Characterising mixing and pollution transport in the urban boundary layer

Air quality models (AQMs) are a critical tool in the management of urban air pollution. They can be used for short-term air quality (AQ) forecasts, and in making planning and policy decisions aimed at abating poor AQ. Vertical turbulent mixing and horizontal advection of pollution are crucial processes controlling human exposure to pollution, since they are responsible for transporting pollution away from areas of high concentration. A simple two-box model is used to investigate the relative importance of urban boundary layer (UBL) pollution transport processes on AQ throughout the day. The lower and upper boxes represent the pollution concentration in the urban canopy and mixed layer respectively. The investigation utilises UBL meteorology and AQ measurements made during an experimental field campaign in London. The results demonstrate that the vertical exchange timescale at canopy top is a key parameter influencing concentration in the canopy. However, canopy height and wind speed in the canopy are likely less important. These findings can be used to inform parametrisation of urban boundary layer pollution transport processes in AQMs. To analyse the vertical mixing of pollution in the convective boundary layer, where the dominant turbulence ranges from mostly parametrised to mostly resolved in numerical weather prediction (NWP), the Met Office Unified Model (UM) is run at horizontal grid lengths ranging from 1.5 km to 55 m over London. A reduced analytical model is developed and used to determine vertical mixing timescales associated with surface released tracers in the UM. It is found that when vertical mixing is mostly resolved, distinctly different vertical mixing of tracers occurs on O(10 min) timescales. This results in a significant influence on surface level tracer concentrations at the city scale compared to when vertical mixing is mostly parametrised. Turbulence in urban canopies is investigated using simulations of flow through a wide range of urban canopy geometries. The general characteristics of momentum mixing length profiles are established and a first-order mixing length closure is formulated that is appropriate for parametrisation of urban canopy turbulence in AQMs. Unlike in vegetation canopies the inflection in the time- and horizontally space-averaged velocity profile does not control turbulent mixing in urban canopies. Overall, this thesis shows that good representation of pollution vertical mixing, both at the scale of the urban canopy and the entire UBL, is crucial for accurate urban AQ prediction

Use of wind pressure coefficients to simulate natural ventilation and building energy for isolated and surrounded buildings

Wind pressure coefficients (Cp) are critical inputs to building energy simulations. Given differences in the free stream wind speed height two categories exist: (1) Cpr (reference height) and (2) Cpl (local opening height). Additionally, Cp data are influenced by the vertical wind profile which is modified by surrounding buildings. However, these dependencies are often overlooked in building energy simulations (BES). We identified three potential biases from the incorrect use of Cp: (1) Cpr is used alongside the wind speed at opening height rather than reference height (where Cpr is defined); (2) Cpr is used with wind profiles that are different from the wind tunnel experiment or CFD simulation used to derive Cpr; and, (3) Cp is used along with the ‘disturbed’ urbanised wind speed instead of the ‘undisturbed’ free stream wind speed. In this study, we quantify the resulting biases from using Cp data incorrectly by assessing impacts on the resulting ventilation rate, indoor overheating risks and cooling energy saving with EnergyPlus for Shanghai's climate. Modifications to the use of Cp are proposed to improve simulation accuracy. Results show biases mostly exceeding the ±10% limit of ASHRAE-14 in all scenarios analysed. Differences are up to −19.0% for natural ventilation rate, 13.2% for indoor overheating degree hours and −14.0% for cooling energy saving, with such errors being larger during heatwave periods. Our study could provide useful guidance for researchers to carry out wind-driven natural ventilation study and estimate indoor overheating risk and energy consumption with better accuracy

Spatial and temporal variation of anthropogenic heat emissions in Colombo, Sri Lanka

Anthropogenic heat emissions (AHEs) should be accounted for when making city, neighbourhood, and building scale decisions about building design, health preparedness (e.g. heat stress), and achieving net zero carbon. Therefore, datasets with spatial and temporal variations are required for the range of global cities, including lower-middle income, low-latitude cities. Here we estimate the 2020 AHEs at 100 m resolution for Colombo, Sri Lanka. The city-wide annual mean is 5.9 W m−2. Seasonal variations are very small linked to small temperature differences, unlike mid- and high-latitude cities. However, the diurnal range of 17.6 to 1.8 W m−2 has three distinct peaks (cf. two often found in mid-latitude cities). Transport, metabolic and building related emissions account for 35, 33, and 32% of the total emissions, respectively. Building emissions are proportionally small (cf. mid-latitudes), as there is neither need for space heating nor frequent use of air conditioning, and little heavy industry. The AHE spatial heterogeneity is large, with annual-average maxima of 124 W m−2 at hectometre scale, but dropping rapidly to 10 W m−2 at kilometre scale. City-wide projections of AHEs from 2020 to 2035 range between 24 and 61% increase

