Tall Tower Research Articles

Eddy covariance with slow-response greenhouse gas analysers on tall towers: bridging atmospheric and ecosystem greenhouse gas networks

Abstract. Greenhouse gas monitoring is important to ensure climate goals are being achieved. This study unveils the potential of using atmospheric tall towers in direct flux measurements, bridging the gap between atmospheric and ecosystem monitoring networks. The ICOS Cities (PAUL) project aims to monitor CO2 emissions in urban areas, where concentrated emissions make them key targets for climate change mitigation. This study explores the synergy between ICOS atmospheric and ecosystem networks by utilizing slow-response analysers (∼ 3 s) on tall atmospheric towers for ecosystem studies using the eddy covariance method. A standard setup with an ultrasonic anemometer and an infrared (IR) fast-response CO2 analyser was installed and compared with measurements from an existing cavity ring-down spectroscopy (CRDS) analyser measuring CO2, CO, and CH4. Deployed on the 100 m Saclay tower near Paris, covering a 43.9 km2 80 % footprint with heavy traffic roads, a nearby heating plant, and a forest, the setup addressed technical challenges and height-induced complexities. Corrections for flux attenuation by high-frequency losses were limited to < 20 % on average for all stabilities and around 11 % for unstable conditions. Elevated mean fluxes for CO2 (10 µmolm-2s-1) and CH4 (200 µmolm-2s-1) were observed from the heating plant wind direction during December and January. Conversely, the forest direction exhibited the strongest sink among all wind directions, with −4 µmolm-2s-1 during July and August. Storage and vertical advection were estimated using the routine three-level profile measurements done in ICOS atmospheric towers. Storage term was of the same magnitude as turbulent flux, increasing at night and de-stocking during the first half of the day. Vertical advection averaged zero on a monthly basis. These results demonstrate the feasibility and versatility of utilizing atmospheric towers for urban emission monitoring, offering valuable insights for emission monitoring strategies worldwide.

Seismic Vibration Control and Multi-Objective Optimization of Transmission Tower with Tuned Mass Damper Under Near-Fault Pulse-like Ground Motions

Although the wind load is usually adopted as the governing lateral load in the design of transmission towers, many tall transmission towers may be damaged or even collapse in high seismic intensity areas, especially under near-fault pulse-like ground motions. To study the seismic vibration control effect of a tuned mass damper (TMD) attached to transmission tower, parametric analyses are conducted in SAP2000 through CSI OAPI programming, including TMD parameters such as the mass ratio μ from 0.5% to 10%, the frequency ratio f from 0.7 to 1.2, and the damping ratio ξ from 0.01 to 0.2. Based on the obtained analysis results, artificial neural network (ANN) is trained to predict the vibration reduction ratios of peak responses and the corresponding vibration reduction cost. Finally, the NSGA-III algorithm is adopted to perform the multi-objective optimization of a transmission tower equipped with TMD. Results show that the vibration reduction ratios first increase and then decrease with the increase of frequency ratio, but first increase and then remain stable with the increase of mass ratio and damping ratio. In addition, ANN fitting can accurately predict the nonlinear relationship between TMD parameters and objective functions. Through multi-objective optimization with the NSGA-III algorithm, TMD can simultaneously and significantly reduce different peak responses of transmission towers under near-fault pulse-like ground motions in a cost-effective manner.

Isotopic Constraints on Nitrous Oxide Emissions From the US Corn Belt

AbstractAgriculture is the dominant source of anthropogenic nitrous oxide (N2O) –a greenhouse gas and a stratospheric ozone depleting substance. The US Corn Belt is a large global N2O source, but there remain large uncertainties regarding its source attribution and biogeochemical pathways. Here, we interpret high frequency stable N2O isotope observations from a very tall tower to improve our understanding of regional source attribution. We detected significant seasonal variability in δ15Nbulk (6.47–7.33‰) and the isotope site preference (δ15NSP = δ15Nα–δ15Nβ, 18.22–25.19‰) indicating a predominance of denitrification during the growing period but of nitrification during the snowmelt period. Isotope mixing models and atmospheric inversions both indicate that indirect emissions contribute substantially (>35%) to total N2O emissions. Despite the relatively large uncertainties, the upper bound of bottom‐up indirect emission estimates are at the lower bound of the isotopic constraint, implying significant discrepancies that require further investigation.

