Attenuation Of Solar Radiation Research Articles

High-resolution spectral atmospheric attenuation measurement for solar power plants

One of the main challenges in solar tower renewable technologies is measurement of solar radiation attenuation at the plants at surface level. This paper describes an improved version of the optical spectrum analysis method for measuring solar radiation attenuation in real time at solar tower plants, as presented in a previous work. The new hardware design and calibration process are explained in detail. This new system has a resolution of 0.25 nm in the VIS range and a precision of 0.5% in real time, improving over the state of the art for the measurement of spectral atmospheric attenuation. These specifications allow the assessment of the contribution of different attenuation factors at surface level, such as absorbance peaks (Na, H, H2O) or scattering and the search for correlation with different weather conditions. They also enable experimental validation of atmospheric extinction simulation methods and their parameters. This work also includes the results of a 6 month-long campaign of solar weighted atmospheric extinction measurements at Atlantica's operating central receiver solar plant PS10 at Sanlúcar la Mayor (Seville, Spain). Fluctuations in the daily averaged transmittance greater than 10% are observed, which shows the importance of monitoring this parameter during the operation of solar plants.

Linke Turbidity Modelling for Braşov Urban Area

An important factor in the solar radiation attenuation is Linke turbidity factor which has a specific value for every area; to model and simulate the solar radiation this key parameter must be determined.

Increased importance of aerosol–cloud interactions for surface PM2.5 pollution relative to aerosol–radiation interactions in China with the anthropogenic emission reductions

Abstract. Surface fine particulate matter (PM2.5) pollution can be enhanced by feedback processes induced by aerosol–radiation interactions (ARIs) and aerosol–cloud interactions (ACIs). Many previous studies have reported enhanced PM2.5 concentrations induced by ARIs and ACIs for episodic events in China. However, few studies have examined the changes in the ARI- and ACI-induced PM2.5 enhancements over a long period, though the anthropogenic emissions have changed substantially in the last decade. In this study, we quantify the ARI- and ACI-induced PM2.5 changes for 2013–2021 under different meteorology and emission scenarios using the Weather Research and Forecasting model with Chemistry (WRF-Chem), and we investigate the driving factors behind the changes. Our results show that, in January 2013, when China suffered from the worst PM2.5 pollution, the PM2.5 enhancement induced by ARIs in eastern China (5.59 µg m−3) was larger than that induced by ACIs (3.96 µg m−3). However, the ACI-induced PM2.5 enhancement showed a significantly smaller decrease ratio (51 %) than the ARI-induced enhancement (75 %) for 2013–2021, making ACIs more important for enhancing PM2.5 concentrations in January 2021. Our analyses suggest that the anthropogenic emission reductions played a key role in this shift. Owing to only anthropogenic emission reductions, the ACI-induced PM2.5 enhancement decreased by 43 % in January, which was lower than the decrease ratio of the ARI-induced enhancement (57 %). The relative change in ARI- and ACI-induced PM2.5 enhancement in July was similar to the pattern observed in January, caused by anthropogenic emission reductions. The primary reason for this phenomenon is that the decrease in ambient PM2.5 for 2013–2021 caused a disproportionately small decrease in the liquid water path (LWP) and an increase in the cloud effective radius (Re) under the condition of high PM2.5 concentrations. Therefore, the surface solar radiation attenuation (and, hence, the boundary layer height reduction) caused by ACIs decreased slower than that caused by ARIs. Moreover, the lower decrease ratio of the ACI-induced PM2.5 enhancement was dominated by the lower decrease ratio of ACI-induced secondary PM2.5 component enhancement, which was additionally caused by the smaller decrease ratio of the air temperature reduction and the relative humidity (RH) increase. Our findings indicate that, with the decrease in ambient PM2.5, the ACI-induced PM2.5 enhancement inevitably becomes more important. This needs to be considered in the formulation of control policies to meet the national PM2.5 air quality standard.

