Relative Wind Direction Research Articles

MODELLING OF WIND-WAVE MISALIGNMENT FOR FLOATING OFFSHORE WIND TURBINES

The influence of the combined effects of wind and waves onto the performance of a Floating Off-Shore Wind Turbine (FOWT) is analyzed. A study of the wind conditions relative to the position of the aerodynamic rotor has been made, analyzing how the angle of incidence of the wind (angle of attack) varies with the wind direction and the inclination of the wind turbine mast as a consequence of the undulatory movement of the waves. This analysis should result in a theoretical model based on the variation of the angle of attack which allows the characterization of the turbine under the combined effect of the oscillation of the sea surface and changes in relative wind direction to the aerodynamic rotor. The results obtained from this research will allow designers and operators to properly manage the situation under which the FOWT is working for a cross action of wave movement and wind direction. A proposed method to compensate for the aforementioned changes in the aerodynamics of the turbine rotor is a so-called “pitch and yaw compensation” system that allows eliminating the effect produced by the variation in the angle of attack and, therefore, minimizing the effect of oscillation on the generated power generated.

Assessment and prediction of PM10 concentration using ARIMA

Urban air pollution is rapidly becoming an environmental issue of global concern, affecting public health, regional weather, and climate. The air quality crisis in cities is mainly caused by vehicle emissions. A city's air quality is assessed using the Air Quality Index (AQI), which analyses concentrations of air pollutants such as PM10, sulphur dioxide SO2, and nitrogen dioxide NO2. The current study on air pollution was carried out in the SG Halli area of Bangaluru and required air pollutant data was collected from the Karnataka State Pollution Control Board (CPCB). With the exception of PM10, the pollutant concentration was within the permissible limits set by the Central Pollution Control Authority (CPCB). Pollutant concentrations were analyzed using meteorological variables such as relative humidity (RH), temperature (T), wind direction (WD), wind speed (WS), and solar radiation (SR). PM10 concentrations are predicted using an auto-regressive integrated moving average (ARIMA) model. PM10 concentrations were well predicted by ARIMA model. On the AQI scale, it can be seen that the atmospheric environment of SG Halli is moderately polluted.

Hydrodynamics and sediment dynamics in Barataria Bay, Louisiana, USA

Barataria Bay is a receiving basin for a large Mid-Barataria Sediment Diversion scheme in Louisiana, USA. In this region, data on sediment transport and hydrodynamics are scarce but essential for the design and planning of future sediment diversion and marsh creation. Four months of bottom boundary layer observations were conducted to study winter and spring hydrodynamics and sediment dynamics in this coastal bay. Hourly waves, tides, currents, and bottom suspended sediment concentrations were measured using multiple optical and acoustic sensors attached to two tripod platforms. High temporal resolution data indicated that the salinity in the northern bay was mainly controlled by northerly winds, and tidal currents kept the salinity high in the southern bay during the winter cold front season. In spring, frequent, pervasive southerly winds and the westward shelf transport of less saline water emerging from the Mississippi River Delta lowered the salinity in the southern bay. Spectral analysis showed that wave-current combined shear stress played the most critical role in triggering sediment resuspension. The Style-Glenn 1-D bottom boundary layer model was applied in sediment flux calculations, and showed that net sediment transport mainly occurred during cold front passages. During two 3-day cold-front events, southward sediment fluxes accounted for 56% of the total sediment flux during the 35-day winter period, revealing their nonlinear, event-driven, and episodic nature. The direction of the sediment transport generally rotated, and its magnitude changed considerably, when southeasterly winds shifted to intensified northwesterly winds. Long-duration southerly pre-frontal winds facilitated wetland sedimentation by transporting sediment to the northern bay during high water level conditions impacted by flooding spring tides or southerly winds. Conversely, northerly winds during cold fronts dominated bidirectional tidal currents and led to southward net sediment transport and possible escape of sediment from the bay. The timing of diversion openings, the orientation of receiving basins, and dominant wind directions in relation to fetch, as well as the dynamic water levels should be considered in the planning and management of future diversion operations in coastal areas.