In vivo biocompatibility and pacing function study of silver ion-based antimicrobial surface technology applied to cardiac pacemakers

INTRODUCTION Evidence suggests that the rate of cardiovascular implantable electronic device (CIED) infections is increasing more rapidly than the rates of CIED implantation and is associated with considerable mortality, morbidity and health economic impact. Antimicrobial surface treatments are being developed for CIEDs to reduce the risk of postimplantation infection within the subcutaneous implant pocket. METHODS AND ANALYSIS The feasibility of processing cardiac pacemakers with the Agluna antimicrobial silver ion surface technology and in vivo biocompatibility were evaluated. Antimicrobially processed (n=6) and control pacemakers (n=6) were implanted into subcutaneous pockets and connected to a part of the muscle using an ovine model for 12 weeks. Pacemaker function was monitored preimplantation and postimplantation. RESULTS Neither local infection nor systemic toxicity were detected in antimicrobial or control devices, and surrounding tissues showed no abnormal pathology or over-reactivity. Semiquantitative scores of membrane formation, cellular orientation and vascularity were applied over five regions of the pacemaker capsule and average scores compared. Results showed no significant difference between antimicrobially processed and control pacemakers. Silver analysis of whole blood at 7 days found that levels were a maximum of 10 parts per billion (ppb) for one sample, more typically ≤2 ppb, compared with <2 ppb for preimplantation levels, well below reported toxic levels. CONCLUSIONS There was no evidence of adverse or abnormal pathology in tissue surrounding antimicrobially processed pacemakers, or deleterious effect on basic pacing capabilities and parameters at 12 weeks. This proof of concept study provides evidence of basic biocompatibility and feasibility of applying this silver ion-based antimicrobial surface to a titanium pacemaker surface

Turbulence characteristics across a range of idealized urban canopy geometries

Good representation of turbulence in urban canopy models is necessary for accurate prediction of momentum and scalar distribution in and above urban canopies. To develop and improve turbulence closure schemes for one-dimensional multi-layer urban canopy models, turbulence characteristics are investigated here by analyzing existing large-eddy simulation and direct numerical simulation data. A range of geometries and flow regimes are analyzed that span packing densities of 0.0625 to 0.44, different building array configurations (cubes and cuboids, aligned and staggered arrays, and variable building height), and different incident wind directions (0 degrees and 45 degrees with regards to the building face). Momentum mixing-length profiles share similar characteristics across the range of geometries, making a first-order momentum mixing-length turbulence closure a promising approach. In vegetation canopies turbulence is dominated by mixing-layer eddies of a scale determined by the canopy top shear length scale. No relationship was found between the depth-averaged momentum mixing length within the canopy and the canopy top shear length scale in the present study. By careful specification of the intrinsic averaging operator in the canopy, an often-overlooked term that accounts for changes in plan area density with height, is included in a first-order momentum mixing-length turbulence closure model. For an array of variable-height buildings, its omission leads to velocity overestimation of up to 17%. Additionally, we observe that the von Karman coefficient varies between 0.20 and 0.51 across simulations, which is the first time such a range of values has been documented. When driving flow is oblique to the building faces, the ratio of dispersive to turbulent momentum flux is larger than unity in the lower half of the canopy, and wake production becomes significant compared to shear production of turbulent momentum flux. It is probable that dispersive momentum fluxes are more significant than previously thought in real urban settings, where the wind direction is almost always oblique

Spatial and temporal variation of anthropogenic heat emissions in Colombo, Sri Lanka

Anthropogenic heat emissions (AHEs) should be accounted for when making city, neighbourhood, and building scale decisions about building design, health preparedness (e.g. heat stress), and achieving net zero carbon. Therefore, datasets with spatial and temporal variations are required for the range of global cities, including lower-middle income, low-latitude cities. Here we estimate the 2020 AHEs at 100 m resolution for Colombo, Sri Lanka. The city-wide annual mean is 5.9 W m−2. Seasonal variations are very small linked to small temperature differences, unlike mid- and high-latitude cities. However, the diurnal range of 17.6 to 1.8 W m−2 has three distinct peaks (cf. two often found in mid-latitude cities). Transport, metabolic and building related emissions account for 35, 33, and 32% of the total emissions, respectively. Building emissions are proportionally small (cf. mid-latitudes), as there is neither need for space heating nor frequent use of air conditioning, and little heavy industry. The AHE spatial heterogeneity is large, with annual-average maxima of 124 W m−2 at hectometre scale, but dropping rapidly to 10 W m−2 at kilometre scale. City-wide projections of AHEs from 2020 to 2035 range between 24 and 61% increase