Divergent apparent temperature sensitivity of forest-floor respiration across a managed boreal forest landscape

Understanding the apparent temperature sensitivity (Q10) of forest floor respiration (Q10Rff) and its plant autotrophic (Q10Ra) and soil heterotrophic (Q10Rh) components is critical for determining the strength and direction of forest carbon cycle-climate feedbacks. However, the spatial variability of Q10Rff and its controlling factors across the spatially heterogeneous boreal forest landscape remains poorly understood. In this study, we used chamber-based respiration measurements conducted on paired natural and trenching plots over three growing seasons (2016–2018) to determine Q10Rff, Q10Rh and Q10Ra to soil temperature across 50 diverse forest stands (ranging 5–211 years old) in a managed landscape in northern Sweden. Additionally, we estimated ecosystem- and landscape-scale Q10 based on conventional and tall tower eddy covariance measurements, respectively, conducted over the same landscape. Our results suggest manifold variations (i.e., 10th to 90th percentiles) of Q10Rff (1.7 to 6.6), with Q10Ra (0.9 to 7.4) showing a greater range than Q10Rh (1.6 to 5.3). Forest-floor understory biomass was the main control of variations in Q10Ra, whereas soil properties explained best those of Q10Rh. Furthermore, a seasonal hysteresis of Q10Rff was observed, with higher values mostly occurring during the late growing season. The magnitude of this hysteresis scaled with stand age in response to concurrent changes in net primary production. The Q10Rff to air temperature declined with increasing stand age, which was attributed to the increased decoupling of air and soil temperatures with canopy development. Despite the considerable stand-level variations, when averaged over the 50 forest stands, Q10Rff to air temperature converged with that of both ecosystem- and landscape-scale respiration. In conclusion, our study highlights the complexity of Q10Rff, which needs to be considered in predictions of the interactions of climate change and management with the carbon cycle of managed boreal forests.

Crack analysis of tall concrete wind towers using an ad-hoc deep multiscale encoder–decoder with depth separable convolutions under severely imbalanced data

An accurate and timely cracking assessment, including the presence, location and crack geometric feature measurement, is crucial for evaluating concrete wind towers. Therefore, the early identification of cracks is a critical procedure in promptly evaluating structural integrity. This study proposed an ad-hoc encoder–decoder network based on DeepLabv3+ with depth separable convolutions to automatically segment cracks from real-world images captured from various concrete wind towers. The combined advantages of the improved DeepLabv3+ and the lightweight MobileNet v2 are suitable as a benchmark due to their high performance and universality. Four experiments were conducted to determine the model design choice and crack feature measurement capability: (1) six parametric tests using various pre-trained base networks and algorithm optimisers, (2) the influence of complex background noise (i.e., handwriting script) on crack segmentation performance, (3) comparative studies with cutting-edge pixel-wise segmentation models and (4) crack feature measurement (i.e., length and width). The research outcome demonstrated that DeepLabv3+ with MobileNet v2 can potentially be applied for efficient and accurate crack segmentation in concrete wind towers with complex backgrounds.

Tall tower observations of a northward surging gust front in central Amazon and its role in the mesoscale transport of carbon dioxide

AbstractHigh‐frequency measurements obtained at two micrometeorological towers are investigated for a rare northward surging gust front that impacted the Amazon Tall Tower Observatory (ATTO), in central Amazon. The gust front originated from a decaying mesoscale convective system (MCS) during the morning hours of 27 December 2021 near Manaus, Amazonas state, northern Brazil, and surged north‐eastward towards the ATTO site. Large temperature drops and vigorous, persistent winds were observed at the towers which lasted for over 4 h despite the gust front being detached from its parent, decaying MCS. More importantly, the gust front was responsible for drastic increases of CO2 concentrations throughout the tower depths, which suggests that the gust front winds horizontally advected CO2‐rich air from a source upstream from the ATTO site. The CO2‐rich outflow is hypothesized to originate from downward transport and/or biomass burning from forest fires in southeastern Amazon, both ideas that are supported by large increases of aerosol concentrations measured at ATTO following the gust front passage. Our results stress the need for further investigations addressing the role played by mesoscale convective circulations in the redistribution of trace gases and aerosols in the Amazon.

