Air Dew Point Research Articles

Air–Sea Interface Parameters and Heat Flux from Neural Network and Advanced Microwave Scanning Radiometer Observations

We present a new approach, based on a multi-parameter back-propagation neural network (BPNN) model, to simultaneously retrieve sea surface wind speed, sea surface temperature, near-surface air temperature, and dewpoint temperature over the global oceans from the Advanced Microwave Scanning Radiometer 2 (AMSR2) onboard the Global Change Observation Mission 1st-Water (GCOM-W1). The model is trained and validated with the collocations of AMSR2 multi-channel (6.9–36.5 GHz) brightness temperatures, under both clear and cloudy conditions, and National Data Buoy Center (NDBC) and Tropical Atmosphere Ocean Project (TAO) buoy measurements along with ECMWF ERA5 reanalysis data. The root-mean-square (rms) errors of BPNN-retrieved sea surface wind speed, sea surface temperature, near-surface air temperature, and dewpoint temperature are 1.13 m/s, 1.02 °C, 1.20 °C, and 1.57 °C, respectively. The first three retrieved geophysical parameters and the estimated relative humidity from near-surface air temperature and dewpoint temperature are used to compute the sensible heat flux (SHF) and latent heat flux (LHF), using an improved bulk flux parametrization. The rms errors of the estimated SHF and LHF from BPNN-derived air–sea interface variables, and those from buoy and reanalysis data, are 18.13 W/m2 and 39.56 W/m2. We also compare SHF and LHF estimates with the Yongxing air–sea flux tower measurements in the northern South China Sea. The estimated SHF and LHF in summer and autumn periods are closer to observations than in winter and spring. The proposed method has potential to derive instantaneous air–sea interface atmospheric and oceanic parameters as well as surface sensible and latent heat fluxes from AMSR2 along-track wide swath observations.

Enhancing the cooling capacity of radiant ceiling panels by latent heat transfer of superhydrophobic surfaces

The cooling capacity of a radiant ceiling panel (RCP) is highly limited in hot and humid climates as the panel surface temperature must be controlled higher than the air dew point to avoid condensation. Previous research suggested that condensation risks can be mitigated by using superhydrophobic surface materials, making ceiling panels applicable with the surface temperature below the air dew point. In this study, the enhanced cooling capacity of RCP due to latent heat transfer is estimated. Firstly, the condensation heat transfer of a superhydrophobic aluminum surface under natural convection in humid air with subcooling degrees between 3 °C and 12 °C was investigated by experiments. The data proved that the heat and mass transfer analogy method can be used to well predict the condensation heat transfer of the superhydrophobic surface with an error within 15%. Based on the finding, the heat and mass transfer analogy and traditional empirical methods were employed to predict the total heat flux of RCP with latent heat transfer. The results indicated an enhancement of 3% to 500% for the total heat flux compared with RCP with only sensible cooling, depending on the panel surface temperature, air temperature and humidity. This study draws a clear picture of how the cooling capacity of RCP can be enhanced via a latent heat transfer process, and this can be realized not necessarily with net moisture removal capacities with hydrophobic surfaces due to the droplet jumping phenomenon and the due re-evaporation process, showing a hidden potential of radiant cooling panels.

The impact of meteorological parameters on PM10 and visibility during the Middle Eastern dust storms.

Air pollution is one of the most pressing issues in populated Middle Eastern cities, in particular for the city of Ahvaz, Iran, imposing deleterious effects on the environment, public health, economy, culture, and other sectors. In this study, we investigate the relationship between meteorological parameters, PM10, AOD, air mass source origin, and visibility during severe desert dust storms (Average3h PM10 > 3200µgm-3) between 2009 and 2012. Six of seven such events occurred between February and March. Interestingly, for the seven cases there was always an alarming PM10 mass concentration peak (137-553µgm-3) between 12:00-18:00 (local time) that was 18-24h before the dominant peak of the storm (3279-4899µgm-3). The maximum wind speed over the multi-day periods examined for the dust storms is usually observed 6h before the alarming PM10 peak. The minimum relative humidity, dew point temperature and air pressure occurred ± 3h around the time of the alarming PM10 peak. Wind speed was the meteorological parameter that was consistently higher around the time of the first peak as compared to the second peak, with the reverse being true for sea level pressure. Based on four years of daily data in Ahvaz, PM10 was positively correlated with wind speed and air temperature and inversely correlated with sea level pressure and RH. An empirically-derived equation with R2 = 0.95 is reported to estimate the maximum PM10 concentration for severe desert dust events in the study region based on meteorological parameters. Finally, AOD is shown to correlate strongly (R2 = 0.86) with PM10 during periods with severe desert dust storms in the region.

