Variation Of Aerosol Optical Depth Research Articles

Aerosol optical depth climatology over Central Asian countries based on Aqua-MODIS Collection 6.1 data: Aerosol variations and sources

The aim of this study is to explore the aerosol optical depth (AOD) – an indicator of air quality, based on satellite data over Central Asia. Due to limited studies and lack of knowledge regarding AOD variations over this region, five countries (Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan) and fifteen sites including the capital cities were selected for the analysis. Long-term Aqua-MODIS Collection 6.1 Deep Blue (DB) AOD observations at 10 km spatial resolution were obtained for 2002–2017 and the Ångström exponent (AE) was calculated using spectral AOD observations. AOD and AE were explored based on seasonal and inter-annual scale. The relationship between aerosol loading and economic indicator (gross domestic product) was also analyzed. Highest frequencies of low AOD and high AE were observed in all countries. Average AOD (AE) values during the study period were 0.17 ± 0.09 (1.29 ± 0.17) for Kazakhstan, 0.11 ± 0.13 (1.41 ± 0.13) for Kyrgyzstan, 0.17 ± 0.14 (1.36 ± 0.18) for Tajikistan, 0.20 ± 0.10 (1.10 ± 0.28) for Turkmenistan, and 0.18 ± 0.09 (1.18 ± 0.24) for Uzbekistan. Summer season experienced highest aerosol loading over Kazakhstan, Tajikistan, and Uzbekistan, whereas spring season experienced highest aerosol loading over Kyrgyzstan and Turkmenistan possibly due to the influence of less precipitation and dust from the arid regions. All fifteen cities selected in this study exhibited increasing aerosol load. Aerosol types based on the relationship between AOD and AE were investigated, results suggested the clean continental aerosol as a major aerosol type over the region, whereas the contribution of mixed aerosols was observed during spring and summer seasons. This study suggests for establishment of ground-based aerosol monitoring stations network and inclusions of modeling works to understand the complex nature of aerosol over this vast landmass.

Aerosol optical properties over Europe: an evaluation of the AQMEII Phase 3 simulations against satellite observations

Abstract. The main uncertainties regarding the estimation of changes in the Earth's energy budget are related to the role of atmospheric aerosols. These changes are caused by aerosol–radiation (ARIs) and aerosol–cloud interactions (ACIs), which heavily depend on aerosol properties. Since the 1980s, many international modeling initiatives have studied atmospheric aerosols and their climate effects. Phase 3 of the Air Quality Modelling Evaluation International Initiative (AQMEII) focuses on evaluating and intercomparing regional and linked global/regional modeling systems by collaborating with the Task Force on the Hemispheric Transport of Air Pollution Phase 2 (HTAP2) initiative. Within this framework, the main aim of this work is the assessment of the representation of aerosol optical depth (AOD) and the Ångström exponent (AE) in AQMEII Phase 3 simulations over Europe. The evaluation was made using remote-sensing data from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors aboard the Terra and Aqua platforms, and the instruments belonging to the ground-based Aerosol Robotic Network (AERONET) and the Maritime Aerosol Network (MAN). Overall, the skills of AQMEII simulations when representing AOD (mean absolute errors from 0.05 to 0.30) produced lower errors than for the AE (mean absolute errors from 0.30 to 1). Regardless of the models or the emissions used, models were skillful at representing the low and mean AOD values observed (below 0.5). However, high values (around 1.0) were overpredicted for biomass burning episodes, due to an underestimation in the common fires' emissions, and were overestimated for coarse particles – principally desert dust – related to the boundary conditions. Despite this behavior, the spatial and temporal variability of AOD was better represented by all the models than AE variability, which was strongly underestimated in all the simulations. Noticeably, the impact of the model selection when representing aerosol optical properties is higher than the use of different emission inventories. On the other hand, the influence of ARIs and ACIs has a little visible impact compared to the impact of the model used.

Potential impacts of Arctic warming on Northern Hemisphere mid-latitude aerosol optical depth

