Annual Average Aerosol Optical Depth Research Articles

Optical and physical characteristics of aerosols over Asia: AERONET, MERRA-2 and CAMS

A comprehensive study on the regional and spatial distributions of aerosol columnar optical and physical characteristics utilizing high-quality Aerosol Robotic Network (AERONET) datasets over Asia (Central, South, South-East, and East Asia), along with spatiotemporal collocated validation of two highly-spatially resolved models (Modern-Era Retrospective Analysis for Research and Applications-2 (MERRA-2) and Copernicus Atmosphere Monitoring Service (CAMS)) simulated aerosol optical depth (AOD) and Ångström exponent (AE) on annual and seasonal scales, is conducted for the first time. AOD is the highest over South Asia in each season, followed by South-East, East, and Central Asia. Annual regional average AOD at 0.50 μm over South Asia is 0.61. Combined influence of both fine mode anthropogenic aerosol emissions from fossil fuel combustion and biomass burning, and coarse mode dust aerosols from seasonal transport lead to higher AOD and total volume concentration (TVC), and exhibit significant spatiotemporal variations. Coarse volume fraction (CVF) and effective radius (Reff) are higher over Central Asia due to the dominance of coarse dust aerosols. East and South-East Asia are dominated by fine mode aerosols and result in higher fine volume concentration (FVC), AE, fine mode fraction (FMF), and lower Reff. Compared to the other regions of the globe (except Africa), AOD is higher over Asia, with higher spatiotemporal variabilities in AOD, AE, FMF, and TVC. Over Asia, the agreement between AERONET and CAMS AOD is better than that of AERONET and MERRA-2 AOD. For high AOD conditions, underestimation in model AODs is higher, and lower fraction of model AODs satisfy the Global Climate Observing System (GCOS) requirement over all regions, and these are more pronounced over Asia. Biases in model AODs are higher over Asia compared to the other regions of the globe, and lower over North America, Europe, and Australia. Higher bias in model AEs compared to AODs over all the regions shows substantial challenges in simulating spectral AOD and appropriate contributions of fine and coarse mode aerosols. These findings over a global aerosol hotspot region, Asia, along with other regions of the globe are crucial for accurate simulation and fine-tuning of aerosol characteristics by regional and global models, and for reducing uncertainties in the assessment of radiative and climate impact of aerosols.

City-Scale Aerosol Loading Changes in the Sichuan Basin from 2001 to 2020 as Revealed by MODIS 1 km Aerosol Product

Long-term high-resolution monitoring of aerosol optical depth (AOD) is necessary to understand air pollution problems and climate change at regional to urban scales. Based on the 1 km AOD dataset retrieved by the MODIS Multi-Angle Implementation of Atmospheric Correction algorithm (MAIAC), the spatial-temporal evolutionary trends of AOD in the Sichuan Basin (SCB), Southwest China, and its 17 subordinate cities were analyzed from 2001 to 2020. In the past 20 years, the annual average AOD in SCB gradually decreased from south to north. The highest AOD of SCB in spring was 0.62, followed by an average AOD value of 0.60 in winter. At the city scale, Zigong, Neijiang, and Ziyang were identified as the three most polluted cities within the SCB. The average AOD in the SCB increased to 0.68 and 0.69 in February and March, respectively, and significantly decreased to 0.41 and 0.43 in June and July, respectively. The interannual AOD in the SCB presented an increasing trend from 2001 to 2010, with a range of 0.50 to 0.70, whereas it showed a decreasing trend from 2011 to 2020, with a range of 0.68 to 0.35. In spring, the annual average AOD at the district level showed significant high values from 2005 to 2012. In winter, the interannual AOD increased significantly, with high values concentrated in 2008, 2010, 2011, and 2013. The occurrence frequency of AOD in the SCB was mainly distributed between 0.2~0.5 and 1.5. There also was an increasing trend of AOD in the SCB from 2001 to 2008 and a decreasing trend from 2009 to 2020. The results of this study hold significance for further understanding the climatic characteristics and environmental effects of regional atmospheric aerosols.