Attachment processes of negative flashes with multiple return strokes to a tall tower observed at close distances

Two downward negative flashes (F1612 & F1613) with multiple return strokes struck to the 356-m Shenzhen Tower were analyzed. The high-speed camera captured upward positive connecting leaders (UCL) for the first strokes of both flashes and two subsequent strokes of F1612. The observations also show that none of the downward negative leader (DNL) completely propagated to the tower tip before the occurrence of the return stroke (RS), so that we inferred that the UCL initiated from the tower tip might exist for each RS of the two flashes. The possible height of the UCL and DNL connecting point above the tower tip for each RS was estimated, which showed a positive correlation to the speed of corresponding DNL. The striking distances estimated for 8 subsequent RSs in F1612 were in a range from 14.6 m to 85.4 m and that for 3 subsequent RSs in F1613 were from 24.2 m to 66.2 m. There was a weak positive linear relationship between the DNL speed and striking distance for subsequent RSs in the two flashes. The DNL speed showed a positive correlation to the peak current of corresponding RS.

Vertical distribution of ozone in spring based on two high tower observations over the Pearl River Delta, China

This study investigates the vertical distribution characteristics of ozone (O3) in the Pearl River Delta (PRD) region during spring, utilising observational data from two tall towers in urban and suburban areas of the PRD, i.e., the 600 m high Canton Tower and the 356 m high Shenzhen Meteorology Gradient Tower (SZMGT), between 2018 and 2020. The observations indicate that the peak times of O3 concentrations differ under polluted and clean conditions, with polluted conditions showing 1–3 h later peaks compared with clean conditions. The diurnal variation in the O3 concentration is more pronounced at the SZMGT than at the Canton Tower. The O3 vertical gradients differ between the two towers, with the Canton Tower showing larger daytime gradients and the SZMGT showing larger nighttime gradients under polluted conditions. The vertical O3 distribution patterns are categorised into three types: Polluted, Moderate, and Good levels. The O3 concentration initially rises with altitude and then decreases under polluted conditions. Elevated O3 is observed in the lower planetary boundary layer (PBL), approximately between 110 and 210 m in height, where the concentration is 1.1–1.4 times higher than the surface level. Both the Moderate and Good levels occur under clean conditions, in which the O3 of the Canton Tower increases with altitude, whereas the O3 of the SZMGT first increases and then decreases with altitude. The correlation between O3 and the meteorological conditions (temperature, relative humidity, wind direction, and wind speed) decreases with increasing altitude. The cluster analysis of backward trajectories identifies three main transport paths affecting the O3 levels: northeasterly continental, southerly oceanic, and easterly coastal paths. Combining the observations from O3 lidar in Guangzhou and Shenzhen and two additional cities within the PRD region, Foshan and Zhongshan, the analysis of a typical pollution case indicates that different cities have different local chemical generation and regional transport contributions to O3 pollution. A conceptual model reflecting the horizontal transport paths and vertical structures of O3 pollution in the spring over the PRD is proposed, which enhances our understanding of the O3 vertical distribution in different cities and contributes to the analysis of the O3 pollution mechanism in the PRD agglomeration.

Estimation of the Equivalent Impedance of Lightning Return-Stroke Channel From Current Waveforms Measured at Tall Towers

Estimation of the Equivalent Impedance of Lightning Return-Stroke Channel From Current Waveforms Measured at Tall Towers

CloudRoots-Amazon22: Integrating Clouds with Photosynthesis by Crossing Scales

Abstract How are rain forest photosynthesis and turbulent fluxes influenced by clouds? To what extent are clouds affected by local processes driven by rain forest energy, water, and carbon fluxes? These interrelated questions were the main drivers of the intensive field experiment CloudRoots-Amazon22 which took place at the Amazon Tall Tower Observatory (ATTO)/Campina supersites in the Amazon rain forest during the dry season, in August 2022. CloudRoots-Amazon22 collected observational data to derive cause–effect relationships between processes occurring at the leaf level up to canopy scales in relation to the diurnal evolution of the clear-to-cloudy transition. First, we studied the impact of cloud and canopy radiation perturbations on the subdiurnal variability of stomatal conductance. Stoma opening is larger in the morning, modulated by the cloud optical thickness. Second, we combined 1-Hz frequency measurements of the stable isotopologues of carbon dioxide and water vapor with measurements of turbulence to determine carbon dioxide and water vapor sources and sinks within the canopy. Using scintillometer observations, we inferred 1-min sensible heat flux that responded within minutes to the cloud passages. Third, collocated profiles of state variables and greenhouse gases enabled us to determine the role of clouds in vertical transport. We then inferred, using canopy and upper-atmospheric observations and a parameterization, the cloud cover and cloud mass flux to establish causality between canopy and cloud processes. This shows the need for a comprehensive observational set to improve weather and climate model representations. Our findings contribute to advance our knowledge of the coupling between cloudy boundary layers and primary carbon productivity of the Amazon rain forest.

