Characterization Of Aerosol Optical Properties Research Articles

Effect of coal type on aerosol optical properties at Ulaanbaatar city

In this study, seasonal characteristics of aerosol optical properties at Ulaanbaatar station of the international network of SKYNET are investigated using ground-based skyradiometer from the years extending from 2017 to 2023. The aerosol optical thickness (AOT) at 500nm wavelength and Angstrom exponent (AE) were determined in winter to evaluate the decrease in air pollution in Ulaanbaatar since implementing the government's decision to use coal briquettes for household heating. During the study period, the monthly mean AOT at 500nm varied throughout the year, with the maximum value of 0.178±0.004 obtained in winter due to households burning large amounts of biomass, and the highest AOT (0.183) was obtained in February. The mean AOT was 0.21 in the winter of 2017-2019, which decreased by 15 per cent to 0.18 in the winter of 2019-2023.

Comparative Analysis of Aerosol Vertical Characteristics over the North China Plain Based on Multi-Source Observation Data

In this paper, multi-source observation, such as aircraft, ground-based remote sensing, and satellite-retrieved data, has been utilized to compare and analyze the vertical characteristics of aerosol optical properties and the planetary boundary layer height (HPBL) over the North China Plain (NCP) region during May–June 2016. Aircraft observations show the vertical profiles of aerosol absorption coefficients (σabs), scattering coefficients (σsca), and extinction coefficients (σext) gradually decrease with altitude, with their maximum values near HPBL. The vertical profiles of σext depended most on the vertical distribution of measured σsca, indicating a significant contribution of scattering aerosols. In addition, the prominent characteristic of the inverse relationship between σext and moisture profile could serve as a reference for predicting air quality in the NCP region. The lower layer pollution during the field experiment was likely caused by the accumulation of fine-mode aerosols, characterized by the vertical distribution of the Ångström exponent and the Aerosol Robotic Network (AERONET) products. Typically, HPBL derived from aircraft and surface Micro Pulse Lidar (MPL) was approximate, while the predicted HPBL by meteorological data indicates an underestimation of ~192 m. Aerosol optical depth (AOD) calculated from aircraft and ground-based remote sensing (such as MPL and AERONET) experienced a strong correlation, and both of them exhibited a similar tendency. However, the AOD retrieved from satellites was significantly larger than that from aircraft and ground-based remote sensing. Overall, the inversion algorithm, cloud identification algorithm, representativeness of the space, and time of the observation may lead to an overestimation or underestimation of AOD under certain circumstances. This study may serve as a re-evaluation of AOD retrieved from multi-source observations and provide a reference to uncover the actual atmospheric environment in the NCP regions.

Optical Properties and Vertical Distribution of Aerosols Using Polarization Lidar and Sun Photometer over Lanzhou Suburb in Northwest China

To better understand aerosol vertical distribution and radiation effects, the seasonal variation and vertical distribution characteristics of aerosol optical properties were analyzed based on the aerosol extinction coefficient, depolarization ratio and backscatter Ångström exponent derived from the dual-wavelength polarization lidar at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) from December 2009 to November 2012. Combining the CE-318 sun photometer, the microphysical, optical and vertical distribution characteristics of aerosol during a dust process were discussed comprehensively. The results revealed that the vertical profiles of the aerosol extinction coefficient and depolarization ratio clearly had seasonal variation characteristics. The aerosol optical depth (AOD) integrating with the aerosol extinction coefficient within 0–2 km in the spring, summer, autumn and winter accounted for 48%, 45%, 56% and 58% of the total AOD, respectively. The non-spherical feature was most distinctive in the spring, followed by the winter, autumn and summer. The particle size of aerosol in the lower layer was larger than that in the upper layer according to the vertical profile of the backscatter Ångström exponent. The cluster analysis of backward trajectory showed SACOL is dominated by dust aerosol in the spring and the mixtures of dust with anthropogenic pollution in the winter. A dust event in April 2010 was selected and the analysis showed that it mainly came from the high-altitude and long-range transportation from the Taklamakan Desert. During this period, the extinction coefficient increased up to 0.9 km−1, the maximum AOD was 2.21 and the SSA ranged from 0.92 to 0.99. The radiation force in the atmosphere reached 126.15 W/m2. It can be found that the influence of aerosol on the atmospheric radiation effect cannot be ignored.