Spatiotemporal Variations of Aerosol Optical Depth and the Spatial Heterogeneity Relationship of Potential Factors Based on the Multi-Scale Geographically Weighted Regression Model in Chinese National-Level Urban Agglomerations

Investigating the spatiotemporal variation characteristics of aerosol optical depth (AOD) and its driving factors is essential for assessing atmospheric environmental quality and alleviating air pollution. Based on a 22-year high-resolution AOD dataset, the spatiotemporal variations of AOD in mainland China and ten national urban agglomerations were explored based on the Mann–Kendall trend test and Theil–Sen median method. Random forest (RF) and multiscale geographically weighted regression (MGWR) were combined to identify the main driving factors of AOD in urban agglomerations and to reveal the spatial heterogeneity of influencing factors. The results showed that areas with high annual average AOD concentrations were mainly concentrated in the Chengdu–Chongqing, Central Plains, Shandong Peninsula, and Middle Yangtze River urban agglomerations. Southern Beijing–Tianjin–Hebei and its surrounding areas revealed the highest AOD pollution during summer, whereas the worst pollution during the remaining three seasons occurred in the Chengdu–Chongqing urban agglomeration. Temporally, except for the Ha-Chang and Mid-Southern Liaoning urban agglomerations, where the average annual AOD increased, the other urban agglomerations showed a decreasing trend. Among them, the Central Plains, Middle Yangtze River, Guanzhong Plain, and Yangtze River Delta urban agglomerations all exhibited a decline greater than 20%. According to the spatial trends, most urban agglomerations encompassed much larger areas of decreasing AOD values than areas of increasing AOD values, indicating that the air quality in most areas has recently improved. RF analysis revealed that PM2.5 was the dominant factor in most urban clusters, followed by meteorological factors. MGWR results show that the influencing factors have different spatial scale effects on AOD in urban agglomerations. The socioeconomic factors and PM2.5 showed strong spatial non-stationarity with regard to the spatial distribution of AOD. This study can provide a comprehensive understanding of AOD differences among urban agglomerations, and it has important theoretical and practical implications for improving the ecological environment and promoting sustainable development.

Coupling Coordination Degree of AOD and Air Pollutants in Shandong Province from 2015 to 2020

In order to reveal the correlation between aerosols and pollution indicators, the MODIS aerosol optical depth (AOD) was used to investigate the distribution of AOD in 16 prefecture-level cities in Shandong Province from 2015 to 2020. This study quantitatively analyzed the coupling degree and the coupling coordination degree between AOD and pollution indicators based on the coupling coordination model. The results showed that: (1) The annual average AOD in Shandong Province showed a rapid downward trend with a mean value of 0.615. The seasonal AOD of Shandong Province and prefecture-level cities was characterized by spring and summer > autumn and winter. The distribution of AOD in Shandong Province showed a spatial pattern of high in the west and low in the east, and high in the surrounding area and low in the middle. The decreasing rate of AOD was high in the west and low in the east. (2) The annual average AOD and Air Quality Index (AQI) were in a highly coupled and coordinated state. Their spatial distribution pattern decreased from west to east. There were certain fluctuations with seasonal changes, with the largest fluctuation in winter. (3) Except for O3, the overall coupling and coordination level between AOD and each pollutant was relatively high. The coupling coordination effect was as follows: C (PM2.5, AOD) and C (PM10, AOD) > C (NO2, AOD) > C (SO2, AOD), and C (CO, AOD) > C (O3, AOD). Except for the O3, its distribution was characterized by highs in the west and lows in the east. The degree of coupling between each pollution indicator and the seasonal average AOD was high. The study showed that there was a high degree of coupling and coordination between pollutant concentration indicators and AOD, and remote sensing AOD data can be used as an effective supplement to regional pollutant monitoring indicators.

