High Aerosol Optical Depth Values Research Articles

Validation of OMI erythemal doses with multi-sensor ground-based measurements in Thessaloniki, Greece

The aim of this study is to validate the Ozone Monitoring Instrument (OMI) erythemal dose rates using ground-based measurements in Thessaloniki, Greece. In the Laboratory of Atmospheric Physics of the Aristotle University of Thessaloniki, a Yankee Environmental System UVB-1 radiometer measures the erythemal dose rates every minute, and a Norsk Institutt for Luftforskning (NILU) multi-filter radiometer provides multi-filter based irradiances that were used to derive erythemal dose rates for the period 2005–2014. Both these datasets were independently validated against collocated UV irradiance spectra from a Brewer MkIII spectrophotometer. Cloud detection was performed based on measurements of the global horizontal radiation from a Kipp & Zonen pyranometer and from NILU measurements in the visible range. The satellite versus ground observation validation was performed taking into account the effect of temporal averaging, limitations related to OMI quality control criteria, cloud conditions, the solar zenith angle and atmospheric aerosol loading. Aerosol optical depth was also retrieved using a collocated CIMEL sunphotometer in order to assess its impact on the comparisons. The effect of total ozone columns satellite versus ground-based differences on the erythemal dose comparisons was also investigated. Since most of the public awareness alerts are based on UV Index (UVI) classifications, an analysis and assessment of OMI capability for retrieving UVIs was also performed.An overestimation of the OMI erythemal product by 3–6% and 4–8% with respect to ground measurements is observed when examining overpass and noontime estimates respectively. The comparisons revealed a relatively small solar zenith angle dependence, with the OMI data showing a slight dependence on aerosol load, especially at high aerosol optical depth values. A mean underestimation of 2% in OMI total ozone columns under cloud-free conditions was found to lead to an overestimation in OMI erythemal doses of 1–5%.While OMI overestimated the erythemal dose rates over the range of cloudiness conditions examined, its UVIs were found to be reliable for the purpose of characterizing the ambient UV radiation impact.

Long-Term Analysis of Aerosol Optical Depth over the Huaihai Economic Region (HER): Possible Causes and Implications

The quality of air is increasingly affecting regional climate and human activity. Collection 6 aerosol products retrieved from the Moderate-Resolution Imaging Spectroradiometer (MODIS) onboard the Terra satellite were validated based on CE-318 sun photometric data to analyze their applicability in the Huaihai economic region (HER) at the Xuzhou and Shouxian sites. The spatio-temporal variations of aerosol optical depth (AOD) were also analyzed over HER from 2000 to 2016, with analyses of the correlation with potential driving factors, including meteorology, vegetation and human factors. HER is an economic cooperation organization with multiple industrial structures, containing coal resource-based cities, a national transportation hub and agricultural and high-altitude areas, which shows regional differences in AOD. The results suggest that MODIS Terra AOD products show good agreement with ground observations, with correlation coefficients of above 0.84 in HER, and the main pollutants for high AOD values are fine particles (the mean Ångström exponent was 1.16). The average annual change in AOD varied with a weak growth trend over the past 17 years, while a transition in 2012 made the tendency change from upward to downward due to the extensive cooperation of cities in the joint prevention and control of the deterioration of the ecological environment. The largest monthly mean AOD value appeared in June, which resulted from significant agricultural residue burning. The spatial distribution of multi-year average AOD occurred with a banded high-value center, extending from the north-west to the south-east. The high aerosol loadings were located in resource-based cities, and industrially developed and south-eastern coastal areas, whereas the regions with relatively low AOD in HER were distributed in the southern agricultural and northern high-altitude areas. The AOD value in the western, northern, and eastern coastal areas of HER showed a significant increasing trend, while no area exhibited a decreasing trend. The average wind speed has the largest negative correlation with the AOD value in terms of the natural driving factors, and GDP (gross domestic product) was more positively correlated with AOD with respect to the human factors, in comparison with population density.