Dynamic Characteristics of Aerosol Optical Properties over Dibrugarh City in the North-Eastern Indian Region during 2018–2021

Aerosols play an important role in the earth's environment across the globe through their involvement in various earth system cycles. The change in the aerosol properties may cause short and long-term impacts, the knowledge of such changes is useful in the estimation of the pollution sources of any region. We have carried out the analysis of the aerosols' optical and radiative properties using AERONET station data from 2018 to 2021 in Dibrugarh City. The higher Aerosol Optical Depth (AOD) values during winter and pre-monsoon months indicate high anthropogenic activities, and biomass burning in Dibrugarh. The impact of various sources and daily meteorological parameters help in understanding the diurnal variations of the AOD, Ångström Exponent (AE), and column water (CW). Fine aerosol fractions dominate the aerosol volume, but sometimes the long-range transport of dust affects aerosol properties during pre-monsoon months (MAM). MODIS-derived AOD and AERONET AOD values show a good correlation, with R2 = 0.68. The highest volume of the aerosols reaches up to 0.11 µm3 µm-2 during pre-monsoon months, whereas it lies below 0.05 µm3 µm-2 in other seasons. SSA values indicate the presence of scattering aerosols but in 2020, a sudden decline in the SSA values shows a strong rise in the absorbing aerosols. Throughout the study period (2018–2021), the positive radiative forcing indicates a rise in atmospheric heating.

Festival Induced Air Quality Perturbation over an Urban Center in Eastern Nepal

An attempt has been made to investigate the changes in the characteristics of aerosol optical properties and a columnar load of carbon monoxide (CO) induced during the Dashain celebration 2018 over Birtamode, Nepal. Ground-based measurements of Aerosol Optical Depth (AOD) were carried out using a Microtops II sun-photometer during 13th to 25th Oct, 2018. AOD values on days before Dashain were in the range of 0.6 which increased above 1 attaining a maximum value of 1.6 on 19th. The AOD values started dropping below 1 on 24th, attaining a daily average of 0.64. The peak values on the respective days were also captured by Moderate Resolution Imaging Spectroradiometer (MODIS) AOD retrievals. A similar pattern was observed with the TROPOspheric Measuring Instrument (TROPOMI) CO column with peak value on the 19th. The air mass trajectories show that the increase in the AOD and CO values is of local origin and the CAMS GFAS wildfire flux of CO and PM2.5 show no change during the study period. However, the spatial analysis of AOD shows that the increased values are of regional nature. The results highlight the necessity of installation of low-cost air quality sensors in the region and utilization of aerosol and trace gaseous products derived from satellite remote sensing instruments at high temporal resolution and the application of chemical transport models.

Advances in the characterization of aerosol optical properties using long-term data from AERONET in Buenos Aires

We present a complete characterization of aerosols in Buenos Aires based on their optical and microphysical properties from a long-term record (19-years) of AERONET V3 observations at the CEILAP-BA site. The baseline climatology indicates that the city has low mean aerosol load (0.11 ± 0.1) and mean Ångström exponent (α) of 1.11 (±0.4). The long-term trend of the monthly median aerosol optical thickness (AOT) is not significant whereas monthly α medians show a significant negative trend. Atmospheric turbidity increases in August and September (40%). Annual and monthly particle size distributions show predominance of the coarse mode. This apportionment can change under particular conditions, e.g., showing increased fine mode load in August and September.The thresholds of α and AOT proposed for four aerosol types allowed a satisfactory classification of aerosols. The relationship between AOT and α clearly illustrated the major contribution to extinction of finer particles under more turbid conditions. This feature—not evident in the baseline climatology— is consistent with the presence of smoke from regional biomass burning. Sporadic intrusions of coarse particles (dust/ash) from remote sources also enhance extinction. The analysis of the interrelations among aerosol properties (fine mode fraction of AOT, volume concentration, spectral curvature, and size distribution) supports these findings. The aerosols seem to undergo aging and/or hydration processes as shown by the relationships among AOT, extinction due to the fine mode, spectral curvature, and aerosol fine mode radius. This comprehensive analysis revealed details associated with the contributions from local and remote anthropogenic and/or natural sources.