气溶胶光学厚度与PM2.5浓度的时空分布特征及其关系——以京津冀大气污染传输通道城市群为例

PDF HTML阅读 XML下载 导出引用 引用提醒 气溶胶光学厚度与PM2.5浓度的时空分布特征及其关系——以京津冀大气污染传输通道城市群为例 DOI: 10.5846/stxb202204100936 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41771178，41671151）；辽宁省高等学校创新人才支持计划项目（LR2017017）；辽宁省教育厅项目（H201783628） Spatiotemporal distribution characteristics and relationship analysis of aerosol optical depth and PM2.5 concentration: Taking the “2+26” urban agglomeration as an example Author: Affiliation: 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:城市人口和产业的聚集伴随化石能源消费的迅速增长，导致空气污染物排放量不断增加，对区域气候产生了不可逆的负面影响。以多源遥感数据为基础，对京津冀大气污染传输通道城市群（"2+26"城市群）2015-2019年气溶胶光学厚度（AOD）、PM2.5浓度的时空分布格局进行分析，从月份、季节、年份三个时间维度定量分析其时空变化规律，并通过计算相关性系数来分析气溶胶光学厚度对PM2.5浓度的影响。主要得出研究结论如下：（1） PM2.5浓度整体呈现冬季>春季>秋季>夏季的趋势，并且表现出高度空间自相关性，2015-2019年间，PM2.5浓度显著下降至40μg/m3以下；（2） AOD平均范围值在0-1之间，总体上呈现春夏季高，秋冬季低的分布特点，到2019年，春夏秋三季AOD浓度呈现明显降低，夏季下降趋势最为显著，AOD同样表现出高度空间自相关性；（3） AOD与PM2.5浓度存在显著的正相关关系。从季节变化上看，相关性呈现出：秋季>夏季>冬季>春季的特点。年均AOD与PM2.5浓度呈现中等正相关关系。因此，定量研究气溶胶光学厚度与PM2.5浓度在时空变化上的相似性以及相关性，可以证明气溶胶对大气污染存在影响关系，为未来城市空气质量管理提供科学思路和依据。 Abstract:The agglomeration of population and industries has led to the rapid growth of fossil energy consumption, resulting in the continuous increase of air pollutant emissions and irreversible negative impacts on the regional climate. Based on the multi-source remote sensing data, this paper analyzed the temporal and spatial distribution of Aerosol Optical Depth (AOD) and PM2.5 in the "2+26" urban agglomeration from 2015 to 2019, and the influence of aerosol optical thickness on PM2.5 concentration was analyzed by calculating the correlation coefficient. The main conclusions are as follows:(1) The overall change of PM2.5 concentration was winter > spring > autumn > summer, and it showed highly spatial autocorrelation. From 2015 to 2019, the PM2.5 concentration has dropped significantly to below 40 μg/m3. (2) The average range of AOD values was between 0 and 1, showing the distribution characteristics of high in spring and summer while low in autumn and winter. By 2019, the concentration of AOD in spring, summer and autumn showed a significant decrease, and was the most significant in summer. AOD also showed a high spatial autocorrelation. (3) There was a significantly positive correlation between AOD and PM2.5 concentration. From the perspective of seasonal changes, the correlation showed the characteristics of autumn>summer>winter>spring. And the annual average AOD and PM2.5 concentration showed a moderately positive correlation.Therefore, a quantitative study of the similarity and correlation between AOD and PM2.5 concentration in spatiotemporal changes can prove the influence of aerosols on air pollution, and provide scientific ideas and basis for future urban air quality management. 参考文献 相似文献 引证文献

Nanomaterials pollutant's emission influencing outdoor recreation in China: Analytical strategies proceeding to sustainable environment

The global demand for bioenergy and nanomaterial utilization has significantly contributed to their source depletion. The impact of outdoor pollutant emissions on residents' health, behavior, physical activity, and sleeping behavior is much less explored. Producing biofuels from organic waste has the potential to unite budget-friendliness and long-term sustainability. Primary biofuels are produced specifically to mitigate environmental problems, and secondary biofuels are produced specifically to mitigate other environmental problems. The high level of pollutants ina certain area can severely restrict human activities and ultimately influence their whole life. The study aims to empirically evaluate the influence of nanomaterials pollutants emissions influencing outdoor recreation in China because its economy is based on fast-paced industrialization and urbanization. Various datasets were collected, including domestic and international tourists from the annual statistics for 2011–2020 from the National Bureau of Statistics of China. Ten years of annual METAR data of visibility (VR), temperature (T), relative humidity (Demirhan), and wind speed (WS) from 30 metrological stations at international airports. Annual average AOD (Aerosol's Optical Depth), O3 (Ozone), CO (Carbon Monoxide), SO4 (Sulphate), and PM2.5 (Particulate Matter) satellite imageries from 2011 to 2020 were obtained from NASA's official portal. The overall picture of satellite observations of pollutants over China describes that the highest level of AOD was observed in regions with greater population concentration than in other areas. We computed a statistical summary, correlation matrix, and Autoregressive Distributed Lag (ARDL) approach. Certain analyses were performed, like Unrestricted Error Correction Models (UECM) and Restricted Error Correction Model (RECM)), bound tests for cointegration, and multiplier estimations for short-term and long-term impacts. UECM and RECM models produced R2 > 0.90 with good F statistics and a p-value of <0.05. A bounds F-test for no cointegration on the ARDL model was performed, and the results show that the p-value = 1e-06 and F = 8.516 with alternative hypothesis = Possible cointegration. Bounds t-test for no cointegration was also performed on UECM model and the results show that t = −2.9066, Lower-bound I(0) = −3.43, Upper-bound I(1) = −5.37, p-value = 0.6138 and alternative hypothesis = Possible cointegration. The study's findings may help Chinese policymakers and stakeholders design effective information strategies to combat air pollution. Effective measures can help alleviate this devastating air quality factor, thus benefiting the tourism industry and enhancing the local inhabitants' welfare.