Performance test of medium-temperature chiller with induction air-conditioning system

Abstract In this paper, medium-temperature chiller with induction air-conditioning system is introduced. Several onsite measurements were carried out on temperature and relative humidity distribution and energy consumption in summer 2020 in order to study the potential performance when applied in hot summer cold winter zone. The performance test results show that (1) the indoor temperature and humidity both comply with the range of design parameters; (2) the corresponding indoor air dew point temperature is much lower than the supply air temperature of air inductive unit, which implies no condensed water or dew on surface of air inductive unit; (3) the performance of the circulation pump, extensive type air handling unit fan; and medium-temperature chiller has exceeded the requirements of national standards.

고층건축물의 높이에 따른 대류열전달률이 실내표면결로에 미치는 영향에 관한 이론적 연구

Although the temperature coefficient between outdoor air temperature and indoor air temperature is used to determine whether condensation occurs, it is reasonable to predict surface condensation using the surface temperature difference between outdoor and indoor. This study is conducted to determine whether condensation occurs by not using the air temperature difference between indoor and outdoor (the existing methods) but by applying the surface temperature difference between indoor and outdoor surfaces. The outdoor surface temperature is affected by air velocity on the building height, thus the convection heat transfer coefficient is different depending on the building height. The indoor surface temperature distribution is 21.4℃～21.5℃ when the existing equation is applied. But by applying the proposed equation, the indoor surface temperature distribution for the lower floor is 13.0～17.8℃, for the middle floor is 12.3℃～ 17.1℃, and for the top floor is 12.0℃～16.8℃. As the indoor surface temperature can be lower than indoor air dew point temperature, surface condensation is possible.

Soil Temperature Prediction via Self-Training: Izmir Case

This paper proposes a new model, called Soil Temperature prediction via Self-Training (STST), which successfully estimates the soil temperature at various soil depths by using machine learning methods. The previous studies on soil temperature prediction only use labeled data which is composed of a variable set X and the corresponding target value Y. Unlike the previous studies, our proposed STST method aims to raise the sample size with unlabeled data when the amount of pre-labeled data is scarce to form a model for prediction. In this study, the hourly soil-related data collected by IoT devices (Arduino Mega, Arduino Shield) and some sensors (DS18B20 soil temperature sensor and soil moisture sensor) and meteorological data collected for nearly nine months were taken into consideration for soil temperature estimation for future samples. According to the experimental results, the proposed STST model accurately predicted the values of soil temperature for test cases at the depths of 10, 20 30, 40, and 50 cm. The data was collected for a single soil type under different environmental conditions so that it contains different air temperature, humidity, dew point, pressure, wind speed, wind direction, and ultraviolet index values. Especially, the XGBoost method combined with self-training (ST-XGBoost) obtained the best results at all soil depths (R2 0.905-0.986, MSE 0.385-2.888, and MAPE 3.109%-8.740%). With this study, by detecting how the soil temperature will change in the future, necessary precautions for plant development can be taken earlier and agricultural returns can be obtained beforehand.

Measurement of indoor environmental parameters and analysis of the condensation phenomenon in urban utility tunnels

Condensation is a major issue in the safe operation of utility tunnels. To address the condensation problem, the indoor air temperature, relative humidity (RH) and surface temperature in an urban utility tunnel in Jining were continuously measured, and the condensation conditions were surveyed and analysed. The results indicated that under natural ventilation conditions, the air temperature in the comprehensive cabin varied from 23.4°C to 24.5°C, the RH fluctuated between 86.4% and 95.3%, and the corresponding air dew point temperature (DPT) remained in the range of 22.2°C–22.9°C. The surface temperature of the water supply pipeline ranged from 17.8°C to 18.5°C, which was far lower than the DPT in the tunnel, resulting in serious condensation. A water supply pipeline with an anti-condensation design was developed based on environmental test data. A 25-mm-thick rubber plastic sponge insulation layer was used to thermally insulate the water supply pipeline, preventing further dew condensation. Furthermore, mechanical ventilation had little effect on reducing the RH in the tunnel and may actually cause dew condensation; therefore, a ventilation control mode was proposed in this study. These results are expected to provide basic data for further research and reference for the safe management of utility tunnels.