Active aerodynamics control of simplified vehicle body in a crosswind condition

In this study, the authors used a steady jet from a slit nozzle to control the bi-stable aerodynamics of a simple vehicle model under crosswind conditions. In general, the aerodynamic coefficients of an automobile change continuously with variations in the relative wind direction (i.e. yaw angle). However, some vehicles show a significant change in their aerodynamics at a certain yaw angle because their wake flow structure changes at that yaw angle. Furthermore, around that critical yaw angle, their aerodynamics sometimes show bi-stability in which both the wake structures before and after the change are stable. The investigated model is the famous simplified model in vehicle aerodynamic research known as the Ahmed model. Its slant angle was set at 32° as a configuration that causes bi-stability at a specific yaw angle range larger than 6°. The active aerodynamic control method was demonstrated in both the model scale wind tunnel test and computational fluid dynamics analysis. The slit jet with 18% of the main flow velocity successfully changed the wake flow structure. This showed that it is possible to improve the aerodynamic characteristics.

VARIATION OF PM10 CONCENTRATION DEPENDING ON THE METEOROLOGICAL PARAMETERS IN TWO BUCHAREST MONITORING STATIONS (IN GREEN AREAS)

This study presents the assessment of the PM10 emissions in areas from the south of Bucharest and Ilfov county, for a period of 11 years, during 2008-2018, taking into consideration the most important meteorological parameters with influence to air pollution, such as relative humidity, temperature, wind direction, and wind speed. During the study period, the mean annual concentrations of PM10 decreased from 43.92 μg/m3 to 29.67 μg/m3, expressed as a percentage change the decrease was 35.45% and 29.03% at the B-4 and B-7 stations, respectively. The Pearson correlation coefficient was significantly higher in the cold season (November-April). In order to further investigate the relations of air quality and wind direction pollution roses were calculated and the results indicate that the highest concentrations of PM10 occur in B-4 and B-7 at the southwestern and west direction of wind.

Atmospheric diffusion profiles and health risks of typical VOC: Numerical modelling study

Volatile organic compounds (VOC) are dominantly from industrial production. Comprehension of atmospheric diffusion of VOC is realistic to discharge reduction. Here, transport ranges of VOC were analyzed by aerodynamics modelling, and validated with on-site monitoring. By combining a terrain evolution model, spatiotemporal distributions of typical VOC, the impacts of wind speeds and directions in relation to topographical parameters were acquired. The model outputs show that the low elevation landscapes experience significant variation in concentration distributions of VOC when accompanied by strong shear flow regimes with non-uniform wind velocities. Case studies suffer 13.0% and 24.2% increases of VOC concentration ratio outside/inside industry park, with long-range transport of VOC indicated by dominances of lower wind speeds and higher humidity. High ratio, from atmospheric diffusion of VOC from industry park, poses great exposure risk to surrounding residents. The spatial map of time-specific health risks, proving VOC concentration accumulation enhancing risks of school-aged children than adults, was consequently produced from models. Overall, addressing the impact of regularities during VOC diffusion on occupational workers and residents will suggest a valuable reference for decision-making of emission-abatement strategies and awareness-raising health-risk interventions.

Using global reanalysis data to quantify and correct airflow distortion bias in shipborne wind speed measurements

