Variability Of Aerosol Optical Properties Research Articles

Temporal and spatial variations of aerosol optical properties over the Korean peninsula during KORUS-AQ

We investigated the temporal and spatial variations of aerosol optical properties over the Korean peninsula during the KORUS-AQ (KORea–United States Air Quality) experiment with ground-based aerosol optical properties measured by remote and in-situ techniques. On the ground, AErosol RObotic NETwork (AERONET) and ground-level particulate matter (PM) concentration from air quality monitoring stations were used. From the NASA DC-8 research aircraft, the airborne Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research instrument (4STAR), an aerosol mass spectrometer (AMS), and a single particle soot photometer (SP2) provided aerosol information. Average hourly fine- and coarse-mode aerosol optical depth (AOD) and fine mode fraction (FMF), were divided into four clusters (background, Seoul Metropolitan Area (SMA), southwest, and east) representing different temporal/spatial variations; the results of those clusters were similar to the clustering results using PM from air quality monitoring stations. The downwind region of SMA was dominant by light-scattering fine-mode aerosols likely due to secondary aerosol formation with high fine-mode AOD and single scattering albedo compared to other regions, even Seoul. The fine-mode aerosols were more spatially homogeneous than coarse-mode aerosols, especially in the west-to-east direction, because fine-mode aerosols are usually transported on a regional scale by westerlies rather than emitted from local emission sources. However, the aerosol size distribution was spatially more homogeneous because of a consistent contribution of fine- and coarse-mode AOD to total AOD regardless of direction between the AERONET sites. During high-aerosol loading episodes, the temporal and spatial variations of aerosol optical properties were similar to those derived from 4STAR and ground-level PM concentrations, providing detailed information on aerosol behavior and characteristics. Using missed-approach flight segments (touchdown and take-off without a full-stop), investigation of diurnal variations over the SMA revealed a significant increase in AOD and Angstrom exponent (AE) in the afternoon compared to morning and noon, especially in the downwind region, because of more active secondary formation resulting from advected and/or emitted local pollutants and precursors. The diurnal variation of PM1 in the downwind region was similar to that of AOD; it was mainly increased during the day by secondary organic aerosols and ammonium nitrate due to large amounts of isoprene and meteorological conditions that supported secondary aerosol formation. Ammonium sulfate also partially led to increasing the PM1, but its behavior was unclear, because RH decreased during the day, which would imply the reduced aqueous-phase oxidation (the major pathway for sulfate production). Compared to the downwind region, ammonium nitrate and refractory black carbon decreased in Seoul because of a slightly decreased traffic volume, dissociation of ammonium nitrate, and increased boundary layer height according to meteorological conditions in the afternoon. The results of this study provide detailed information on aerosol behavior given the synergy of the various measurement platforms used. Along with the evidence of active photochemical reactions taking place in the downwind region, such data will be useful in formulating policies that improve air quality in Korea.

Study of aerosol optical properties at different tourist places of Nepal

The comparative study of aerosol optical properties at different tourist places of Nepal has been performed. Langtang BC, Lumbini, Pokhara, Kathmandu-bode, EVK2-CNR, Jomsom and Kyanjin_Gompa were the places chosen for observation. We have analyzed the monthly and seasonal variation of aerosol optical properties for a different year of the above-mentioned places. AOD was found to be maximum in spring due to vegetation fire and land clearing for crop cultivation and, then in winter due to biomass burning, heating needs, pollution from bricks kilns, factories, and vehicles that contribute to winter haze. It consequently decreases in summer and was found to be minimum in autumn as summer constituent both dry and wet days and autumn starts with the ending of monsoon. But it was quite different in the case of Pokhara where it was minimum in summer than in autumn as Pokhara is the only city where maximum rainfall occurs in summer. We have also studied the relation between AOD and the corresponding wavelength. It was acclaimed that the AOD of shorter wavelength is more than the longer one which is because of the angstrom exponent. The relation between AOD and precipitated water has been observed and noticed one to one correspondence except July and August. The cross-correlation between these two factors found to be very high indicating a time lag of approximately 2 months with the presence of aerosol on cloud condensation nuclei (CCN).
 BIBECHANA 18 (2021) 170-183

Long-term variation in aerosol optical properties and their climatic implications over major cities of Pakistan

