Variability Of Aerosol Optical Properties Research Articles

Evaluation of Nocturnal Aerosol Optical Depth Determining From a Lunar Photometry in Lanzhou of Northwest China

AbstractA Cimel Sun‐sky‐lunar photometer (CE318‐T) is designed to perform daytime and nighttime photometric measurements and calculate diurnal cycle of aerosol optical depth (AOD). Nevertheless, the determination of nocturnal AOD from CE318‐T requires a precise knowledge of extraterrestrial lunar irradiance, which significantly changes with moon's phase angle (MPA) and lunar libration in a single night. This study evaluated the 1‐year nocturnal AODs at Lanzhou by using three different methods, which were validated by collocated measurements of DIAL Lidar (as a reference) and Cimel software (as a proxy). The results indicated that three independent approaches could implement a similar performance to compute nocturnal AOD near full moon phase (i.e., MPA = 0°) under moderate aerosol loading. The spectral AOD values at nighttime calculated by ROLO Lunar Langley (Robotic Lunar Observatory model) and Sun‐moon Gain Factor (SMGF) methods are significantly underestimated under low moon's illumination or high MPA (MPA < −47° or MPA > 47°) and distinctly dependent on MPA. The RIMO correction factor (RCF) (ROLO Implementation for Moon photometry Observation correction factor) method could compensate the underestimated extraterrestrial lunar irradiances of ROLO model for about 6.76%–9.78%, and thus greatly improve the calculation accuracy of nighttime AOD. The day/night coherence transition test has demonstrated that we would obtain a good diurnal variation of AODs at Lanzhou after RCF correction. The overall averages of nocturnal AOD440nm differences between Cimel software and ROLO model and SMGF method are 0.064 ± 0.024 and 0.052 ± 0.022, respectively, while the corresponding difference of RCF is less than 0.021 ± 0.014 for all wavelengths, falling within uncertainty range of AERONET AOD products (∼±0.02). The diurnal variations of AODs determined from RCF method agree well with synchronous results of DIAL Lidar, with total mean AOD532nm differences of 0.038 ± 0.024 and 0.023 ± 0.017 in daytime and nighttime, respectively. The spectral AODs computed from RCF method are well consistent with Cimel software, although there are some discrepancies under low AOD cases (AOD440nm < 0.30), and the overall average of AOD440nm differences are less than −0.0053 ± 0.002 and −0.0185 ± 0.013 in daytime and nighttime, respectively. Our results confirmed that the CE318‐T photometer can be reasonably calculated nighttime AOD and Ångström exponent (AE440–870nm) at urban Lanzhou by using three independent methods, although the former two need to be greatly improved under low moon's illumination. The RCF method was proved to reliably calculate nocturnal AOD from moonlight irradiance, which didn't rely on MPA. A more accurate lunar irradiance model needs to be developed to improve the underestimation of current ROLO model. Long‐term climatological information of nocturnal AOD is crucial for comprehensively characterizing the diurnal variations of aerosol optical properties and atmospheric boundary layer structure during the winter at typical northern city of China, which deserves to be further investigated in the future.

Construction of Aerosol Model and Atmospheric Correction in the Coastal Area of Shandong Peninsula

Applying standard aerosol models for atmospheric correction in nearshore coastal waters introduces significant uncertainties due to their inability to accurately represent aerosol characteristics in these regions. To improve the accuracy of remote sensing reflectance (Rrs) products in the nearshore waters of the Shandong Peninsula, this study develops an aerosol model based on aerosol data collected from the Mu Ping site in the coastal area of the Shandong Peninsula, enabling tailored atmospheric correction for this specific region. Given the pronounced seasonal variations in aerosol optical properties, monthly aerosol models were developed. The monthly aerosol model is derived using the average values of aerosol microphysical properties. Compared to the standard aerosol model, this model is more effective in characterizing the absorption and scattering characteristics of aerosols in the study area. Corresponding lookup tables for the aerosol model were created and integrated into the NIR-SWIR atmospheric correction algorithm. According to the accuracy evaluation indexes of RMSD, MAE, and UPD, it can be found that the atmospheric correction results of the aerosol model established in this paper are better than those of the standard aerosol model, especially in the 547 nm band. It demonstrates that the new aerosol model outperforms the standard model in atmospheric correction performance. With the increasing availability of aerosol observational data, the aerosol model is expected to become more accurate and applicable to other satellite missions.