The weather and climate conditions can provide favorable or unfavorable atmospheric background for the maintenance and development of haze events. This study investigates the potential impacts of Arctic warming on the variation of Northern Hemisphere mid-latitude aerosol optical depth (AOD) in winter when haze often occurs. We first analyze the spatio-temporal variability of wintertime AOD in mid-latitudes of Northern Hemisphere from NASA MERRA-2 for the period of 1980–2016 using the empirical orthogonal function analysis and morlet wavelet analysis. It showes increasing trend for AOD in East China and North India and decreasing trend for AOD in Europe and North America during last 37 years while inter-decadal fluctuations exist. In addition to the temporal trends of AOD, two long-term periodic variations with periods of about 7 and 11 years exist, which implies the potential impacts from natural variabilities. Further analysis shows high correlations between the mid-latitude winter AOD (WA) and Arctic summer (May and June) surface temperature (T56). Moreover, the Arctic summer surface temperature demonstrates similar periodic variations with periods of about 7–9 and 11–13 years. Both of these indicate the potential impacts of Arctic summer warming on mid-latitude winter pollution. We then analyze the temporal correlations between Arctic summer temperature and mid-latitude winter AOD in different regions. Arctic T56 correlates negatively with WA in Europe and North America, and positively with that in East Asia, North India and Middle East. Particularly, T56 in western sea of Novaya Zemlya has the most prominent correlation with the WA in mid-latitudes of East Asia, especially in East China. This implies that Arctic T56 in the Arctic circle of Europe could be used for rough estimates of winter AOD in East Asia.

Variation in MERRA-2 aerosol optical depth and absorption aerosol optical depth over China from 1980 to 2017

4258 instantaneous 550 nm Aerosol Optical Depth (AOD) values were compared between the second Modern-Era Retrospective analysis for Research and Applications (MERRA-2) and the Aerosol Robotic Network (AERONET) in four seasons at 12 AERONET sites across China. The correlation coefficients (R) in spring, summer, autumn and winter were 0.88, 0.92, 0.91 and 0.87, respectively. The MERRA-2 AOD was compared with the Moderate resolution Imaging Spectroradiometer (MODIS/Aqua) AOD over China from 2003 to 2017, and good agreement was obtained. 4501 daily AOD values were compared between MERRA-2 and MODIS at 16 sites over China. Spatial distribution and temporal variation of MERRA-2 AOD over China were analyzed from 1980 to 2017. Mean values of MERRA-2 AOD indicated that high AOD mainly appeared in the eastern, southeastern and central China, while low AOD mostly occurred in the western and northeastern China. Mean AOD values over China during this study period in each month was also discussed, and similar spatial distribution (high AOD in developed areas, low AOD in rural and less developed areas) was found in each month. Slight AOD increase could be observed in the 1980s and 1990s, and a rapid increase happened from 2001 to 2010, followed by an AOD decrease between 2011 and 2017. Annual variation of mean AOD of the whole China (the Yangtze River Delta) showed a slight increase of 0.0010 (0.0045) per year from 1980 to 1999, a rapid increase of 0.0096 (0.0271) per year between 2000 and 2009, and a decrease of −0.0089 (−0.0206) per year from 2010 to 2017. Annual AOD Variation in Jing-jin-ji and Pearl River Delta is similar to that in the Yangtze River Delta. In four seasons, AOD change was similar to the annual AOD variation except winter with a slight decrease of −0.0012 per year between 1980 and 1999. AOD variation over China before and after the Pinatubo volcanic eruption in the Philippines in June 1991 was analyzed to get a better understanding of the transport and the impact on the environment from volcanic pollutants. AOD variation trend over China was studied in two periods. The increasing trend appeared in most part of China from 1980 to 2009, while a decreasing trend could be found in almost the entire China between 2010 and 2017. Spatial and temporal variation of MERRA-2 Absorption Aerosol Optical Depth (AAOD), Black Carbon Absorption Aerosol Optical Depth (BCAAOD) and Dust Absorption Aerosol Optical Depth (DUAAOD) were analyzed during the period between 1980 and 2017. BCAAOD (66.30%) and DUAAOD (30.56%) offered the major contribution to total AAOD in China. 38 years of variation of AAOD over China is mainly due to the variation of BCAAOD. BCAAOD experienced an increase (1980–2007) and a decrease (2008–2017) during the 38 years in China.

Temporal variability of atmospheric aerosol optical depth over European territory of Russia according to data of the ground-based and satellite observations: tendency of aerosol “enlightenment”

The results of studies of atmospheric aerosol over the territory of Russia are of great interest from the point of view of ecological and climatic problems. The paper presents the results of spatial and temporal variability of Aerosol Optical Depth (AOD) over the European territory of the Russian Federation in the period 1999 – 2016 yy. The assessments were carried out using the original AOD extraction method based on ground-based observations of the Russian actinometric network, and also on the satellite observations of MODIS. The general regularities of spatial variations in the aerosol optical depth over Russia are revealed: a monotonic decrease from the southwest to the northeast with localized areas having different aerosol loads due to the global and regional factors of their formation. The AOT increase in spring and summer is associated with a seasonal increase in temperature and humidity and with changes in the underlying surface. “Purification” of the atmosphere from aerosol is caused by the absence of large volcanic eruptions and by industrial “calm” conditions during the last decade. Negative tendencies are less pronounced in the fall than in spring and summer. To compare the atmospheric AOT values obtained from the MODIS, AERONET and GMS data, we have compiled a combined archive of daily AOT values synchronized in pairs for the 3 types of observations (GMS, MODIS and AERONET): “Aerosol optical thickness of the atmosphere by satellite and ground observations ". The data of the comparison of terrestrial and satellite data for AOD are presented only in averaged form and need further consideration.