The present study investigates long-term variation in aerosol optical properties (AOP) and their associated climatic implications over selected cities of Chitral, Gwadar, Karachi, Lahore, Peshawar and Quetta in Pakistan for the period 2005–2018. For this purpose, aerosol optical depth (AOD) and aerosol index (AI) are retrieved from Moderate Resolution Imaging Spectroradiometer (MODIS) and Ozone Monitoring Instrument (OMI). Results revealed annual increasing trend of AOD with maximum values in summer during the study period over all study regions, except for Chitral. Similar annual trend was observed for AI but with minimum values in summer. Further, temperature and relative humidity (RH) showed significant relationships with AOD along with evidences of precipitation influences. In addition, the trajectory analysis of Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) Model confirmed the arrival of both short and long-range air masses to the receptor sites. Similarly, the direct aerosol radiative forcing (DARF) and direct aerosol radiative forcing efficiency (DARFE) were calculated using Clouds and the Earth's Radiant Energy System (CERES) data. The multiyear mean monthly atmospheric DARF values of 8.80, 16.32, 10.74, 21.64, 9.10 and 10.94 W/m2 were observed over Chitral, Gwadar, Karachi, Lahore, Peshawar and Quetta, respectively. Consequently, the maximum heating rate (HR) of 0.48 K/day (Chitral), 0.93 K/day (Gwadar), 0.51 K/day (Karachi), 1.23 K/day (Lahore), 0.44 K/day (Peshawar) and 0.56 K/day (Quetta) showed a net warming effect during 2005–2018. These results can give an insight into aerosol concentration and can form the basis for aerosol-induced climatic implications in the study area.

Long-term (2008–2017) analysis of atmospheric composite aerosol and black carbon radiative forcing over a semi-arid region in southern India: Model results and ground measurement

To achieve an in-depth understanding of radiative forcing due to aerosols is a crucial challenge for climate change studies. The first-ever long-term measurement of direct shortwave composite and black carbon aerosol radiative properties over a semi-arid region, Anantapur, in southern India is presented. Long-term variations in Aerosol Optical Depth (AOD) and Black Carbon (BC) mass concentration from December 2007 to November 2017 are discussed with specific emphasis on intra-seasonal variation in aerosol optical properties, meteorology, transport pathways, and their implications for direct short wave radiative forcing over Anantapur. The intra-seasonal mean AOD showed strong seasonal dependence with the highest (0.47 ± 0.03) during summer and lowest (0.28 ± 0.03) during the monsoon. Meanwhile, the intra-seasonal mean (±σ) BC mass concentration was about 3.57 ± 0.45, 2.60 ± 0.58, 1.22 ± 0.18 and 2.24 ± 0.28 μg m−3 during winter, summer, monsoon and post-monsoon respectively. Furthermore, there is an obvious temporal variation in intra-seasonal BC mass concentration during the dry season (winter and summer). To be more specific, the intra-seasonal mean (±σ) BC mass concentration before 2012 (after 2012) during the dry season was about 3.37 ± 0.7 μg m−3 (2.80 ± 0.58 μg m−3), respectively. Concentration weighted trajectory analyses (CWT) revealed that the air masses originated from the continental and polluted environments located in the central and northern parts of India (except monsoon), in regulating BC mass concentration over measurement location. Further, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) derived aerosol vertical extinction profiles (532 nm) showed that majority aerosols (>250 Mm−1) are confined within 2 km from the surface during winter while in summer particles are distributed throughout the profile (~6 km) with extinction coefficient varying between 200 and 250 Mm−1. The Santa Barbara Discrete Ordinate Radiative Transfer (SBDART) model estimated intra-seasonal mean direct shortwave composite aerosol radiative forcing (DARF) in the atmosphere (ATM) was about 31.13 ± 3.36, 34.82 ± 3.89, 17.10 ± 1.15, and 17.44 ± 1.81 Wm-2 during winter, summer, monsoon and post-monsoon, respectively. The positive signs of ATM forcing in all seasons indicate a warming of the atmosphere, and the corresponding heating rate was around a factor of two higher during the dry season (0.92 ± 0.12 Kday−1) than the wet season (monsoon and post-monsoon) (0.49 ± 0.04 Kday−1). The intra-seasonal mean BC forcing in ATM before 2012 (After 2012) during the dry season was about 24.14 ± 2.85Wm-2(20.09 ± 2.59Wm-2), respectively. The contribution of BC alone to the composite forcing during the study period over the station was ~68%. These findings would be helpful for regional climate studies and making air pollution control policy over the region.

