between 0.5% and 13% of the characteristic velocity above the urban canopy U(ref), which was referenced at a height 2.5 times of the building height. The range of the exchange velocity coefficient U(E)/U(ref) is higher than that observed in idealised regular cube arrays, mainly due to the enhanced flow mixing associated with the inhomogeneity of the urban geometry and particularly with tall buildings. This work may provide useful insight to urban designers and planners interested in examining the variation of city breathability as a local dynamic morphological parameter with the local building packing density.

An experimental study of the flow through and over two dimensional rectangular roughness elements: Deductions for urban boundary layer parameterizations and exchange processes

This paper investigates the flow through and over two-dimensional rectangular roughness elements, arranged in a building-street canyon geometry through a series of experiments. Geometries of different packing densities of the roughness elements (λp) were examined and the packing density values ranged from λp = 0.30 to 0.67. The purpose of the work is: (i) to investigate the flow physics observed both at the boundary layer scale as well as at the scale within the roughness elements for a range of packing densities, (ii) to deduce parameterizations of the adjusted rough boundary layer and their variation with a change in the packing density, and (iii) given a particular interest in and application to the urban atmosphere, a final aim at the roughness-element scale is to deduce the variation of the breathability with the packing density variation. Particle image velocimetery measurements of the velocity flow field as well as the turbulent kinetic energy and the Reynolds Stress (within and up to well-above the street canyons) were conducted. The results reveal qualitative flow features as well as features of the adjusted boundary layer structure—in particular the roughness and inertial sublayers, which can be associated with the surface roughness length, zero-plane displacement thickness, and the friction velocity. The lowest friction velocities are exhibited in the geometries with the highest- and lowest packing densities while the maximum friction velocities are observed in the medium-packed geometries. The exchange processes and breathability at the level of the roughness elements top were characterized and quantified by a mean exchange velocity. The results show that unlike friction velocity, the normalized exchange velocity (over the mean bulk velocity) for the most dense and sparse geometries differ by more than 80%, with the denser-packed geometries exhibiting lower exchange velocities; this is shown to be related with the thickness of the developed roughness sublayer.

A Scale-Adaptive Approach for Spatially-Varying Urban Morphology Characterization in Boundary Layer Parametrization Using Multi-Resolution Analysis

Urban morphology characterization is crucial for the parametrization of boundary-layer development over urban areas. One complexity in such a characterization is the three-dimensional variation of the urban canopies and textures, which are customarily reduced to and represented by one-dimensional varying parametrization such as the aerodynamic roughness length

Classification of Buildings in Cyprus Based on Their Energy Performance

z_{0}

Buoyancy-generated turbulent flows in semi-enclosed regions: a computational fluid dynamics study

z0 and zero-plane displacement