Changes In Solar Radiation Research Articles

Linking Holocene East Asian monsoon variability to solar forcing and ENSO activity: Multi-proxy evidence from a peatland in Northeastern China

High-resolution proxy-based paleoenvironmental records derived from peatlands provide important insights into climate changes over centennial to millennial timescales. In this study, we present a composite climatic index (CCI) for the Hani peatland from northeastern China, based on an innovative combination of pollen-spore, phytolith, and grain size data. We use the CCI to reconstruct variations of the East Asian summer monsoon (EASM) intensity during the Holocene. This is accomplished with complete ensemble empirical mode decomposition (CEEMD), REDFIT, and cross-wavelet coherency analysis to reveal the periodicities (frequencies) of the multi-proxy derived CCI sequences and to assess potential external forcing of the EASM. The results showed that periodicities of ca. 300–350, 475, 600, 1075, and 1875 years were present in the Hani CCI sequence. Those periodicities are consistent with previously published periodicities in East Asia, indicating they are a product of external climate controls over an extensive region, rather than random variations caused by peatland-specific factors. Cross-wavelet coherency analysis between the decomposed CCI components and past solar activity reconstructions suggests that variations of solar irradiation are most likely responsible for the cyclic characteristics at 500-year frequency. We propose a conceptual model to interpret how the sun regulates the monsoon climate via coupling with oceanic and atmospheric circulations. It seems that slight solar irradiation changes can be amplified by coupling with ENSO events, which result in a significant impact on the regional climate in the East Asian monsoon area.

Dynamic system modeling of thermally-integrated concentrated PV-electrolysis

Understanding the dynamic response of a solar fuel processing system utilizing concentrated solar radiation and made of a thermally-integrated photovoltaic (PV) and water electrolyzer (EC) is important for the design, development and implementation of this technology. A detailed dynamic non-linear process model is introduced for the fundamental system components (i.e. PV, EC, pump etc.) in order to investigate the coupled system behavior and performance synergy notably arising from the thermal integration. The nominal hydrogen production power is ∼2 kW at a hydrogen system efficiency of 16–21% considering a high performance triple junction III-V PV module and a proton exchange membrane EC. The device operating point relative to the maximum power point of the PV was shown to have a differing influence on the system performance when subject to temperature changes. The non-linear coupled behavior was characterised in response to step changes in water flowrate and solar irradiance and hysteresis of the current-voltage operating point was demonstrated. Whilst the system responds thermally to changes in operating conditions in the range of 0.5–2 min which leads to advantageously short start-up times, a number of control challenges are identified such as the impact of pump failure, electrical PV-EC disconnection, and the potentially damaging accentuated temperature rise at lower water flowrates. Finally, the simulation of co-generation of heat and hydrogen for various operating conditions demonstrates the significant potential for system efficiency enhancements and the required development of control strategies for demand matching is discussed.

Impact of Urbanization on Sunshine Duration from 1987 to 2016 in Hangzhou City, China

Worldwide solar dimming from the 1960s to the 1980s has been widely recognized, but the occurrence of solar brightening since the late 1980s is still under debate—particularly in China. This study aims to properly examine the biases of urbanization in the observed sunshine duration series from 1987 to 2016 and explore the related driving factors based on five meteorological stations around Hangzhou City, China. The results inferred a weak and insignificant decreasing trend in annual mean sunshine duration (−0.09 h/d decade−1) from 1987 to 2016 in the Hangzhou region, indicating a solar dimming tendency. However, large differences in sunshine duration changes between rural, suburban, and urban stations were observed on the annual, seasonal, and monthly scales, which can be attributed to the varied urbanization effects. Using rural stations as a baseline, we found evident urbanization effects on the annual mean sunshine duration series at urban and suburban stations—particularly in the period of 2002–2016. The effects of urbanization on the annual mean sunshine duration trends during 1987−2016 were estimated to be −0.16 and −0.35 h/d decade−1 at suburban and urban stations, respectively. For urban stations, the strongest urbanization effect was observed in summer (−0.46 h/d decade−1) on the seasonal scale and in June (−0.63 h/d decade−1) on the monthly scale. The notable negative impact of urbanization on local solar radiation changes was closely related to the changes in anthropogenic pollutions, which largely reduced the estimations of solar radiation trends in the Hangzhou region. This result highlights the necessity to carefully consider urbanization impacts when analyzing the trend in regional solar radiation and designing cities for sustainable development.