Integrating satellite and model data to explore spatial-temporal changes in aerosol optical properties and their meteorological relationships in northwest India

This study aims to analyze the temporal and spatial distribution of Aerosol Optical Properties across Northwest India using aerosol data from MODIS (Moderate Resolution Imaging Spectroradiometer) and OMI (Ozone Monitoring Instrument) sensors from 2003 to 2022. Therefore, this study investigated the decadal, interannual, and seasonal changes in aerosol optical properties, vegetation index, and meteorological parameters in the northwest Indian region (8 boxes). Using GIOVANNI (Goddard Earth Sciences Data and Information Services Center (GES DISC) Online Visualization and Analysis Infrastructure), we retrieved daily and monthly Aqua and Terra MODIS products of aerosol optical depth (AOD), Angstrom exponent (AE), normalized difference vegetation index (NDVI), and OMI aerosol index (AI) to examine the spatiotemporal variations by using statistical approaches. The results demonstrated that the decadal averages of aerosol properties showed values of AOD 0.35 (Aqua) and 0.34 (Terra) and AE 1.20 (Aqua) and 1.10 (Terra) with the highest levels during the post-monsoon. Notably, the mean interannual concentrations of AOD and NDVI consistently surpass 0.3, and AE and AI exceed 1 in most locations, underscoring the persistence of high aerosol loading. Also, the study revealed a negative decadal change in AOD of about −8.24 %, while AE, AI, and NDVI showed positive decadal changes of about 9.24 %, 15.09 %, and 12.67 %, respectively. In addition, aerosol optical properties and local meteorology strongly correlated (−0.8 to +0.8). Principal Component Analysis (PCA) identifies meteorological parameters as significant drivers, with the first three components explaining over 70 % of the variation in aerosol optical properties. The NOAA HYSPLIT trajectory model suggests that the long-distance dust transport from the Arabian Peninsula frequently penetrates Gujarat province and then to northwest India. The results contributed to air quality management strategies and provided valuable insights into regional climate and air quality with the influence of meteorology.

Variation of Aerosol Optical Properties over Cluj-Napoca, Romania, Based on 10 Years of AERONET Data and MODIS MAIAC AOD Product

Aerosols play an important role in Earth’s climate system, and thus long-time ground- based measurements of aerosol optical properties are useful in understanding this role. Ten years of quality-assured measurements between 2010 and 2020 are used to investigate the aerosol climatology in the Cluj-Napoca area, in North-Western Romania. In this study, we analyze the aerosol optical depth (AOD), single scattering albedo (SSA) and angstrom exponent obtained by the CIMEL sun photometer, part of the aerosol robotic network (AERONET), to extract the seasonality of aerosols in the region and investigate the aerosol climatology of the area. Higher aerosol loads are found during July and August. The angstrom exponent has the lowest values in April and May, and the highest in August. The classification of aerosols using AERONET data is performed to separate dust, biomass burning, polluted urban, marine and continental-dominant aerosol mixtures. In addition, the study presents the validation efforts of the Multi-Angle Implementation of Atmospheric Correction (MAIAC) dataset against AERONET AOD over a 10-year period.

Seasonal variation of aerosol optical properties in a coastal city of southeast China: Based on one year of measurements