Long-term Variability of Aerosol Optical Properties at Mauna Loa

ABSTRACT We investigated the variability of the aerosol scattering (σsp; 1974–2015) and absorption (σap; 2000–2015) coefficients at the Mauna Loa Observatory using surface in situ measurements. Although σsp decreased during the morning (1.85 ± 3.43 Mm–1 at 550 nm, 8–11 local standard time [LST]), it increased during the afternoon (3.72 ± 7.63 Mm–1 at 550 nm, 14–17 LST) due to the development of thermally induced boundary layer winds. No distinct diurnal variation was observed in σap. The obvious increase in σsp and σap during the spring under free troposphere conditions (8–11 LST) is attributed to long-range-transported aerosols from Asia, especially dust and pollution aerosols from Northeast Asia and biomass burning aerosols from Southeast Asia. Accordingly, σsp increased from 1974 till 2015 (at 1.89% year–1), whereas no significant trend was noted for either σsp or σap from 2000 till 2015. An increasing trend for σsp prevailed in air masses originating in Northeast Asia (+0.51 Mm–1 decade–1).

Interdecadal variation in aerosol optical properties and their relationships to meteorological parameters over northeast China from 1980 to 2017

Northeast China has undergone rapid urbanisation with increased anthropogenic emissions, and the types and absorption properties of aerosols may affect regional climate change. MERRA-2 (Modern-Era Retrospective analysis for Research and Applications, version 2) distributions of aerosol optical depth (AOD), Ångström exponent (AE), and absorption aerosol optical depth (AAOD) from 1980 to 2017 was studied to estimate the climatology of aerosol optical properties over Northeast China. The highest AOD and AAOD occurred in Liaoning Province range from 0.3 to 0.4 and 0.02–0.03, respectively. The spacial distribution of black carbon (BC) AOD was similar to AAOD with maximum value in Liaoning province about 0.04 related to the emission sources and human activities. The seasonal interdecadal distribution indicated larger dust (DU) AOD in Liaoning (0.12) and organic carbon (OC) AOD in Heilongjiang (0.18). The contribution of SO4 to total AOD was significant in autumn and winter, and BC particles contributed 70% to total AAOD in all seasons. The decadal change in AOD was positive for 2000–2009 (0.2/decadal) due to the increased dust events happening in spring. The positive correlation between AOD and relative humidity (RH) at surface was about 0.4–0.6; the negative correlation between AOD and surface wind speed (WS) (−0.6), planetary boundary layer height (PBLH) (−0.2 to −0.6), sea level pressure (SLP) (−0.2) was found over the study period. This study’s findings enable more comprehensive understanding of the distribution of aerosols optical properties and regional climatology in Northeast China.

Seasonal variation in particle contribution and aerosol types in Shanghai based on satellite data from MODIS and CALIOP

Although the concentration of atmospheric particulate matter in Shanghai has declined in recent years, aerosols remain one of the major pollutants affecting air quality. Herein, spatio-seasonal variation in aerosol optical properties and aerosol types were studied over a 10-year period (2006–2015) in Shanghai, China, using satellite data from Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP). The average aerosol optical depth values for central urban and suburban areas of Shanghai were between 0.9 and 1.0. Clear seasonal variation in aerosol concentrations occurred, causing strongest attenuation in summer and weakest attenuation in autumn. Polluted dust, polluted continental (urban/industrial) and smoke aerosols were the main aerosol types. Desert dust aerosols occurred in the Shanghai area at higher altitudes (greater than 3 km) in spring, related to dusty weather in the north; while in winter, smoke aerosols occurred at high altitudes, related to haze pollution in the north. The aerosols detected in autumn were mainly from local sources, comprising polluted dust, polluted continental, and smoke aerosols. Aerosols in Shanghai clearly reflect both local and regional sources at different times.