Extensive characterization of aerosol optical properties and chemical component concentrations: Application of the GRASP/Component approach to long-term AERONET measurements

A recently developed GRASP/Component approach (GRASP: Generalized Retrieval of Atmosphere and Surface Properties) was applied to AERONET (Aeronet Robotic Network) sun photometer measurements in this study. Unlike traditional aerosol component retrieval, this approach allows the inference of some information about aerosol composition directly from measured radiance, rather than indirectly through the inversion of optical parameters, and has been integrated into the GRASP algorithm. The newly developed GRASP/Component approach was applied to 13 AERONET sites for different aerosol types under the assumption of aerosol internal mixing rules to analyze the characteristics of aerosol components and their distribution patterns. The results indicate that the retrievals can characterize well the spatial and temporal variability of the component concentration for different aerosol types. A reasonable agreement between GRASP BC retrievals and MERRA-2 BC products is found for all different aerosol types. In addition, the relationships between aerosol component content and aerosol optical parameters such as aerosol optical depth (AOD), fine-mode fraction (FMF), absorption Ångström exponent (AAE), scattering Ångström exponent (SAE), and single scattering albedo (SSA) are also analyzed for indirect verifying the reliability of the component retrieval. It was demonstrated the GRASP/Component optical retrievals are in good agreement with AERONET standard products [e.g., correlation coefficient (R) of 0.93–1.0 for AOD, fine-mode AOD (AODF), coarse-mode AOD (AODC) and Ångström exponent (AE); R = ~ 0.8 for absorption AOD (AAOD) and SSA; RMSE (root mean square error) < 0.03 for AOD, AODF, AODC, AAOD and SSA]. Thus, it is demonstrated the GRASP/Component approach can provide aerosol optical products with comparable accuracy as the AERONET standard products from the ground-based sun photometer measurements as well as some additional important inside on aerosol composition.

Study of aerosol optical properties at two urban areas in the north of Vietnam with the implication for biomass burning impacts.

The spatiotemporal distribution and characterization of aerosol optical properties in the north of Vietnam were investigated extensively using the long-term measurements obtained from Moderate Resolution Imaging Spectroradiometer (MODIS) (from 2010 to 2019) and two Aerosol Robotic Network (AERONET) stations (Nghia Do, Hanoi City, from 2010 to 2019 and Son La from 2012 to 2019) located in fast-developing urban areas. This study also analyzed the tendency of AOD over different wavelengths as well as the influences of meteorological parameters and boundary layer height (BLH) on AOD and Ångström exponent (AE). The annual mean AOD500 at Nghia Do and Son La stations were 0.81 and 0.78, respectively. Our results revealed the existence of particles emitted from anthropogenic activities in Hanoi and Son La with the dominance of fine particles (more than 90% of the AE440-870 were larger than 1). Besides, a high percentage of AE440-870 larger than or approximately 1.5 during the dry and transition months in Son La indicated the existence of biomass-burning aerosol particles due to forest fires and burning of agriculture residuals. The classification results for aerosol types showed the presence of both biomass burning and urban/industrial aerosol types at Nghia Do and Son La sites. Among the investigated meteorological parameters, surface solar radiation expressed a significant correlation with AE440-870 in all three seasons at the two sites due to the secondary formation of fine particles induced by the high solar radiation condition. The impacts of meteorological parameters and BLH on AOD were not observed simultaneously during three seasons at Nghia Do and Son La stations.