Decreasing of the air humidity by the ventilation control in the St. Barbara mine

The St. Barbara mine is a visitor mine having a large amount of timbering support which is deteriorating fast due to the high humidity conditions. The air conditioning system of mining is not suitable and also expensive for implementation in a shallow non-productive mine. As there are no usual air contaminants in the visitor mines, ventilation could be powered only when a dew point of outside air is below the strata temperature. Applying this rule would certainly avoid condensation, but also raises a potential for partial dehumidification of mine walls as moisture can evaporate in these conditions. A microclimate analysis, based on one-year data, has showed that these favorable conditions of the outside air occur through the major part of the year. Their availability is mostly 100%, but during summertime there are periods when it drops down to 13%. A real time monitoring system with programable microcontroller allows the automatic ventilation control and adjustment to the psychrometric conditions.

The Anatomy of the South Carolina U.S.A. Coastal Sea Breeze 2019-2020

The study presented herein is the analysis of Sodar based instrument measurements of air temperature, dew point, and vertical wind speed and direction, recorded at two South Carolina sites, Waties Island in North Myrtle Beach and in Sumter, and at three atmospheric ground stations. Two of the ground stations are National Weather Service stations near the Sodars and one is a Coastal Carolina University Sea-Econet, as a part of the National Oceanic & Atmospheric Administration, MESO program, weather-sensor site on the Coastal Carolina University campus in Conway South Carolina. Objectives of this study are to establish specific values of winds, land and sea temperatures, precipitation and dew points associated with the changes induced by passages of the Sea Breeze Front, and to examine differences in the station-to-station incarnation of the Sea Breeze circulation. Variability from station to station in the nature and timing of Sea Breeze Front passage is found to be a function of relative proximity to the coast with Sea Breeze Front passage occurring earliest at the North Myrtle Beach site (the station at the coast), then at Sumter (~100 km inland) and finally Aiken at >100 km inland. Satellite based estimates of the percentages of onshore penetration distances from the coast are depicted. Wind vectors and air temperatures associated with onsets and passages of the Sea Breeze display robust wind fields directed onshore perpendicular to the coastline. Kinematical descriptors of the Sea Breeze wind particle motions are presented and display coherent stable elliptical motions during the late summer to early fall but are absent during the winter.

Integration of Multisource Data to Estimate Downward Longwave Radiation Based on Deep Neural Networks

Downward longwave radiation (DLR) at the surface is a key variable of interest in fields, such as hydrology and climate research. However, existing DLR estimation methods and DLR products are still problematic in terms of both accuracy and spatiotemporal resolution. In this article, we propose a deep convolutional neural network (DCNN)-based method to estimate hourly DLR at 5-km spatial resolution from top of atmosphere (TOA) brightness temperature (BT) of the Himawari-8/Advanced Himawari Imager (AHI) thermal channels, combined with near-surface air temperature and dew point temperature of ERA5 and elevation data. Validation results show that the DCNN-based method outperforms popular random forest and multilayer perceptron-based methods and that our proposed scheme integrating multisource data outperforms that only using remote sensing TOA observations or surface meteorological data. Compared with state-of-the-art CERES-SYN and ERA5-land DLR products, the estimated DLR by our proposed DCNN-based method with physical multisource inputs has higher spatiotemporal resolution and accuracy, with correlation coefficient (CC) of 0.95, root-mean-square error (RMSE) of 17.2 W/m², and mean bias error (MBE) of -0.8 W/m² in the testing period on the Tibetan Plateau.