Abstract. At sea, wind forcing is responsible for the formation and development of surface waves and represents an important source of near-surface turbulence. Therefore, processes related to near-surface turbulence and wave breaking, such as sea spray emission and air–sea gas exchange, are often parameterised with wind speed. Thus, shipborne wind speed measurements provide highly relevant observations. They can, however, be compromised by flow distortion due to the ship's structure and objects near the anemometer that modify the airflow, leading to a deflection of the apparent wind direction and positive or negative acceleration of the apparent wind speed. The resulting errors in the estimated true wind speed can be greatly magnified at low wind speeds. For some research ships, correction factors have been derived from computational fluid dynamic models or through direct comparison with wind speed measurements from buoys. These correction factors can, however, lose their validity due to changes in the structures near the anemometer and, thus, require frequent re-evaluation, which is costly in either computational power or ship time. Here, we evaluate if global atmospheric reanalysis data can be used to quantify the flow distortion bias in shipborne wind speed measurements. The method is tested on data from the Antarctic Circumnavigation Expedition onboard the R/V Akademik Tryoshnikov, which are compared to ERA-5 reanalysis wind speeds. We find that, depending on the relative wind direction, the relative wind speed and direction measurements are biased by −37 % to +22 % and -17∘ to +11∘ respectively. The resulting error in the true wind speed is +11.5 % on average but ranges from −4 % to +41 % (5th and 95th percentile). After applying the bias correction, the uncertainty in the true wind speed is reduced to ±5 % and depends mainly on the average accuracy of the ERA-5 data over the period of the experiment. The obvious drawback of this approach is the potential intrusion of model biases in the correction factors. We show that this problem can be somewhat mitigated when the error propagation in the true wind correction is accounted for and used to weight the observations. We discuss the potential caveats and limitations of this approach and conclude that it can be used to quantify flow distortion bias for ships that operate on a global scale. The method can also be valuable to verify computational fluid dynamic studies of airflow distortion on research vessels.

CAA research programme – Helicopter Operations to Moving Offshore Helidecks

ABSTRACTThe background and rationale for the research reported in this paper is detailed in the companion paper subtitled Part A: Modelling the on-deck helicopter Reserve of Stability (ROS).This paper (Part B) derives the fundamental principles underpinning the safe operational envelope and the definition of Motion Severity and Wind Severity Indices (MSI/WSI), and then presents the probabilistic modelling methodology developed for calculating safe limits for these parameters (MSI/WSI limits curves). The introduction of the Relative Wind Direction (RWD) as an additional limiting parameter is also discussed, together with an explanation of how RWD limits have been derived and how they are linked with the MSI/WSI limits calculation.The MSI/WSI limits modelling methodology presented in this paper builds on the analytical helicopter stability modelling discussed in Part A. It uses a probabilistic approach to manage the variability in helicopter operations across the UK and to deal with the uncertainty of predicting helideck motion and wind conditions for the period the helicopter is landed on the helideck based on measurements taken prior to landing. This has been developed with the assistance of industry experts and has been subjected to consultation with stakeholders in the UK with the aim of identifying the right balance between enhancing safety and preserving operability.A new Helideck Monitoring System (HMS) standard has been developed which incorporates the MSI/WSI/RWD functionality. The standard was published by the Helideck Certification Agency in April 2018 with a compliance date of 31 March 2021. Operations to moving decks not equipped with HMS meeting the new standard will be restricted to stable helideck conditions.