Aerosols have a significant impact on both direct and indirect radiative effects and are considered to be one of the largest contributors to the uncertainty in global climate change assessment. In this study, continuous one-year-round in-situ observations of aerosol optical properties were conducted in the southeastern coastal city of Xiamen, China, and the effects of chemical composition on aerosol optical properties were analyzed to assess the environmental and climate effects of aerosols. The scattering coefficient (σsp), absorption coefficient (σap), single scattering albedo (SSA) showed significant seasonal variations. The σsp and σap showed obvious bimodal diurnal patterns, with peaks occurring in the morning peak and evening, while the diurnal patterns of SSA were reversed. The results of the chemical component-based estimation reconstruction of σsp illuminated that OM, NH4NO3, (NH4)2SO4 were the main contributors to the σsp. The concentration weighted trajectory (CWT) method was used to characterize the contributing sources of each chemical component affecting σsp. The main contributing source areas were elucidated and varied slightly with species and season. The wind dependence analysis reflected that σap was mainly influenced by local emissions, while σsp was affected by both local emissions and regional transport. The contribution sources of σsp and σap were investigated using potential source contribution function (PSCF) method. The contributing source of σsp and σap in Xiamen were clarified, and varied slightly with seasonal differences. This study revealed the aerosol optical properties in the southeastern coastal urban areas of China and provided a scientific basis for the estimation of the factors affecting climate change.

Study of aerosol optical properties in Lumbini, Nepal

The mixture of different sized particles (fine and coarse) with air composition forms aerosols. Increased economic activities, vehicles, and rapid urbanization made Lumbini one of the heavily polluted regions in Nepal. Data are extracted from AERONET websites between 2013 to 2019 with standard deviation. We are mainly focused on understanding variations in aerosol optical properties: aerosol optical depth (AOD), angstrom parameter (α and β), visibility, single-scattering albedo (SSA), refractive index (real and imaginary), and asymmetry parameter (AP) in the Lumbini region. The maximum value of AOD (675nm) in Lumbini occurred mostly during post-monsoon season (0.61 ± 0.38) whereas, the values of AOD were found to be lower during the monsoon season (0.18 ± 0.12). Most of the AOD values are found to be greater than 0.4, indicating the higher level of pollution in the study area. There is a positive correlation between perceptible water and AOD, maximum correlation (0.4) occurs at the lowest AOD (440nm) while the minimum (0.1) at the highest AOD (1020nm). The turbidity coefficient (β) has an adverse effect on visibility. The Visibility over Lumbini was found to be highest (20 km) during monsoon. Single-scattering albedo (SSA) accretions occur at wavelengths between 440 and 675 nm, but the pattern changes from 675 to 1020 nm. All parameters were found to be distinct and seasonal fluctuations among this station are mainly due to the different aerosols availability such as biomass burning, mixed aerosols, and anthropogenic aerosols over the Lumbini site.

Inversion and analysis of aerosol optical properties and lidar ratios based on sky-radiometer and Raman lidar measurements in Xi’an, China

The aerosol observations in Xi’an (34.25°N, 108.983°E), a typical urban site in Northwest China, were conducted using a sky-radiometer from January 2015 to March 2018. Multi-year variations of aerosol optical properties (AOPs) and lidar ratios (LRs) were simultaneously analyzed and calculated. In particular, LRs in 340 nm were compared and validated using the UV-Raman lidar (RL) measurements. During the study period, aerosol optical depth at 500 nm (AOD500) had significant seasonal variation, with a maximum value of 0.68 in winter and a minimum value of 0.59 in autumn. Ångström exponent (AE) exhibited different seasonal variation patterns, and the minimum (0.81) and maximum (1.06) values appeared in spring and summer, respectively. The spectral difference between AE400–675 and AE675–870 indicated that high AOD675 values (>1.0) were affected by accidental factors (e.g., dust weather in spring and winter) and the accumulation of fine particle aerosols across all seasons. The relationship between AOD500 and AE400–870 was used to distinguish different aerosol types. Overall, mixed aerosols (MX) accounted for the largest contribution (ranging from 40.14% in autumn to 69.9% in spring), followed by biomass-burning or urban/industrial aerosols (BB/UI) (with the smallest value of 19.9% in spring, and the largest value of 43.66% in winter). Single-scattering albedo (SSAs) experienced weak seasonal variation, with a minimum in winter and a maximum in spring. The seasonal aerosol volume size distributions (VSDs) generally exhibited the trimodal patterns. The particle radius (R) of less than 0.5 μm is considered as fine mode, the coarse mode is R greater than 2.5 μm, and the middle mode is located somewhere in between them. The real CRI were ∼1.41–1.43, with no significant difference among different seasons. Besides, the LRs derived by combining sky-radiometer with Mie-scattering theory changed greatly with weather from 49.95 ± 8.89 in summer to 63.95 ± 6.77 in autumn, which were validated by RL with the errors within a certain height range of less than 10%. We confirmed the feasibility of using the LR of UV band from sky-radiometer as a reference value for the Fernald or Klett method.