Solar dimming or brightening in the upper reaches of the Yangtze River Basin under 1.5 °C and 2 °C global warming targets?

Solar radiation, as the primary energy source of the Earth, influences the climate conditions and changes of our planet. Whether solar dimming or brightening would occur in the future under 1.5 °C and 2 °C global warming background was an important question. In this study, climate data under four Representative Concentration Pathway (RCP) scenarios were used to calculate and analyse temporal and spatial changes of solar radiation in the upper reaches of the Yangtze River Basin for the future period 2020-2099. Results showed that surface solar radiation would increase under RCP2.6 and RCP4.5, while it would decrease under RCP6.0 and RCP8.5. Especially, dramatic solar dimming would occur in all years in the future under RCP8.5, which indicated that the fluctuations of the amount of solar energy in the future were related to the emission scenarios. Spatially, under global warming 1.5 °C, solar brightening would occur mainly in the central regions and become weaker with the higher emission scenarios. However, under global warming 2 °C, solar dimming would occur mainly in the upper Jinsha River Basin and the lower reaches of the Jialing River Basin and become stronger with the higher emission scenarios. Relative to the other three RCP, obvious and dramatic solar dimming would occur under RCP8.5 in the total area.

Impact of global dimming/brightening on estimating Angström-Prescott parameters based on geographically weighted regression in China

Variations of solar radiation is related to energy planning and architectural designing. It is important to estimate solar radiation from other climate factors because of the limited measurement solar radiation data. In this study, temporospatial changes of solar radiation and sunshine hour are analysed for global dimming/brightening periods based on meteorological data in China. Results show that the trends of solar radiation and sunshine hour are both decreasing dramatically for 1961–1990 (the global dimming period) but levelling off for 1991–2010 (the global brightening period), which indicates that sunshine hour can be used the reliable indicator of solar radiation. Spatially, the change trends of solar radiation are consistent with sunshine hour in 36 stations during the period of 1961–1990, but they are consistent in just 27 stations during the period of 1991–2010. To assess the impact of changing solar radiation on Angstrom-Prescott parameters (a and b) in the equation of solar radiation estimation from sunshine hour, geographically weighted regression is developed to calculate a and b. There is not dramatic difference in the spatial patterns of a and b for the period of 1961–2010 and 1961–1990. However, there is significantly inconsistent changes in a and b during the global brightening period compared with the global dimming period, which suggests that global dimming/brightening has important impact on estimating solar radiation from sunshine hour, with dramatic variability among different regions.

The effect of solar radiation change on the maize yield gap from the perspectives of dry matter accumulation and distribution

The uneven distribution of solar radiation is one of the main reasons for the variations in the yield gap between different regions in China and other countries of the world. In this study, different solar radiation levels were created by shading and the yield gaps induced by those levels were analyzed by measuring the aboveground and underground growth of maize. The experiments were conducted in Qitai, Xinjiang, China, in 2018 and 2019. The maize cultivars Xianyu 335 (XY335) and Zhengdan 958 (ZD958) were used with planting density of 12×104 plants ha–1 under either high solar radiation (HSR) or low solar radiation (LSR, 70% of HSR). The results showed that variation in the solar radiation resulted in a yield gap and different cultivars behaved differently. The yield gaps of XY335 and ZD958 were 8.9 and 5.8 t ha–1 induced by the decreased total intercepted photosynthetically active radiation (TIPAR) of 323.1 and 403.9 MJ m-2 from emergence to the maturity stage, respectively. The average yield of XY335 was higher than that of ZD958 under HSR, while the average yield of ZD958 was higher than that of XY335 under LSR. The light intercepted by the canopy and the photosynthetic rates both decreased with decreasing solar radiation. The aboveground dry matter decreased by 11.1% at silking and 21% at maturity, and the dry matter of vegetative organs and reproductive organs decreased by 9.8 and 20.9% at silking and by 12.1 and 25.5% at physiological maturity, respectively. Compared to the HSR, the root weights of XY335 and ZD958 decreased by 54.6 and 45.5%, respectively, in the 0–60 cm soil layer under LSR at silking stage. The aboveground and underground growth responses to different solar radiation levels explained the difference in yield gap. Selecting suitable cultivars can increase maize yield and reduce the yield gaps induced by variation of the solar radiation levels in different regions or under climate change.