Scaling of precipitation extremes with temperature in China’s mainland: Evaluation of satellite precipitation data

This study explores the sensitivity (termed scaling factor, SF) of daily and 30-minute precipitation extremes with several temperature variables, i.e., within-day surface air temperature (SAT) and dew point temperature (DPT), and antecedent SAT and DPT (corresponding to temperatures one day before a precipitation event, denoted as SAT-C and DPT-C) across China’s mainland. To this end, we used observed daily meteorological data from CN05.1 dataset and 30-minute precipitation data from the Integrated Multisatellite Retrievals for the Global Precipitation Measurement (IMERG). Our results reveal a mix of the positive and negative SFs of extreme daily precipitation with SAT across climatic zones, with peak-like structures developing at higher temperatures (between 17 and 24 °C). Although almost all the SFs turn to positive when SAT-C, DPT, and DPT-C are used, a peak structure is observed over some parts of each climate zone, especially in tropical regions. A comparison between the SFs of the full temperature range and the temperature range before peak structure reveals that a single scaling rate is not valid for the entire temperature range. Moreover, the SFs calculated based on the temperature range before the peak structure (for all four types of temperatures) follow better the Clausius-Clapeyron scaling (∼7%/°C) than the SFs of the full temperature range except for the tropical region. Daily SFs based on IMERG data are mostly comparable to CN05.1 results, with discrepancies mainly in tropical and plateau climates (roughly 25% of the study area). However, IMERG’s 30-min precipitation extremes do not rise as much as expected (even decrease in some parts of the country) with increasing temperatures, contrary to common observations reported in previous studies. It suggests that another precipitation dataset is needed for scaling precipitation extremes at a 30-minute scale, at least for China’s mainland.

Seasonal Dynamics of Photochemical Performance of PS II of Terrestrial Mosses from Different Elevations

Mosses are critical components of tropical forest ecosystems and have multiple essential ecological functions. The drying and rehydrating and often hot environments in tropical regions present some of the greatest challenges for their photosynthetic activities. There is limited knowledge available on the physiological responses to the changing environments such as temperature and water pattern changes for terrestrial mosses. We examined the seasonal dynamics of photochemical performance of PS II through the measuring of chlorophyll fluorescence of 12 terrestrial mosses in situ from five different elevations by Photosynthesis Yield Analyzer MINI-PAM-II, along with the seasonal changes of climatic factors (air temperature, dew point, relative humidity and rainfall), which were collected by local weather stations and self-deployed mini weather stations. The results showed a great seasonality during observing periods, which, mainly the changes of rainfall and relative humidity pattern, presented significant impacts on the photochemical performance of PS II of terrestrial mosses. All these tested moss species developed a suitable regulated and non-regulated strategy to avoid the detrimental effect of abiotic stresses. We found that only Hypnum plumaeforme, Pterobryopsis crassicaulis and Pogonatum inflexum were well adapted to the changes of habitat temperature and water patterns, even though they still experienced a lower CO2 assimilation efficiency in the drier months. The other nine species were susceptible to seasonality, especially during the months of lower rainfall and relative humidity when moss species were under physiologically reduced PS II efficiency. Anomobryum julaceum, Pogonatum neesii, Sematophyllum subhumile, Pseudotaxiphyllum pohliaecarpum and Leucobryum boninense, and especially Brachythecium buchananii, were sensitive to the changes of water patterns, which enable them as ideal ecological indicators of photosynthetic acclimation to stressed environments as a result of climate change.

Evidence of dynamical transition and maximum predictability of air temperature, relative humidity and dew point temperature

Monitoring and predicting the climatic phenomenon are the major global concern because of its devasting effects on people's lives and their environments. As a result of this, there is a need to understand the natural processes that control the dynamic evolution of the climatic phenomenon. Air temperature and relative humidity data collected from Nsukka station by the Centre for Atmospheric Research (CAR), measured in 5 minutes time steps from 1st January till 31st December, 2012 have been analysed. Dew point temperature was calculated from the actual readings of air temperature and relative humidity using appropriate empirical relation. In this paper, Average Mutual Information (AMI), False Nearest Neighbour (FNN) and Lyapunov Exponent methods were used to study changes and transitions in the dynamics of these meteorological parameters or temporal deviations from their overall dynamical regimes. The results show that the dynamic model needed to describe the data has 4-5 dimensions for air temperature, 4-6 for relative humidity and 4-5 for dew point temperature. Positive and negative Lyapunov exponents were observed in the air temperature, relative humidity and dew point temperature time series. This indicates that there exists periodicity inherent in the chaotic behaviour of these meteorological time series, causing a transition from chaoticity (positive Lyapunov exponent) to periodicity (negative Lyapunov exponent) and thereafter to chaoticity (positive Lyapunov exponent). The results, therefore, provide additional information about the climate transitions, maximum predictability and also, for formulating a weather prediction model.