Moderate Imaging Resolution Spectroradiometer (MODIS) Aerosol Optical Depth Retrieval for Aerosol Radiative Forcing

The present study uses the Aerosol Optical Depth (AOD) retrieved from Moderate Imaging Resolution Spectroradiometer (MODIS) data for the period from January 2011 until December 2015 over an urban area in Kuching, Sarawak. The results show the minimum AOD value retrieved from MODIS is -0.06 and the maximum value is 6.0. High aerosol loading with high AOD value observed during dry seasons and low AOD monitored during wet seasons. Multi plane regression technique used to retrieve AOD from MODIS (AODMODIS) and different statistics parameter is proposed by using relative absolute error for accuracy assessment in spatial and temporal averaging approach. The AODMODIS then compared with AOD derived from Aerosol Robotic Network (AERONET) Sunphotometer (AODAERONET) and the results shows high correlation coefficient (R2) for AODMODIS and AODAERONET with 0.93. AODMODIS used as an input parameters into Santa Barbara Discrete Ordinate Radiative Transfer (SBDART) model to estimate urban radiative forcing at Kuching. The observed hourly averaged for urban radiative forcing is -0.12 Wm−2 for top of atmosphere (TOA), -2.13 Wm−2 at the surface and 2.00 Wm−2 in the atmosphere. There is a moderate relationship observed between urban radiative forcing calculated using SBDART and AERONET which are 0.75 at the surface, 0.65 at TOA and 0.56 in atmosphere. Overall, variation in AOD tends to cause large bias in the estimated urban radiative forcing.

Long-term variations of aerosol optical depth and aerosol radiative forcing over Iran based on satellite and AERONET data.

In this study, three different sensors of satellites including the Moderate Resolution Imaging Spectroradiometer (MODIS), Multi-angle Imaging SpectroRadiometer (MISR), and Total Ozone Mapping Spectrometer (TOMS) were used to study spatial and temporal variations of aerosols over ten populated cities in Iran. Also, the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model was used for analyzing the origins of air masses and their trajectory in the area. An increasing trend in aerosol concentration was observed in the most studied cities in Iran during 1979-2016. The cities in the western part of Iran had the highest annual mean of aerosol concentration. The highest aerosol optical depth (AOD) value (0.76±0.51) was recorded in May 2012 over Ahvaz, and the lowest value (0.035±0.27) was recorded in December 2013 over Tabriz. After Ahvaz, the highest AOD value was found over Tehran (annual mean 0.11±0.20). The results show that AOD increases with increasing industrial activities, but the increased frequency of aerosols due to land degradation and desertification is more powerful in Iran. The trajectory analysis by the HYSPLIT model showed that the air masses come from Egypt, Syria, and Lebanon and passed over the Iraq and then reached to Iran during summer. Aerosol radiative forcing (ARF) has been analyzed for Zanjan (Aerosol Robotic Network site) during 2010-2013. The ARF at surface and top of the atmosphere was found to be ranging from - 79 to - 10Wm-2 (average - 33.45Wm-2) and from - 25 to 6Wm-2 (average - 12.80Wm-2), respectively.

Long-term variations of AOD from an AERONET station in the central Arabian Peninsula

In this study, we analyze the variation of the aerosol optical depth (AOD) at 500 nm using measurements from January 1999 to August 2015 in the central Arabian Peninsula. The magnitudes of the annual, monthly, seasonal, and hourly trends of the AOD are studied and statistically tested using the least-squares method and supported by Mann-Kendall rank statistics at different significance levels. A significant increase of about 0.119 in the annual mean AOD is found for the entire period. AOD increased in all the seasons, in which the spring trend is the highest (0.289/17 years) and significant. The high AOD value found in spring may be attributed to the effect of dust events transported by northeasterly winds from the arid and semi-arid regions around the Arabian Gulf. In its monthly basis, AOD values in January, July, August, and September show no significant trends. On the contrary, March, April, June, and December show a clear increasing trend with different significance levels. April shows the highest increases in AOD (0.021/year), about 81.58% higher than the mean April value. Variations of the AOD on the hourly scale are investigated. Increasing trends with different significance levels are found and established. We found that the early mornings and very late afternoons presented the highest increasing trend. For the rest of the day, the AOD varies slightly due to the meteorological processes.