Long-term variation of aerosol optical properties associated with aerosol types over East Asia using AERONET and satellite (VIIRS, OMI) data (2012–2019)

We analyzed annual and seasonal frequency in aerosol type over an 8-year period (2012–2019) to identify aerosol parameter trends over four ground sites and country regions in Korea, China, and Japan by using the Aerosol Robotic Network (AERONET), and the satellite-based Visible Infrared Imaging Radiometer Suite (VIIRS) and Ozone Monitoring Instrument (OMI). Decreasing trends are shown for aerosol optical depth (AOD), Ångström exponent (AE), and fine mode fraction (FMF) in all countries. The decreasing trend in these data is considered to be due to a decrease in anthropogenic emissions. For the aerosol type frequency, decreases in the proportions of carbonaceous aerosols (CA) and non-absorbing aerosols (NA) were shown in the ground and satellite data, respectively. At most sites, the fractions of low AOD case (LOW) increased, whereas those of the Black and Brown Carbon (BC + BrC) category decreased. In Seoul, the fraction of LOW increased from 48.9% to 70.0%, and that of BC + BrC decreased continuously from 20.4% to 11.1% during 2012–2019. Beijing, on the other hand, showed decreasing LOW from 83.3% (2012) to 52.0% (2019), and that of BC + BrC increased significantly, from 2.4% to 26.2%. The satellite data showed that the percentage of LOW increased continuously, while that of NA aerosols decreased continuously in East Asia. A noticeable decrease in the fraction of CA was detected in China [21.5% (2013) to 11.2% (2019)]. In all countries, CA and NA aerosols had the greatest effect in winter and summer, respectively. We also detected significant differences between the fractions of NA and BC between the ground and satellite data. Changes in aerosol type and properties were observed concurrently in all ground and satellite data, and changes in aerosol type may explain the increasing and decreasing trends that we recorded for most parameters. Consistent results from both ground and satellite data suggest a steady decreasing in fine aerosol pollution in East Asia.

Variations in Aerosol Optical Properties over East Asian Dust Storm Source Regions and Their Climatic Factors during 2000–2021

The East Asian dust storms occur in western and northern China, and southern Mongolia every year, particularly in spring. In this study, we use satellite aerosol products to demonstrate the spatial and temporal variation in aerosol optical depth (AOD) from MODIS, and the absorbing aerosol index (AAI) from TOMS and OMI, over the main dust storm source regions (MDSR), and to investigate their relationship to vegetation coverage (NDVI), soil properties (surface soil moisture content and soil temperature 0–10 cm underground), and climatic factors (surface wind speed, air temperature at 2 m above the ground, and precipitation) in spring for the period of 2000–2021. Compared with dust storm occurrence frequency (DSF) observed at surface stations, MODIS AOD, TOMS AAI, and OMI AAI showed consistent spatial distributions and seasonal variations with DSF in the MDSR, with correlation coefficients of 0.88, 0.55, and 0.88, respectively. The results showed that AOD and AAI over the MDSR decreased during 2000–2005, 2006–2017, and 2000–2021, but increased during 2017–2021.The improvements in vegetation coverage and soil moisture together with favorable climatic factors (the increase in temperature and precipitation and the decrease in surface wind speed) resulted in the decreasing trend of AOD and AAI during 2000–2005, 2006–2017, and the entire period of 2000–2021. Conversely, the increase in surface wind speed, the decrease in temperature and the low soil moisture in 2018 and 2020 were the reasons for the increases in AOD and AAI over the MDSR during 2017–2021. The combination effects of surface wind, temperature, soil moisture, and vegetation coverage would determine DSF, AOD, and AAI, in the end, under global climate change.