Study on Morphometrical Urban Aerodynamic Roughness Multi-Scale Exploration Using LiDAR Remote Sensing

This study proposes the use of light detection and ranging (LiDAR) remote sensing (RS) to support morphometric research for estimating the aerodynamic roughness length (z0 ) of building placement on various scales. A LiDAR three-dimensional point cloud (3DPC) data processing graphical user interface (GUI) was developed to explore the z0 and related urban canopy parameters (UCPs) in the Incheon metropolitan area in South Korea. The results show that multi-scale urban aerodynamic roughness exploration is viable and can address differences in urban building data at various spatial resolutions. Although validating morphological multi-scale UCPs using dense tall towers is challenging, emerging low-cost and efficient methods can serve as substitutes. However, further efforts are required to link the measured z0 to building form regulations, such as floor area ratio, and expand RS research to obtain more quantitative and qualitative knowledge.

A sensitivity-based estimation method for investigating control co-design relevance

Abstract. Control co-design is a promising approach for wind turbine design due to the importance of the controller in power production, stability, load alleviation, and the resulting coupled effects on the sizing of the turbine components. However, the high computational effort required to solve optimization problems with added control design variables is a major obstacle to quantifying the benefit of this approach. In this work, we propose a methodology to identify if a design problem can benefit from control co-design. The estimation method, based on post-optimum sensitivity analysis, quantifies how the optimal objective value varies with a change in control tuning. The performance of the method is evaluated on a tower design optimization problem, where fatigue load constraints are a major driver, and using a linear quadratic regulator targeting fatigue load alleviation. We use the gradient-based multi-disciplinary optimization framework Cp-max. Fatigue damage is evaluated with time-domain simulations corresponding to the certification standards. The estimation method applied to the optimal tower mass and optimal cost of energy show good agreement with the results of the control co-design optimization while using only a fraction of the computational effort. Our results additionally show that there may be little benefit to using control co-design in the presence of an active frequency constraint. However, for a soft–soft tower configuration where the resonance can be avoided with active control, using control co-design results in a taller tower with reduced mass.

Occurrence of a “forever chemical” in the atmosphere above pristine Amazon Forest

Per- and polyfluoroalkyl substances (PFAS), often referred to as “forever chemicals”, are a class of man-made, extremely stable chemicals, which are widely used in industrial and commercial applications. Exposure to some PFAS is now known to be detrimental to human health. By virtue of PFAS long residence times, they are widely detected in the environment, including remote locations such as the Arctics, where the origin of the PFAS is poorly understood. It has been suggested that PFAS may be transported through contaminated waters, leading to accumulation in coastal areas, where they can be aerosolised via sea spray, thereby extending their geographical distribution far beyond their original source regions.The aim of this work is to investigate, for the first time, whether “forever chemicals” could be transported to areas considered to be pristine, far from coastal sites. This study was performed at the Amazonian Tall Tower Observatory (ATTO), a unique remote site situated in the middle of the Amazon rainforest, where a restricted PFAS, perfluorooctanoic acid (PFOA), was observed with concentrations reaching up to 2 pg/m3. A clear trend of increasing concentration with sampling height was observed and air masses from the south over Manaus had the highest concentrations. Atmospheric lifetime estimations, removal mechanisms supported by measurements at two heights (320 and 42 m above the rainforest), and concentration spikes indicated a long-range transport of PFOA to pristine Amazon rainforest. Potential sources, including industrial activities in urban areas, were explored, and historical fire management practices considered.This research presents the first measurements of PFAS in the atmosphere of Amazon rainforest. Remarkably, even in this remote natural environment, appreciable levels of PFAS can be detected. This study provides valuable insights into the long-range transport of the anthropogenic “forever chemical” into a remote natural ecosystem and should raise awareness of potential environmental implications.

How do technological choices affect the economic and environmental performance of offshore wind farms?

The ongoing energy transition towards fully sustainable energy systems requires designing wind farms looking beyond the sole levelized cost of energy, in order to concurrently ensure not only the economic profitability but also the environmental friendliness of future plants. Within this new approach to design, it becomes necessary to understand the effects that various possible technological choices have on both the economic and the environmental performance of wind farms. This study presents a framework designed to support these coupled economic-environmental assessments. The capabilities of the code are showcased by analysing the impact of different choices in terms of support structure type, specific power, tower height, powertrain type, and array and export voltage level for an exemplary offshore farm, chosen here as the IEA Wind 740-10-MW Reference Offshore Wind Plant with irregular layout. While the effects of many technological choices on the cost of energy are already well understood by industry, the present analysis shows that — at least in this specific case — climate change impacts are mainly driven by steel production, due to the massive amount of required material, but also, interestingly, by vessel activities. A low specific power, tall towers, and a high export cable voltage appear to offer the greatest potential for the concurrent improvement of the environmental and economic performance of the plant.