Intra-day solar irradiation forecast using machine learning with satellite data

Northwest China is rich in solar resource and the photovoltaic manufacturing industry is developing rapidly. Accurate solar radiation forecast suitable for the northwest desert area has become an urgent need. In this work, we use the classical machine learning models (SVM and RF) that are more complex than traditional statistical models to forecast intra-day global solar irradiance (GHI). Since there are some uncertainties in solar radiation attenuation models. We explore an approach that requires little preprocessing to enter satellite data as input: the mean of the satellite image window. Such a process provides a direct GHI forecast without using the clear sky index as a proxy. The model includes several satellite channels, not only visible channels. Since China's Fengyun-4 series satellites (FY-4) are the new generation of stationary meteorological satellite and have not yet been fully tested and applied to solar irradiance prediction, the regional average of each channels (Channel01∼Channel07) of FY-4A satellite cloud image are taken as important parameters input of the ML model, with lead time from 10 min to 3 h. The combination of climatology and persistence (Clim-Pers) model is chosen as the benchmark model. Our cases studies in Yuzhong, Minqin and Dunhuang show that the FS of RF model is higher than the SVM model in all forecast cases, and the performance advantage becomes more obvious when the lead time beyond 90 min. The FS values of RF model in Yuzhong, Minqin and Dunhuang site at time horizons 10 min-3 h are 13.5–37.6%, 18.2–35.8% and 17.3–34.2%, respectively, the forecast performance is very stable in different climate types. Therefore, it is a good and simple way to improve the accuracy of ultra-short-term solar forecasting by introducing satellite observations into the ML model.

Qualitative Analysis of the Cooling Potential of the Streetside Vegetation of Kharagpur, West Bengal, India

The urban heat island (UHI) effect is a major challenge in contemporary urban planning. The large number of paved surfaces, anthropogenic activities and combustion of fossil fuels are the major contributors of this phenomenon. Urban green spaces are known to mitigate the UHI. Since streets constitute a major portion of the urban areas, greening the streets can help reduce heat stress significantly. To study the impact of orientation and density of the street side vegetation on their cooling potential in Kharagpur, West Bengal, India.
 A suitable site, meeting the orientation and the density of vegetation criteria, was chosen for collecting the primary data through an instrument survey. Ambient temperature, surface temperature and solar radiation data was collected from the thirteen cross-sections marked across the site. As part of the preliminary data processing, relative variations of ambient temperature, surface temperature and the solar radiation attenuation was calculated. The values pertaining to these three secondary parameters were used to form matrices corresponding to each of the trees of each of the cross-sections. These matrices were then compared with their corresponding matrices to estimate which side exhibited a higher cooling potential. Besides, a colour-coded matrix was also generated from the calculated shade index to evaluate the amount of incident solar radiation blocked by each of these trees.
 This study corroborates the previous findings that the shade providing trees can alter the microclimate of the area. Besides, it was also observed that the Northern pavements of the east-west oriented streets are cooler than the Southern pavement. Furthermore, it was also noticed that if the crown of the tree is present at a greater height from the ground, then lower solar angle results in less blockage of the incident solar radiation. Also, it was evident that a higher density of tall, shade providing trees, maximally block incident solar radiation on a street. This study can help in understanding the pattern of cooling potential of the street side vegetation in a warm and humid climatic zone like Kharagpur so that the plantation can be planned judiciously.

An Observational and Modeling Study of Inverse‐Temperature Layer and Water Surface Heat Flux

AbstractAn “inverse‐temperature layer” (ITL) of water temperature increasing with depth is predicted based on physical principles and confirmed by in situ observations. Water temperature and other meteorological data were collected from a fixed platform in the middle of a shallow inland lake. The ITL persists year‐around with its depth on the order of one m varying diurnally and seasonally and shallower during daytimes than nighttimes. Water surface heat flux derived from the ITL temperature distribution follows the diurnal cycle of solar radiation up to 300 W m−2 during daytime and down to 50 W m−2 during nighttime. Solar radiation attenuation in water strongly influences the ITL dynamics and water surface heat flux. Water surface heat flux simulated by two non‐gradient models independent of temperature gradient, wind speed and surface roughness using the data of surface temperature and solar radiation is in close agreement with the ITL based estimates.