Temporal and Spatial Distribution Characteristics of Aerosol Optical Properties in Urban Agglomerations on the North Slope of the Tianshan Mountains

In order to explore the temporal and spatial distribution characteristics of atmospheric aerosol optical depth (AOD) in the urban agglomeration on the northern slope of the Tianshan Mountains, the temporal and spatial distribution characteristics and trends of changes in the AOD in the study area from 2000 to 2019 were analyzed by MODIS aerosol products(MCD19-A2). For 2016-2019, when the AOD was relatively stable, the parameters such as the AOD and Ångström wavelength index (α) were analyzed using multi-band sun photometer ground-based remote sensing technology. The results showed that ① the spatial distribution of AOD in the study area was consistent with the topography, and high values were mainly distributed in the low altitude area. The spatial distribution of AOD in the four seasons showed a strong seasonal change from spring (0.15±0.03) > autumn (0.14±0.03) > summer (0.14±0.02). ② In terms of time, the annual average AOD value of the study area was 0.12 from 2000 to 2019 with an annual growth rate of 1.03%, thereby showing an overall increasing trend. The annual variation in the monthly mean value of AOD was bimodal; the first and second peaks were in May and November. The main reason for the increase in AOD was the release and transmission of dust from natural sources and heating. ③ Under the influence of dust weather, the AOD changed sharply in spring, and the size and change range of aerosol particles were larger than those in summer. The high value of AOD in the study area was mainly affected by coarse mode particles. The moisture absorption growth of fine mode particles caused a fluctuation in the AOD, but it was not the cause of the high value of AOD.

Long-term multi-source data analysis about the characteristics of aerosol optical properties and types over Australia

Abstract. The spatiotemporal distributions of aerosol optical properties and major aerosol types, along with the vertical distribution of major aerosol types over Australia, are investigated based on multi-year Aerosol Robotic Network (AERONET) observations at nine sites, the Moderate Resolution Imaging Spectroradiometer (MODIS), Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2), Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), and back-trajectory analysis from the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT). During the observation period from 2001–2020, the annual aerosol optical depth (AOD) at most sites showed increasing trends (0.002–0.029 yr−1), except for that at three sites, Canberra, Jabiru, and Lake Argyle, which showed decreasing trends (−0.004 to −0.014 yr−1). In contrast, the annual Ångström exponent (AE) showed decreasing tendencies at most sites (−0.045 to −0.005 yr−1). The results showed strong seasonal variations in AOD, with high values in the austral spring and summer and relatively low values in the austral fall and winter, and weak seasonal variations in AE, with the highest mean values in the austral spring at most sites. Monthly average AOD increases from August to December or the following January and decreases during March–July. Spatially, the MODIS AOD showed obvious spatial heterogeneity, with high values appearing over the Australian tropical savanna regions, Lake Eyre Basin, and southeastern regions of Australia, while low values appeared over the arid regions in western Australia. MERRA-2 showed that carbonaceous aerosol over northern Australia, dust over central Australia, sulfate over densely populated northwestern and southeastern Australia, and sea salt over Australian coastal regions are the major types of atmospheric aerosols. The nine ground-based AERONET sites over Australia showed that the mixed type of aerosols (biomass burning and dust) is dominant in all seasons. Moreover, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) showed that polluted dust is the dominant aerosol type detected at heights 0.5–5 km over the Australian continent during all seasons. The results suggested that Australian aerosol has similar source characteristics due to the regional transport over Australia, especially for biomass burning and dust aerosols. However, the dust-prone characteristic of aerosol is more prominent over central Australia, while the biomass-burning-prone characteristic of aerosol is more prominent in northern Australia.

Spatio-Temporal Distribution and Variation Characteristics of Aerosol Optical Properties in Henan Province

The temporal variation and spatial distribution characteristics of aerosol optical depth (AOD), aerosol column mass concentration (AMC), and fine mode fraction (FMF) were analyzed based on the aerosol product information obtained from MODIS/Terra C6.1 from 2001 to 2018 in the Henan province. The spatial distribution of AOD and AMC in all seasons are high in the east and low in the west, and high in the north and low in the south, which was related to the special topography, population distribution, and number of enterprises in each region. Meanwhile, the spatial distribution of FMF is opposite to that of AOD and AMC. In spring, AMC was the highest, while FMF was the lowest, indicating that it was mainly affected by dust aerosol in spring. AOD and FMF were the highest in summer, while the AMC was lower, mainly because the high values of AOD in summer were caused by the hygroscopic growth of aerosol. The increase of rainwater scouring and secondary aerosol generation led to the domination of fine-mode aerosols in summer. In autumn and winter, the AOD and AMC were relatively low, and the FMF was slightly higher than in spring. The AOD and AMC in the Henan Province showed a decreasing annual trend, while the FMF exhibited an increasing trend. The average monthly peak-valley difference of AOD, AMC, and FMF decreased after 2011.