Aerosol properties and their influences on low warm clouds during the Two-Column Aerosol Project

Abstract. Twelve months of measurements collected during the Two-Column Aerosol Project field campaign at Cape Cod, Massachusetts, which started in the summer of 2012, were used to investigate aerosol physical, optical, and chemical properties and their influences on the dependence of cloud development on thermodynamic (i.e., lower tropospheric stability, LTS) conditions. Relationships between aerosol loading and cloud properties under different dominant air-mass conditions and the magnitude of the first indirect effect (FIE), as well as the sensitivity of the FIE to different aerosol compositions, are examined. The seasonal variation in aerosol number concentration (Na) was not consistent with variations in aerosol optical properties (i.e., scattering coefficient, σs, and columnar aerosol optical depth). Organics were found to have a large contribution to small particle sizes. This contribution decreased during the particle growth period. Under low-aerosol-loading conditions, the liquid water path (LWP) and droplet effective radius (DER) significantly increased with increasing LTS, but, under high-aerosol-loading conditions, LWP and DER changed little, indicating that aerosols significantly weakened the dependence of cloud development on LTS. The reduction in LWP and DER from low- to high-aerosol-loading conditions was greater in stable environments, suggesting that clouds under stable conditions are more susceptible to aerosol perturbations than those under more unstable conditions. High aerosol loading weakened the increase in DER as LWP increased and strengthened the increase in cloud optical depth (COD) with increasing LWP, resulting in changes in the interdependence of cloud properties. Under both continental and marine air-mass conditions, high aerosol loading can significantly increase COD and decrease LWP and DER, narrowing their distributions. Magnitudes of the FIE estimated under continental air-mass conditions ranged from 0.07±0.03 to 0.26±0.09 with a mean value of 0.16±0.03 and showed an increasing trend as LWP increased. The calculated FIE values for aerosols with a low fraction of organics are greater than those for aerosols with a high fraction of organics. This implies that clouds over regions dominated by aerosol particles containing mostly inorganics are more susceptible to aerosol perturbations, resulting in larger climate forcing, than clouds over regions dominated by organic aerosol particles.

Modelling aerosol optical properties over urban environment (New Delhi) constrained with balloon observation

Vertical variation in aerosol optical properties [e.g. Single Scattering Albedo (SSA) and aerosol extinction coefficient] over a polluted environment is extremely important for better understanding of columnar radiative characteristics. The present case study over a typical polluted environment (New Delhi) discusses the vertical profile (ground to 700 m) of modelled optical properties of atmospheric particles at different altitudes. Here, we used the aerosol physico-chemical data generated in the tethered balloon-based observation conducted at CSIR-NPL, New Delhi (28° 38′ 10″ N, 77° 10′ 17″ E) from 21st −27th February 2014. Based on the microscopic observations of individual particles, we developed the aerosol model shapes (coated spheres) for simulating their optical properties. Total three cases were considered for simulating the aerosol optics at varying altitude; Case A: External mixture of coated dust and coated sulfate particles; Case B: External mixture of coated dust, coated sulfate, coated OC (Organic Carbon) and coated EC (Elemental Carbon) (with assumption that 6% EC at ground level); Case C: External mixture of coated dust, coated sulfate, coated OC and coated EC (with assumption that 10% EC at ground level). At 550 nm wavelength, the value of SSA has been found to be highest (i.e. 0.985) at 200 m altitude for Case A while Case B (i.e. 0.9523) and Case C (i.e. 0.9291) show highest values at 500 m altitude. SSA was found to be maximum at 500 m altitude for both Case B and Case C due to the presence of lowest graphitic counts at that particular altitude. Case B and Case C exhibit similar pattern but differ in magnitude, this is due to two EC extremities at ground level i.e. minima (6%) and maxima (10%). The percentage deviation in SSA from ground level to 700 m was found to be highest for Case C (i.e. 5.95%) followed by Case B (i.e. 4.19%) and Case A (i.e. 1.4%). Modelled aerosol optical properties within boundary layer may improve our understanding about the thermodynamics of lower atmosphere.

Long-term spatiotemporal variations of aerosol optical depth over Yellow and Bohai Sea.