An Assessment of the Influences of Clouds on the Solar Photovoltaic Potential over China

Clouds are important modulators of the solar radiation reaching the earth’s surface. However, the impacts of cloud properties other than cloud cover are seldom mentioned. By combining the satellite-retrieved cloud properties, the latest radiative transfer model, and an advanced PVLIB-python software for solar photovoltaic (PV) estimation, the impacts of different types of clouds on the maximum available solar PV potential (measured with the plane-of-array-irradiance, POAI) are quantified. The impacts of ice and liquid water clouds are found to be the highest on Tibetan Plateau over western China in spring, and central and southern China in winter, respectively. The reduction of POAI by liquid water clouds is almost twice of that by ice clouds except for spring. It is found that the POAI can be reduced by 27–34% by all clouds (ice + liquid water clouds) in different seasons. The sensitivities of the solar PV potential to the changes in cloud properties including the cloud fraction, cloud top pressure, cloud effective radius, and cloud water path are also analyzed. Three kinds of settings of PV panel tilting, namely fixed tilt, one-axis tracking, and two-axis tracking, are considered. It is found that the cloud properties are essential to estimate the solar PV potentials, especially for the cloud fraction. The attenuation of solar radiation by clouds are growingly larger as the solar plane tilting settings get more complicated. The outlook of solar PV potential is quite variable as the changes in cloud properties are highly uncertain in the future climate scenarios.

The crucial role of blue light as a driver of litter photodegradation in terrestrial ecosystems

Background and aimWherever sunlight reaches litter, there is potential for photodegradation to contribute to decomposition. Although recent studies have weighed the contribution of short wavelength visible and ultraviolet (UV) radiation as drivers of photodegradation, the relative importance of each spectral region across biomes and plant communities remains uncertain.MethodsWe performed a systematic meta-analysis of studies that assessed photodegradation through spectrally selective attenuation of solar radiation, by synthesizing 30 published studies using field incubations of leaf litter from 110 plant species under ambient sunlight.ResultsGlobally, the full spectrum of sunlight significantly increased litter mass loss by 15.3% ± 1% across all studies compared to darkness. Blue light alone was responsible for most of this increase in mass loss (13.8% ± 1%), whereas neither UV radiation nor its individual constituents UV-B and UV-A radiation had significant effects at the global scale, being only important in specific environments. These waveband-dependent effects were modulated by climate and ecosystem type. Among initial litter traits, carbon content, lignin content, lignin to nitrogen ratio and SLA positively correlated with the rate of photodegradation. Global coverage of biomes and spectral regions was uneven across the meta-analysis potentially biasing the results, but also indicating where research in lacking.ConclusionsAcross studies attenuating spectral regions of sunlight, our meta-analysis confirms that photodegradation is a significant driver of decomposition, but this effect is highly dependent on the spectral region considered. Blue light was the predominant driver of photodegradation across biomes rather than UV radiation.

Reformulation of the Used Model to Estimate Soil Temperature

The Earth is permanently surrounded by cloud cover that, particularly, is an essential component in the planet’s energy balance. In turn, cloud cover intervenes in the main conditioning factor for soil temperature: solar radiation. In particular, the soil thermal amplitude should be dampened with the attenuation of solar radiation. However, the scientific community rarely analyzes this relationship, neglecting the model that is used to estimate the soil temperature. In this context, the present study seeks to reformulate the model by inserting a variable referent to cloud cover. Thus, to achieve this objective, a physical-mathematical review of the heat flow in the vertical profile of soil is performed. The reformulated model indicates the influence of cloud cover, intervening for both the soil’s heating (nighttime period) and cooling (daytime period). Finally, the reformulated model should be employed to estimate the soil thermal behavior (in particular, on “overcast sky” days).

Atmospheric attenuation measurement system for commercial solar plants based on optical spectrum analysis

The measurement of the solar radiation attenuation is one of the main challenges in concentrating solar power technologies. This work presents a new strategy for this measurement, based on the analysis of the VIS and IR spectra, and its related system. The optical design of the system and its implementation in a central receiver solar power plant is described, and the experimental results are detailed. We present, to the best of our knowledge, the first measurements of the atmospheric attenuation spectrum in a solar power plant. This system provides direct measurements of real atmospheric attenuation values, which opens the way to analyze the impact of aerosols and meteorological conditions at surface level in this attenuation.

Impact of COVID-19 induced lockdown on land surface temperature, aerosol, and urban heat in Europe and North America.