Solar radiation prediction using boosted decision tree regression model: A case study in Malaysia.

Reliable and accurate prediction model capturing the changes in solar radiation is essential in the power generation and renewable carbon-free energy industry. Malaysia has immense potential to develop such an industry due to its location in the equatorial zone and its climatic characteristics with high solar energy resources. However, solar energy accounts for only 2-4.6% of total energy utilization. Recently, in developed countries, various prediction models based on artificial intelligence (AI) techniques have been applied to predict solar radiation. In this study, one of the most recent AI algorithms, namely, boosted decision tree regression (BDTR) model, was applied to predict the changes in solar radiation based on collected data in Malaysia. The proposed model then compared with other conventional regression algorithms, such as linear regression and neural network. Two different normalization techniques (Gaussian normalizer binning normalizer), splitting size, and different input parameters were investigated to enhance the accuracy of the models. Sensitivity analysis and uncertainty analysis were introduced to validate the accuracy of the proposed model. The results revealed that BDTR outperformed other algorithms with a high level of accuracy. The funding of this study could be used as a reliable tool by engineers to improve the renewable energy sector in Malaysia and provide alternative sustainable energy resources.

Boost Chopper Behaviors in Solar Photovoltaic System

This paper investigates the behaviors of Boost DC Chopper used in Photovoltaic energy systems where the solar irradiation changes during the day time causing current and voltage changes. Varying the solar irradiation causes output chopper voltage changes in order to keep working at maximum extracted solar power. The chopper voltage changes leading to variable duty cycle operation of chopper switch and causes a significant change in switch losses in terms of the dissipated power. In addition to that the chopper behaviors are studied when the chopper voltage is boosting up to a predetermined reference value leading to a significant change in chopper current, voltage, duty cycle and occurred losses. A mathematical model for chopper performances and switch losses is derived, and a simulation model using Matlab/ Simulink platforms is conducted to follow the chopper behaviors. Simulation results for concreteSUNPOWER panel type SPR-315E-WHT-D with 315 Watts peak indicates that during the daylight time transistors are exposed to complicated changes in their current, voltage and dissipated power. Furthermore changing the output voltage according to load requirements causes heavy stress on the transistor in terms of current, oscillations and losses as well. Simulation results show that there are optimized values of irradiation, chopper voltage and duty cycle where the transistor losses are minimized. In addition to that, projecting the transistor losses over the daylight time at a given irradiation rate shows how these losses vary among the year, and the amount of energy dissipated across the main chopper switch which is around 2970 Whr/yr for the present case. Furthermore, the conducted simulation also shows the occurred in the transistor behaviors when solar irradiation changes, and can be serving for further studies.

Optimal Energy Management of Battery Supercapacitor aided Solar PV Powered Agricultural Feed Mill using Pontryagin's Minimum Principle