CAA research programme – Helicopter Operations to Moving Offshore Helidecks

ABSTRACTThe oil and gas industry relies heavily on helicopters for transporting personnel and cargo to and from offshore installations and support vessels. A growing number of offshore helicopter operations are to moving helidecks, which include large vessels such as FPSOs, drill ships, and semi-submersibles, as well as smaller service vessels. Landing a helicopter on a moving helideck presents additional challenges to those faced on fixed helidecks, not only at the point of touchdown but also for the entire period the helicopter remains on the helideck.The UK Civil Aviation Authority (CAA), on behalf of the joint CAA/industry Helicopter Safety Research Management Committee has led a comprehensive programme of research over a number of years, aimed at improving the operational safety of helicopters landing on moving helidecks. The work focused on the aspect of the stability of helicopters once landed on a moving helideck, this being the main source of in-service incidents and accidents as evidenced in the Mandatory Occurrence Reports. The project culminated in the development of a new standard for Helideck Monitoring Systems (HMS), which was published by the Helideck Certification Agency in April 2018 with an implementation compliance date of 31 March 2021. Operations to moving helidecks not equipped with HMS meeting the new standard will be restricted to stable deck conditions from this date. The research underpinning the new standard is presented in two papers.This paper (Part A), presents the analytical approach that has been developed to model the Reserve of Stability (ROS) for all modes of failure of a helicopter on a moving offshore helideck.The analytical model covers all modes of on-deck failure (roll-over and sliding), for any nose wheel tricycle undercarriage helicopter. The mathematical expressions that have been derived are remarkably simple, physically intuitive, and make the relative contribution of all the destabilising factors easy to understand and assess. These analytical expressions can be used to calculate the ROS of any helicopter in real time, as well as for calculating an envelope of safe operating limits.This approach has many advantages compared to conventional ‘black box’ modelling methods. The main advantage is that it simplifies the modelling of the destabilising effect of helideck motion and allows the most salient parameters governing on-deck ROS to be defined, namely the Measure of Motion Severity, the instantaneous wind speed as the Measure of Wind Severity, and the wind direction relative to the helicopter (Relative Wind Direction).The main rotor lift generated during the time the helicopter remains on-deck (at Minimum Pitch on Ground, MPOG) has been one of the most important unknowns that this research programme has sought to address. An empirical model for estimating the lift at MPOG has been developed, based on experimental and field data. Practical methods for quantifying fuselage wind drag and the vertical position of the centre of gravity were also developed, which allow different helicopter types to be assessed without recourse to helicopter Original Equipment Manufacturer (OEM) proprietary information or models. Finally, a comparison and evaluation of the model against dedicated field trial measurements is presented, together with a discussion of the modelling strengths and weaknesses, and recommendations for further work.

Impact of elevated outdoor MRT station towards passenger thermal comfort: A case study in Jakarta MRT

Comfort of the train passengers is the main priority of modern mass rapid transit (MRT) management. Objective of this paper is to investigate the thermal comfort of the elevated MRT station in tropical climate. The first step of this study was to conduct literature review on human thermal comfort, environment ergonomics, computational fluid dynamic (CFD), computational aeroacoustics (CAA), and predicted mean vote (PMV). Air quality in elevated MRT station was measured based on several parameters: relative humidity, wind speed, temperature, and wind direction. A 3D model of MRT designed was used to describe existing condition prior to simulations with CFD and CAA softwares. Predicted mean vote is arranged based on the value of metabolism, wind speed, ambient temperature, mean radiant temperature, amount of insulation from clothing, and relative humidity. Whereas predicted percentage of dissatisfi ed (PPD) can be derived from PMV calculations. The analysis shows that the average PMV of existing condition for elevated outdoor MRT station is 3.6 (extremely hot) with PPD is 100% (all passengers felt discomfort). Some recommendations to reduce heat stress were addressed such as: adding plant, changing materials of the MRT station, and change the design of the elevated MRT station. Modifying open elevated MRT station into indoor elevated MRT station with installing six units of AC (2pk, ±23°C) can improve air quality and maintain the thermal comfort scale of PMV to be –0.04 (comfort) with PPD of < 8%. Based on the analysis, it can be concluded that the most suitable design for elevated MRT station in tropical climate (hot and humid) is indoor MRT station with pay attention to both direct and indirect heat exposure that hit the station.

Use of mathematical models and computer software for analysis of traffic noise

Abstract Noise measurement and evaluation of the existing noise situation is carried out in the vicinity of selected roads to demonstrate the need for the design of anti-noise measures or to assess the effectiveness of the measures. The selection and number of measuring points, time and intervals, the road noise measurement procedure and the measuring instruments used shall be used in accordance with the provisions of the STN ISO 1996-1 and STN ISO 1996-2 standards. During the measurement, it is also necessary to determine the microclimatic conditions of measurement, such as temperature and relative humidity, wind direction and speed, barometric pressure, duration and intensity of precipitation at the measuring point. The determinant for the definition of road traffic noise is the equivalent sound level A or the equivalent sound level in the third octave bands over a given time interval. In specific cases, it is possible to determine the equivalent sound pressure level from individual vehicle transit.