The outbreak of SARS CoV-2 (COVID-19) has posed a serious threat to human beings, society, and economic activities all over the world. Worldwide rigorous containment measures for limiting the spread of the virus have several beneficial environmental implications due to decreased anthropogenic emissions and air pollutants, which provide a unique opportunity to understand and quantify the human impact on atmospheric environment. In the present study, the associated changes in Land Surface Temperature (LST), aerosol, and atmospheric water vapor content were investigated over highly COVID-19 impacted areas, namely, Europe and North America. The key findings revealed a large-scale negative standardized LST anomaly during nighttime across Europe (–0.11 °C to –2.6 °C), USA (–0.70 °C) and Canada (–0.27 °C) in March–May of the pandemic year 2020 compared to the mean of 2015–2019, which can be partly ascribed to the lockdown effect. The reduced LST was corroborated with the negative anomaly of air temperature measured at meteorological stations (i.e. –0.46 °C to –0.96 °C). A larger decrease in nighttime LST was also seen in urban areas (by ∼1–2 °C) compared to rural landscapes, which suggests a weakness of the urban heat island effect during the lockdown period due to large decrease in absorbing aerosols and air pollutants. On the contrary, daytime LST increased over most parts of Europe due to less attenuation of solar radiation by atmospheric aerosols. Synoptic meteorological variability and several surface-related factors may mask these changes and significantly affect the variations in LST, aerosols and water vapor content. The changes in LST may be a temporary phenomenon during the lockdown but provides an excellent opportunity to investigate the effects of various forcing controlling factors in urban microclimate and a strong evidence base for potential environmental benefits through urban planning and policy implementation.

Spectral Relative Attenuation of Solar Radiation through a Skylight Focused on Preventive Conservation: Museo De L’almoina in Valencia (Spain) Case Study

The aim of the present study was to evaluate the relative attenuation of VIS, UV and NIR solar radiation through a large pond skylight into the interior of the l’Almoina Archaeological Museum (Valencia, Spain), and to determine how relative attenuation varied throughout the year and time of day. Measurements were taken at 9:00 a.m., 12:00 p.m. and 3:00 p.m. during July 2019 and January 2020. Relative attenuation values were obtained from the measurement of spectral irradiance in the exterior and at different points in the interior by means of two Ocean Optics spectrometers: HR4000CG-UV-NIR for VIS (400–700 nm) and NIR (700–1000 nm) bands, and FLAME-S-UV-VIS for UV-A (280–315 nm) and UV-A (315–400 nm) bands. The central points of the skylight had relative attenuation at 520 nm, reaching a value of 50% in summer at noon and 38% in the afternoon. At noon in winter, there were two relative attenuation peaks above 33% at 520 nm and at 900 nm. For mean relative attenuation, in the UVB range, the highest relative attenuation (20%) was inside the ruins in the morning in both summer and winter, and the UVA band relative attenuation was quite constant throughout the museum, but lower than that of the UVB band, in the range 0–3%.

Assessment of UVB solar radiation in four different selected climate locations in Saudi Arabia

ABSTRACT In this paper, we used the data measurements of average hourly and monthly of UV solar radiation from 2003 to 2017 at four different selected locations in Saudi Arabia for optimisation and evaluation of UVB, UVBest., UVI and KtUVB solar radiation and total ozone column TOC (DU). The scattering phenomena on by stratospheric ozone is high extremely attenuation of UVB solar radiation. The predicted values of UVB solar radiation are a good agreement with the measurement of the UVB solar radiation. The accuracy between measured and predicted values of UVB solar radiation in selected locations in the present research varies from 1.27 to 3.87%. The maximum values of the total ozone column TOC are occur between March and April months at all selected locations with exception Taif site which occur between April and may months, and in whole the highest values of TOC occur about Spring time in all study locations.The relation between UVI and (SZA) at all selected locations in the present research is discussed. The monthly average has a correlation coefficient equal to 72%, 82%, 85% and 83% at Al-Baha, Abha, Jeddah and Taif sites, respectively, so the SZA is responsible for variations of UVI by 72%, 82%, 85% and 83% at Al-Baha, Abha, Jeddah and Taif locations for the monthly values respectively.