Study of variation of aerosol optical properties over a high altitude station in Indian Western Himalayan region, palampur using raman lidar system

Study of variation of aerosol optical properties over a high altitude station in Indian Western Himalayan region, palampur using raman lidar system

Long-Term Variation of Aerosol Optical Properties Associated with Aerosol Types Over East Asia Using Aeronet and Satellite (Viirs, Omi) Data

Long-Term Variation of Aerosol Optical Properties Associated with Aerosol Types Over East Asia Using Aeronet and Satellite (Viirs, Omi) Data

A large reduction of direct aerosol cooling over Poland in the last decades

AbstractThis paper presents an analysis of the long‐term (1982–2015) variability of aerosol optical properties, as well as aerosol and greenhouse gases (GHG) direct radiative forcing (RF) in central Europe on the basis of MERRA‐2 reanalysis and ground‐based observation. Calculations of longwave (LW) and shortwave (SW) RF were made with the use of the off‐line Fu‐Liou radiative transfer model and were preceded by the sensitivity study of the code's input parameters. Then, the long‐term mean as well as the annual variability for selected regions of aerosol optical properties and radiative forcing were analysed. The mean AOD trend was −0.056 ± 9% per decade and AOD was reduced by 48% between 1982 and 2015. While for 1982–1990 the trend per decade was −0.12 ± 20%, for 1991–2000 it was −0.17 ± 17% and only −0.02 ± 31% in the last 15 years (2001–2015). The trend of the aerosol radiative forcing (ARF) was 1.52 ± 0.12 W·m−2/10 year and 1.21 ± 0.19 W·m−2/10 year at top of the atmosphere (TOA) and at Earth's surface, respectively. The trend for GHG was significantly smaller and it equalled 0.27 ± 0.01 W·m−2/10 year at TOA and 0.17 ± 0.01 W·m−2/10 year at the surface. Changes in GHG and aerosol direct effect produced additional 3.2 ± 0.2 W·m−2 at TOA, which could be associated with the observed regional climate warming. The change of the direct aerosol effect was about 4 times the GHG RF. The influence of aerosol loading reduction on the radiation budget was significantly higher in the 1990s of the 20th century in comparison to the first decades of the 21st. The effect of aerosol reduction has significant impact on air temperature changes during warm season and negligible during winter.

Long-term variations in aerosol optical properties, types, and radiative forcing in the Sichuan Basin, Southwest China

Long-term variations in aerosol optical properties, types, and radiative forcing over the Sichuan Basin (SCB) and surrounding regions in Southwest China were investigated based on two-decade data (2001−2020) from the Moderate Resolution Imaging Spectroradiometer, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation, and the Santa Barbara DISORT Atmospheric Radiative Transfer model. The results showed that the aerosol optical depth (AOD550nm) in the SCB, a major polluted region in Southwest China, experienced an increasing tendency at a rate of +0.052 yr−1 during 2001–2006; thereafter, it decreased speedy up from −0.020 to −0.058 yr−1 over recent years, whereas the interannual variation in Ångström exponent (AE470–660nm) presented a persistently increasing trend during 2001–2020, with a rate of +0.014 yr−1. An improved atmospheric environment but an enhanced fine particle contribution to regional aerosols in the SCB was observed. Over the polluted SCB region, the dominant aerosol types were biomass burning/urban industrial and mixed-type aerosols with the proportions of 80.7%–87.5% in regional aerosols, with a higher frequency of clean aerosols in recent years, reflecting an effect of controlling anthropogenic emission in the SCB owing to governmental regulation. By contrast, few changes were observed in the aerosol types and amounts in the eastern Tibetan Plateau (ETP), where clean continental aerosols dominate with high proportion of 93.7% in the clean atmospheric environment. A significant decline in polluted anthropogenic aerosols was observed below 3 km over the SCB, resulting in the regional aerosol extinction coefficients at 532 nm (EC532nm) were declined by −0.22 km−1 from 2013 to 2020. Notably, the decreases in aerosol radiative forcing within the atmosphere were found in the SCB and the adjacent northern Yunnan-Guizhou Plateau (NYGP) and ETP, with −41.6%, −33.7%, and −13.6%, respectively during 2013–2020. This indicates that such an attenuated aerosol heating rate in the atmosphere, caused by aerosol variation, could alter the atmospheric thermal structure over the SCB and surrounding areas for regional changes of environment and climate in recent years.