The commercialization of renewable energy sources is often obstructed due to the cost of energy storages such as batteries, which are unavoidable due to intermittent nature of these energy sources. Average power density and low cycle life of batteries lead to frequent replacement and put additional economic burden toward the replacement cost at its end-of-life. The battery supercapacitor-hybrid energy storage system (BS-HESS) with efficient energy management system (EMS) has shown the potential to improve the battery life in various applications. Here, we exploit the Pontryagin's minimum principle (PMP) for optimal power-split between battery and supercapacitor in HESS for a stand-alone photovoltaic assisted agricultural feed mill such that the battery life is improved. Also, we employ a new technique called hybrid maximum power point tracking, by introducing an extra term in the performance index, to take care of the effects of partial shading and provide fast response to sudden change in solar irradiance. We verify the effectiveness of the proposed PMP-based EMS via simulation and comparison with conventional methods. Simulation results show that the HESS along with PMP-based EMS can improve the battery cycle life compared to rule-based EMS and battery-only storage. Finally, we implement the proposed PMP-based EMS in hardware prototype to prove its practicality. The results obtained are satisfactory.

Validation of Genetic Algorithm Optimized Hidden Markov Model for Short-term Photovoltaic Power Prediction

Significantly, incentives and energy guidelines are expanding the deployment of renewable energy (RE) systems in developing countries. A substantial amount of RE-based electrical power is generated over the last ten years, due to global warming issues. Solar photovoltaic (PV) is being incredibly utilized because of its boundless quality. However, the inherent intermittency of PV power production at high penetration level to the grid leads to complications related grid reliability, stability and transportable unit of electric power. A viable approach to addressing this problem is to develop a reliable power forecast model for the short-term horizon related to scheduling and transmission. Based on an existing forecast model built on genetic algorithm (GA)-optimized hidden Markov model (HMM), this paper implements the model validation process using more recent input dataset. Model evaluation is based on the computation of normalized root mean square error (nRMSE). As the validation result, HMM+GA is sufficient to accurately forecast PV P o under clear sky day (CSD) condition. Contrariwise, for cloudy days (CDs) presenting instantaneous changes in solar irradiance ( G s ) between some hours of the day, HMM+GA adapted with a correction factor (x); articulated as HMM+GA+x; is adequate to forecast the P o more precisely when the average change in the absolute value of G s () in the morning () is greater than 128% and/or when in the evening () exceeds 90%. Particularly, the average nRMSE of 2.63% showed that HMM+GA with or without x are suitable techniques for forecasting PV P o on an hourly basis. Therefore, the validation results are in harmony with those of the baseline models. https://dorl.net/dor/20.1001.1.13090127.2021.11.2.28.7

Identifiability Evaluation of Crucial Parameters for Grid Connected Photovoltaic Power Plants Design Optimization

This paper aims to assess the impact of different key factors on the optimized design and performance of grid connected photovoltaic (PV) power plants, as such key factors can lead to re-design the PV plant and affect its optimum performance. The impact on the optimized design and performance of the PV plant is achieved by considering each factor individually. A comprehensive analysis is conducted on nine factors such as; three objectives are predefined, five recent optimization approaches, three different locations around the world, changes in solar irradiance, ambient temperature, and wind speed levels, variation in the available area, PV module type and inverters size. The performance of the PV plant is evaluated for each factor based on five performance parameters such as; energy yield, sizing ratio, performance ratio, ground cover ratio, and energy losses. The results show that the geographic location, a change in meteorological conditions levels, and an increase or decrease in the available area require the re-design of the PV plant. A change in inverter size and PV module type has a significant impact on the configuration of the PV plant leading to an increase in the cost of energy. The predefined objectives and proposed optimization methods can affect the PV plant design by producing completely different structures. Furthermore, most PV plant performance parameters are significantly changed due to the variation of these factors. The results also show the environmental benefit of the PV plant and the great potential to avoid green-house gas emissions from the atmosphere.