Long-term Variation of Absorption and Total Aerosol Optical Properties over Typical Provinces of China from Satellite Observations

Increase of atmospheric aerosols has a profound impact on the Earth’s climate. It’s also one of the crucial factors that cuasesd more fequent air pollution events in China. Monthly average Aerosol Optical Depth (AOD) from MODIS and UltraViolet Absorbing aerosol Index (UVAI) from OMI during 2011 to 2019 are used to analyse the trend of absorption and total aerosol optical properties over three typical provinces of China, namely Shandong, Gansu and Guangdong provinces. The results show the average annual AOD of the three provinces are all decreasing while UVAI rises during this period. In addition, the monthly variation of AOD and UVAI are also obviously different over these provinces. In particular, the peak value of AOD appeared in July and the trough appeared in December over Shandong Province. And the peak appeared in April over Gansu Province, but AOD decrease slower then over Shandong Province. And there were two peaks in April and August over Guangdong Province. For UVAI, the peaks over Shandong and Gansu provinces both occur in January, while that over Guangdong Province appears in March. Above mentioned differences in the long-term trend and monthly variation of AOD and UVAI might be closely related to the meteorological conditions and aerosol emission of these three provinces.

Spatiotemporal Distribution of Aerosol Optical Depth Based on Landsat Data in the Hinterland of the Guanzhong Basin and Its Relationship with Urbanization

Aerosol optical depth (AOD) is one of the most fundamental optical properties of aerosols that characterizes the attenuation of light by aerosols and is an indicator of regional air pollution. Based on the blue band surface reflectance database from the MOD09A1 products for the period 2000-2019 and the ASTER spectral database, AOD was estimated from Landsat TM/OLI data using the deep blue algorithm (DB). Multi-year average/annual average and seasonal AOD values for the period 2000-2019 were then calculated to analyze the spatial characteristics and temporal variations of AOD using the empirical orthogonal function method (EOF). Furthermore, the impacts of urbanization on the spatio-temporal distribution of AOD were analyzed. The obtained results are summarized as follows:① The multi-year average AOD spatial distribution in the hinterland of the Guanzhong Basin was significantly affected by topography and human activities, with higher AOD values and variationsin areas of low altitude and high-intensity human activities compared to the surrounding mountains. Thus, changes in AOD in the study area are mainly affected by anthropogenic factors. AOD also showed significant seasonal variations, whereby spring (0.34) > summer (0.33) > autumn (0.23) > winter (0.12), and the largest regional differences occurred in summer; ② The annual average AOD (from 2000-2019) showed the trend of "increase-decrease-increase", and reached a maximum in 2005, with the high AOD area gradually moving to the south. The distribution of AOD values in spring and summer was relatively discrete, while it is in a low-value agglomeration state in winter; ③ Three main AOD spatial distribution modes were identified based on the EOF, which had cumulative contribution rate of 83.0%. The spatial distribution trend of AOD showed regional consistency, with feature vectors consistent with the altitude, thus reflecting the difference of AOD at different altitudes. Taking the Qinling Mountains as the dividing line, the AOD presented the "north-south" pattern, AOD showed a "north-south" pattern, reflecting the uniqueness of the regional development in the Guanzhong Basin compared to the southern Qinling Mountains. The "southeast-northwest" distribution pattern indicated that the AOD presented a reverse change trend between urban and non-urban; and ④ The results of correlation analysis between the AOD and urbanization revealed a positive correlation with permanent population density (R2=0.707, P<0.05), impervious surface density (R2=0.377, P<0.05), and industrial POI density (R2=0.727, P<0.5). These results are significant for improving the monitoring of air quality in the Guanzhong Basin and for the construction of an urban ecological environment.

MAIAC AOD and PM2.5 Mass Concentrations Characteristics and Correlation Analysis in Beijing-Tianjin-Hebei and Surrounding Areas

Based on the MAIAC AOD and PM2.5 mass concentration data for the Beijing-Tianjin-Hebei region and surrounding areas from 2014 to 2018, the temporal and spatial differences in Aerosol Optical Depth (AOD) and PM2.5 mass concentrations were explored and their correlation was analyzed by linear regression. The results show that the daily average concentration of PM2.5 exceeds the standard for 33% and 57% of measurements based on the daily average standard values of the World Health Organization IT.1 and IT.2, respectively, indicating serious pollution levels. The annual average concentrations of PM2.5 and Terra and Aqua MAIAC AOD all show downward trends. The PM2.5 concentrations are high in winter and spring and low in summer and autumn; Terra and Aqua AOD values are high in spring and summer and low in autumn and winter. The seasonal and annual average concentrations of PM2.5 and AOD all show the regional pattern of "low in the north and high in the south". High-value areas are mainly located in southern Hebei, southwestern Shanxi, western Shandong, and northern Henan, while low-value areas are mainly located in northwestern Shanxi, northern Hebei, and eastern Shandong. The annual average concentration of PM2.5 is between 27 and 99μg·m-3, and the annual average AOD is between 0.20 and 0.69. The correlation between Aqua AOD and PM2.5 concentration is strong whereas and the correlations between Terra AOD, Aqua AOD, and PM2.5vary significantly in different seasons; overall, correlations are strongest in spring and winter and weakest in summer and autumn. After vertical-humidity correction, the correlation between satellite AOD and PM2.5 data is significantly improved.