Effects of different correction algorithms on absorption coefficient – a comparison of three optical absorption photometers at a boreal forest site

Abstract. We present a comparison between three absorption photometers that measured the absorption coefficient (σabs) of ambient aerosol particles in 2012–2017 at SMEAR II (Station for Measuring Ecosystem–Atmosphere Relations II), a measurement station located in a boreal forest in southern Finland. The comparison included an Aethalometer (AE31), a multi-angle absorption photometer (MAAP), and a particle soot absorption photometer (PSAP). These optical instruments measured particles collected on a filter, which is a source of systematic errors, since in addition to the particles, the filter fibers also interact with light. To overcome this problem, several algorithms have been suggested to correct the AE31 and PSAP measurements. The aim of this study was to research how the different correction algorithms affected the derived optical properties. We applied the different correction algorithms to the AE31 and PSAP data and compared the results against the reference measurements conducted by the MAAP. The comparison between the MAAP and AE31 resulted in a multiple-scattering correction factor (Cref) that is used in AE31 correction algorithms to compensate for the light scattering by filter fibers. Cref varies between different environments, and our results are applicable to a boreal environment. We observed a clear seasonal cycle in Cref, which was probably due to variations in aerosol optical properties, such as the backscatter fraction and single-scattering albedo, and also due to variations in the relative humidity (RH). The results showed that the filter-based absorption photometers seemed to be rather sensitive to the RH even if the RH was kept below the recommended value of 40 %. The instruments correlated well (R≈0.98), but the slopes of the regression lines varied between the instruments and correction algorithms: compared to the MAAP, the AE31 underestimated σabs only slightly (the slopes varied between 0.96–1.00) and the PSAP overestimated σabs only a little (the slopes varied between 1.01–1.04 for a recommended filter transmittance >0.7). The instruments and correction algorithms had a notable influence on the absorption Ångström exponent: the median absorption Ångström exponent varied between 0.93–1.54 for the different algorithms and instruments.

Variability of black carbon aerosol concentrations and sources at a Mediterranean coastal region

To investigate the temporal variation of aerosol optical properties and evaluate the main emission sources of black carbon (BC) considering different seasons in a typical Mediterranean coastal environment, a field campaign was conducted during February–July 2019 at the Central Adriatic coastal area. Real-time measurements of aerosol light absorption were continuously obtained using an aethalometer while the Aethalometer model source apportionment data, optimized by using levoglucosan measurements, were evaluated against the modelling results of the LOTOS-EUROS chemical transport model. The measured mean equivalent BC mass concentration of 0.57 ± 0.64 μg m−3 was the lowest observed in the Mediterranean region. BC from fossil fuel (BCff) dominated the area throughout the study period with a maximum in winter and elevated levels by the approaching summer tourist season. Diel variability of BC concentrations from biomass burning (BCbb) was observed during stable winter conditions, with clear morning and evening concentration peaks, consistent with the profile of residential heating by wood burning. Up to 88% of BC concentrations were attributed to European emission sectors, with stationary source combustion, transportation, shipping and agriculture sectors being the most influential contributors. Source apportionment of BC highlighted that, in addition to biomass burning, small combustion fossil fuel sources, including land traffic and shipping, should be more strictly controlled in order to limit BC pollution in Mediterranean coastal areas. This study serves as a basis of comparison for future studies addressing air quality and pollution source apportionment in the Adriatic and/or the Mediterranean coastal regions in efforts of mitigation and adaptation to climate change.