Lidar-assisted yaw control for wind turbines using a 9-beam nacelle lidar demonstrator

In this study, the relationship between lidar-assisted yaw control and the measurement parameters was clarified using an experimental approach. To investigate the influence of the nacelle lidar configuration on lidar-assisted yaw control, two scan patterns and pulse-integration number settings were varied. The field tests revealed that, in most cases, the relative wind direction was reduced by the lidar-assisted control. The condition with high lidar data availability avoids the influence of noise, and the lidar-assisted control reduces the relative wind direction. These results suggest that in lidar-assisted yaw control, the management of the appropriate lidar data availability is more important than the scan pattern.

A Geophysical Model Function for Wind Speed Retrieval From C-Band HH-Polarized Synthetic Aperture Radar

Synthetic aperture radar (SAR) imagery is routinely acquired at HH-polarization in high-latitude areas for measuring surface wind over the ocean. However, in the contrary of VV-polarization, there is no HH-polarization geophysical model function (GMF) exists to directly retrieve wind speed from SAR images. In general, HH-polarized normalized radar cross section (NRCS) is thus converted into VV-polarization and then conventional CMOD functions are used with auxiliary wind direction information for wind speed retrieval. In this letter, we propose a new GMF for SAR ocean surface wind speed retrieval, called CMODH, which relates the C-band NRCS acquired at HH-polarization over the ocean, to the 10-m height wind speed, incident angle, and relative wind direction. We first use more than 220 000 ENVISAT ASAR radar backscatter measurements collocated with ASCAT winds to derive the CMODH coefficients. Subsequently, 1459 RADARSAT-2 (RS-2) and 428 Sentinel-1A/B (Sl-1A/B) HH-polarized SAR acquisitions under different wind speeds are matched to in situ buoy observations to validate CMODH. The statistical comparisons between SAR-observed and simulated NRCS show a bias of −0.07 dB and a root-mean-square error of 1.62 dB for RS-2, and −0.01 dB and 2.48 dB for S1-1A/B. These results suggest that the proposed CMODH has the potential to directly retrieve ocean surface wind speeds using C-band SAR images acquired at HH-polarization, with no need for NRCS transformation by using various empirical and theoretical polarization ratio models.

Coupled rainfall and water vapour stable isotope time series reveal tropical atmospheric processes on multiple timescales

AbstractHigh‐frequency stable isotope data are useful for validating atmospheric moisture circulation models and provide improved understanding of the mechanisms controlling isotopic compositions in tropical rainfall. Here, we present a near‐continuous 6‐month record of O‐ and H‐isotope compositions in both water vapour and daily rainfall from Northeast Australia measured by laser spectroscopy. The data set spans both wet and dry seasons to help address a significant data and knowledge gap in the southern hemisphere tropics. We interpret the isotopic records for water vapour and rainfall in the context of contemporaneous meteorological observations. Surface air moisture provided near‐continuous tracking of the links between isotopic variations and meteorological events on local to regional spatial scales. Power spectrum analysis of the isotopic variation showed a range of significant periodicities, from hourly to monthly scales, and cross‐wavelet analysis identified significant regions of common power for hourly averaged water vapour isotopic composition and relative humidity, wind direction, and solar radiation. Relative humidity had the greatest subdiurnal influence on isotopic composition. On longer timescales (weeks to months), isotope variability was strongly correlated with both wind direction and relative humidity. The high‐frequency records showed diurnal isotopic variations in O‐ and H‐isotope compositions due to local dew formation and, for deuterium excess, as a result of evapotranspiration. Several significant negative isotope anomalies on a daily scale were associated with the activity of regional mesoscale convective systems and the occurrence of two tropical cyclones. Calculated air parcel back trajectories identified the predominant moisture transport paths from the Southwest Pacific Ocean, whereas moisture transport from northerly directions occurred mainly during the wet season monsoonal airflow. Water vapour isotope compositions reflected the same meteorological events as recorded in rainfall isotopes but provided much more detailed and continuous information on atmospheric moisture cycling than the intermittent isotopic record provided by rainfall. Improved global coverage of stable isotope data for atmospheric water vapour is likely to improve simulations of future changes to climate drivers of the hydrological cycle.