HEAT SINK-PCM DEVICE FOR PV EFFICIENCY IMPROVEMENT

This paper is focused on the development of a second stage of a previous work where the PV panel efficiency is improved by using a hybrid system made up of a PCM attached to the rear side of the panel. This evolved stage incorporates a heat sink unit to improve the distribution of the heat removed from the panel; this improvement reduces the elapsed time to reach the steady state in the PCM, thus in the PV panel. A shorter time generates not only a lower operational temperature, but also a higher efficiency since the photovoltaic panel evolves in a dynamic situation due to continuous changes in solar radiation. Temperature reduction depends on solar radiation level, from barely 2.5o C, at early morning or late afternoon, where solar radiation is low, up to a maximum of 14.5o C at midday for a solar radiation level of 900 W/m 2 . The PV panel efficiency has been improved up to 9% for the peak solar radiation at midday. Tests have proved the most effective period in PV efficiency improvement is in the range of ± 4 hours around midday based on an average solar day of 12 h. Efficiency improvement in this period is over 6.9% in the whole range. Outside this range, the efficiency improvement drops to a less of 3%. The global efficiency obtained using the hybrid heat sink-PCM system varies from 8.54% at early morning or late afternoon to 14.64% around midday. A correlation process has been developed to predict the temperature evolution of the PV panel under specific solar radiation conditions. The correlation predicts hourly values of PV panel efficiency improvement as well as global efficiency with almost 100% accuracy.

Changes in the Total Solar Irradiance and climatic effects

The correlation between the averaged reconstructed March temperature record for Kyoto, Japan, and the reconstructed Total Solar Irradiance (TSI) over 660 years from 1230 to 1890 gives evidence with 98% probability that the Little Ice Age with four cold periods is forced by variations of TSI. If the correlation is restricted to the period 1650–1890, with two cold periods in the 17th and 19th century and for which two independent reconstructed March temperature records are available, the probability of solar forcing increases to 99.99%. As solar irradiance variations have a global effect there has to be a global climatic solar forcing impact. However, by how much global temperature were lower during these minima and with what amplitude TSI was varying is not accurately known. The two quantities, global temperature and TSI, are linked by the energy equilibrium equation for the Earth system. The derivation of this equation with respect to a variation of the solar irradiance has two terms: A direct forcing term, which can be derived analytically and quantified accurately from the Stefan-Boltzmann law, and a second term, describing indirect influences on the surface temperature. If a small TSI variation should force a large temperature variation, then it has to be the second indirect term that strongly amplifies the effect of the direct forcing. The current knowledge is summarized by three statements:During the minima periods in the 13th, 15/16th, 17th, and 19th centuries the terrestrial climate was colder by 0.5–1.5 °C;Indirect Top-down and Bottom-up mechanisms do not amplify direct forcing by a large amount, i.e. indirect solar forcing is of the same magnitude (or smaller) as direct solar forcing;The radiative output of the Sun cannot be lower by more than 2 Wm−2 below the measured present-day TSI value during solar cycle minimum.These three statements contradict each other and it is concluded that at least one is not correct. Which one is a wrong statement is presently not known conclusively. It is argued that it is the third statement and it is speculated that over centennial time scales the Sun might vary its radiance significantly more than observed so far during the last 40 years of space TSI measurements. To produce Maunder minimum type cold climate excursions, a TSI decrease of the order of 10 Wm−2 is advocated.

Impact of climate change on water sector in Gumbasa Watershed, Central Sulawesi, Indonesia

Global climate change resulting in increased or decreased rainfall volume, rising temperatures, may also be associated with changes in season patterns, wind patterns, air humidity, and solar irradiance. This study aims to determine the potential hazards arising in the water sector due to climate change. This research was conducted in Gumbasa Watershed, Central Sulawesi, Indonesia. Primary data used in this research are characteristic of land, while secondary data include rain data, climatology data and earth map. The data of rain used by the nearest station are Bora Station, Kulawi, Palolo, Bangga Bawah, and Wuasa, whereas climatology data is used at Bora Station. Some of the methods used to complete this study are: 1) regional rainfall; 2) evapotranspiration; 3) water availability; 4) CDF statistical analysis; 5) climate change projections; 6) potential hazards. Based on the analysis performed, it can be concluded: 1) there is no danger of decreasing water availability for all periods (1993-2052); 2) there is a high flood hazard in the period 2013-2022, while the other periods do not occur due to flood hazard; 3) low drought hazards occur in the period 2003-2012, while for other periods there is no drought hazard.