City-level variations in aerosol optical properties and aerosol type identification derived from long-term MODIS/Aqua observations in the Sichuan Basin, China

In recent decades, the Sichuan Basin (SCB) has suffered from severe aerosol pollution. Based on the long-term (2003–2018) aerosol optical properties dataset derived from the Moderate Resolution Imaging Spectroradiometer (MODIS), this study investigated the spatial distribution and interannual variation of aerosol optical depth (AOD) and fine-mode fraction (FMF) as well as the aerosol type at city-level in the SCB. The spatial distribution of AOD exhibited a decreasing trend from the centre of SCB to surrounding areas with high AOD approximately 1.0. The high FMF value was approximately 0.9 in surrounding southern areas. The frequency of occurrence of AOD < 0.2 was approximately 30%–40%. AOD in SCB exhibited a negative trend of approximately −0.03/year and FMF showed a significant positive trend of approximately 0.01–0.02/year. The proportion of continental background aerosols was higher in surrounding areas of SCB. The BB/UI (biomass burning/urban-industrial) aerosols in the central urban area increased significantly to approximately 50%. Mix aerosols were mainly distributed in the north, accounting for approximately 35%–45%. A large proportion of dust aerosols (30%–35%) was noted in the east SCB. The results of this study are of great scientific significance for the analysis of aerosol optical extinction at city level in the SCB of China.

Long-term variations of aerosol optical properties over Wuhan with polarization lidar

Aerosols greatly impact the global and regional climate system and public health. We conducted lidar measurements at Wuhan (30.53°N, 114.37°E) from October 2010 to June 2020 and analyzed the massive dataset with an automatic lidar processing algorithm, to investigate the long-term variations of aerosols. Lidar-derived total aerosol optical depth (AOD) at 532 nm shows an interannual decrease of −0.049 since 2010. Compared with AODs in other megacities worldwide, the AOD for Wuhan shows the largest decrease rate. After separating AOD contributions from boundary layer (BL) and free troposphere (FT), different evolution patterns are revealed with AOD decrease rates of −0.009 and −0.044 per year for FT and BL, respectively, which indicates more than 80% of AOD decrease are associated with reductions of local emissions. In addition, BL AOD was always larger than FT AOD before COVID-19 lockdown. However, this relation was conversed thereafter, with the lowest value of 0.125 for BL AOD since 2010, which is only the half of FT AOD within the same period. This feature corroborates strong influences of COVID-19 lockdown on human activities and local emissions. These findings can improve our understandings of regional aerosol responses to pollution controls and aerosol direct impacts on regional climate.

Aerosols from anthropogenic and biogenic sources and their interactions – modeling aerosol formation, optical properties, and impacts over the central Amazon basin

Abstract. The Green Ocean Amazon experiment – GoAmazon 2014–2015 – explored the interactions between natural biogenic forest emissions from central Amazonia and urban air pollution from Manaus. Previous GoAmazon 2014–2015 studies showed that nitrogen oxide (NOx = NO + NO2) and sulfur oxide (SOx) emissions from Manaus strongly interact with biogenic volatile organic compounds (BVOCs), affecting secondary organic aerosol (SOA) formation. In previous studies, ground-based and aircraft measurements provided evidence of SOA formation and strong changes in aerosol composition and properties. Aerosol optical properties also evolve, and their impacts on the Amazonian ecosystem can be significant. As particles age, some processes, such as SOA production, black carbon (BC) deposition, particle growth and the BC lensing effect change the aerosol optical properties, affecting the solar radiation flux at the surface. This study analyzes data and models SOA formation using the Weather Research and Forecasting with Chemistry (WRF-Chem) model to assess the spatial variability in aerosol optical properties as the Manaus plumes interact with the natural atmosphere. The following aerosol optical properties are investigated: single scattering albedo (SSA), asymmetry parameter (gaer), absorption Ångström exponent (AAE) and scattering Ångström exponent (SAE). These simulations were validated using ground-based measurements at three experimental sites, namely the Amazon Tall Tower Observatory – ATTO (T0a), downtown Manaus (T1), Tiwa Hotel (T2) and Manacapuru (T3), as well as the U.S. Department of Energy (DOE) Gulfstream 1 (G-1) aircraft flights. WRF-Chem simulations were performed over 7 d during March 2014. Results show a mean biogenic SOA (BSOA) mass enrichment of 512 % at the T1 site, 450 % in regions downwind of Manaus, such as the T3 site, and 850 % in areas north of the T3 site in simulations with anthropogenic emissions. The SOA formation is rather fast, with about 80 % of the SOA mass produced in 3–4 h. Comparing the plume from simulations with and without anthropogenic emissions, SSA shows a downwind reduction of approximately 10 %, 11 % and 6 % at the T1, T2 and T3 sites, respectively. Other regions, such as those further downwind of the T3 site, are also affected. The gaer values increased from 0.62 to 0.74 at the T1 site and from 0.67 to 0.72 at the T3 site when anthropogenic emissions are active. During the Manaus plume-aging process, a plume tracking analysis shows an increase in SSA from 0.91 close to Manaus to 0.98 160 km downwind of Manaus as a result of SOA production and BC deposition.