Multi-Time Scale Analysis of Regional Aerosol Optical Depth Changes in National-Level Urban Agglomerations in China Using Modis Collection 6.1 Datasets from 2001 to 2017

With the rapid development of China’s economy and industry, characterizing the spatial and temporal changes of aerosols in China has attracted widespread attention from researchers. The national-level urban agglomerations are the most concentrated areas of China’s economic, population and resource. Studying the spatial and temporal changes of aerosol optical depth (AOD) in these regions has practical guiding significance for effective monitoring of atmospheric particulate pollution. This paper analyzed the spatial and temporal variations of AOD in China’s urban agglomerations during 2001–2017 by using Terra Moderate resolution Imaging Spectroradiometer (MODIS) Collection 6.1 (C6.1) Level 2 aerosol products (MOD04_L2). Five national-level urban agglomerations were chosen: Yangtze River Delta (YRD), Pearl River Delta (PRD), Beijing-Tianjin-Hebei (BTH), Yangtze River Middle-Reach (YRMR) and Cheng-Yu (CY). We analyzed the change patterns of AOD in different urban agglomerations at multi-time scales and built a time series decomposition model to mine the long-term trend, seasonal variation and abnormal change information of AOD time series. The result indicated that averaged AOD values in the five urban agglomerations were basically increased first and then decreased at the annual time scale during 2001–2017. The averaged AOD showed strong seasonal differences and AOD values in spring and summer were typically higher than those in autumn and winter. At the monthly time scale, the AOD typically varied from low in cold months to high in warm months and then decreased during the rainy periods. Time series decompositions revealed that a notable transition around 2007–2008 dominated the long-term overall trend over the five selected urban agglomerations and an initial upward tendency followed by a downward tendency was observed during 2001–2017. This study can be utilized to provide decision-making basis for atmospheric environmental governance and future development of urban agglomerations.

Evaluation of night-time aerosols measurements and lunar irradiance models in the frame of the first multi-instrument nocturnal intercomparison campaign

The first multi-instrument nocturnal aerosol optical depth (AOD) intercomparison campaign was held at the high-mountain Izaña Observatory (Tenerife, Spain) in June 2017, involving 2-min synchronous measurements from two different types of lunar photometers (Cimel CE318-T and Moon Precision Filter Radiometer, LunarPFR) and one stellar photometer. The Robotic Lunar Observatory (ROLO) model developed by the U.S. Geological Survey (USGS) was compared with the open-access ROLO Implementation for Moon photometry Observation (RIMO) model. Results showed rather small differences at Izaña over a 2-month time period covering June and July, 2017 (±0.01 in terms of AOD calculated by means of a day/night/day coherence test analysis and ± 2% in terms of lunar irradiance). The RIMO model has been used in this field campaign to retrieve AOD from lunar photometric measurements.No evidence of significant differences with the Moon's phase angle was found when comparing raw signals of the six Cimel photometers involved in this field campaign.The raw signal comparison of the participating lunar photometers (Cimel and LunarPFR) performed at coincident wavelengths showed consistent measurements and AOD differences within their combined uncertainties at 870 nm and 675 nm. Slightly larger AOD deviations were observed at 500 nm, pointing to some unexpected instrumental variations during the measurement period.Lunar irradiances retrieved using RIMO for phase angles varying between 0° and 75° (full Moon to near quarter Moon) were compared to the irradiance variations retrieved by Cimel and LunarPFR photometers. Our results showed a relative agreement within ± 3.5% between the RIMO model and the photometer-based lunar irradiances.The AOD retrieved by performing a Langley-plot calibration each night showed a remarkable agreement (better than 0.01) between the lunar photometers. However, when applying the Lunar-Langley calibration using RIMO, AOD differences of up to 0.015 (0.040 for 500 nm) were found, with differences increasing with the Moon's phase angle. These differences are thought to be partly due to the uncertainties in the irradiance models, as well as instrumental deficiencies yet to be fully understood.High AOD variability in stellar measurements was detected during the campaign. Nevertheless, the observed AOD differences in the Cimel/stellar comparison were within the expected combined uncertainties of these two photometric techniques. Our results indicate that lunar photometry is a more reliable technique, especially for low aerosol loading conditions.The uncertainty analysis performed in this paper shows that the combined standard AOD uncertainty in lunar photometry is dependent on the calibration technique (up to 0.014 for Langley-plot with illumination-based correction, 0.012–0.022 for Lunar-Langley calibration, and up to 0.1 for the Sun-Moon Gain Factor method). This analysis also corroborates that the uncertainty of the lunar irradiance model used for AOD calculation is within the 5–10% expected range.This campaign has allowed us to quantify the important technical difficulties that still exist when routinely monitoring aerosol optical properties at night-time. The small AOD differences observed between the three types of photometers involved in the campaign are only detectable under pristine sky conditions such as those found in this field campaign. Longer campaigns are necessary to understand the observed discrepancies between instruments as well as to provide more conclusive results about the uncertainty involved in the lunar irradiance models.