Moisture-indicating cellulose aerogels for multiple atmospheric water harvesting cycles driven by solar energy

A hygroscopic cellulose aerogel can visually indicate the sorption/desorption process achieving a flexible response to changes in RH and solar radiation. Fast sorption kinetics make it achieve multiple water production cycles during one sunny day.

Autonomous complex for electro-thermal heating of oil wells fed by a photovoltaic installation

Paraffin deposits are a serious problem causing complications in oil production. This article describes the creation of a complex operatingonphotovoltaic installations to combat paraffin deposits. The authors offer an innovative method for accurate calculation of the parameters of photovoltaic installations, taking into account changes in total solar radiation, geographical and climatic conditions, the angle of inclination of solar panels, characteristics of the power source, and oil parameters. Measurements of solar radiation are carried out on the basis of mathematical and simulation modeling in Matlab Simulink. The results of the studies confirm the adequacy of the proposed method of oil well heating. This method of electric heating has a simple design and does not require underground works and well shutdown. Thus, it will improve the efficiency of oil production, prevent the formation of paraffin deposits, and ensure energy savings by reducing power losses and electricity consumption.

PERFORMANCE ANALYSIS OF A SMALL-SCALE GRID-CONNECTED PHOTOVOLTAIC SYSTEM:A REAL CASE STUDY IN EGYPT

Renewable energy sources, especially PV systems, which become more significant sources of energy, are attracting considerable commercial interest. Nonetheless, the integration of the PV power plants to the utility grids may cause several operational problems for distribution networks. The severity of these problems directly depends on the percentage of PV penetration and the geography of the installation. Hence, knowing the possible impact of small grid-connected PV systems on distribution networks can provide feasible solutions before practical implementations in real-time. The electrical power generated from photovoltaic (PV) array depends mainly on the weather conditions. So, the PV solar grid-connected inverters should equip with the control system to meet a fast response of solar irradiance change. This study includes performance analysis for data and measurements which real-time from the PV grid-connected system site according to Egyptian PV-LV code-2014, simulation by using MATLAB/Simulink, and cost analysis for connecting small-scale 39.78 kW photovoltaic (SSPV) system to LV distribution networks. Power quality parameters are measured for the output of the installed PV system at the Holy Family School in Helwan, Egypt. The proposed system model is built on MATLAB/Simulink and simulated under daily weather conditions to test its operating performance. The power quality indices at the inverter output side have been measured using PA-9-plus power quality analyzer. The cost analysis of SSPV generator based on the weather conditions will lead to new investments. The system has been installed in October 2016, produces 68.966MWh/year annual energy yield, and reaches its initial cost in 6.2198 years. The produced electricity by the system is injected directly into the grid without storage devices (On-grid Plant).

ЗАСТОСУВАННЯ МАТЕМАТИЧНОЇ МОДЕЛІ ДЛЯ АНАЛІЗУ ТЕПЛОВОЇ РОБОТИ БЕТОННОГО СОНЯЧНОГО КОЛЕКТОРА

Бетонні сонячні колектори давно застосовуються в якості низькотемпературних водопідігрівачів, наприклад для підігріву води в басейнах. Їхніми основними перевагами є дешевизна, простота виконання та високі експлуатаційні якості. Одним з сучасних напрямків застосування бетонних сонячних колекторів є їх інтегрування в фасади та дахи будівель та споруд. Їх можна встановлювати на будівлях, що мають історичну цінність, не порушуючи їх зовнішній вигляд. Перевагою таких систем є естетичність та міцність, через те що вони не містять крихкого скляного покриття. В той же час абсорбери без скління, особливо в холодний сезон та нічний час, можуть мати значні втрати тепла за рахунок конвективного теплообміну з навколишнім повітрям, а також через довгохвильове випромінювання в атмосферу. Для аналізу впливу різних факторів на теплову роботу сонячної системи з бетонним колектором використовували математичну модель. Вона розраховує зміни прямого і розсіяного сонячного випромінювання на поверхню колектора протягом дня з урахуванням місця розташування і орієнтації приймаючої поверхні, пори року і доби. В моделі вирішується задача нестаціонарної теплопровідності в бетонній плиті з вбудованою системою труб з циркулюючою рідиною та баком-акумулятором. Режим добового водоспоживання враховується шляхом зміни режиму роботи циркуляційного насоса. Модель застосовувалась для аналізу роботи бетонних колекторів для умов України. Виконані порівняльні розрахунки теплової роботи заскленого та незаскленого бетонного колектора. Показано, що в умовах роботи бетонного колектора із замкнутим контуром на ефективність сонячної системи істотно впливає об’єм теплового бака-акумулятора і режим відбору води, так як після закінчення сонячного дня значна частина тепла, накопиченого бетонним абсорбером, може бути втрачена в навколишнє середовище. Була розглянута можливість покращення корисного використання тепла, що накопичується бетонним абсорбером, після закінчення сонячного дня за рахунок збільшення об’єму бака-акумулятора і різних режимів його розгрузки.