In this study, MODerate resolution Imaging Spectroradiometer (MODIS) Collection 6.1 (C6.1) level-2 Dark Target (DT) Aerosol Optical Depth (AOD) observations at 550nm (AOD550) for the highest quality flag assurance (QA = 3) were obtained to analyze spatiotemporal variations of aerosol optical properties over the Yellow and the Bohai Sea from 2002 to 2017. Spectral AOD observations at 470nm (AOD470) and 660nm (AOD660) were obtained to calculate Angstrom Exponent (AE470-660) and classify the aerosol types including clean continental (CC), clean maritime (CM) biomass and urban industrial (BUI), dust (D), and mixed (MXD) aerosol types. Results showed a very distinct spatial pattern of AOD distribution over the Bohai Sea which looks suspicious, i.e., high aerosol loadings (AOD > 0.8) throughout the entire time period, whereas relative low AOD distribution was observed over the adjacent land pixels especially in autumn and winter, which suggested that the DT algorithm might be influenced by a large number of sediments located in the Bohai Sea. Significant differences in spatial distributions were found in different seasons in terms of area coverage as a maximum number of pixels were available during autumn, and regional high and low aerosol loadings were observed during autumn and summer, respectively. Trend analysis from 2002 to 2017 showed that AOD was increased up to 0.04 over the Bohai Sea and decreased up to 0.04 over the Yellow Sea, and this trend varies from month to month. Aerosol classification showed significant contributions of BUI and CC over the region, and contributions of CM, DUST, and MXD aerosols over the Yellow Sea were relatively high compared to the Bohai Sea.

Variability of Aerosol Optical Properties Observed at a Polluted Marine (Gosan, Korea) and a High-altitude Mountain (Lulin, Taiwan) Site in the Asian Continental Outflow

We investigated the variability of in-situ and columnar aerosol optical properties (AOPs) at two regional background sites in the Asian continental outflow from 2012 to 2014. The monthly variability of the AOPs at each site is described in terms of its relationship with regional-scale atmospheric circulation patterns and the resulting changes in air mass sources. The median aerosol scattering and absorption coefficient values for sub-10 µm particles (σsp10 μm and σap10 μm) were larger at the polluted marine site, Gosan (GSN; σsp10 μm: 59.94 Mm–1, σap10 μm: 4.73 Mm–1), than at the high-altitude mountain site, Lulin (LLN; σsp10 μm: 17.07 Mm–1, σap10 μm: 1.72 Mm–1). Elevated σsp10 μm and σap10 μm at GSN in May and June can be explained by the accumulation of locally emitted aerosols along with long-range transported aerosols during conditions of stagnant synoptic patterns, enhanced particle formation and subsequent growth. The significant peaks of σsp10 μm and σap10 μm, with median values of 50.76 Mm–1 and 5.92 Mm–1, at LLN during March and April are attributable to biomass burning aerosols transported from northern Indochina and southern China. The LLN site was mostly influenced by clean free troposphere air and maritime air masses during the other months, showing medians of 14.65 ± 19.81 Mm–1 and 1.46 ± 1.86 Mm–1 for σsp10 μm and σap10 μm, respectively. Lower median sub-micron to sub-10 µm ratios for the aerosol scattering and absorption coefficients at GSN (0.60 and 0.81, respectively) than at LLN (0.81 and 0.91, respectively) are indicative of the larger proportion of coarse aerosols, such as sea salt and dust, at GSN. The single-scattering albedo for sub-10 µm particles showed similar median values at both sites (GSN: 0.93 ± 0.02, LLN: 0.91 ± 0.03).

Impact of Biomass Burning in South and Southeast Asia on Background Aerosol in Southwest China

ABSTRACT Biomass burning (BB) in Southeast Asia is particularly pronounced during the dry season. However, the complex topography and long-range transport inherent to Southeast Asia have limited local research on pollution resulting from BB. In this study, the monthly variation in aerosol optical properties at six sites in Southeast Asia (Chiang Mai, Mukdahan, Bac-Lieu, Penang, Singapore, and Bandung) and the fire-point distribution have been analyzed in detail. The Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model was used to simulate the 72-hour back-trajectory from the Shangri-La atmospheric background station in Yunnan Province, China. Our results showed that BB was more common on the Indochinese Peninsula from March to May, whereas it was more common on the Malay Archipelago from August to October due to the latitudinal difference and crop harvest season. Significant BB activity on the Indochinese Peninsula in March resulted in a high surge in extinction (AODt440nm = 1.32 ± 0.69, AODf440nm = 1.24 ± 0.59) by particles with a smaller diameter (AE = 1.68 ± 0.13) in Chiang Mai. Mapping the long-range transport of BB aerosols reveals that Shangri-La’s pollution was primarily affected by emissions from northern-central India (accounting for 45.2%), and Bangladesh and northern Myanmar (accounting for 38.7%), which indicates that the aerosol pollution on the Yunnan-Guizhou Plateau in springtime could have originated on the southern periphery of the Tibetan Plateau. The results also indicate that BB emission in Southeast Asia had a limited impact on pollution in Southwest China but a relatively large effect on local areas. This study is the first to analyze the trend of aerosols produced from BB in Southeast Asia via ground-based observation, which deepens our understanding of the potential effects of BB aerosols transported long-range from outside Southwest China.