Ocean Surface Wind Speed Retrieval Using Simulated RADARSAT Constellation Mission Compact Polarimetry SAR Data

We investigated the use of C-band RADARSAT Constellation Mission (RCM) synthetic aperture radar (SAR) for retrieval of ocean surface wind speeds by using four new channels (right circular transmit, vertical receive (RV); right circular transmit, horizontal receive (RH); right circular transmit, left circular transmit (RL); and right circular transmit, right circular receive (RR)) in compact polarimetry (CP) mode. Using 256 buoy measurements collocated with RADARSAT-2 fine beam quad-polarized scenes, RCM CP data was simulated using a “CP simulator”. Provided that the relative wind direction is known, our results demonstrate that wind speed can be retrieved from RV, RH and RL polarization channels using existing C-band model (CMOD) geophysical model function (GMF) and polarization ratio (PR) models. Simulated RR-polarized radar returns have a strong linear relationship with speed and are less sensitive to relative wind direction and incidence angle. Therefore, a model is proposed for the RR-polarized synthetic aperture radar (SAR) data. Our results show that the proposed model can provide an efficient methodology for wind speed retrieval.

EFFECTS OF METEOROLOGICAL VARIABLES ON NITROGEN DIOXIDE VARIATION

<p>The study presents results of the measurements of the atmospheric nitrogen dioxide concentration and simultaneous meteorological variables: average temperature, air pressure, and relative humidity, speed and wind direction. The data were collected from July 2015 to June 2017 at stations located in Banja Luka (locality Centre). Nitrogen dioxide is one of the major environmental pollutants which has negative impact on plants growth, atmospheric chemistry and climate change. Levels of nitrogen dioxide in air samples and meteorological variables from urban zone of Banja Luka were determined at locality, which is highly populated area, with intensive traffic. The study presents average measured values of nitrogen dioxide, together with maximal and minimal values and relationship between nitrogen dioxide and meteorological variables, i. e. for pollution modelling together with meteorological variables. Statistical analysis confirms string of rolls, which shows directional connection between nitrogen dioxide and meteorological variables. Correlation between nitrogen dioxide and temperature (r= -0.207), wind speed (r= -0.130) and relative humidity (r= -0.048) was negative and significant during the measurement period.</p>

Meteorological pattern analysis assisted daily PM2.5 grades prediction using SVM optimized by PSO algorithm

Daily PM2.5 level has significant influence on human health, which is attracting increasing attention. The prediction of PM2.5 grades has thus become an important factor closely related to social development. In the past decades, many prediction methodologies for PM2.5 have been developed, including regression analysis, neural network model, and support vector machine model. Despite these progresses, it still remains a great challenge to predict the PM2.5 grades more accurately and efficiently. In this work, we applied meteorological pattern analysis to assist the support vector machine (SVM) model for PM2.5 class prediction. Cosine similarity was first used to extract three most relevant ones from six common meteorological parameters (atmospheric pressure, relative humidity, air temperature, wind speed, wind direction, cumulative precipitation) to give the needed meteorological pattern for SVM model. Higher prediction accuracy was then obtained with the selected pattern composed by relative humidity, wind speed and wind direction. Moreover, genetic algorithm (GA) and particle swarm optimization (PSO) algorithm were investigated for optimizing the parameters in the process of SVM classification, with PSO-SVM presenting the highest accuracy and efficiency (forecasting time significantly reduced by 25%). We further introduced the criteria of precision, recall and F1-score to evaluate the prediction results of PSO-SVM in each PM2.5 grade. Meanwhile, comparative studies confirmed that PSO-SVM displayed better performance than Adaboost and ANN models for the applied meteorological pattern analysis assisted PM2.5 grades prediction. These obtained results indicate the validity of meteorological pattern analysis for efficient air quality forecasting.