Temporal characteristics of aerosol optical properties over the glacier region of northern Pakistan

Glacier melting due to light-absorbing aerosol has become a growing issue in recent decades. The emphasis of this study is to examine aerosol loadings over the high mountain glacier region of northern Pakistan between 2004 and 2016, with sources including local emissions and long-range transported pollution. Optical properties of aerosols were seasonally analyzed over the glacier region (35–36.5°N; 74.5–77.5°E) along with three selected sites (Gilgit, Skardu, and Diamar) based on the Ozone Monitoring Instrument (OMI). The aerosol sub-type profile was analyzed with Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model was used to understand the origin of air masses arriving in the study region. The highest values of aerosol optical depth (AOD) and single scattering albedo (SSA) occurred during spring, whereas aerosol index (AI) and absorption AOD (AAOD) exhibited maximum values in winter and summer, respectively. The minimum values of AOD, AI, AAOD, and SSA occurred in winter, autumn, winter, and autumn, respectively. The results revealed that in spring and summer the prominent aerosols were dust, whereas, in autumn and winter, anthropogenic aerosols were prominent. Trend analysis showed that AI, AOD, and AAOD increased at the rate of 0.005, 0.006, and 0.0001 yr−1, respectively, while SSA decreased at the rate of 0.0002 yr−1. This is suggestive of the enhancement in aerosol types over the region with time that accelerates melting of ice. CALIPSO data indicate that the regional aerosol was mostly comprised of sub-types categorized as dust, polluted dust, smoke, and clean continental. The types of aerosols defined by OMI were in good agreement with CALIPSO retrievals. Analysis of the National Oceanic and Atmospheric Administration Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model revealed that air parcels arriving at the glacier region stemmed from different source sites.

Vertical characterization of aerosol optical properties and brown carbon in winter in urban Beijing, China

Abstract. Aerosol particles are of importance in the Earth's radiation budget since they scatter and absorb sunlight. While extensive studies of aerosol optical properties have been conducted at ground sites, vertical measurements and characterization are very limited in megacities. In this work, we present simultaneous real-time online measurements of aerosol optical properties at ground level and at 260 m on a meteorological tower from 16 November to 13 December in 2016 in Beijing along with measurements of continuous vertical profiles during two haze episodes. The average (±1σ) scattering and absorption coefficients (bsca and babs; λ=630 nm) were 337.6 (±356.0) and 36.6 (±33.9) Mm−1 at 260 m, which were 26.5 % and 22.5 % lower than those at ground level. Single scattering albedo (SSA), however, was comparable between the two heights, with slightly higher values at ground level (0.89±0.04). Although bsca and babs showed overall similar temporal variations between ground level and 260 m, the ratios of 260 m to ground varied substantially from less than 0.4 during the clean stages of haze episodes to &gt; 0.8 in the late afternoon. A more detailed analysis indicates that vertical profiles of bsca, babs, and SSA in the low atmosphere were closely related to the changes in meteorological conditions and mixing layer height. The mass absorption cross section (MAC) of equivalent black carbon (eBC, λ=630 nm) varied substantially from 9.5 to 13.2 m2 g−1 in winter in Beijing, and it was strongly associated with the mass ratio of coating materials on refractory BC (rBC) to rBC (MR), and also the oxidation degree of organics in rBC-containing particles. Our results show that the increases in MAC of eBC in winter were mainly caused by photochemically produced secondary materials. Light absorption of organic carbon (brown carbon, BrC) was also important in winter, which on average accounted for 46 (±8.5) % and 48 (±9.3) % of the total absorption at 370 nm at ground level and 260 m, respectively. A linear regression model combined with positive matrix factorization analysis was used to show that coal combustion was the dominant source contribution of BrC (48 %–55 %) followed by biomass burning (17 %) and photochemically processed secondary organic aerosol (∼20 %) in winter in Beijing.