Contrasting variation in aerosol optical properties during dust episodes in the Middle East and Southwest Asia: Model results and ground measurement

Dust storms deteriorated air quality over the Gulf Region, Iraq, Iran, and Pakistan during the last decade. The purpose of this study is to investigate the changes in aerosol optical and radiative properties during a dust episode over the various locations in the Middle East and Southwest Asia using data from the MODerate resolution Imaging Spectroradiometer (MODIS) and the Aerosol Robotic Network (AERONET) during March, 2012. Maximum aerosol optical depth (AOD) values were found to be 2.18, 1.30, 4.33 and 1.80 over Lahore, Kanpur, Kaust, and Mezaira, respectively. The Volume Size Distributions, Single Scattering Albedo, Refractive Index, and Asymmetry parameter indicated that coarse mode aerosols were predominant relative to fine mode aerosols during the dust event. The average shortwave aerosol radiative forcing (ARF) values at the earth’s surface were found to be -96±45 W m-2, -86±22 W m-2, -77±51 W m-2, and -75±40 W m-2, over Lahore, Kanpur, Kaust and Mezaira, respectively. Likewise, the averaged ARF values over Lahore, Kanpur, Kaust and Mezaira at the top of the atmosphere (TOA) were found to be -45±25 W m-2, -27±9 W m-2, -41±29 W m-2, and -75±40 W m-2, respectively. The large differences between surface and TOA forcing produced significant heating within the atmosphere.

Two-Way Relationship between Aerosols and Fog: A Case Study at IGI Airport, New Delhi

ABSTRACT The frequency and intensity of fog episodes during the winter season has been increasing during the past decade over the megacity of Delhi due to the high pollution load. The role of atmospheric aerosols is very important in the life cycle of fog in the urban areas. This paper presents the results on the variation in aerosol optical properties (scattering and absorption coefficients) and the black carbon (BC) mass concentration during the foggy period in winter (December 2015 to February 2016) at the Indira Gandhi International (IGI) Airport, New Delhi. The interaction between scattering and absorbing aerosols, and fog before, during and after the foggy period has been studied as a typical case. The BC mass concentration, along with the aerosol scattering and absorption coefficients, increased before and during the initial phase of the dense foggy period. However, there was a steep decrease in them after the sustained period of dense fog, which suggests possible scavenging by fog droplets. Also, it was observed that the decrease in ambient temperature and depression temperature (DT) and the increase in relative humidity (RH) played a major role in sustaining the dense fog despite the reduction in aerosol load. The single-scattering albedo (SSA) decreased during the dense fog due to a higher reduction of the scattering aerosols than the absorbing ones. Both the scattering and the absorption coefficients showed a significant correlation with cloud condensation nuclei (CCN).

중남미 지역 에어로졸 광학특성의 시공간 변화

중남미 지역 10개 지점 AERONET (AErosol Robotic NETwork)의 직달일사 AOD(aerosol optical depth) 자료를 이용하여 에어로졸 광학특성의 시공간 분포를 분석하였다. Ward의 계층적 군집분석을 적용하여 10개 지점을 안데스와 아마존 그리고 기타 군집으로 구분하였다. 아마존과 안데스 군집에서는 건기에 발생하는 생체 소각의 영향으로 미세입자 AOD가 9월에 가장 높았으며, 아마존 군집은 서아프리카에서 이송되는 광물먼지의 영향으로 연중 조대입자 AOD가 다른 군집에 비해 높았다. 우기에는 강수의 효과로 미세입자 및 조대입자 AOD가 감소하였다. 10개 지점 모두 미세입자 AOD가 높았으며, 지리적 특성에 따라 조대입자의 기여도가 다양하였다. 각 측정지점 간 상관관계 분석 결과, 아마존과 안데스에 위치한 네 지점은 미세입자의 영향이 중요하였다. 기타 군집은 해안에 인접하여 AOD가 낮았고 측정소 간 상관성도 작았다.

