Christos Halios

Meteorology, air quality, and health in London: The ClearfLo project

AbstractAir quality and heat are strong health drivers, and their accurate assessment and forecast are important in densely populated urban areas. However, the sources and processes leading to high concentrations of main pollutants, such as ozone, nitrogen dioxide, and fine and coarse particulate matter, in complex urban areas are not fully understood, limiting our ability to forecast air quality accurately. This paper introduces the Clean Air for London (ClearfLo; www.clearflo.ac.uk) project’s interdisciplinary approach to investigate the processes leading to poor air quality and elevated temperatures.Within ClearfLo, a large multi-institutional project funded by the U.K. Natural Environment Research Council (NERC), integrated measurements of meteorology and gaseous, and particulate composition/loading within the atmosphere of London, United Kingdom, were undertaken to understand the processes underlying poor air quality. Long-term measurement infrastructure installed at multiple levels (street and eleva...

Developing a research strategy to better understand, observe and simulate urban atmospheric processes at kilometre to sub-kilometre scales

A Met Office/Natural Environment Research Council Joint Weather and Climate Research Programme workshop brought together 50 key international scientists from the UK and international community to formulate the key requirements for an Urban Meteorological Research strategy. The workshop was jointly organised by University of Reading and the Met Office.

Temporal evolution of the main processes that control indoor pollution in an office microenvironment: a case study

The aim of this study is to examine the relative contribution of the outdoor concentration, the ventilation rate, the geometric characteristics of the indoor environment (i.e., extent of indoor surfaces and indoor volume), the deposition, and chemical reactions to the indoor air quality of the office microenvironment. For this case study, the NO, NO2, and O3 concentrations indoors and outdoors and TVOCs and CO2 concentrations indoors were measured in an office microenvironment in Athens, Greece, that was ventilated both naturally and mechanically. The calculated ventilation and loss rates and the measured outdoor concentrations of NO, NO2, and O3 were set as input to Multi-chamber Indoor Air Quality Model in order to study the temporal variation of the indoor NO, NO2, and O3 concentrations. Results showed that when the ventilation rate and outdoor concentration are high, the relative contribution of the transport process contributes significantly, while the chemical process depends on the contemporary interplay between the indoor O3, NO, and NO2 concentrations and lighting levels. The significance of each process was further examined by performing sensitivity tests, and it was found that the most important parameters were the deposition velocities, the UV infiltration rates (which determines the indoor chemical reaction rates), the ventilation rates, and the filtration (when a mechanical ventilation system is used). The effect of the hydrocarbon chemistry was not significant.

Studying the Effect of Indoor Sources and Ventilation on the Concentrations of Particulates in Dining Halls

Abstract The impact of ventilation on indoor particulate pollution is highlighted by numerous studies. The aim of the present study is to examine the influence of ventilation on the levels of particulate concentrations found in dining halls where a large number of students are accommodated. Indoor particulate sources were also quantified and their influence on the particulate concentrations was examined. Measurements were conducted in four University dining halls, which are located in different parts of the city of Athens. Indoor and outdoor CO2, PM1, PM2.5 and PM10 concentrations along with the number of occupants and smokers were measured in each dining hall during the accommodation of the students. Measurements were repeated for five working days in each dining hall. Ventilation rates were estimated by applying a methodology that involves the solution of the mass balance equation for the CO2 concentrations. The indoor particulate production rates were estimated by performing consecutive numerical experiments with the Multi Chamber Indoor Air Quality Model (MIAQ). Median CO2 concentrations ranged between 1043 μg m-3 and 1590 μg m-3 and ventilation rates ranged between 0.58 h-1 and 5.15 h-1. The respective values for PM1 ranged between 8.6 μg m-3 and 22 μg m-3, for PM2.5 between 17 μg m-3 and 60 μg m-3 and for PM10 between 24 μg m-3 and 78 μg m-3. The Pearson correlation coefficient between the log transformed ventilation rates and the PM10 concentrations were found to be -0.6. Median values of the total production rates were found to range between 100 μg min-1 and 5500 μg min-1 and are highly correlated with the number of occupants (Pearson correlation coefficient 0.86). Examination of the origin of the particulate sources indicated that, in the majority of cases, re-suspension is more significant than combustion sources. Significant short-term variation (one hour time interval) of the various sources was also observed. Even though the production rates were significantly elevated, the measured particulate concentrations were moderate due to the high air change rates obtained. These findings support the results of other studies that highlight the significance of ventilation in environments where indoor sources are prominent.