Impact of COVID-19 Control Measures on Trace Gases (NO2, HCHO and SO2) and Aerosols over India during Pre-monsoon of 2020

To prevent the transmission of COVID-19, India implemented country-wide restrictions on socio-economic activities. Using satellite observations for the pre-monsoon (March–April–May) season, we explore the effect of the extended lockdown, on nitrogen dioxide (NO2), formaldehyde (HCHO), sulfur dioxide (SO2) and aerosol optical depth (AOD) over India. In this present study we evaluate and quantify the changes in pollutants across six different geographical zones along with the six most populous cities in the country. During April–May the lockdown have resulted in a net decrease in NO2 column density over India in 2020 compared to 2017–2019 average for the same months. Maximum average seasonal reduction of both NO2 (–5.6%) and HCHO (–1.3%) occurred over southern India (SI). Compared to March and April, anomalous HCHO for all the regions decreased in May. Anomalous surface cooling induced lower volatile organic carbons (VOCs) emission and slower VOC oxidation due to absence of high nitric oxide led to decrease in HCHO. A reduction in NO2 was also seen over the top six populous Indian cities, with Mumbai recording the highest decrease (–33.7%). But only Chennai showed a substantial decrease (–6.8%) in HCHO. A significant seasonal reduction in SO2 was noted over western India (WI) and SI. Additionally, widespread decline covering all the zones was found in the pre-monsoon AOD. In April, the decrease occurred primarily over the Indo-Gangetic-Plains (IGP) and eastern India, while in May a marked homogeneous reduction was noted over entire India. Aerosol induced attenuation of incident solar radiation leads to concurrent changes in MERRA2 insolation during pre-monsoon of 2020. Furthermore, reduced anthropogenic aerosols resulted in reduction of availed cloud condensation nuclei (CCN) leading to larger cloud droplet size and hence increased precipitation during pre-monsoon, 2020.

Atmospheric water vapor radiative effects on shortwave radiation under clear skies: A global spatiotemporal analysis

This global study analyzes how the total column water vapor (in terms of precipitable water, PW) is related to the attenuation of shortwave solar radiation (SWR) using data from the MERRA-2 reanalysis during 2000–2014 and SWR simulations obtained with the REST2 clear-sky radiation model. The water vapor radiative effect (WVRE) on SWR attenuation is investigated by comparing the clear-sky SWR predictions under humid and ideally dry atmospheres, whereas the quantitative effect of PW on WVRE is determined using the concept of precipitable water efficiency (PWE).At global scale, WVRE exhibits a distinct seasonal pattern ranging from –80.2 to 0 W m‐2, with lower values in humid regions where PW is typically high (>4 cm), making the water vapor contribution relatively small. This is attributed to the saturation effect in water vapor absorption. Over arid regions, the solar irradiance attenuation is mainly controlled by the high aerosol loads, and less negative WVRE values are found. Over high-altitude regions, the low PW reduces the atmospheric absorption, resulting in low absolute WVRE magnitudes.PWE is found to extend globally between –133.7 and 0 W m‐2 cm‐1 on a monthly scale. This range is smaller on a long-term mean monthly or annual basis. On a long-term basis, the monthly PWE results are mainly concentrated between −20 and 0 W m−2 cm−1, generating leptokurtic and left-skewed distributions peaking between −10 and −8 W m−2 cm−1, depending on month. PWE is inversely related to PW on a long-term annual scale, indicating that PWE tends to zero under very humid conditions. A general nonlinear model is proposed to evaluate the hourly PWE at global scale on a monthly basis, separately for the two hemispheres.A PW trend analysis reveals that the Middle East, equatorial regions, central Europe, and Australia exhibit significant temporal trends, further inducing significant trends in WVRE. For those areas, WVRE trends are calculated between −3.3 and 1.5 W m−2 over the entire 15-year period.In addition, the global WVRE over landmasses is classified in terms of the Köppen-Geiger (KG) climate classification system. The most pronounced radiative effects are found over the equatorial regions, with an average WVRE of −63 W m−2. The Arid KG class provides a complex WVRE pattern ranging from −66 to −24 W m−2. Further segregation of this class shows strongly variable WVRE, induced by local climate differentiation. Over Warm Temperate climates, WVRE is found to vary widely according to the various KG subclasses. For the Cold climate class, PW is mainly concentrated around 1 cm and WVRE is low. The Polar regions include high mountains where WVRE is low, with a median close to −28 W m−2.