Long-term variations in solar radiation, diffuse radiation, and diffuse radiation fraction caused by aerosols in China during 1961-2016.

The effects of atmospheric aerosols on the terrestrial climate system are more regional than those of greenhouse gases, which are more global. Thus, it is necessary to examine the typical regional effects of how aerosols affect solar radiation in order to develop a more comprehensive understanding. In this study, we used global AErosol RObotic NETwork (AERONET) data and robust radiation observational evidence to investigate the impact of aerosols on total radiation, diffuse radiation, and the diffuse radiation fraction in China from 1961 to 2016. Our results showed that there were different temporal changes in the aerosol optical depth (AOD), total solar radiation, diffuse radiation and diffuse radiation fraction over the past 56 years. Specifically, the 550 nm AOD from 2005 to 2016 decreased significantly, with annual average AOD of 0.51. Meanwhile, the average total solar radiation reduced by 2.48%, while there was a slight increase in average diffuse radiation at a rate of 3.10 MJ·m-2·yr-1. Moreover, the spatial heterogeneities of AOD, total radiation, diffuse radiation, and the diffuse radiation fraction in China were significant. Aerosol particle emissions in the developed eastern and southern regions of China were more severe than those in the western regions, resulting in higher total radiation and diffuse radiation in the western plateau than in the eastern plain. In addition, aerosols were found to have negative effects on total radiation and sunshine hours, and positive effects on diffuse radiation and diffuse radiation fraction. Further, the diffuse radiation fraction was negatively correlated with sunshine hours. However, there was a positive correlation between AOD and sunshine hours. These results could be used to assess the impacts of climate change on terrestrial ecosystem productivity and carbon budgets.

The contribution of aerosols chemical components to aerosol optical depth: The method and the case in Dunhuang

Based on the aerosol chemical components and aerosol optical depth (AOD) observation in Dunhuang, China, the Non-Negative Least Squares method has been innovatively applied to calculate the monthly averaged water-soluble aerosol density and obtain corresponding aerosol particles, and to further calculate AOD by upgrading the relevant parameters in Optical Properties of Aerosols and Clouds (OPAC). The obtained water-soluble aerosol density ranges from 1.87 to 2.12 g/cm3. The density of water-soluble aerosols is higher in winter half-year which are mainly affected by the local dust particles and polluted aerosols caused by domestic heating. The upgraded OPAC precisely simulated seasonal AOD, except in DJF(December–January-February) which has more mineral and soot (EC, Elemental Carbon). Dividing single water-soluble aerosol into the sulfate portion and other water-soluble portions can improve the accuracy of particle number of aerosols in OPAC. The AOD results in upgraded OPAC are between 0.26 and 0.44 at 500 nm. The annual average absolute error is 0.109, which is higher in DJF and MAM (March–April-May) when more dust events occur. The annual-average multi-band AOD results show good range (0.18–0.40) and consistency (y = 0.43× + 0.17) as well. Sulfate, nitrate and soot(EC) which belonging to anthropogenic aerosols accounted for more than 60% of the contribution on AOD, and showed a clear bimodal structure with the peak at March and November. The contribution on AOD of sulfate and nitrate in March exceeded the value in November by 5%, but no significant difference in EC and mineral. The upgraded OPAC results did not show significant deviations from the observed AOD in MAM, JJA (June–July-August) and SON (September–October-November), or even in the annual results. Natural source aerosol has a certain seasonal periodicity and is difficult to control. Therefore, controlling the emissions of sulfate, nitrate and soot (EC) belonging to anthropogenic aerosols can effectively reduce AOD and improve the visibility in Dunhuang.

Aerosol characteristics at the three poles of the Earth as characterized by Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations

Abstract. To better understand the aerosol properties over the Arctic, Antarctic and Tibetan Plateau (TP), the aerosol optical properties were investigated using 13 years of CALIPSO (Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations) L3 data, and the back trajectories for air masses were also simulated using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The results show that the aerosol optical depth (AOD) has obvious spatial- and seasonal-variation characteristics, and the aerosol loading over Eurasia, Ross Sea and South Asia is relatively large. The annual-average AODs over the Arctic, Antarctic and TP are 0.046, 0.024 and 0.098, respectively. Seasonally, the AOD values are larger from late autumn to early spring in the Arctic, in winter and spring in the Antarctic, and in spring and summer over the TP. There are no significant temporal trends of AOD anomalies in the three study regions. Clean marine and dust-related aerosols are the dominant types over ocean and land, respectively, in both the Arctic and Antarctic, while dust-related aerosol types have greater occurrence frequency (OF) over the TP. The OF of dust-related and elevated smoke is large for a broad range of heights, indicating that they are likely transported aerosols, while other types of aerosols mainly occurred at heights below 2 km in the Antarctic and Arctic. The maximum OF of dust-related aerosols mainly occurs at 6 km altitude over the TP. The analysis of back trajectories of the air masses shows large differences among different regions and seasons. The Arctic region is more vulnerable to mid-latitude pollutants than the Antarctic region, especially in winter and spring, while the air masses in the TP are mainly from the Iranian Plateau, Tarim Basin and South Asia.