Association between rheumatoid arthritis disease activity, progression of functional limitation and long-term risk of orthopaedic surgery : Combined analysis of two prospective cohorts supports EULAR treat to target DAS thresholds

Objectives: To examine the association between disease activity in early rheumatoid arthritis (RA), functional limitation and long-term orthopaedic episodes. Methods: Health Assessment Questionnaire (HAQ) disability scores were collected from two longitudinal early RA inception cohorts in routine care; Early Rheumatoid Arthritis Study and Early Rheumatoid Arthritis Network from 1986 to 2012. The incidence of major and intermediate orthopaedic surgical episodes over 25 years was collected from national data sets. Disease activity was categorised by mean disease activity score (DAS28) annually between years 1 and 5; remission (RDAS≤2.6), low (LDAS>2.6-3.2), low-moderate (LMDAS≥3.2-4.19), high-moderate (HMDAS 4.2-5.1) and high (HDAS>5.1). Results: Data from 2045 patients were analysed. Patients in RDAS showed no HAQ progression over 5 years, whereas there was a significant relationship between rising DAS28 category and HAQ at 1 year, and the rate of HAQ progression between years 1 and 5. During 27 986 person-years follow-up, 392 intermediate and 591 major surgeries were observed. Compared with the RDAS category, there was a significantly increased cumulative incidence of intermediate surgery in HDAS (OR 2.59 CI 1.49 to 4.52) and HMDAS (OR 1.8 CI 1.05 to 3.11) categories, and for major surgery in HDAS (OR 2.48 CI 1.5 to 4.11), HMDAS (OR 2.16 CI 1.32 to 3.52) and LMDAS (OR 2.07 CI 1.28 to 3.33) categories. There was no significant difference in HAQ progression or orthopaedic episodes between RDAS and LDAS categories. Conclusions: There is an association between disease activity and both poor function and long-term orthopaedic episodes. This illustrates the far from benign consequences of persistent moderate disease activity, and supports European League Against Rheumatism treat to target recommendations to secure low disease activity or remission in all patients.Peer reviewedFinal Published versio

Exceptional atmospheric conditions in June 2023 generated a northwest European marine heatwave which contributed to breaking land temperature records

The Northwest European shelf experienced unprecedented surface temperature anomalies in June 2023 (anomalies up to 5 °C locally, north of Ireland). Here, we show the shelf average underwent its longest recorded category II marine heatwave (16 days). With state-of-the-art observation and modelling capabilities, we show the marine heatwave developed quickly due to strong atmospheric forcing (high level of sunshine, weak winds, tropical air) and weak wave activity under anticyclonic weather regimes. Once formed, this shallow marine heatwave fed back on the weather: over the sea it reduced cloud cover and over land it contributed to breaking June mean temperature records and to enhanced convective rainfall through stronger, warmer and moister sea breezes. This marine heatwave was intensified by the last 20-year warming trend in sea surface temperatures. Such sea surface temperatures are projected to become commonplace by the middle of the century under a high greenhouse gas emission scenario

Exceptional atmospheric conditions in June 2023 generated a northwest European marine heatwave which contributed to breaking land temperature records

The Northwest European shelf experienced unprecedented surface temperature anomalies in June 2023 (anomalies up to 5 °C locally, north of Ireland). Here, we show the shelf average underwent its longest recorded category II marine heatwave (16 days). With state-of-the-art observation and modelling capabilities, we show the marine heatwave developed quickly due to strong atmospheric forcing (high level of sunshine, weak winds, tropical air) and weak wave activity under anticyclonic weather regimes. Once formed, this shallow marine heatwave fed back on the weather: over the sea it reduced cloud cover and over land it contributed to breaking June mean temperature records and to enhanced convective rainfall through stronger, warmer and moister sea breezes. This marine heatwave was intensified by the last 20-year warming trend in sea surface temperatures. Such sea surface temperatures are projected to become commonplace by the middle of the century under a high greenhouse gas emission scenario