Characterization of aerosol optical properties using multiple clustering techniques over Zanjan, Iran, during 2010-2013.

Discrimination of aerosol types is very important, because different aerosols are created from diverse sources having different chemical, physical, and optical properties. In the present study, we have analyzed the seasonal classification of aerosol types by multiple clustering techniques, using AERosol Robotic NETwork (AERONET) data during 2010-2013 over Zanjan, Iran. We found that aerosol optical depth (AOD) showed pronounced seasonal variations of a summer high and winter low. Conversely, the values of the Angstrom exponent (AE) in winter and fall were higher than in spring and summer, which confirmed the presence of fine particles, while the low value of AE in the summer and spring represented the existence of coarse particles. Single Scattering Albedo (SSA) variations revealed the presence of scattering aerosols like dust in spring, summer, and fall while the dominance of absorbing-type aerosols in winter were also observed. The influence of local anthropogenic activities has caused a higher concentration of fine aerosols, and a higher fine mode fraction (FMF) of AOD in winter was recorded. Classification of aerosol types was carried out by analyzing different aerosol properties such as AOD versus AE, extinction Angstrom exponent (EAE) versus SSA, EAE versus absorption Angstrom exponent (AAE), FMF AOD versus EAE, and SSA versus FMF AOD. The analysis revealed the presence of dust and polluted dust in spring, summer, and fall in the atmosphere of Zanjan. Urban/industrial aerosols were available in all seasons, especially in fall and winter. The mixed aerosols existed in all seasons over the study location; however, no biomass burning aerosols were found. The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) aerosol subtype profiles showed the dominance of dust and polluted dust in spring and summer. However, the presence of polluted dust and industrial smoke during fall and winter were also noted over the study site.

Characterization of aerosol optical properties and model computed radiative forcing over a semi-arid region, Kadapa in India

In this paper, we present the optical and radiative properties of aerosols for the first time measured at Yogi Vemana University (YVU) campus (14.47°N, 78.82°E, 138 m above sea level), Kadapa, a semi-arid region in southern India during December 2013–February 2015. The collocated measurements of aerosol optical depth (AOD) and black carbon (BC) mass concentration are carried out at Kadapa using the ten channels Multi-Wavelength solar Radiometer (MWR) and seven wavelengths Aethalometer, respectively. This work mainly focused on studying the temporal and spectral behavior of aerosol properties, and their implications to the aerosol direct radiative forcing (ADRF). The respective seasonal mean values of AOD at 500 nm were found to be 0.33 ± 0.01, 0.46 ± 0.05, 0.27 ± 0.02 and 0.37 ± 0.06 during the winter, summer, monsoon and post-monsoon, with an annual mean of 0.38 ± 0.18. It is revealed that the Ångström exponent (AE or α380–850) value was observed to be maximum (minimum) in March (July) with 1.75 ± 0.19 (0.65 ± 0.14) indicates a predominance of fine (coarse) mode aerosols. Added to this, the diurnal variations of BC mass concentration exhibited two maxima with peaks occurred during 07:00–08:00 h and 20:00–21:00 h local time (LT), and a minimum of the afternoon hours around 13:00–16:00 h LT. Further, the AOD-AE relationship was investigated over Kadapa, and the results conclude that the urban-industrial/biomass burning (UI/BB) type aerosols are more dominated during the study period. The OPAC model retrieved single scattering albedo (SSA) at 500 nm was found to vary between 0.83 and 0.92 with relatively lower values during winter, suggest an increase in absorbing type aerosols produced from anthropogenic activities. The SBDART model computed seasonal averaged ADRF within the atmosphere (ADRFATM) was found to be 26.7 ± 2.3, 25.1 ± 1.0, 17.8 ± 3.9 and 18.3 ± 2.6 W m−2 during the summer, winter, monsoon and post-monsoon seasons, respectively at Kadapa. This illustrated that the absorption of solar radiation in the ATM is high which produces a significant amount of heating effect, resulted in a maximum atmospheric heating rate of 0.75 K day−1.