Evaluation of Landsat-8 and Sentinel-2A aerosol optical depth retrievals across Chinese cities and implications for medium spatial resolution urban aerosol monitoring.

In urban environments, aerosol distributions may change rapidly due to building and transport infrastructure and human population density variations. The recent availability of medium resolution Landsat-8 and Sentinel-2 satellite data provide the opportunity for aerosol optical depth (AOD) estimation at higher spatial resolution than provided by other satellites. A year of 30 m Landsat-8 and 10 m Sentinel-2A AOD data retrieved using the Land Surface Reflectance Code (LaSRC) were compared with coincident ground-based Aerosol Robotic Network (AERONET) Version 3 AOD data for 20 Chinese cities. Stringent selection criteria were used to select contemporaneous data - only satellite and AERONET data acquired within 10 minutes were considered. The average satellite retrieved AOD over a 1470 m × 1470 m window centered on each AERONET site was derived to capture fine scale urban AOD variations. AERONET Level 1.5 (cloud-screened) and Level 2.0 (cloud-screened and also quality assured) data were considered. For the 20 urban AERONET sites in 2016 there were 106 (Level 1.5) and 67 (Level 2.0) Landsat-8 AERONET AOD contemporaneous data pairs, and 118 (Level 1.5) and 89 (Level 2.0) Sentinel-2A AOD data pairs. The greatest AOD values (>1.5) occurred in Beijing, suggesting that the Chinese capital was one of the most polluted cities in China in 2016. The LaSRC Landsat-8 and Sentinel-2A AOD retrievals agreed well with the AERONET AOD data (linear regression slopes > 0.96; coefficient of determination r2 > 0.90; root mean square deviation < 0.175) and demonstrate that the LaSRC is an effective and applicable medium resolution AOD retrieval algorithm over urban environments. The Sentinel-2A AOD retrievals had better accuracy than the Landsat-8 AOD retrievals, which is consistent with previously published research. The implications of the research and the potential for urban aerosol monitoring by combining the freely available Landsat-8 and Sentinel-2 satellite data are discussed.

Investigating the Aerosol Optical Depth and Angstrom Exponent and Their Relationships with Meteorological Parameters Over Lahore in Pakistan

In the present work, AERONET (AErosol RObotic NETwork) data of 2006–2014 have been used to analyze the variations in aerosol optical depth (AOD) at 500 nm and Angstrom exponent (440/870) (AE). In order to have an in-depth knowledge of aerosol variability, we have analyzed the association of aerosol properties with the meteorological parameters such as temperature, mean sea level pressure, rainfall, dew point, and dust storm frequency. Long-term observations of MODIS-AOD are also validated with AERONET-AOD over Lahore. The peak monthly mean value of AOD is found in July (1.00 ± 0.34) with the corresponding AE value of 0.85 ± 0.29 pointing toward the fact that desert/soil dust aerosols dominated the atmosphere of Lahore. The lowest value of AOD is found in February (0.47 ± 0.26) with the corresponding AE value of 1.22 ± 0.29 representing the presence of urban/industrial aerosols in the atmosphere over Lahore. The monthly mean AE value is found to be maximum in January (1.36 ± 0.15), whereas lowest value of AE is found in June (0.55 ± 0.25). AOD shows positive correlations with temperature, dew point, relative humidity, visibility, rain and dust storm frequency, and negative with mean sea level pressure and wind speed. AE exhibits positive correlations with relative humidity and mean sea level pressure, while with temperature, dew point, visibility, rain and dust storm frequency, it shows negative correlations.