Contrasting aerosol optical and radiative properties between dust and urban haze episodes in megacities of Pakistan

Satellite and ground based remote sensors provide vital information about aerosol optical and radiative properties. Analysis of aerosol optical and radiative properties during heavy aerosol loading events in Pakistan are limited and, therefore, require in-depth examination. This work examines aerosol properties and radiative forcing during Dust Episodes (DE) and Haze Episodes (HE) between 2010 and 2014 over mega cities of Pakistan (Karachi and Lahore). Episodes having the daily averaged values of Aerosol Optical Depth (AOD) exceeding 1 were selected. DE were associated with high AOD and low Ångström Exponent (AE) over Karachi and Lahore while high AOD and high AE values were associated with HE over Lahore. Aerosol volume size distributions (AVSD) exhibited a bimodal lognormal distribution with a noticeable coarse mode peak at a radius of 2.24 μm during DE, whereas a fine mode peak was prominent at a radius 0.25 μm during HE. The results reveal distinct differences between HE and DE for spectral profiles of several parameters including Single Scattering Albedo (SSA), ASYmmetry parameter (ASY), and the real and imaginary components of refractive index (RRI and IRI). The AOD-AE correlation revealed that dust was the dominant aerosol type during DE and that biomass burning and urban/industrial aerosol types were pronounced during HE. Aerosol radiative forcing (ARF) was estimated using the Santa Barbra DISORT Atmospheric Radiative Transfer (SBDART) model. Calculations revealed a negative ARF at the Top Of the Atmosphere (ARFTOA) and at the Bottom Of the Atmosphere (ARFBOA), with positive ARF within the Atmosphere (ARFATM) during both DE and HE over Karachi and Lahore. Furthermore, estimations of ARFATM by SBDART were shown to be in good agreement with values derived from AERONET data for DE and HE over Karachi and Lahore.

Temporal variability in aerosol characteristics and its radiative properties over Patiala, northwestern part of India: Impact of agricultural biomass burning emissions

A comprehensive measurements of aerosol optical depth (AOD), particulate matter (PM) and black carbon (BC) mass concentrations have been carried out over Patiala, a semi-urban site in northwest India during October 2008 to September 2010. The measured aerosol data was incorporated in an aerosol optical model to estimate various aerosol optical parameters, which were subsequently used for radiative forcing estimation. The measured AOD at 500 nm (AOD500) shows a significant seasonal variability, with maximum value of 0.81 during post-monsoon (PoM) and minimum of 0.56 during winter season. The Ångström exponent (α) has higher values (i.e. more fine-mode fraction) during the PoM/winter periods, and lower (i.e. more coarse-mode fraction) during pre-monsoon (PrM). In contrast, turbidity coefficient (β) exhibits an opposite trend to α during the study period. BC mass concentration varies from 2.8 to 13.9 μg m−3 (mean: 6.5 ± 3.2 μg m−3) during the entire study period, with higher concentrations during PoM/winter and lower during PrM/monsoon seasons. The average single scattering albedo (SSA at 500 nm) values are 0.70, 0.72, 0.82 and 0.75 during PoM, winter, PrM and monsoon seasons, respectively. However, inter-seasonal and inter-annual variability in measured aerosol parameters are statistically insignificant at Patiala. These results suggest strong changes in emission sources, aerosol composition, meteorological parameters as well as transport of aerosols over the station. Higher values of AOD, α and BC, along with lower SSA during PoM season are attributed to agriculture biomass burning emissions over and around the station. The estimated aerosol radiative forcing within the atmosphere is positive (i.e. warming) during all the seasons with higher values (∼60 Wm−2) during PoM–08/PoM–09 and lower (∼40 Wm−2) during winter–09/PrM–10. The present study highlights the role of BC aerosols from agricultural biomass burning emissions during post-monsoon season for atmospheric warming at Patiala.