Electromagnetic fields of lightning return stroke to wind turbines with discontinuous impedance model

This study introduces an electric field calculation model for wind turbine return strokes, incorporating impedance discontinuity within the turbine, a feature not considered in traditional tall tower models. The model introduces a reflection coefficient, ρx, at the connection between the blades and the tower. Disregarding the generation of upward leaders, this paper calculates the electric field of subsequent return strokes for different distances from the wind turbine and for different model parameters. The results demonstrate that changes in the reflection coefficient ρx affect oscillation amplitude and also slightly influence the pulse width, with a negative ρx leading to smaller and more frequent pulses. Contrasts with measured waveforms indicate that models with a constant reflection coefficient are inaccurate. Adopting variable reflection coefficient values yields a more accurate match. This approach offers a new perspective for electromagnetic field calculations in lightning-struck structures, emphasizing the significance of impedance dynamics of return stroke channel.

Instrumentation for Sub-Ampere Lightning Current Measurement on a Tall Meteorological Tower in Complex Electromagnetic Environment

Measurement of lightning current plays a critical role in the field of atmospheric electricity. Traditionally, Rogowski coils or low-resistance shunts were employed for measuring lightning currents in the range from several amperes up to several hundreds of kilo-amperes, and high-value resistors were utilized for measuring corona discharge currents at sub-ampere levels. However, these approaches were not suitable for continuously recording the vast range of lightning currents. For this sake, we have developed a lightning current measurement system equipped with a shock-tolerant low-noise amplifier module. With the system installed on a tall tower, sub-ampere level currents just before the lightning initiation were observed for the first time. To confirm the authenticity of the recorded currents, the background noise of the measurement system and surrounding environment were identified, and a digital multi-frequency notch filter was proposed for de-noising. Results show that the system can achieve a current identification level of 50 mA even in complex electromagnetic environments, while having a measurement capability of 220 kA.

Amazonian aerosol size distributions in a lognormal phase space: characteristics and trajectories

Abstract. This study introduces a first glance at Amazonian aerosols in the N–Dg–σ phase space. Aerosol data, measured from May 2021 to April 2022 at the Amazon Tall Tower Observatory (ATTO), were fitted by a multi-modal lognormal function and separated into three modes: the sub-50 nm, the Aitken (50–100 nm), and the accumulation modes. The fit results were then evaluated in the N–Dg–σ phase space, which represents a three-dimensional space based on the three lognormal fit parameters. These parameters represent, for a given mode i, the number concentration (Ni), the median geometric diameter (Dg,i), and the geometric standard deviation (σi). Each state of a particle number size distribution (PNSD) is represented by a single dot in this space, while a collection of dots shows the delimitation of all PNSD states under given conditions. The connections in ensembles of data points show trajectories caused by pseudo-forces, such as precipitation regimes and vertical movement. We showed that all three modes have a preferential arrangement in this space, reflecting their intrinsic behaviors in the atmosphere. These arrangements were interpreted as volumetric figures, elucidating the boundaries of each mode. Time trajectories in seasonal and diurnal cycles revealed that fits with the sub-20 nm mode are associated with rainfall events that happen in the morning and in the afternoon. But in the morning they grow rapidly into the Aitken mode, and in the afternoon they remain below 50 nm. Also, certain modes demonstrated well-defined curves in the space, e.g., the seasonal trajectory of the accumulation mode follows an ellipsoid, while the diurnal cycle of the sub-50 nm mode in the dry season follows a linear trajectory. As an effect of the precipitation on the PNSDs and vice versa, N and Dg were found to increase for the sub-50 nm mode and to decrease for the Aitken and accumulation modes after the precipitation peak. Afternoons with precipitation were preceded by mornings with larger particles of the accumulation mode, whose Dg was ∼ 10 nm larger than in days without precipitation. Nevertheless, this large Dg in the morning seems to influence subsequent rainfall only in the dry season, while in the wet season both N and Dg seem to have the same weight of influence. The observed patterns of the PNSDs in the N–Dg–σ phase space showed to be a promising tool for the characterization of atmospheric aerosols, to contribute to our understanding of the main processes in aerosol–cloud interactions, and to open new perspectives on aerosol parameterizations and model validation.