Variability in atmospheric aerosols and effects of humidity, wind and InterTropical discontinuity over different ecological zones in Nigeria

The effects of humidity, wind, and InterTropical Discontinuity (ITD) movement on seasonal distribution of atmospheric aerosols were assessed over different ecological zones in Nigeria. Satellite-observed aerosol optical depth (AOD), humidity, wind speed, and precipitation/ITD data were used. The Moderate Resolution Imaging Spectroradiometer (MODIS) AOD time series of dataset were used. The MODIS AOD retrievals were at the wavelength of 550 nm and AOD data was re-scaled and sub-divided into seasonal and annual distributions to investigate the variations in Aerosol. Kriging spatial interpolation model was used to analyze the aerosol seasonal distribution. Correlations analysis was used to evaluate the degree of influence of humidity, wind speed, and precipitation/ITD on the seasonal distribution of aerosol over six ecological zones; Sahel, Sudan, Guinea, Rainforest, Freshwater, and Mangrove zones in Nigeria. The results show that the AOD over Nigeria is influenced by meteorological factors, but much more influenced by dust source outside the country. AOD appears much more during Harmattan season than Wet and Dry seasons; with AOD ≥0.46, with considerable concentration in Sahel ecological zone than other ecological zones. The results show a strong significant relationship between aerosol distribution and meteorological, principally humidity with R2 ≥ 0.65 @ p < 0.05. The study reveals that for daily variation of AOD, wind speed, humidity and precipitation as well as spatial distribution of dust source in and outside the country are important drivers.

阿拉伯海区域气溶胶时空动态变化及海域叶绿素a浓度特征

PDF HTML阅读 XML下载 导出引用 引用提醒 阿拉伯海区域气溶胶时空动态变化及海域叶绿素a浓度特征 DOI: 10.5846/stxb201804290973 作者: 作者单位: 西南大学地理科学学院,西南大学地理科学学院,中国科学院遥感与数字地球研究所,中国农业科学院农业信息研究所;中国农业科学院农业信息研究所,西南大学地理科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 中国科学院战略性先导科技专项（XDA19030302） Spatio-temporal dynamic characteristics of aerosol and chlorophyll a concentration in the Arabian Sea Author: Affiliation: School of Geographical Sciences, Southwest University,School of Geographical Sciences, Southwest University,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:基于2003-2017年的MODIS/Aqua气溶胶和海洋叶绿素a浓度遥感数据资料，分析了阿拉伯海域气溶胶光学厚度（AOD）的时空动态变化及海域叶绿素a浓度（Chl-a）特征，并探讨了该海域气溶胶和海洋叶绿素a浓度的关系。结果表明：阿拉伯海区域AOD和Chl-a的空间分布都呈现出显著的季节性变化，且总体呈现出由近岸向外海逐渐降低的特征，其大小和分布受到陆源沙尘影响显著；海域AOD夏季高于春季，冬季高于秋季，15年间海域AOD整体呈现增加趋势，其中东部海域增加较明显，北部海域无显著变化；海域Chl-a秋冬季明显高于春夏季，变异性较高；由春冬季AOD与Chl-a的相关系数分析发现，二者相关性在阿拉伯海西北部区域显著性相关，且呈现出由北向南、由近海岸向外海区逐渐减弱的趋势。 Abstract:The spatial distribution and temporal variation of aerosol optical depth (AOD) and the characteristics of chlorophyll a concentration (Chl-a) in the Arabian Sea, were inter-annually and seasonally analyzed by utilizing the MODIS/Aqua AOD and chlorophyll products during 2003 to 2017, and the relationship between the aerosol and chlorophyll a concentration was discussed for the sea area. The results showed that the spatial distributions of AOD and Chl-a changed more significantly with the seasons in the Arabian Sea, and generally showed a gradual decrease from offshore to the open seas. The value and spatial distribution of the AOD and Chl-a were obviously affected by the dust in the land-sourced desert. The AOD was higher in summer than spring, and in winter was higher than that in autumn. During the past 15 years there appeared an increasing trend of the AOD, especially in its east coastal area, but no significant change occurred in the north coast. The specific performance of Chl-a was higher in autumn and winter, lower in spring and summer, and its variability was high. From the correlation coefficient analysis between AOD and Chl-a in spring and winter, the correlation between AOD and Chl-a was significantly correlated in the northwestern Arabian Sea, and it showed a trend of decreasing from north to south and from the coast to the outer sea. 参考文献 相似文献 引证文献

Features of temporal variability of aerosol optical depth in the Middle Urals according to long-term observations at the urban and background sites

Features of temporal variability of aerosol optical depth in the Middle Urals according to long-term observations at the urban and background sites

Analysis of spatial and temporal variability of aerosol optical depth over China using MODIS combined Dark Target and Deep Blue product