Exploring the drivers of the increased ozone production in Beijing in summertime during 2005–2016

Abstract. In the past decade, average PM2.5 concentrations decreased rapidly under the strong pollution control measures in major cities in China; however, ozone (O3) pollution emerged as a significant problem. Here we examine a unique (for China) 12-year data set of ground-level O3 and precursor concentrations collected at an urban site in Beijing (PKUERS, campus of Peking University), where the maximum daily 8 h average (MDA8) O3 concentration and daytime Ox (O3+NO2) concentration in August increased by 2.3±1.2 ppbv (+3.3±1.8 %) yr−1 and 1.4±0.6 (+1.9±0.8 %) yr−1, respectively, from 2005 to 2016. In contrast, daytime concentrations of nitrogen oxides (NOx) and the OH reactivity of volatile organic compounds (VOCs) both decreased significantly. Over this same time, the decrease of particulate matter (and thus the aerosol optical depth) led to enhanced solar radiation and photolysis frequencies, with near-surface J(NO2) increasing at a rate of 3.6±0.8 % yr−1. We use an observation-based box model to analyze the combined effect of solar radiation and ozone precursor changes on ozone production rate, P(O3). The results indicate that the ratio of the rates of decrease of VOCs and NOx (about 1.1) is inefficient in reducing ozone production in Beijing. P(O3) increased during the decade due to more rapid atmospheric oxidation caused to a large extent by the decrease of particulate matter. This elevated ozone production was driven primarily by increased actinic flux due to PM2.5 decrease and to a lesser extent by reduced heterogeneous uptake of HO2. Therefore, the influence of PM2.5 on actinic flux and thus on the rate of oxidation of VOCs and NOx to ozone and to secondary aerosol (i.e., the major contributor to PM2.5) is important for determining the atmospheric effects of controlling the emissions of the common precursors of PM2.5 and ozone when attempting to control these two important air pollutants.

Experimental analysis of exergy efficiency and entropy generation of diamond/water nanofluids flow in a thermosyphon flat plate solar collector

The performance of flat plate solar collector was experimentally investigated using nanodiamond nanofluid that circulates in it under thermosyphon conditions. The nanofluids were prepared by adding nanodiamond (ND) nanoparticles at 0.2, 0.4, 0.6, 0.8 and 1.0% volume concentrations into the distilled water. The study was performed to analyze the collector thermal efficiency, exergy efficiency, entropy generation, heat transfer coefficient, friction factor and power consumption requirement in the test time interval between 10:00 a.m. to 16:30 p.m. The experimental results show that the trend of these parameters is strongly influenced by the changes of solar irradiation. The highest collector thermal efficiency of 69.85% is achieved by 1.0 vol% ND/water nanofluid with 12.7% increase over that when pure water is used. Water as the working fluid generates a maximum entropy of 5.725 W/K, and this value drops to 5.541 W/K when 1.0 vol% ND/water nanofluid is used. Heat transfer irreversibility is shown by Bejan number to be the dominant contributor to the total entropy, and the entropy generation number shows that the ND/water nanofluid is more sensitive to entropy generation than water as the working fluid.