First validation of high-resolution satellite-derived methane emissions from an active gas leak in the UK

Abstract. Atmospheric methane (CH4) is the second-most-important anthropogenic greenhouse gas and has a 20-year global warming potential 82 times greater than carbon dioxide (CO2). Anthropogenic sources account for ∼ 60 % of global CH4 emissions, of which 20 % come from oil and gas exploration, production and distribution. High-resolution satellite-based imaging spectrometers are becoming important tools for detecting and monitoring CH4 point source emissions, aiding mitigation. However, validation of these satellite measurements, such as those from the commercial GHGSat satellite constellation, has so far not been documented for active leaks. Here we present the monitoring and quantification, by GHGSat's satellites, of the CH4 emissions from an active gas leak from a downstream natural gas distribution pipeline near Cheltenham, UK, in the spring and summer of 2023 and provide the first validation of the satellite-derived emission estimates using surface-based mobile greenhouse gas surveys. We also use a Lagrangian transport model, the UK Met Office's Numerical Atmospheric-dispersion Modelling Environment (NAME), to estimate the flux from both satellite- and ground-based observation methods and assess the leak's contribution to observed concentrations at a local tall tower site (30 km away). We find GHGSat's emission estimates to be in broad agreement with those made from the in situ measurements. During the study period (March–June 2023) GHGSat's emission estimates are 236–1357 kg CH4 h−1, whereas the mobile surface measurements are 634–846 kg CH4 h−1. The large variability is likely down to variations in flow through the pipe and engineering works across the 11-week period. Modelled flux estimates in NAME are 181–1243 kg CH4 h−1, which are lower than the satellite- and mobile-survey-derived fluxes but are within the uncertainty. After detecting the leak in March 2023, the local utility company was contacted, and the leak was fixed by mid-June 2023. Our results demonstrate that GHGSat's observations can produce flux estimates that broadly agree with surface-based mobile measurements. Validating the accuracy of the information provided by targeted, high-resolution satellite monitoring shows how it can play an important role in identifying emission sources, including unplanned fugitive releases that are inherently challenging to identify, track, and estimate their impact and duration. Rapid, widespread access to such data to inform local action to address fugitive emission sources across the oil and gas supply chain could play a significant role in reducing anthropogenic contributions to climate change.

Recurrent Lightning Spots: Where Lightning Strikes More Than Twice

AbstractThe expression “lightning never strikes twice” is questioned in this paper because, among the randomness of lightning impacts, some spots are hit even more than twice year after year. This article introduces the recurrent lightning spots (RLS) concept, which are locations periodically impacted by cloud‐to‐ground lightning every consecutive year over a certain period. RLS are investigated in two regimes, with markedly different lightning climatology but similar orography, for 10 consecutive years: Catalonia (North East of Spain, Europe) and Barrancabermeja (North Central Colombia, South America). Results revealed 148 and 916 RLS in Catalonia and Barrancabermeja, respectively. RLS in both regions are typically found to be related to tall structures, mountain peaks, and steep terrain. The method allowed us to identify those tall towers and orographic relief frequently affected by lightning that are not detected with the mere computation of the ground flash density. In the case of Catalonia, some RLS are found offshore. Besides the scientific interest in understanding lightning, the new concept of RLS provides additional and valuable information applicable to lightning protection engineering.

Statistical assessment of the concentration fluctuations in street canyons via time-resolved wind tunnel experiments

Time-resolved wind tunnel experiments are performed for three periodic street canyon configurations: one of uniform (H/W = 1) and two of variable building height (consisting of 0.5H and 1.5H tall towers in aligned and staggered arrangements) for perpendicular wind direction. The velocity field is mapped using Laser Doppler Anemometry (LDA), and the tracer gas concentration is sampled using Fast Flame Ionization Detection (FFID). The concentration field is characterized by the mean concentration and the characteristic percentiles of the concentration-time series, such as the median and the peak, represented by the 99th percentile, in a total of 1138 sampling points. The probability distribution of the concentration in each point is modeled using the gamma distribution, which is fitted based on the mean and the variance of the measured time series. The results show that the mean pedestrian exposure to air pollutants is significantly lower in the case of heterogeneous roof height, although the mean concentration at the leeward corner of the source canyon can locally exceed those of the uniform street canyons for both tower arrangements of variable building height. Moreover, it is shown that the concentration peaks for both tower configurations can significantly exceed those of the uniform canyons case, especially near the sources.