Grey Correlation Analysis of Haze Impact Factor PM2.5

In recent years, frequent severe haze weather has formed in China, including some of the most populated areas. We found that these smog-prone areas are often relatively a “local climate” and aim to explore this series of scientific problems. This paper uses remote sensing and data mining methods to study the correlation between haze weather and local climate. First, we select Beijing, China and its surrounding areas (East longitude 115°20′11″–117°40′35″, North latitude 39°21′11″–41°7′51″) as the study area. We collected data from meteorological stations in Beijing and Xianghe from March 2014 to February 2015, and analyzed the meteorological parameters through correlation analysis and a grey correlation model. We study the correlation between the six influencing factors of temperature, dew point, humidity, wind speed, air pressure and visibility and PM2.5, so as to analyze the correlation between haze weather and local climate more comprehensively. The results show that the influence of each index on PM2.5 in descending order is air pressure, wind speed, humidity, dew point, temperature and visibility. The qualitative analysis results confirm each other. Among them, air pressure (correlation 0.771) has the greatest impact on haze weather, and visibility (correlation 0.511) is the weakest.

Simulation of thermal and humid environment of rural residence envelope inner surface during the plum rains season in Changsha China

The Plum Rains Season (PRS) has the typical characteristics of outdoor air temperature dramatic changes and high air humidity in the hot summer and cold winter region in China. Even if the indoor heat source and moisture production is constant, when the outdoor air temperature rises rapidly during high air humidity PRS, the building envelope temperature heats up much more slower than the indoor air temperature and therefore the wall surface temperature is lower than the indoor air dewpoint which leads to condensation phenomenon, resulting in deterioration of insulation performance, mouldy walls, deterioration of indoor air quality. At present, there is a lack of research on the factors affecting condensation in rural residence during PRS. This paper evaluates the impact of occupants’ habit of window opening modes and building construction parameters on the building envelope surface condensation in Changsha during PRS. Using Designer'Simulation Toolkit (DeST) simulated and analysed the impact of key parameters such as window-to-wall ratio, exterior wall reflectivity, window opening mode (open/close), and external wall insulation on the building indoor thermal and humid environment. The condensation risk X is proposed to evaluate the condensation possibility on the building envelope's inner surface. The results show that from the perspective of anti-condensation: The rural residential building in Changsha should balance the window-wall ratio against better natural lighting; Keeping windows closed during PRS can effectively alleviate the condensation problem while the insulation in the external wall layer could aggravate the condensation.

Estimate of The Dynamical Change of Air TemperAture, Relative Humidity and Dew Point TemperaTure for Some Selected Station in Iraq

Relative humidity can be inferred from the dew point values. When the air temperature and dew point temperatures are very close, the air has high relative humidity. The converse is true when there is a large difference between the air temperature and the dew point temperature, indicating the presence of low humidity air. To understand the expected changes in the climatic elements in the atmosphere, changes in temperature behavior, dew point, and relative humidity have been studied This study used data obtained from the European Center (ECMWF), which includes monthly and annual mean temperatures, dew, and relative humidity during the period (1988-2018) for selected stations in Iraq. The highest values of temperature and dew were recorded in July and August, and they were accompanied by a decrease in relative humidity. The highest value of relative humidity was recorded in December and January, accompanied by a decrease in temperature and dew, as we note through the results that there is an inverse relationship between relative humidity, temperature, and dew point Relative humidity changes when the temperature rises or falls, and the relative humidity may be higher in the morning when the temperature drops. The lowest amount of relative humidity during the day is when the temperature rises, the highest temperature value was recorded on 21July 2017 (12:00 PM) for Basra Station, while the highest relative value is humidity in Basra Governorate. Mosul station on January 21, 2014 (12:00 AM), and the reason is due to meteorological factors and the nature of the geographical area.