A comprehensive database of the optical properties of irregular aerosol particles for radiative transfer simulations

AbstractA database (TAMUdust2020) of the optical properties of irregular aerosol particles is developed for applications to radiative transfer simulations involving aerosols, particularly dust and volcanic ash particles. The particle shape model assumes an ensemble of irregular hexahedral geometries to mimic complex aerosol particle shapes in nature. State-of-the-art light scattering computational capabilities are employed to compute the single-scattering properties of these particles for wide ranges of values of the size parameter, the index of refraction, and the degree of sphericity. The database therefore is useful for various radiative transfer applications over a broad spectral region from ultraviolet to infrared. Overall, agreement between simulations and laboratory/in-situ measurements is achieved for the scattering phase matrix and backscattering of various dust aerosol and volcanic ash particles. Radiative transfer simulations of active and passive spaceborne sensor signals for dust plumes with various aerosol optical depths and the effective particle sizes clearly demonstrate the applicability of the database for aerosol studies. In particular, the present database includes, for the first time, robust backscattering of nonspherical particles spanning the entire range of aerosol particle sizes, which shall be useful to appropriately interpret lidar signals related to the physical properties of aerosol plumes. Furthermore, thermal infrared simulations based on in-situ measured refractive indices of dust aerosol particles manifest the effects of the regional variations of aerosol optical properties. This database includes a user-friendly interface to obtain user-customized aerosol single-scattering properties with respect to spectrally dependent complex refractive index, size, and the degree of sphericity.

Climatological variations in aerosol optical depth and aerosol type identification in Liaoning of Northeast China based on MODIS data from 2002 to 2019

The climatological variations of aerosol optical properties are significant in the study of aerosol effect on regional environment. The MODIS level 2 aerosol optical depth (AOD) products (MOD04/MYD04) at 10 km were used to identify the spatial distribution, interdecadal trends, and aerosol types from 2002 to 2019 in Liaoning province over Northeast China. The highest AOD was distributed in central Liaoning, with a peak value of approximately 0.6 and the fine mode fraction (FMF) was higher in eastern Liaoning about 0.8. The overall AOD for Liaoning in summer was significantly higher than that in other seasons, and the higher AOD values were observed in central Liaoning and the area around Bohai Rim (up to approximately 0.7). The frequency of 0.1 ≤ AOD < 0.2 and 0.2 ≤ AOD < 0.3 was highest in 14 cities of Liaoning. For FMF > 0.8, the cities were categorised into those with an increase frequency of 15% to 20%, and those with a decrease frequency of 5% to 10%. During 2014 to 2019, the interannual variation in AOD in Liaoning exhibited a significant downward trend, with a minimum AOD of approximately 0.25 in 2019. The FMF in Liaoning from 2002 to 2019 exhibited a fluctuating trend around 0.5. The AOD in Liaoning showed an increasing trend from 2002 to 2008 with a maximum of approximately 0.02/year and a clear decreasing trend from 2009 to 2019 of approximately −0.02/year. Maritime aerosol mostly occurred in cities in western Liaoning accounted for 20.58% to 36.52%. Dust aerosol had a considerable influence on central Liaoning accounting for 2.95% to 16.18%. In eastern Liaoning, continental background aerosol accounted for 36.69% to 43.30%. These results revealed the influence of AOD and fine particles on aerosol extinction in Northeast China and provided important information for the climate change in Northeast Asia.