This study reviews spatial and temporal variability of aerosol optical depth (AOD) at 550 nm, obtained with Moderate Resolution Imaging Spectroradiometer (MODIS) (Terra) Collection 6.1 aerosol products with use of combined Dark Target and Deep Blue algorithm. Data was analyzed for 18-year period from 2000 to 2017 over the territory of the whole continental China, covering the largest cities as well as various ecological and geographical regions. Spatial distribution of AOD has distinct geographical differences with gradual decrease from the east to the west of the country. The lowest values (up to 0.25) of annual mean AOD at 550 nm occur in sparsely populated areas on the Tibetan Plateau and in the north forest ecosystems in the north-eastern part of China. Areas of desert and semidesert landscapes of Northwest China are characterized by high concentrations of naturally occurring aerosols with moderate values of AOD (0.4–0.7). The most populous regions (Pearl River Delta, Yangtze River Delta, North China Plain, and Sichuan Basin) with the highest density of agricultural and industrial activity are characterized with maximum values of AOD (over 0.7). Seasonal variation of aerosols in the most regions of China has maximum AODs in spring or summer and minimum in autumn or winter. Angstrom exponent (AE), being 0.31–1.7 for the most part of China, was used to detect the size of aerosol particles, with the lowest values (0.31–0.84) in desert north and north-west regions of the country, and the higher values in the south (1.3–1.7). Comparison of results, obtained with MODIS Terra and AERONET (Aerosol Robotic Network) at 550 nm, demonstrate a high interrelation (r = 0.8949), where 68.3% fall within the range of expected errors, set by MODIS over the land (± 0.05 ± 0.15 × AOD). The conducted Pearson’s correlation analysis between various cities of the country showed that cities in one region with shortest distances from one another demonstrated higher correlations, suggesting distinct regional dependence in aerosols distribution.

Spatiotemporal variations of photosynthetically active radiation and the influencing factors in China from 1961 to 2016

Daily measurements of photosynthetically active radiation (PAR) and other meteorological parameters at 16 stations in China during 2005–2015 were used to develop the all-weather Adaptive-Network-based Fuzzy Inference System (ANFIS) PAR models. The ANFIS models were compared with other semi-empirical and semi-physical methods, and the results showed that ANFIS models using global solar radiation (G) as input parameter provided more accurate estimates than other models. Daily PAR values during 1961–2016 were reconstructed using meteorological parameters at 908 meteorological stations, and the spatiotemporal characteristics of PAR in China were analyzed. The daily PAR ranged from 20.03 to 36.29 mol m−2 day−1 with annual mean value being about 29.03 mol m−2 day−1 in China during 1961–2016. The PAR values were generally higher in Qinghai-Tibet Plateau (QTP) and Inner Mongolian Plateau (IMP) and lower in Northeast and Southeast China, especially in the Sichuan Basin. PAR decreased in most part of China, especially in Northeast China, with the minimum value being about − 0.11 mol m−2 day−1 year−1 during 1961–2016. The increasing trend only appeared in Southwest China with the maximum value being about 0.02 mol m−2 day−1 year−1. Annual mean daily G, PAR fraction (Fp, the ratio of PAR and G), sunshine duration (SSD), relative humidity (RH), and water pressure (MP) were further analyzed to find the influencing parameters for PAR. The results showed that G, Fp, and SSD were the major factors for influencing PAR in most part of China, but in some areas, RH and MP influenced the PAR more effectively. Finally, the monthly variations of aerosol optical depth (AOD) in the Yangtze River Basin gathered from the Moderate Resolution Imaging Spectroradiometer (MODIS) Level 3 Atmosphere Product during 2002–2016 were analyzed, which was one important factors influencing the PAR values in summer and winter months.

Analysis of the aerosol and the ozone observations at a southwest peninsular coastal station using microtops sunphotometer

This study analyses the variations of aerosol optical depth, total column ozone and water vapour, measured by a Microtops-II (MICRO-processor based Total Ozone Portable Spectrometer) ozonometer/sunphotometer over a coastal station in southwest peninsular India, Kochi. Observations of ozone and aerosols are analysed for a period, May 2012 to May 2013. Satellite data sets available over the region are also analysed, and a comparison is made with the in situ data. Sunphotometer measured 1020 nm aerosol optical depth (AOD) shows a temporal variability with an increase in AOD during the summer (high value of 0.35 in May 2012) and fewer values near 0.2 during the winter and the post-monsoon seasons. Satellite observations also show a similar pattern of variability with high AOD during the summer. Water vapour is maximum (near 3.5 cm) during the pre-monsoon and the summer monsoon and minimum (below 2 cm in January 2013) during the winter. Ozone shows seasonal variability with a minimum concentration during the winter (230 Dobson Unit (DU) in January 2013) and maximum (280 DU in May 2012) during the summer. OMI (Ozone measuring Instrument) onboard Aura satellite overestimates the column ozone by 10 DU in comparison with the Microtops ozonometer. However, the sunphotometer and satellite observations show a similar pattern of temporal variability with a small difference in magnitude during certain months. The zonal ozone distribution shows a seasonal variability with a reverse gradient between the summer and the winter.