The Effects of Aerosol on the Retrieval Accuracy of NO2 Slant Column Density

We investigate the effects of aerosol optical depth (AOD), single scattering albedo (SSA), aerosol peak height (APH), measurement geometry (solar zenith angle (SZA) and viewing zenith angle (VZA)), relative azimuth angle, and surface reflectance on the accuracy of NO2 slant column density using synthetic radiance. High AOD and APH are found to decrease NO2 SCD retrieval accuracy. In moderately polluted (5 × 1015 molecules cm−2 < NO2 vertical column density (VCD) < 2 × 1016 molecules cm−2) and clean regions (NO2 VCD < 5 × 1015 molecules cm−2), the correlation coefficient (R) between true NO2 SCDs and those retrieved is 0.88 and 0.79, respectively, and AOD and APH are about 0.1 and is 0 km, respectively. However, when AOD and APH are about 1.0 and 4 km, respectively, the R decreases to 0.84 and 0.53 in moderately polluted and clean regions, respectively. On the other hand, in heavily polluted regions (NO2 VCD > 2 × 1016 molecules cm−2), even high AOD and APH values are found to have a negligible effect on NO2 SCD precision. In high AOD and APH conditions in clean NO2 regions, the R between true NO2 SCDs and those retrieved increases from 0.53 to 0.58 via co-adding four pixels spatially, showing the improvement in accuracy of NO2 SCD retrieval. In addition, the high SZA and VZA are also found to decrease the accuracy of the NO2 SCD retrieval.

AOD distributions and trends of major aerosol species over a selection of the world's most populated cities based on the 1st version of NASA's MERRA Aerosol Reanalysis

NASA recently extended the Modern-Era Retrospective Analysis for Research and Application (MERRA) with an atmospheric aerosol reanalysis which includes five particulate species: sulfate, organic matter, black carbon, mineral dust and sea salt. The MERRA Aerosol Reanalysis (MERRAero) is an innovative tool to study air quality issues around the world for its global and constant coverage and its distinction of aerosol speciation expressed in the form of aerosol optical depth (AOD). The purpose of this manuscript is to apply MERRAero to the study of urban air pollution at the global scale by analyzing the AOD over a period of 13years (2003–2015) and over a selection of 200 of the world's most populated cities in order to assess the impacts of urbanization, industrialization, air quality regulations and regional transport which affect urban aerosol load. Environmental regulations and the recent global economic recession helped to decrease the AOD and sulfate aerosols in most cities of North America, Europe and Japan. Rapid industrialization in China over the last two decades resulted in Chinese cities having the highest AOD values in the world. China has nevertheless recently implemented emission control measures, which are showing early signs of success in many cities of Southern China, where AOD decreased substantially over the last 13years. The AOD over South American cities, dominated by carbonaceous aerosols, also decreased over the last decade due to an increase in commodity prices which slowed deforestation activities in the Amazon rainforest. At the opposite, recent urbanization and industrialization in India and Bangladesh resulted in a strong increase of AOD, sulfate and carbonaceous aerosols in most cities of these two countries. The AOD over most cities in Northern Africa and Western Asia changed little over the last decade. Emissions of natural aerosols, which cities in these two regions tend to be mostly impacted by, don't tend to fluctuate significantly on an annual basis.

Radiative Effects and Optical Properties of Aerosol during Two Dust Events in 2013 over Zanjan, Iran

ABSTRACTAerosol optical propertieslike Aerosol Optical Depth (AOD), Angstrom Exponent (AE), ASYmmetry parameter(ASY), Single Scattering Albedo (SSA), and Aerosol Volume Size Distribution(AVSD) have been analyzed for the atmosphere of Zanjan, a city in NorthwestIran. These properties have been studied usingthe ground-based AErosol RObotic NETwork (AERONET)duringthe periods from 8 to18 May and 8 to 14 June, 2013. During thestudy period, 14th May and 10th June are identified asdusty days, and AOD at 500 nm reached a peak value of 0.64 and 0.80, on thesedays. The high values of AOD and low values of AE during dusty days illustratethat coarse mode particles like dust are dominant. In the visible spectrum ASY usually decreasesand then somewhat increases in the near infrared region. Both SSA and AVSD suggest predominance of coarseparticles on the dusty days. The Santa Barbara DISORT AtmosphericRadiative Transfer (SBDART) model is utilized to simulate the solar irradiancevalues for the above-mentioned periods at the earth's surface, within theatmosphere, and at the Top of the Atmosphere (TOA). The results show thatdominant aerosol types are dust particles which have a coolingeffect on the earth's surfaceduring the studyperiods, especially on two dusty days, 14 May, and10 June. The correlation coefficient shows a very good agreement between theARF values retrieved from AERONET and SBDART simulation results.