The influence of aerosols on the NO2 photolysis rate in a suburban site in North China

The photolysis of NO2 is an important driving force of tropospheric ozone. The intensity of this photolysis reaction affects atmospheric oxidation and photochemical pollution process. Photolysis rate of nitrogen dioxide (JNO2) is affected by aerosols, temperature, solar zenith angle (SZA), clouds, and so on. Among them, aerosol is an important influencing factor because of its complicated and irregular change; aerosol quantitative effect on JNO2 is constructive for the coordinated control of O3 and particulate matter. In order to quantitatively assess the impact of aerosols on JNO2 in the long-term, the reconstructed JNO2 data in a suburban site in North China from 2005 to 2019 are used. We found that JNO2 and aerosol optical depth (AOD) presented logarithmic relations under different solar zenith angle (SZA) levels, the aerosol attenuation effect on JNO2 decreased as AOD increased. Two main influencing factors of JNO2, SZA, and AOD, were fitted into a quadratic polynomial to quantify the AOD effect on JNO2. The results showed that the average annual AOD effect on JNO2 in Xianghe from 2005 to 2019 was −28.6% compared to an aerosol free atmosphere; the seasonal mean AOD effect in spring, summer, autumn, and winter was −27.1% and −35.1%, −25.5% and −26.3%, respectively. During the study period, JNO2 increased with an average of 5 × 10−5 s−1 per year, while the annual average aerosol optical depth (AOD) was 0.80 ± 0.10, showing an overall downward trend. Annual mean AOD attenuation effect on JNO2 decreased over time; the decreases were larger in spring and summer, and smaller in autumn and winter.

Aerosol optical properties and its type classification based on multiyear joint observation campaign in north China plain megalopolis

Since haze and other air pollution are frequently seen in the North China Plain (NCP), detail information on aerosol optical and radiative properties and its type classification is demanded for the study of regional environmental pollution. Here, a multiyear ground-based synchronous sun photometer observation at seven sites on North China Plain megalopolis from 2013 to 2018 was conducted. First, the annual and seasonal variation of these characteristics as well as the intercomparsion were analyzed. Then the potential relationships between these properties with meteorological factors and the aerosol type classification were discussed. The results show: Particle volume exhibited a decreasing trend from the urban downtown to suburban and the rural region. The annual average aerosol optical depth at 440 nm (AOD440) varied from ∼0.43 to 0.86 over the NCP. Annual average single-scattering albedo at 440 nm (SSA440) varied from ∼0.89 to 0.93, indicating a moderate to slight absorption capacity. Average absorption aerosol optical depth at 440 nm (AAOD440) varied from ∼0.07 to 0.10. The absorption Ångström exponent (AAE) (∼0.89–1.40) indicated the multi-types of absorptive matters originated form nature and anthropogenic emission. The discussion of aerosol composition showed a smaller particle size of aerosol from biomass burning and/or fossil foil consumption with enhanced aerosol scattering and enlarged light extinction. Aerosol classification indicated a large percentage of mixed absorbing aerosol (∼20%–49%), which showed increasing trend between relative humidity (RH) with aerosol scattering and dust was an important environmental pollutant compared to southern China.

Spatial and Temporal Characteristics of AOD and Angström Exponent in the Yangtze River Delta Based on MODIS_C061

Considering the Yangtze River Delta as the research region, the applicability of the Terra-MODIS C061 deep blue algorithm (DB) AOD products was evaluated using Aerosol Robotic Network (AERONET) ground-based observations. The results demonstrated that the correlation between Terra-MODIS C061 deep blue algorithm (DB) aerosol optical depth (AOD) and AERONET AOD was high (0.95). Characteristics of spatial distribution and temporal variation of AOD and Angström exponent (AE) from 2000 to 2018 in the study area were analyzed using MOD04_L2 products from 2000 to 2018. The results showed that the AOD in the Yangtze River Delta was distributed as "eastern and northern plains high and southern and western mountains low". The AE showed a "northern low and south high" pattern. In terms of temporal distribution, from 2003 to 2007, the annual average AOD increased significantly, with a growth rate of 23%. After 2011, the AOD showed a downward trend. From 2001 to 2003, the annual average of AE rapidly increased, while after 2012, the AE decreased gradually. The AOD showed obvious seasonal changes in the Yangtze River Delta region, with high values in summer and low values in winter. The highest AOD was observed in June (0.84) in all monthly averages, while the lowest was observed in August (0.40). The seasonal average AE was high in autumn and low in spring. The highest AE of 1.47 was observed in September in all monthly averages, and the lowest of 1.08 was observed in March. Aerosol types in the Yangtze River Delta region were investigated according to the relationship between AOD and AE. The results suggested that the urban industrial aerosol was the main aerosol type in the region, followed by mixed type and clean continental aerosols.