Condensation performance of superhydrophobic aluminium surface material used for cooled ceiling panels under highly humid indoor conditions

The application of radiant cooling systems is very limited in hot and humid areas due to condensation. Research on superhydrophobic surface (SHS) materials has shown the potential of restricting the size of condensate drops on these materials, which provides possibilities for preventing dripping and thereby alleviating condensation risks for cooled ceiling panels, but there are few studies on the anti-condensation performance of these materials under the scale and conditions of building applications. An experimental study of condensation on superhydrophobic materials under indoor conditions is presented in this article. Two material samples with a size of 2.5 cm, including a superhydrophobic aluminum sheet and a pure aluminium sheet, were affixed on a cooled ceiling panel to perform the experiment under the following condition: temperature is 25°C ± 0.5°C, relative humidity is 80% ± 5%, and air dew point is 21.4°C. The panel was cooled by chilled water of 6°C for eight hours. The measured temperature on sample surfaces was about 13.5°C during the experiment. After eight-hour condensation, the diameter of drops on the superhydrophobic aluminum sheet was less than 150 μm, while the max drop on the pure aluminum sheet was near 4 mm. The results suggested that the size of condensate drops on superhydrophobic surface materials can be largely restricted during a long-time indoor operation below the dew point, which shows their potential for constructing condensation-free radiant cooling panels.

Experimental study on control strategies of radiant floor cooling system with direct-ground cooling source and displacement ventilation system: A case study in an office building

Radiant cooling systems need optimized control strategies to provide superior comfort while maximizing energy-savings. The field measurement method was used to study the operational control of radiant floor cooling (RFC) with a direct-ground cooling source and displacement ventilation (DV) systems. The control methods for the composite system were proposed based on three factors including floor surface temperature relative to the indoor air dew point temperature, the range of indoor/outdoor air temperature and humidity, and the indoor thermal and humidity loads to be countered. These factors were considered in three typical scenarios: intermittent operation, variable initial temperature and humidity conditions, and sudden increases in indoor heat gain, so that maintaining the operative temperature within 26–27 °C. The system required that precooling time of the RFC was 2.5–3 times the time to achieve 63% of the temperature change for intermittent operation on weekends, while the DV system was started 1–1.5 h before work time when initial indoor air humidity was higher than 75% and indoor air temperature was higher than 26 °C, and supply air flow rate was increased to maximum value under sudden increases in indoor heat gain. The results concluded that dynamic optimal control of the radiant cooling system was achieved.

Relative importance of meteorological variables on air quality and role of boundary layer height

To gain insight on the meteorological effects of air pollution, we study the relative importance of surface meteorological variables and boundary layer height (BLH) on six major air pollutants according to the orders of variables being selected in a forward variable selection algorithm. It is found that there was a strong agreement in the orders of relative importance for the major pollutants among six major cities in North China, which implies regularities in the meteorological processes of air pollution in that region. In particular, PM2.5, PM10, SO2 and CO shared a common variable importance order and were mostly impacted by the dew point temperature and air pressure, while the NO2 and O3 were mostly influenced by the boundary layer height (BLH) and temperature, respectively. We evaluate the impacts of BLH on the pollution levels given the surface meteorological variables. It is found that BLH can be well modeled by the surface meteorological variables. Thus, air quality assessment without using BLH would also produce adequate results.

Optimization on airflow distribution for anti-condensation of high-voltage switchgear using CFD method

High-voltage switchgear is indispensable for power system. Condensation of the switchgear occurs frequently due to water vapor infiltration and water accumulation in cable trench, which may cause large-scale blackout of the power system. Effective dehumidification measures are crucial to safe and stable operation of the switchgear. In this paper, an air-conditioning based dry-air dehumidification measure is proposed for anti-condensation of the switchgear. Different airflow distributions are studied by numerical simulation of the thermal-humidity environment within the switchgear. Results show that the performance of the proposed dehumidification system is satisfactory. The switchgear wall temperature can be up to 7.6 °C higher than the return air dew point temperature, and the moisture content differences between the supply and return air can be more than 3.4 g/kg. Besides, some optimization measures for improving the dehumidification effect are proposed. After the optimization of the airflow distribution, the relative humidity and the temperature of the return air are reduced by 3.3% and 1.3 °C, respectively.