MODIS 자료의 에어로졸의 광학적 두께를 이용한 제주지역의 지표면 PM2.5농도 추정

본 연구는 제주 고산에서 Moderate Resolution Imaging Spectroradiometer(MODIS)로 산출된 Aerosol Optical Depth(AOD)와 지표면 <TEX>$PM_{2.5}$</TEX>와의 상관성 연구를 수행하였다. 이를 위해 위성자료, 선포토미터, Optical Particle Counter(OPC), Micro Pulse Lidar(MPL)자료가 사용되었다. 2009년 10월 14일부터 24일까지 고산에서 측정된 선포토미터 L2.0자료와 <TEX>$PM_{2.5}$</TEX> 자료의 초기 상관성 검토에서는 <TEX>$R^2=0.48$</TEX>의 상관성을 보였지만 고산에서 측정된 Micro-Pulse Lidar Network(MPLNet)의 에어로졸 수직분포 데이터를 사용하여 옅은 구름이나 황사의 영향을 제거한 후에는 상관성이 개선되어 <TEX>$R^2=0.60$</TEX> 이상의 값이 산출되었다. 이러한 결과는 인공위성 자료로부터 측정된 AOD를 이용하여 대기 미세먼지 감시에 활용할 수 있는 가능성을 확인하여 주었다. In this study, correlations between Moderate Resolution Imaging Spectroradiometer (MODIS) derived Aerosol Optical Depth (AOD) values and surface-level <TEX>$PM_{2.5}$</TEX> concentrations at Gosan, Korea have been investigated. For this purpose, data from various instruments, such as satellite, sunphotometer, Optical Particle Counter (OPC), and Micro Pulse Lidar (MPL) on 14-24 October 2009 were used. Direct comparison between sunphotometer measured AOD and surface-level <TEX>$PM_{2.5}$</TEX> concentrations showed a <TEX>$R^2=0.48$</TEX>. Since the AERONET L2.0 data has significant number of observations with high AOD values paired to low surface-level <TEX>$PM_{2.5}$</TEX> values, which were believed to be the effect of thin cloud or Asian dust. Correlations between MODIS AOD and <TEX>$PM_{2.5}$</TEX> concentration were increased by screening thin clouds and Asian dust cases by use of aerosol profile data on Micro-Pulse Lidar Network (MPLNet) as <TEX>$R^2$</TEX> > 0.60. Our study clearly demonstrates that satellite derived AOD is a good surrogate for monitoring atmospheric PM concentration.

Analysis of incoming biomass burning aerosol plumes over southern Brazil

AbstractWe characterized the aerosol particles and their transport to southern Brazil during the austral winter months of June, July, and August from 2002 to 2011. To obtain the aerosol optical depth (AOD) (0.55 μm) and the Ångström exponent (0.47–0.66 μm), we used MODIS data. High values of AOD were observed in 2002, 2005, 2007, and 2010, with the highest values in August. We also used the CCATT–BRAMS model to simulate the AOD in southern Brazil. Both approaches suggest an increase of the AOD in the northwestern part of the region, evidence for the transport of biomass burning plumes from central Brazil.

Spatial distribution and temporal variation of aerosol optical depth in the Sichuan basin, China, the recent ten years

