Silvana Di Sabatino

End-user Perspective of Low-cost Sensors for Outdoor Air Pollution Monitoring

Low-cost sensor technology can potentially revolutionise the area of air pollution monitoring by providing high-density spatiotemporal pollution data. Such data can be utilised for supplementing traditional pollution monitoring, improving exposure estimates, and raising community awareness about air pollution. However, data quality remains a major concern that hinders the widespread adoption of low-cost sensor technology. Unreliable data may mislead unsuspecting users and potentially lead to alarming consequences such as reporting acceptable air pollutant levels when they are above the limits deemed safe for human health. This article provides scientific guidance to the end-users for effectively deploying low-cost sensors for monitoring air pollution and peoples exposure, while ensuring reasonable data quality. We review the performance characteristics of several low-cost particle and gas monitoring sensors and provide recommendations to end-users for making proper sensor selection by summarizing the capabilities and limitations of such sensors. The challenges, best practices, and future outlook for effectively deploying low-cost sensors, and maintaining data quality are also discussed. For data quality assurance, a two-stage sensor calibration process is recommended, which includes laboratory calibration under controlled conditions by the manufacturer supplemented with routine calibration checks performed by the end-user under final deployment conditions. For large sensor networks where routine calibration checks are impractical, statistical techniques for data quality assurance should be utilised. Further advancements and adoption of sophisticated mathematical and statistical techniques for sensor calibration, fault detection, and data quality assurance can indeed help to realise the promised benefits of a low-cost air pollution sensor network.

Assessment of Planetary Boundary-Layer Schemes in the Weather Research and Forecasting Mesoscale Model Using MATERHORN Field Data

The study was aimed at understanding the deficiencies of numerical mesoscale models by comparing predictions with a new high-resolution meteorological dataset collected during the Mountain Terrain Atmospheric Modelling and Observations (MATERHORN) Program. The simulations focussed on the stable boundary layer (SBL), the predictions of which continue to be challenging. High resolution numerical simulations (0.5-km horizontal grid size) were conducted to investigate the efficacy of six planetary boundary-layer (PBL) parametrizations available in the advanced research version of the Weather Research and Forecasting model. One of the commonly used PBL schemes was modified to include eddy diffusivities that account for enhanced momentum transport compared to heat transport in the SBL, representing internal wave dynamics. All of the tested PBL schemes, including the modified scheme, showed a positive surface temperature bias. None of the PBL schemes was found to be superior in predicting the vertical wind and temperature profiles over the lowest 500 m, however two of the schemes appeared superior in capturing the lower PBL structure. The lowest model layers appear to have a significant impact on the predictions aloft. Regions of sporadic flow interactions delineated by the MATERHORN observations were poorly predicted, given such interactions are not represented in typical PBL schemes.

Direct measurements of the drag force over aligned arrays of cubes exposed to boundary-layer flows

Wind tunnel measurements of the total drag force for aligned arrays of cubes exposed to two different boundary-layer flows at three flow velocities are discussed. The drag force for eight different building packing densities λp (from 0.028 to 1) is measured with a standard load cell generating a novel dataset. Different λp are reproduced by increasing the number of buildings on the same lot area; this represents a real situation that an urban planner is faced with when a lot area of a given (fixed) size is allocated to the development of new built areas. It is assumed that the surrounding terrain is uniform and there is a transition from a given roughness (smooth) to a new roughness (rough). The approaching flow will adjust itself over the new surface within a distance that in general may be larger than the horizontal length covered by the array. We investigate the region where the flow adjustment occurs. The wide range of packing densities allowed us to analyse in detail the evolution of the drag force. The drag force increases with increasing packing densities until it reaches a maximum at an intermediate packing density (λpxa0=xa00.25 in our case) followed by a slight decrease at larger packing densities. The value of the drag force depends on the flow adjustment along the array which is evaluated by introducing the parameter “drag area” to retrieve information about the drag distribution at different λp. Results clearly suggest a change of the distribution of the drag force, which is found to be relatively uniform at low packing densities, while most of the force acts on first rows of the arrays at large packing densities. The drag area constitutes the basis for the formulation of a new adjustment length scale defined as the ratio between the volume of the air within the array and the drag area. The proposed adjustment length scale automatically takes into account the change in drag distribution along the array for a better parameterization of urban effects in dispersion models.

Global assessment of heat wave magnitudes from 1901 to 2010 and implications for the river discharge of the Alps

Heat waves represent one of the most significant climatic stressors for ecosystems, economies and societies. A main topic of debate is whether they have increased or not in intensity and/or their duration due to the observed climate change. Firstly, this is because of the lack of reliable long-term daily temperature data at the global scale; secondly, because of the intermittent nature of such phenomena. Long datasets are required to produce a reliable and meaningful assessment. In this study, we provide a global estimate of heat wave magnitudes based on the three most appropriate datasets currently available, derived from models and observations (i.e. the 20th Century Reanalyses from NOAA and ECMWF), spanning the last century and before. The magnitude of the heat waves is calculated by means of the Heat Wave Magnitude Index daily (HWMId), taking into account both duration and amplitude. We compare the magnitude of the most severe heat waves occurred across different regions of the world and we discuss the decadal variability of the larger events since the 1850s. We concentrate our analysis from 1901 onwards, where all datasets overlap. Our results agree with other studies focusing on heat waves that have occurred in the recent decades, but using different data. In addition, we found that the percentage of global area covered by heat wave exceeding a given magnitude has increased almost three times, in the last decades, with respect to that measured in the early 20th century. Finally, we discuss the specific implications of the heat waves on the river runoff generated in the Alps, for which comparatively long datasets exist, affecting the water quality and availability in a significant portion of the European region in summer.

Impact of ship emissions on local air quality in a Mediterranean city's harbour after the European sulphur directive

We present a modelling approach to investigate the impact of ship emissions in the port of Brindisi (IT) on local air quality. The focus is on the impact on pollutant concentrations due to the implementation of the MARPOL Annex VI and the associated NOx technical code 2008 (concerning NOx emissions) and the Directives 2005/33/EU-2012/33/EU (concerning the sulphur content of maritime fuels). Emissions are estimated through an adapted MEET methodology using appropriate emission factors for manoeuvring and hotelling phases. Numerical simulations of NOx, SO2 and primary PM10 are performed by means of the mesoscale model BOLCHEM coupled off-line with ADMS-Urban. The impact of present and future ship emissions on air quality in the port area is evaluated. After the implementation of the Directives 2005/33/EU-2012/33/EU for the year 2012 SO2 showed a significant concentration reduction especially close to the port area, while primary PM10 concentration reduction was minor, as well as that of NOx, as a consequence of the NOx technical code. No significant reductions were found for the year 2020.

Stratified Flow Past a Hill: Dividing Streamline Concept Revisited

The Sheppard formula (Q J R Meteorol Soc 82:528–529, 1956) for the dividing streamline height

Boundary-Layer Atmospheric Processes in Mountainous Terrain: Results from MATERHORN-X

H_mathrm{s}

The impacts of building height variations and building packing densities on flow adjustment and city breathability in idealized urban models

Hs assumes a uniform velocity