On the variability of the surface environment response to synoptic forcing over complex terrain: a multivariate data analysis approach

Synoptic climatology relates the atmospheric circulation with the surface environment. The aim of this study is to examine the variability of the surface meteorological patterns, which are developing under different synoptic scale categories over a suburban area with complex topography. Multivariate Data Analysis techniques were performed to a data set with surface meteorological elements. Three principal components related to the thermodynamic status of the surface environment and the two components of the wind speed were found. The variability of the surface flows was related with atmospheric circulation categories by applying Correspondence Analysis. Similar surface thermodynamic fields develop under cyclonic categories, which are contrasted with the anti-cyclonic category. A strong, steady wind flow characterized by high shear values develops under the cyclonic Closed Low and the anticyclonic H–L categories, in contrast to the variable weak flow under the anticyclonic Open Anticyclone category.

Studying geometric structures in meso-scale flows

Geometric shapes of coherent structures such as ramp or cliff like signals, step changes and waves, are commonly observed in meteorological temporal series and dominate the turbulent energy and mass exchange between the atmospheric surface layer and the layers above, and also relate with low-dimensional chaotic systems. In this work a simple linear technique to extract geometrical shapes has been applied at a dataset which was obtained at a location experiencing a number of different mesoscale modes. It was found that the temperature field appears much better organized than the wind field, and that cliff-ramp structures are dominant in the temperature time series. The occurrence of structural shapes was related with the dominant flow patterns and the status of the flow field. Temperature positive cliff-ramps and ramp-cliffs appear mainly during night time and under weak flow field, while temperature step and sine structures do not show a clear preference for the period of day, flow or temperature pattern. Uniformly stable, weak flow conditions dominate across all the wind speed structures. A detailed analysis of the flow field during two case studies revealed that structural shapes might be part of larger flow structures, such as a sea-breeze front or down-slope winds. During stagnant conditions structural shapes that were associated with deceleration of the flow were observed, whilst during ventilation conditions shapes related with the acceleration of the flow.

30 minute averaged overview data from the Silsoe Refresh Cube Campaign (RCC)

All 30 minute averaged data taken during the Refresh Cube Campaign (RCC) at Silsoe using the 6 m^3 test structure at the site and eight other 6 m^3 straw cubes undertaken as part of the PhD work of Gough (2017) and forms the full-scale experiments of the REFRESH project. The data-set is split into two sections: an isolated cube and the array case with three different opening set-ups being undertaken for both array and isolated. The array was in place October 2014 to April 2015, and the cube was isolated from May 2015 to July 2015. Details of the experimental set-ups are available in publications. The data contained within this document are 30 minute averaged and quality controlled using code previously used for the ACTUAL project. The data set contains wind speeds, wind directions, internal and external temperatures, surface pressures, CO_2 concentrations and ventilation rates calculated from the pressure difference methods. Internal and external measurements are included for the flow.

Ground-Based Aerosol Optical Depth Inter-Comparison Campaigns at EUSAAR Sites in Athens, Greece

This work summarises an aerosol optical depth (AOD) inter-comparison campaign conducted from June to September 2009 in Athens under the EUSAAR (European Super-Sites for Atmospheric Aerosol Research) Programme. A PFR (precision filter radiometer) travelling standard from the GAW-PFR network was first located at the NCSR “Demokritos” Institute (267 m asl), and then at the Institute for Space Applications and Remote Sensing of the National Observatory of Athens (ISARS/NOA, 191 m). ISARS/NOA has a CIMEL sun-photometer which is part of AERONET. Concurrent data at two co-incident channels showed that the λ = 865 nm but not the 500 nm channel at ISARS/NOA fulfilled the WMO Global Atmosphere Watch criterion of traceability.

Studying Surface Observed Meteorological Characteristics Under Different Synoptic Scale Circulation Patterns

This work aims to study surface meteorological patterns under different synoptic scale categories. Multivariate Data Analysis techniques were applied on two datasets including surface meteorological elements, and meteorological variables in the lower troposphere (850 and 700 hPa). For the former, three principal components were found, related to the thermodynamic status of the surface environment and the two components of the wind speed. For the lower troposphere dataset three principal components were related with: (1) the thermodynamic status, (2) the wind field at 850 hPa, and (3) the direction of the flow at 700 hPa. Principal components from the surface dataset were related with atmospheric circulation categories via Correspondence Analysis. Canonical Correlation Analysis between the surface and upper air datasets revealed: (1) the strong thermodynamic connection of the surface and the upper air environment and (2) a very weak connection between the surface flow field and the upper air circulation indicating the influence of the local topography.