The applicability of the MODIS (Moderate Resolution Imaging Spectroradiometer) aerosol optical depth (AOD) product was verified using CE-318 sun photometric data for the Sichuan area. The results show that MODIS_3K AOD agrees well with the AOD derived from the CE-318 sun photometer, with a high correlation coefficient (R2 = 0.91). And we used the MODIS AOD product analyzed the spatial distribution and temporal variation of the annual, seasonal and monthly distribution of AOD in the Sichuan area over the last ten years (2006–2015). In the Sichuan area, the mean change of AOD over the 10-year period showed a significant decreasing trend, reaching its maximum in 2010 and its minimum in 2015. Considering only the first five years, the lowest value was reached in 2008 and the overall trend was a standard symmetrical “V” type. Over the later five years, the annual average AOD value showed an overall decreasing trend. The monthly averaged AOD indicated a “double peaks” fluctuation trend; the two peaks appeared in March and August, and AOD changes were relatively small between September and January. Overall, the average value of AOD reached its highest values in spring, and its lowest values in autumn. In the city of Chengdu, the monthly and seasonal changes in the trend were essentially the same as those of the whole Sichuan area; However, the Chengdu AOD monthly and seasonal average change rate was higher than that of Sichuan as a whole. This shows that Chengdu is still the main contributor to the enhanced AOD value for the entire Sichuan region. The spatial distribution of AOD values indicates an “east high, west low” situation across the Sichuan area and Chengdu is one of three cities with the highest AOD values. However, the spatial variation of AOD trend value indicated an “east low, west high” the spatial distribution across the Sichuan region, opposite to the spatial distribution. Moreover, in the past 10 years, the overall AOD changes in Sichuan showed a downward trend, especially in Chengdu, suggesting that environmental remediation measures have achieved initial improvements. But, average AOD of some parts of western Sichuan is increasing, indicating that other regions in Sichuan should strengthen their management and remediation of haze weather.

Columnar aerosol characteristics and radiative forcing over the Doon Valley in the Shivalik range of northwestern Himalayas.

Spectral aerosol optical depth (AOD) measurements obtained from multi-wavelength radiometer under cloudless conditions over Doon Valley, in the foothills of the western Himalayas, are analysed during the period January 2007 to December 2012. High AOD values of 0.46±0.08 and 0.52±0.1 at 500nm, along with low values of Ångström exponent (0.49±0.01 and 0.44±0.03) during spring (March-May) and summer (June-August), respectively, suggest a flat AOD spectrum indicative of coarse-mode aerosol abundance compared with winter (December-February) and autumn (September-November), which are mostly dominated by fine aerosols from urban/industrial emissions and biomass burning. The columnar size distributions (CSD) retrieved from the King's inversion of spectral AOD exhibit bimodal size patterns during spring and autumn, while combinations of the power-law and unimodal distributions better simulate the retrieved CSDs during winter and summer. High values of extinction coefficient near the surface (∼0.8-1.0km-1 at 532nm) and a steep decreasing gradient above are observed via CALIPSO profiles in autumn and winter, while spring and summer exhibit elevated aerosol layers between ∼1.5 and 3.5km due to the presence of dust. The particle depolarisation ratio shows a slight increasing trend with altitude, with higher values in spring and summer indicative of non-spherical particles of dust origin. The aerosol-climate implications are evaluated via the aerosol radiative forcing (ARF), which is estimated via the synergy of OPAC and SBDART models. On the monthly basis, the ARF values range from ∼ -30 to -90Wm-2 at the surface, while aerosols cause an overall cooling effect at the top of atmosphere (approx. -5 to -15Wm-2). The atmospheric heating via aerosol absorption results in heating rates of 1.2-1.6Kday-1 during March-June, which may contribute to changes in monsoon circulation over northern India and the Himalayas.

Study on Regional Variations of Aerosol Loading Using Long Term Satellite Data Over Indian Region

Satellite-based measurements of aerosols are one of the most effective ways to understand the role of aerosols in climate in terms of spatial and temporal variability. In the present study, we attempted to analyse spatial and temporal variations of satellite derived aerosol optical depth (AOD) over Indian region using moderate resolution imaging spectrometer over a period of 2001–2011. Due to its vast spatial extent, Indian region and adjacent oceanic regions are divided into different zones for analysis. The land mass is sub divided into five different zones such as Indo Gangetic Plain (IGP), Indian mainland, North Eastern India (NE), South India-1 (SI-1), South India-2 (SI-2). Oceanic areas are divided into Arabian Sea and Bay of Bengal. Arabian Sea is further divided as three zones viz. Northern AS (NAS), Central AS (CAS) and Eastern AS (EAS) zones. Bay of Bengal is divided as North BoB (NBoB), West BoB (WBoB), Central BoB (CBoB), and East BoB (EBoB). The study revealed that among all the land regions, IGP showed the highest peak AOD value (0.52 ± 0.17) while SI-2 showed the lower values of AOD in all the months compared to all India average. The maximum AOD is observed during premonsoon season for all regions. During the winter, average AOD levels were substantially lower than the summer averages. Peak of aerosol loading (0.35 ± 0.159) is observed in March over NE region, whereas in all other regions, peak is observed during May. Frequency distribution of long term AOD ( 0.5) shows a shift of frequency distribution of AOD from 0.5. Oceanic areas also shows seasonal variation of AOD. Over Arabian Sea, high AOD values with greater variations were observed in summer monsoon season while in Bay of Bengal it is observed during winter monsoon. This is due to the high wind speed prevailing in Arabian Sea during monsoon season which results in production of more sea salt aerosol. Highest AOD values are observed over NAS during monsoon season and over NBOB during winter season. Lowest AOD values with its lower variations observed in both the central region of Arabian Sea and Bay of Bengal.