Exploring the spatial-temporal characteristics of the aerosol optical depth (AOD) in Central Asia based on the moderate resolution imaging spectroradiometer (MODIS).

Central Asia has become a key node of the belt and road corridor. It is located in arid and semi-arid climate regions, and it is a region where the contribution of global aerosols of sand and dust is continuous. However, few studies have been conducted on the Central Asian aerosol optical depth. Therefore, this paper relied on the belt and road sustainable development dataset to analyze the spatial-temporal variations in the AOD in Central Asia and provide spatial-temporal characteristics of the AOD for environmental services. We analyzed the spatial and temporal variation in the aerosol optical depth (AOD) in Central Asia by using MODIS/AQUA C6 MYD08_M3 images from 2008 to 2017. The results showed that (1) the annual average AOD in Central Asia in the past decade varied from 0.183 to 0.232, which indicated a slow decline starting in 2014. The percentage of average annual decline was approximately 0.18%, and the regular distinct revealed the distribution characteristics of AOD. In different years, the Central Asian region exhibited the similar monthly change characteristics: from July to December, the AOD decreased, and from December to February, it increased. In different seasons, the Central Asian region exhibited the different seasonal change characteristics: the AOD value was higher in the spring and summer. The mean values in the spring, summer, autumn, and winter were 0.273, 0.240, 0.155, and 0.183, respectively, and the standard deviations were 0.036, 0.038, 0.025, and 0.048, respectively. (3) Based on spatial distribution characteristics, the Tarim Basin, Aral Sea region, and Ebinur Lake area were high value areas, and Kazakhstan was a low value area. The AOD of the surrounding area of the Aral Sea had increased in the last 5years, while that of Kazakhstan, Uzbekistan, and Turkmenistan had decreased. The AOD of the Taklamakan area exhibited an inter-annual change. Sand dust aerosols were the largest contributors to the AOD in the Taklamakan area. The rising trend of the AOD in the Aral Sea area was clear, with an average annual increase of 0.234%, and the contribution of salt dust aerosols to the AOD increased. The average annual AOD in the Ebinur Lake area remained stable.

Long-term (2008–2018) aerosol properties and radiative effect at high-altitude sites over western trans-Himalayas

Analysis of the climatology of aerosol properties is performed over Hanle (4500 m) and Merak (4310 m), two remote-background sites in the western trans-Himalayas, based on eleven years (2008–2018) of sun/sky radiometer (POM-01, Prede) measurements. The two sites present very similar atmospheric conditions and aerosol properties allowing us to examine them as continuous single-data series. The annual average aerosol optical depth at 500 nm (AOD500) is 0.04 ± 0.03, associated with an Ångström exponent (AE440–870) of 0.58 ± 0.35 and a single scattering albedo (SSA500) of 0.95 ± 0.05. AOD500 exhibits higher values in May (~0.07) and lower in winter (~0.03), while AE400–870 minimizes in spring, indicating influence by coarse-mode dust aerosols, either emitted regionally or long-range transported. The de-convolution of AOD500 into fine and coarse modes justifies the aerosol seasonality and sources, while the marginal diurnal variation in all aerosol properties reveals a weak influence from local sources, except for some few aerosol episodes. The aerosol-volume size distribution presents a mode value at ~10 μm with secondary peaks at accumulation (~ 2 μm) and fine modes (~0.03 μm) and low variability between the seasons. A classification of the aerosol types based on the fine-mode fraction (FMF) vs. SSA500 relationship reveals the dominance of aerosols in the FMF range of 0.4–0.6, characterized as mixed (39%), followed by fine aerosols with high scattering efficiency (26%), while particles related to dust contribute ~21%, with low fractions of fine-absorbing aerosols (~13%). The aerosol radiative forcing (ARF) estimates reveal a small cooling effect at the top of the atmosphere (−1.3 Wm−2), while at the surface, the ARF ranges from −2 Wm−2 to −6 Wm−2 on monthly basis. The monthly-mean atmospheric radiative forcing (~1 to 4 Wm−2) leads to heating rates of 0.04 to 0.13 K day−1. These ARF values are higher than the global averages and may cause climate implications over the trans-Himalayan region.