Meteorological Variables That Affect Visibility Degradation and Their Seasonal Trends in the Niger Delta Region of Nigeria

The study of visibility in the Niger Delta region is necessary because it reflects the atmospheric changes caused by economic expansion in Nigeria. Cities in the Niger Delta (especially Port Harcourt) are the most polluted cities in the country and therefore visibility degradation has become one of the major environmental challenge in Nigeria. Analysis of a 31 years (1981-2012) monthly mean horizontal visibility data and monthly mean datasets of meteorological parameters such as relative humidity and wind direction obtained from Nigerian Meteorological Agency (NIMET) and the National Centre for Environmental Prediction (NCEP) for Calabar, Uyo, Port Harcourt, Owerri, Warri and Akure was done using statistical techniques. A correlation analysis was done and the annual visibility variability indexes from (NIMET) shows significant correlation with the (NCEP) datasets for R/humidity at r=0.1334 and Wind direction at r=0.1210 respectively at 90% confidence level from t-test. This study concluded that the relationship of the atmospheric visibility and meteorological factors are closely related. The results showed that visibility is more correlated with Relative humidity in places with high hydrocarbon activities leading to excess aerosol loading like Port Harcourt while it is better correlated with wind direction in places with less hydrocarbon activities like Calabar and Akure. The results of this study can assist policy makers and operators in establishing positive strategies to improve the air quality.

Effects of Some Meteorological Parameters on Visibility in the Niger Delta Region of Nigeria

Effects of meteorological parameters of relative humidity and wind direction on visibility in the Niger Delta, Nigeria (4.15°N-7.17°N, 5.05°E-8.68°E) for a period of 31 years (1981-2012) have been investigated. The data on visibility, relative humidity and wind direction were obtained from Nigerian Meteorological Agency (NIMET) and National Center for Environmental Prediction (NCEP) respectively. The visibility and meteorological data were analyzed to study the temporal variation of atmospheric visibility and its relationship with meteorological parameters in the region. The analysis was done using statistical techniques and the results show that cities in the Eastward (Calaber, Uyo and Port Harcourt) have more inverse correlation between Relative humidity and visibility while Westward cities (Owerri, Warri and Akure) are more directly correlated to visibility. Again it shows that visibility is more correlated with relative humidity in places of high hydrocarbon activities like Port Harcourt while it is better correlated with wind direction in places with less hydrocarbon activities like Akure.

Microclimate simulation and model optimization of the effect of roadway green space on atmospheric particulate matter

Urban green spaces have the potential to mitigate and regulate atmospheric pollution. However, existing studies have primarily focused on the adsorption effect of different plants on atmospheric particulate matter (PM), whereas the effect of green space on PM has not been adequately addressed. In this study, the effect of different urban green space structures and configurations on PM was investigated through the 3D computational fluid dynamics (CFD) model ENVI-met by treating the green space as a whole based on field monitoring, and at the same time, the regulatory effect of green space on PM was examined by integrating information about the forest stand, PM concentration, and meteorological factors. The results show that the green space primarily affected wind speed but had no significant effect on relative humidity, temperature, or wind direction (P > 0.05). The PM concentration was significantly positively correlated with the relative humidity (P < 0.01), significantly negatively correlated with temperature (P < 0.05), but not significantly correlated with wind speed and direction (P > 0.05). Comparison with the measured values reveals that the ENVI-met model well reflected the differences in PM concentrations between different green spaces and the effect of green space on PM. In different green space structures, the uniform-type structure performed rather poorly at purifying PM, the concave-shaped structure performed the best, and the purifying effectiveness of the incremental-type and convex-shaped structure of green space was higher in the rear region than in the front region; in contrast, the degressional-type green space structure was prone to cause aggregation of the PM in the middle region. Broadleaf and broadleaf mixed forests had a better purifying effectiveness on PM than did coniferous forests, mixed coniferous forests, and coniferous broadleaf mixed forests. The above results are of great significance for urban planning and maximizing the use of urban green space resources.