Landsat 8-based inversion methods for aerosol optical depths in the Beijing area

As an essential component of the Earth-atmosphere system, aerosols have important impacts on the atmospheric environment and human health. Based on the data sourced from Landsat 8 satellite images, the goal of this paper is to retrieve aerosol optical depth (AOD) in the Beijing area by means of the MODIS Dark Target (DT) Method and the visible near-infrared (VNIR) atmospheric correction method (ACM), of which the accuracy is verified by observation data from AERONET. Furthermore, analysis was conducted to assess the effects of the two specific inversion methods on AOD values and AOD distribution characteristics in Beijing. The results indicate the following: 1) both the DT method and the VNIR method can be used successfully in the inversion of AOD in Beijing with Landsat 8 satellite data, while the DT method generates a slightly higher accuracy than that of the VNIR method, in which the root mean squared error (RMSE) values are 0.195 and 0.282, respectively; 2) AOD distribution in Beijing is presented with significant regional features, in which the areas with high AOD values were mainly concentrated in six districts (Dongcheng, Xicheng, Chaoyang, Fengtai, Haidian, and Shijingshan) and their surrounding areas. In addition, the AOD values are relatively low in the southwestern and northern regions of Beijing, which was mainly due to minor impacts of human activity and transportation.

Assessment of aerosols optical properties and radiative forcing over an Urban site in North-Western India

ABSTRACTThe present work is aimed to analyze aerosols optical properties and to estimate aerosol radiative forcing (ARF) from January to December 2013, using sky radiometer data over Rohtak, an urban site in North-Western India. The results reveal strong wavelength dependency of aerosol optical depth (AOD), with high values of AOD at shorter wavelengths and lower values at longer wavelength during the study period. The highest AOD values of 1.07 ± 0.45 at 500 nm were observed during July. A significant decline in Ångström exponent was observed during April–May, which represents the dominance of coarse mode particles due to dust-raising convective activities. Aerosols’ size distribution exhibits a bimodal structure with fine mode particles around 0.17 µm and coarse mode particles with a radius around 5.28 µm. Single scattering albedo values were lowest during November–December at all wavelengths, ranging from 0.87 to 0.76, which corresponds to the higher absorption during this period. Aerosols optical properties retrieved during observation period are used as input for SBDART (Santa Barbara DISORT Atmospheric Radiative Transfer) to estimate the direct ARF at the surface, in the atmosphere and at the top of the atmosphere (TOA). The ARF at the TOA, surface and in the atmosphere are found to be in the range of −4.98 to −19.35 W m−2, −8.01 to −57.66 W m−2 and +3.02 to +41.64 W m−2, respectively. The averaged forcing for the whole period of observations at the TOA is −11.26 W m−2, while at the surface it is −38.64 W m−2, leading to atmospheric forcing of 27.38 W m−2. The highest (1.168 K day−1) values of heating rate was estimated during November, whereas the lowest value (0.084 K day−1) was estimated for the February.