Impact of Diwali Festival on Aerosol Optical Properties over an Urban City, Ahmedabad (India)

An attempt has been made to investigate changes in the characteristics of aerosol optical properties induced during Diwali/ New Year celebrations of 2012 over an urban city, Ahmedabad (India). Ground based measurements of average Aerosol Optical Depth (AOD) were carried out using a Microtops-II at Physics Department, Gujarat University, Ahmedabad during 10th to 16th Nov, 2012. AOD on the day just after Diwali is found to increase significantly; around 75% compared to pre-Diwali days for visible wavelength, remained at higher level for one more day (next day of New Year). Turbidity factor (β) also changed considerably, to a high value of 0.34 on the next day of Diwali, indicating a significant increase in aerosol loading associated with Diwali/ New Year festivities. Normal anti-correlation between Angstrom exponent (α) and turbidity parameter (β) is not seen on days following Diwali. The AOD and β values in the evening of the next day of Diwali increased to about 164% and 171% respectively compared to pre-Diwali days evenings; such an increase associated with the festivities has not been reported at any part of the country. Spectral variation of AOD also shows a significant change in the pattern during following two days of celebrations compared to pre-Diwali days. It is seen to follow power law more closely. Significant increase in AOD and change in spectral pattern suggest an increase of fine/accumulation mode particles due to Diwali/ New Year festivities.

Seasonal variation of columnar aerosol optical properties and radiative forcing over Beijing, China

Long-term seasonal characteristics of aerosol optical properties and radiative forcing at Beijing (during March 2001–March 2015) were investigated using a combination of ground-based Sun/sky radiometer retrievals from the AERONET and a radiative transfer model. Aerosol optical depth (AOD) showed a distinct seasonal variation with higher values in spring and summer, and relatively lower values in fall and winter. Average Angstrom exponent (AE) in spring was lower than other seasons, implying the significant impact of dust episodes on aerosol size distribution. AE mainly distributed between 1.0 and 1.4 with an obvious uni-peak pattern in each season. The observation data showed that high AODs (>1.0) were clustered in the fine mode growth wing and the coarse mode. Compared to AOD, seasonal variation in single scattering albedo (SSA) showed an opposite pattern with larger values in summer and spring, and smaller ones in winter and fall. The highest volume size distribution and median radius of fine mode particles occurred in summer, while those of coarse mode particles in spring. The averaged aerosol radiative forcing (ARF) at the top of the atmosphere (TOA) in spring, summer, fall and winter were −33 ± 22 W m-2, -35 ± 22 W m-2, -28 ± 20 W m-2, and -24 ± 23 W m-2 respectively, and these differences were mainly due to the SSA seasonal variation. The largest positive ARF within atmosphere occurred in spring, implying strong warming in the atmosphere. The low heating ratio in summer was caused by the increase in water vapor content, which enhanced light scattering capacity (i.e., increased SSA).

Impact of Atmospheric Inversion Effects on Solar-Induced Chlorophyll Fluorescence: Exploitation of the Apparent Reflectance as a Quality Indicator

In the last decade, significant progress has been made in estimating Solar-Induced chlorophyll Fluorescence (SIF) by passive remote sensing techniques that exploit the oxygen absorption spectral regions. Although the O2–B and the deep O2–A absorption bands present a high sensitivity to detect SIF, these regions are also largely influenced by atmospheric effects. Therefore, an accurate Atmospheric Correction (AC) process is required to measure SIF from oxygen bands. In this regard, the suitability of a two-step approach, i.e., first an AC and second a Spectral Fitting technique to disentangle SIF from reflected light, has been evaluated. One of the advantages of the two-step approach resides in the derived intermediate products provided prior to SIF estimation, such as surface apparent reflectance. Results suggest that errors introduced in the AC, e.g., related to the characterization of aerosol optical properties, are propagated into systematic residual errors in the apparent reflectance. However, of interest is that these errors can be easily detected in the oxygen bands thanks to the high spectral resolution required to measure SIF. To illustrate this, the predictive power of the apparent reflectance spectra to detect and correct inaccuracies in the aerosols characterization is assessed by using a simulated database with SCOPE and MODTRAN radiative transfer models. In 75% of cases, the aerosol optical thickness, the Angstrom coefficient and the scattering asymmetry factor are corrected with a relative error below of 0.5%, 8% and 3%, respectively. To conclude with, and in view of future SIF monitoring satellite missions such as FLEX, the analysis of the apparent reflectance can entail a valuable quality indicator to detect and correct errors in the AC prior to the SIF estimation.