Seasonal Stages of Chlorophyll‐a Vertical Distribution and Its Relation to the Light Conditions in the Black Sea From Bio‐Argo Measurements

AbstractThe year‐to‐year seasonal variability of the vertical distribution of concentration of chlorophyll‐a (Chla) in the Black Sea, its relation to light (photosynthetically available irradiance [PAR]), and mixing conditions were studied based on the 6‐year (2014–2019) measurements of Bio‐Argo floats. Variations in PAR caused by changes in incoming solar radiation and light attenuation determine the position of the deep chlorophyll maximum (DCM). During all seasons, the DCM was located between isolume of daily integrated PAR of 0.080 and 10.0 mole photons m−2 d−1. Analysis of Bio‐Argo data allowed to distinguish seven different stages of Chla seasonal variability. In February, the minimum of Chla in the entire water column was often observed in areas with a deep mixed layer (Stage 1), followed by the March early spring peak, occupying both the mixed layer and the seasonal thermocline (Stage 2). In April–May, Chla decreased throughout the 0–40 m layer, which was accompanied by the maximum in light penetration and an increase in Chla in the deepest layers (Stage 3). In summer, two deep peaks of Chla were distinguished: the first, a thin and shallow peak in June, and the second, a large and deeper peak in August (Stage 4 and 5). The August peak was followed by the deepest seasonal minimum of Chla in September–October, coincided with the autumn rise of the zooplankton biomass (Stage 6). Autumn–winter convection in November–January led to the third seasonal peak of Chla (Stage 7). The study discusses the role of various abiotic and biotic factors in the formation of each of these stages.

Multi-year field assessment of seasonal variability of photovoltaic soiling and environmental factors in a desert environment

In this study, we investigated multi-year seasonal trends of photovoltaic (PV) soiling in the desert environment conditions of Qatar. Field measurements of PV modules’ power and environmental factors were recorded continuously from 2014 to 2019. The PV soiling loss varied significantly from month to month, showing repeated seasonal trends; the year-to-year variability was not significant. Soiling rates in cold, warm, and rainy seasons appeared to be quite different and influenced by environmental factors. Over the six years of study, 75% of days had a negative soiling rate (i.e., increase in soiling on the PV panels), while the remaining 25% of days had a positive value due to the resuspension of the dust from the panels occurring by the strong wind. Key influential factors in the seasonal soiling variability and their respective correlations were also presented. It was found that a minimum rainfall of 3 mm only was required to fully clean the PV modules. Dust storms mainly occurred in summer months, when soiling losses accumulated in these most soiled months, yet the impact of dust storms during the winter season was found to be more severe than during the summer. Overall, dust storms caused 8% attenuation of solar radiation reaching the PV panels and increased the annual average soiling rate by 23% comparatively to non-dust storm days. Our study shows seasonal soiling profiles in an Arabian desert environment, which may allow PV plant operators to optimize their cleaning schedules and thereby reducing plant operational and maintenance costs.

AATTENUATION—The Atmospheric Attenuation Model for CSP Tower Plants: A Look-Up Table for Operational Implementation

Attenuation of solar radiation between the receiver and the heliostat field in concentrated solar power (CSP) tower plants can reduce the overall system performance significantly. The attenuation varies strongly with time and the average attenuation at different sites might also vary strongly from each other. If no site specific attenuation data is available, the optimal plant design cannot be determined and rough estimations of the attenuation effect are required leading to high uncertainties of yield analysis calculations. The attenuation is caused mainly by water vapor content and aerosol particles in the lower atmospheric layer above ground. Although several on-site measurement systems have been developed during recent years, attenuation data sets are usually not available to be included during the plant project development. An Atmospheric Attenuation (AATTENUATION) model to derive the atmospheric transmittance between a heliostat and receiver on the basis of common direct normal irradiance (DNI), temperature, relative humidity, and barometric pressure measurements was developed and validated by the authors earlier. The model allows the accurate estimation of attenuation for sites with low attenuation and gives an estimation of the attenuation for less clear sites. However, the site-dependent coefficients of the AATTENUATION model had to be developed individually for each site of interest, which required time-consuming radiative transfer simulations, considering the exact location and altitude, as well as the pre-dominant aerosol type at the location. This strongly limited the application of the model despite its typically available input data. In this manuscript, a look-up table (LUT) is presented which enables the application of the AATTENUATION model at the site of interest without the necessity to perform the according complex radiative transfer calculations for each site individually. This enables the application of the AATTENUATION model for virtually all resource assessments for tower plants and in an operational mode in real time within plant monitoring systems around the world. The LUT also facilitates the generation of solar attenuation maps on the basis of long-term meteorological data sets which can be considered during resource assessment for CSP tower plant projects. The LUTs are provided together with this manuscript as supplementary files. The LUT for the AATTENUATION model was developed for a solar zenith angle (SZA) grid of 1°, an altitude grid of 100 m, 7 different standard aerosol types and the standard AFGL atmospheres for mid-latitudes and the tropics. The LUT was tested against the original version of the AATTENUATION model at 4 sites in Morocco and Spain, and it was found that the additional uncertainty introduced by the application of the LUT is negligible. With the information of latitude, longitude, altitude above mean sea level, DNI, relative humidity (RH), ambient temperature (Tair), and barometric pressure (bp), the attenuation can be now derived easily for each site of interest.