Regional trends of aerosol optical depth and their impact on cloud properties over Southern India using MODIS data

Remote sensing of global aerosols has constituted a great scientific interest in a variety of applications related to global warming and climatic change. In the present study we investigate the spatial and temporal variations of aerosol optical properties and its impact on various properties of clouds over Southern India for the last ten years (2005–2014) by using Moderate Resolution Imaging Spectroradiometer (MODIS) data retrieved from the onboard Terra and Aqua satellites. The spatial distributions of annual mean lowest Aerosol Optical Depth (AOD) value is observed in Bangalore (BLR) (0.22±0.04) and the highest AOD value is noted in Visakhapatnam (VSK) (0.39±0.05). Similarly high Fine Mode Fraction (FMF) is noticed over VSK and Thiruvananthapuram (TVM), while lower values are observed in Anantapur (ATP), Hyderabad (HYD), Pune (PUNE) and BLR. From the results, a negative correlation was found between AOD and Cloud Top Temperature (CTT), Cloud Top Pressure (CTP) where as, a positive correlation was observed between AOD and Cloud Fraction (CF), Water Vapor (WV) over the selected regions. Monthly average AOD and FMF are plotted for analysis of the trends of aerosol loading in a long-term scale and both values showed statistically significant enhancing trend over all regions as derived from the MODIS measurements. Further, the annual variation of spatial correlation between MODIS and MISR (Multi - Angle Imaging Spectro Radiometer) AOD has been analyzed and the correlation coefficients are found to be higher in two of the regions VSK and PUNE (>0.8), and considerably lower for TVM (<0.7).

Optical properties of aerosols over a tropical rain forest in Xishuangbanna, South Asia

Observation and analysis of the optical properties of atmospheric aerosols in a South Asian tropical rain forest showed that the annual mean aerosol optical depth (AOD) and aerosol Ångström exponent (α) at 500nm were 0.47±0.30 (± value represents the standard deviation) and 1.35±0.32, respectively, from 2012 to 2014, similar with that of Amazon region. Aerosol optical properties in this region varied significantly between the dry and wet seasons. The mean AOD and α were 0.50±0.32 and 1.41±0.28, respectively, in the dry season and 0.41±0.20 and 1.13±0.41 in the wet season. Because of the combustion of the rich biomass in the dry season, fine modal smoke aerosols increased, which led to a higher AOD and smaller aerosol control mode than in the wet season. The average atmospheric humidity in the wet season was 85.50%, higher than the 79.67% during the dry season. In the very damp conditions of the wet season, the aerosol control mode was relatively larger, while AOD appeared to be lower because of the effect of aerosol hygroscopic growth and wet deposition. The trajectories were similar both in dry and wet, but with different effects on the aerosol concentration. The highest AOD values 0.66±0.34 (in dry) and 0.45±0.21 (in wet) both occurred in continental air masses, while smaller (0.38–0.48 in dry and 0.30–0.35 in wet) in oceanic air masses. The range of AOD values during the wet season was relatively narrow (0.30–0.45), but the dry season range was wider (0.38–0.66). For the Ångström exponent, the range in the wet season (0.74–1.34) was much greater than that in the dry season (1.33–1.54).

Aerosol Properties in Central Kalimantan Due to Peatland Fire

ABSTRACTThe optical properties of aerosol could describe the potential source of prevalent pollutants of certain area. With the annual occurrences of biomass burning over the peat swamp forest, the study of aerosol characters in Central Kalimantan province becomes important. Aerosols from Aerosol Robotic Network (AERONET) data network combine with some environmental parameters, i.e., rainfall, visibility, surface humidity and hotspot number are investigated. Here we use the data from 2012 to 2014 collected from AERONET in Palangkaraya. We found a strong relationship between aerosol properties and environmental parameters (rainfall, hotspot number, visibility). Variability of aerosol properties such as aerosol optical depth (AOD), Angstrom exponent number, and its fine mode are consistent with the dry period between August and October when most fire episodes occur. In fact, the increase of aerosol loading occurs mostly when the monthly rainfall reaches below 150 mm month–1 (dry period), as the cut off number of our analyses. Considerable reduction of visibility below 500 m occurs whenever AOD is above 3.0. During observation period, we found that aerosol sources at this location originate from dust, marine aerosol, continental and urban aerosol, and biomass burning. The biomass burning aerosol gave a substantially high AOD values that reach almost 6.0 and fine feature as an indication of highly concentrated smoke from peatland source. Moreover, smouldering combustion from peat land is characterized by high value of single scattering albedo observed in the location.