Retrieval of Aerosol Components Using Multi-Wavelength Mie-Raman Lidar and Comparison with Ground Aerosol Sampling

We verified an algorithm using multi-wavelength Mie-Raman lidar (MMRL) observations to retrieve four aerosol components (black carbon (BC), sea salt (SS), air pollution (AP), and mineral dust (DS)) with in-situ aerosol measurements, and determined the seasonal variation of aerosol components in Fukuoka, in the western region of Japan. PM2.5, PM10, and mass concentrations of BC and SS components are derived from in-situ measurements. MMRL provides the aerosol extinction coefficient (α), particle linear depolarization ratio (δ), backscatter coefficient (β), and lidar ratio (S) at 355 and 532 nm, and the attenuated backscatter coefficient (βatt) at 1064 nm. We retrieved vertical distributions of extinction coefficients at 532 nm for four aerosol components (BC, SS, AP, and DS) using 1α532 + 1β532 + 1βatt,1064 + 1δ532 data of MMRL. The retrieved extinction coefficients of the four aerosol components at 532 nm were converted to mass concentrations using the theoretical computed conversion factor assuming the prescribed size distribution, particle shape, and refractive index for each aerosol component. MMRL and in-situ measurements confirmed that seasonal variation of aerosol optical properties was affected by internal/external mixing of various aerosol components, in addition to hygroscopic growth of water-soluble aerosols. MMRL overestimates BC mass concentration compared to in-situ observation using the pure BC model. This overestimation was reduced drastically by introducing the internal mixture model of BC and water-soluble substances (Core-Gray Shell (CGS) model). This result suggests that considering the internal mixture of BC and water-soluble substances is essential for evaluating BC mass concentration in this area. Systematic overestimation of BC mass concentration was found during summer, even when we applied the CGS model. The observational facts based on in-situ and MMRL measurements suggested that misclassification of AP as CGS particles was due to underestimation of relative humidity (RH) by the numerical model in lidar analysis, as well as mismatching of the optical models of AP and CGS assumed in the retrieval with aerosol properties in the actual atmosphere. The time variation of lidar-derived SS was generally consistent with in-situ measurement; however, we found some overestimation of SS during dust events. The cause of this SS overestimation is mainly due to misclassifying internally mixing DS as SS, implying that to consider internal mixing between DS and water-soluble substances leads to better estimation. The time-variations of PM2.5 and PM10 generally showed good agreement with in-situ measurement although lidar-derived PM2.5 and PM10 overestimated in dust events.

Primary sources control the variability of aerosol optical properties in the Antarctic Peninsula

Aerosol particle optical properties were measured continuously between years 2013–2015 at the Marambio station in the Antarctic Peninsula. Annual cycles of particle scattering and absorption were studied and explained using measured particle chemical composition and the analysis of air mass transport patterns. The particle scattering was found elevated during the winter but the absorption did not show any clear annual cycle. The aerosol single scattering albedo at nm was on average 0.96 0.10, with a median of 0.99. Aerosol scattering Ångström exponent increased during summer, indicating an increasing fraction of fine mode particles. The aerosol was mainly composed of sea salt, sulphate and crustal soil minerals, and most of the particle mass were in the coarse mode. Both the particle absorption and scattering were increased during high wind speeds. This was explained by the dominance of the primary marine sea-spray and wind-blown soil dust sources. In contrast, the back-trajectory analysis suggested that long-range transport has only a minor role as a source of absorbing aerosol at the peninsula.

Monthly and seasonal variations of aerosol optical properties and direct radiative forcing over Zanjan, Iran