Cloudiness Information Services for Solar Energy Management in West Africa

In West Africa (WA), interest in solar energy development has risen in recent years with many planned and ongoing projects currently in the region. However, a major drawback to this development in the region is the intense cloud cover that reduces the incoming solar radiation when present and causes fluctuations in solar power production. Therefore, understanding the occurrence of clouds and their link to the surface solar radiation in the region is important for making plans to manage future solar energy production. In this study, we use the state-of-the-art European Centre for Medium-range Weather Forecasts ReAnalysis (ERA5) dataset to examine the occurrence and persistence of cloudy and clear-sky conditions in the region. Then, we investigate the effects of cloud cover on the quantity and variability of the incoming solar radiation. The cloud shortwave radiation attenuation (CRASW↓) is used to quantify the amount of incoming solar radiation that is lost due to clouds. The results showed that the attenuation of incoming solar radiation is stronger in all months over the southern part of WA near the Guinea Coast. Across the whole region, the maximum attenuation occurs in August, with a mean CRASW↓ of about 55% over southern WA and between 20% and 35% in the Sahelian region. Southern WA is characterized by a higher occurrence of persistent cloudy conditions, while the Sahel region and northern WA are associated with frequent clear-sky conditions. Nonetheless, continuous periods with extremely low surface solar radiation were found to be few over the whole region. The analysis also showed that the surface solar radiation received from November to April only varies marginally from one year to the other. However, there is a higher uncertainty during the core of the monsoon season (June to October) with regard to the quantity of incoming solar radiation. The results obtained show the need for robust management plans to ensure the long-term success of solar energy projects in the region.

Wintertime nitrate formation pathways in the north China plain: Importance of N2O5 heterogeneous hydrolysis

Strict emission control measures have been implemented in the North China Plain (NCP) to improve air quality since 2013. However, heavy particulate matter (PM) pollution still frequently occurs in the region especially during wintertime, and the nitrate contribution to fine PM (PM2.5) has substantially increased in recent several years. Nitrate aerosols, which are formed via nitric acid (HNO3) to balance inorganic cations in the particle phase, have become a major fraction of PM2.5 during wintertime haze events in the NCP. HNO3 is mainly produced through homogeneous (NO2+OH, NO3+VOCs) and heterogeneous pathways (N2O5 heterogeneous hydrolysis) in the atmosphere, but the contribution of the two pathways to the nitrate formation remains elusive. In this study, the Weather Research and Forecasting model with Chemistry (WRF-Chem) was applied to simulate a heavy haze episode from 16 to December 31, 2016 in the North China Plain, and the source-oriented method (SOM) and brute force method (BFM) were both used to evaluate contributions of the heterogeneous pathway to the nitrate formation. The results demonstrated that the near-surface nitrate contributions of the heterogeneous pathway were about 30.8% based on the BFM, and 51.6% based on the SOM, indicating that the BFM might be subject to underestimating importance of the heterogeneous pathway to the nitrate formation. The SOM simulations further showed that the heterogeneous pathway dominated the nighttime HNO3 production in the planetary boundary layer, with an average contribution of 83.0%. Although N2O5 was photolytically liable during daytime, the heterogeneous N2O5 hydrolysis still contributed 10.1% of HNO3, which was caused by substantial attenuation of incident solar radiation by clouds and high PM2.5 mass loading. Our study highlighted the significantly important role of N2O5 heterogeneous hydrolysis in the nitrate formation during wintertime haze days.