Characteristics of aerosol optical depth over land types in central Asia

Aerosols are an important contributor to global atmospheric changes and have critical effects on the climate system. Regionally, aerosols in central Asia comprise a significant portion of global aerosols. Based on aerosol optical depth (AOD)Level 2 daily product data and land cover type product data, the long-term AOD characteristics of six major land use/cover types and their relationships with landscape metrics are discussed. Contribution analysis is applied to quantitatively estimate the effects of land use/cover on regional AOD over central Asia. The results show that series of daily AODs over six land uses/covers display remarkable annual cyclic variations and obvious seasonal changes. The annual average AODs for barren land and cropland are highest, followed by regional AODs. There are different frequencies and times of occurrence for high AOD values of various land types. Urban areas are one of the major contributors to the regional atmosphere in winter; grasslands have a great influence on regional AOD decreases. Barren land always has a high contribution to the regional AOD. The land use types affected by anthropogenic activities were smaller contributors to regional aerosols than barren lands affected by climate factors. This paper advances the understanding of relationship between aerosols and land use/cover and facilitates land use decision making.

LONG TEMPORAL ANALYSIS OF THE MODIS AEROSOL PRODUCT OVER HUAIHAI ECONOMIC REGION IN CHINA

Abstract. The Huaihai Economic Region (HER, 32.5–36.5°N, 114–121°E) with a land area of 178,000 km2, which contains 20 cities, is one of the earliest regional economic cooperative organizations in China. The huge population (100 million, about 7% of the China’s population), local heavy industries, chemical enterprises and vehicle emissions have resulted in serious air pollution. In this paper, a long-term aerosol optical depth (AOD) data set from 2000 to 2018 over HER with 10 km spatial resolution has been produced and analyzed from the latest version of MODIS (MODerate resolution Imaging Spectroradiometer) aerosol products. Validation results show that MODIS AOD has a strong correlation relationship (r = 0.94, slope = 0.92) with Aeronet Robotic Network (AERONET) over HER. The seasonal average AOD maps indicate that the high AOD values mainly occurred with a banding distribution from southeastern to northwestern HER, with AODs larger in summer and spring than in fall and winter. Temporally, the monthly average AOD has increased since 2000 and reached the highest level in 2011 (+0.02/year); then it has obviously declined from 2012 to 2018 (−0.05/year), owing to strict air pollution control implemented since 2012. In general, the annual average AOD over HER is 0.71 for the past nearly 20 years, and in 2018, the annual average AOD firstly lower than that in 2000. The study suggests that there has been a slightly improvement in air quality over HER and long-term and sustainable efforts should be made.

The aerosol optical properties and PM2.5 components over the world's largest industrial zone in Tangshan, North China

To achieve an in-depth understanding of the aerosol optical properties in the highly-industrial region of Tangshan, we provided systematic aerosol optical properties analysis in this largest industrial zone for the first time. The aerosol optical datasets (2013.05–2015.04) and chemical component data of PM2.5 (2014–2015) obtained from the Tangshan site of the campaign on atmospheric aerosol research (CARE-China) network were analyzed. The results showed that the Tangshan region was seriously affected by fine-mode industrial aerosols all year, which would promote the accumulation of pollutants and influence the atmospheric circulation through changing the vertical temperature gradient. The annual average aerosol optical depth (AOD) and Ångstrӧm exponent (α) were 0.80±0.26 and 1.05±0.10, respectively. The aerosol optical properties revealed significant seasonal characteristics. The maximum seasonal average AOD (1.03±0.62) and α (1.12±0.19) accompanied the highest seasonal secondary inorganic aerosol concentrations (SIA: SO42−,NO3−,NH4+), 53.33μg/m3, occurred in summer, and this phenomenon was attributed to the photochemical reactions favored by the high temperature and humidity. During the spring, frequent dust events led to the maximum Ca2+ concentration of 6.57μg/m3 and the lowest seasonal α of 0.98±0.31. Coal was used for generating heat in winter, resulting in the highest levels of pollutant emissions (Cl−, Elemental carbon (EC) and organic carbon (OC)). The aerosol type classifications showed that the industrial aerosols were the main controls in the summer and fall, representing 56%–58% of the total aerosols. While for spring and winter, mixed aerosols represented 53%–54% of the total aerosols. Hygroscopic growth effect of aerosols existed all year, which could enhance the negative radiative forcing and eventually cool the earth-atmosphere system. The classification Wing for Tangshan data showed high AOD values (>0.70) were mainly clustered in the fine-mode growth wing and coarse-mode. Of these values, summer showed a dense AOD distribution and the highest magnitude of fine-mode AODs, with a corresponding fine particle fraction of η~90% and an Rf ~0.20μm. In addition, spring showed the most coarse-mode aerosols.