Aerosol optical properties and radiative forcing over Zanjan in northwest of Iran has been analyzed during 2010–2013. The aerosol optical and radiative properties are less studied over Zanjan, and therefore, require a careful and in depth analysis. The optical properties like Aerosol Optical Depth (AOD), Ångström Exponent (AE), ASYmmetry parameter (ASY), Single Scattering Albedo (SSA), and Aerosol Volume Size Distribution (AVSD) have been evaluated using the ground-based AErosol RObotic NETwork (AERONET) data. Higher AOD while relatively lower AE were observed in the spring and summer, which showed the presence of coarse mode particles in these seasons. An obvious increase of coarse mode particles in AVSD distribution, as well as a higher value of SSA represented considerable addition of coarse mode particles like dust into the atmosphere of Zanjan in these two seasons. Increase in AE, while a decrease in AOD was detected in the winter and fall. The presence of fine particles indicates the dominance of particles like urban-industrial aerosols from local sources especially in the winter. The Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model was utilized to calculate the Aerosol Radiative Forcing (ARF) at the Top of the Atmosphere (TOA), earth's surface and within the atmosphere. The annual averaged ARF values were −13.47 W m−2 and −36.1 W m−2 at the TOA and earth's surface, respectively, which indicate a significant cooling effect. Likewise, the ARF efficiencies at the TOA and earth's surface were −65.08 W m−2 and −158.43 W m−2, respectively. The annual mean atmospheric ARF and heating rate within the atmosphere were 22.63 W m−2 and 0.27 Kday−1 respectively, represented the warming effect within the atmosphere. Finally, a good agreement was found between AERONET retrieved ARF and SBDART simulated ARF.

Contrast in column-integrated aerosol optical properties during heating and non-heating seasons at Urumqi — Its causes and implications

Aerosol optical properties were retrieved from two years' worth of Sunphotometer measurements at Urumqi, an urban station in western China. Distinct seasonal variations of aerosol optical properties were revealed. During the heating season, mean aerosol optical depth at 550nm (τa), Angstrom exponent calculated from aerosol optical depth at wavelength of 440 and 870nm (α) as well as PM2.5 concentration were 0.58±0.33, 1.11±0.34 and 79.5±69.6μgm−3, respectively, which contrasted their counterparts during the non-heating season of 0.32±0.22, 0.79±0.26, and 35.0±20.1μgm−3. Seasonal variations of τa and PM2.5 at Urumqi contrasted with corresponding values in eastern China. Enhancement of τa was associated with fine mode radius (rf) exceeding 0.15μm. Relative humidity frequently exceeded 80% during the heating season, which probably resulted in rf>0.15 as a result of the hygroscopic growth under the humid environment. rf was larger than value assigned to the fine-mode dominated aerosol models used in the dark-target algorithm of the Moderate Resolution Spectroradiometer (MODIS). Annual mean single scattering albedo at 550nm (ω) was 0.87 that was close to the value assigned to the absorption aerosol model in the MODIS algorithm. ω increased as τa increased, probably as a result of the growth of aerosol size. ω of dust aerosols at Urumqi was slightly lower than that in dust source and downwind regions. Substantial differences in aerosol optical and physical properties and their seasonal variation between western and eastern China require maintaining long-term ground based remote sensing aerosols, which would be expected to play an important role in studying aerosol's effects on weather, climate and atmospheric environment.

Observations of aerosol optical properties at a coastal site in Hong Kong, South China

Abstract. Temporal variations in aerosol optical properties were investigated at a coastal station in Hong Kong based on the field observation from February 2012 to February 2015. At 550 nm, the average light-scattering (151 ± 100 Mm−1) and absorption coefficients (8.3 ± 6.1 Mm−1) were lower than most of other rural sites in eastern China, while the single-scattering albedo (SSA = 0.93 ± 0.05) was relatively higher compared with other rural sites in the Pearl River Delta (PRD) region. Correlation analysis confirmed that the darkest aerosols were smaller in particle size and showed strong scattering wavelength dependencies, indicating possible sources from fresh emissions close to the measurement site. Particles with Dp of 200–800 nm were less in number, yet contributed the most to the light-scattering coefficients among submicron particles. In summer, both ΔBC / ΔCO and SO2 / BC peaked, indicating the impact of nearby combustion sources on this site. Multi-year backward Lagrangian particle dispersion modeling (LPDM) and potential source contribution (PSC) analysis revealed that these particles were mainly from the air masses that moved southward over Shenzhen and urban Hong Kong and the polluted marine air containing ship exhausts. These fresh emission sources led to low SSA during summer months. For winter and autumn months, contrarily, ΔBC / ΔCO and SO2 / BC were relatively low, showing that the site was more under influence of well-mixed air masses from long-range transport including from South China, East China coastal regions, and aged aerosol transported over the Pacific Ocean and Taiwan, causing stronger abilities of light extinction and larger variability of aerosol optical properties. Our results showed that ship emissions in the vicinity of Hong Kong could have visible impact on the light-scattering and absorption abilities as well as SSA at Hok Tsui.