A simplified aerosol retrieval algorithm for Himawari-8 Advanced Himawari Imager over Beijing

High temporal aerosol optical depth (AOD) is useful for inversing modelling of emissions and for comprehensively understanding the climatology of aerosol. Geostationary satellite has been used to derive AOD over land and ocean. In this study, a novel simplified aerosol retrieval algorithm for Advanced Himawari-8 imager (SARAHI) is developed to retrieve hourly AOD over Beijing from a new-generation geostationary meteorological satellite—Himawari-8, which carries the Advanced Himawari Imager (AHI). The algorithm is based on a simplified radiative transfer model and surface reflectance derived from one-month AHI apparent data. Measurements from AErosol RObotic NETwork (AERONET) sites and JAXA Himawari Monitor Version 2.0 Aerosol Retrieval product (L2ARP2.0) are used to evaluate the performance of AOD retrievals from SARAHI algorithm. There are 73.5%, 78.2%, 74.7% of AOD retrievals falling in the Expected error lines at Beijing_CAMS, Beijing_RADI, and Xianghe sites, respectively. The correlation coefficient is larger than 0.92 with small root mean square error (RMSE) of 0.134–0.164. The retrievals can also reflect the temporal variations of AOD very well. The results indicate that the SARAHI AOD algorithm can derive the regional AOD accurately and is better than the L2ARP2.0 AOD.

Validation of Himawari-8 aerosol optical depth retrievals over China

High temporal resolution (every 10 min) aerosol observations are rarely provided by satellite sensors. The Advanced Himawari Imager (AHI) aboard Himawari-8 can provide aerosol optical depth (AOD) over China with this frequency. The sensor provides great opportunity to retrieve the particle matter near the ground and improve air quality modeling using the aerosol products. However, there is still lack of quality validation about AHI AOD. A comprehensive research was conducted to evaluate the performance of AHI aerosol products based on sixteen sun-photometers stations in AErosol RObotic NETwork (AERONET) and Sun–Sky Radiometer Observation Network (SONET) over China. The overall comparison of AHI AOD and ground AOD shows a high correlation (R2 = 0.67). However, there is only 55% of AHI AOD falling in the expected error envelops (±0.05 ± 0.2*AOD ground). AOD bias between AHI AOD and ground AOD increases with the AOD magnitude. The accuracy of AHI AOD is also highly depend on seasons and surface land cover types. Best performance of AHI aerosol retrievals is shown in summer and for urban region. The diurnal variability validation shows that AHI AOD catch the diurnal AOD variations well, especially for summer. Large differences between AHI AOD and MODerate-resolution Imaging Spectrometer (MODIS) aerosol products are shown, especially for northwest China. The analysis indicates that the uncertainties of AHI aerosol retrievals are induced by large errors of aerosol models and surface reflectance estimation in the algorithm.

Comparison of AVHRR aerosol optical depth production against CARSNET data in China

This study presents a dedicated evaluation of a newly released satellite aerosol product derived from Advanced Very-High-Resolution Radiometer (AVHRR) measurements by using the Deep Blue/SOAR aerosol retrieval algorithm. Aerosol product from the Chinese Aerosol Network (CARSNET) is used as the ground truth in the comparison. Comparison of AVHRR and CARSNET aerosol optical depth (AOD) products during 2006–2011 shows that the accuracy and precision of AVHRR AOD demonstrate complicated spatial and seasonal dependence. First, AVHRR AOD is in good agreement with CARSNET AOD over eastern urban areas in China. 45%–78% of data points fall within the expected error range (±0.05 ± 0.25× AOD) over there. Second, in regions with natural vegetation cover and relatively clean environment conditions, low correlation is observed due to small AOD loadings (<0.2 and < 0.6, respectively) and small AOD variations (<1.0). Third, for dust affected arid and semi-arid dry regions and western urban regions, AVHRR AOD products need further great improvement. A large regional variation of AOD bias with increasing CARSNET AOD may be due to insufficient representation of aerosol properties in the algorithm. The systematic underestimation of AVHRR AOD in most sites likely attributes to improper surface reflectance estimation, which should be furthermore improved in the deep blue algorithm. AVHRR has great potential in the retrieval of the historical AOD record from 1979 to the present, therefore, one would expect that AVHRR aerosol products would contribute to furthering our understanding of aerosol effects on climate and environment.