Impact of dust events on aerosol optical properties over Iraq

The spatial and temporal characteristics of aerosol optical properties (AOP) were analyzed in order to find out the hotspot aerosol sources over Iraq and surrounding regions. The correlation of AOP with the frequency of dust events (dust storm (DS), rising dust (RD), suspended dust (SD)) over 12 Iraqi stations is evaluated during the study period (January 2005–December 2014). The AOP: aerosol absorption optical depth (AAOD), aerosol extinction optical depth (AOD), and aerosol single scattering albedo (SSA) at 388 and 500 nm and aerosol index (AI), are derived from the Ozone Monitoring Instrument (OMI) on board the Aura satellite. Three well-known spatial interpolation techniques: inverse distance weighting, radial basis function with three sub-types, and kriging with three sub-types, are examined in ArcGIS software. Statistical analysis is applied to compute the station probability of dust events and its correlation with AOP. Results showed that the spline with the lowest RMSE and MPE near zero is the optimum method for estimating AOP. The spatial mean of AAOD, AOD, and AI (SSA) have the same pattern with high (low) mean values over the south and northwest of Iraq, Kuwait, and the northeast of Saudi Arabia. The seasonal variability of AAOD and AOD over the Iraqi stations showed that high (low) values occurred during spring and summer (winter) and concluded that AAOD is a responsible component for variation in AOD. DS and RD probability is higher over stations in the middle and south of Iraq than the stations in the north. High SD probability is over Mosul, Baghdad, and Nasiriya stations. The correlation of AOP with dust events suggests that the AAOD component is more important in the study of DS than SSA and AI while AI is a good index for the study of RD and SD in the study region.

Ground-based characterization of aerosol spectral optical properties of haze and Asian dust episodes under Asian continental outflow during winter 2014

Abstract. Long-range transported (LRT) haze can affect the regional radiation budget and the air quality in areas downwind of the Asian continental outflow. Because in situ observations of spectral aerosol optical properties of the LRT haze are rare, an intensive characterization of aerosol optical properties is needed. This study characterized the spectral optical properties of the LRT haze and Asian dust originating from the Asian continent. Integrated chemical and optical measurements of aerosol particles were carried out in a downwind area of the Asian continental outflow (Daejeon, South Korea) during winter 2014. High concentrations of PM10 (particulate matter with a diameter ≤ 10 µm) and light scattering coefficients at 550 nm, σs, 550, were observed during a long-range transport (LRT) haze episode (PM10 = 163.9 ± 25.0 µg m−3; σs, 550 = 503.4 ± 60.5 Mm−1) and Asian dust episode (PM10 = 211.3 ± 57.5 µg m−3; σs, 550 = 560.9 ± 151 Mm−1). During the LRT haze episode, no significant change in the relative contribution of PM2. 5 (particulate matter with a diameter ≤ 2.5 µm) chemical components was observed as particles accumulated under stagnant atmospheric conditions (13–17 January 2014), suggesting that the increase in PM2. 5 mass concentration was caused mainly by the accumulation of LRT pollutants. On the other hand, a gradual decrease in Ångström exponent (Å) and a gradual increase in single scattering albedo (ω) and mass scattering efficiency (MSE) were observed during the stagnant period, possibly due to an increase in particle size. These results imply that a change in particle size rather than chemical composition during the stagnant period is the dominant factor affecting the aerosol optical properties. During the Asian dust episode, a low PM2. 5 ∕ PM10 ratio and Å(450∕700) were observed with average values of 0.59 ± 0.06 and 1.08 ± 0.14, respectively, which were higher than those during the LRT haze episode (0.75 ± 0.06 and 1.39 ± 0.05, respectively), indicating that PM2. 5 ∕ PM10 mass ratios and Å(450∕700) can be used as tracers to distinguish aged LRT haze and Asian dust under the Asian continental outflow.