Diurnal variation of aerosol optical depth and PM&amp;lt;sub&amp;gt;2.5&amp;lt;/sub&amp;gt; in South Korea: a synthesis from AERONET, satellite (GOCI), KORUS-AQ observation, and the WRF-Chem model

Abstract. Spatial distribution of diurnal variations of aerosol properties in South Korea, both long term and short term, is studied by using 9 AERONET (AErosol RObotic NETwork) sites from 1999 to 2017 and an additional 10 sites during the KORUS-AQ (Korea–United States Air Quality) field campaign in May and June of 2016. The extent to which the WRF-Chem (Weather Research and Forecasting coupled with Chemistry) model and the GOCI (Geostationary Ocean Color Imager) satellite retrieval can describe these variations is also analyzed. On a daily average, aerosol optical depth (AOD) at 550 nm is 0.386 and shows a diurnal variation of 20 to −30 % in inland sites, which is larger than the AOD of 0.308 and diurnal variation of ±20 % seen in coastal sites. For all the inland and coastal sites, AERONET, GOCI, and WRF-Chem, and observed PM2.5 (particulate matter with aerodynamic diameter less than 2.5 µm) data generally show dual peaks for both AOD and PM2.5, one in the morning (often at ∼08:00–10:00 KST, Korea Standard Time, especially for PM2.5) and another in the early afternoon (∼14:00 KST, albeit for PM2.5 this peak is smaller and sometimes insignificant). In contrast, Ångström exponent values in all sites are between 1.2 and 1.4 with the exception of the inland rural sites having smaller values near 1.0 during the early morning hours. All inland sites experience a pronounced increase in the Ångström exponent from morning to evening, reflecting an overall decrease in particle size in daytime. To statistically obtain the climatology of diurnal variation of AOD, a minimum requirement of ∼2 years of observation is needed in coastal rural sites, twice as long as that required for the urban sites, which suggests that the diurnal variation of AOD in an urban setting is more distinct and persistent. While Korean GOCI satellite retrievals are able to consistently capture the diurnal variation of AOD (although it has a systematically low bias of 0.04 on average and up to 0.09 in later afternoon hours), WRF-Chem clearly has a deficiency in describing the relative change of peaks and variations between the morning and afternoon, suggesting further studies for the diurnal profile of emissions. Furthermore, the ratio between PM2.5 and AOD in WRF-Chem is persistently larger than the observed counterparts by 30 %–50 % in different sites, but spatially no consistent diurnal variation pattern of this ratio can be found. Overall, the relatively small diurnal variation of PM2.5 is in high contrast with large AOD diurnal variation, which suggests the large diurnal variation of AOD–PM2.5 relationships (with the PM2.5 ∕ AOD ratio being largest in the early morning, decreasing around noon, and increasing in late afternoon) and, therefore, the need to use AOD from geostationary satellites to constrain either modeling or estimate of surface PM2.5 for air quality application.

Natural and anthropogenic contributions to long-term variations of SO2, NO2, CO, and AOD over East China

Concentrations of atmospheric pollutants over East China have varied considerably during the past decades. These variations are partly due to variations of human activities, e.g., increasing energy consumption and implementation of government emission control policies, and partly to natural fluctuations. This study aims to separate the effects of natural processes and anthropogenic activities on the increase/decrease of the concentrations of some of the most important pollutants (SO2, NO2, CO and aerosols) over East China in the last decade. This was achieved by the comparison of the temporal variations in long-term time series of satellite-retrieved aerosol optical depth (AOD) and vertical column densities (VCDs) of SO2, NO2, and CO, with those in model-simulated time series of the natural variations only. The latter were created by the use of the same anthropogenic emissions throughout the whole simulation, while using re-analysis data (MERRA) to describe meteorological processes and natural emissions. Thus, the comparison between observed and simulated temporal variations reveals the effects due to anthropogenic emissions only, assuming that the atmospheric processes affect natural and anthropogenic species in the same way. In the analysis, a Kolmogorov–Zurbenko (KZ) filter is used to extract long-term components from both the observed and simulated data and normalization to the situation at a certain reference point is used to eliminate bias between observations and simulations. By this new method, natural and anthropogenic contributions to long-term variations of trace gases and AOD are quantitatively estimated. The results show that NO2 VCDs increased from 2004 to 2011 by 76% and of the overall increase in this period only 1% ± 1% was attributed to natural factors, 99% ± 1% attributed to anthropogenic factors. AOD increased by 24% between 2001 and 2011 and of the overall increase 24% ± 32% was due to natural factors and 76% ± 32% was due to anthropogenic factors. SO2 VCDs decreased by 15% from 2007 to 2013, natural and anthropogenic factors contributed respectively 16% ± 14% and 84% ± 14% to the overall decrease in this period. CO decreased since 2003 with 13% and of the overall decrease 6% ± 6% was due to natural factors and 94% ± 6% was due to anthropogenic factors.