Carbonaceous particles have been confirmed as major components of ambient aerosols in urban environments and are related to climate impacts and environmental and health effects. In this study, we collected different-size particulate matter (PM) samples (PM1, PM2.5, and PM10) at an urban site in Lanzhou, northwest China, during three discontinuous one-month periods (January, April, and July) of 2019. We measured the concentrations and potential transport pathways of carbonaceous aerosols in PM1, PM2.5, and PM10 size fractions. The average concentrations of OC (organic carbon) and EC (elemental carbon) in PM1, PM2.5, and PM10 were 6.98 +/- 3.71 and 2.11 +/- 1.34 mu g/m(3), 8.6 +/- 5.09 and 2.55 +/- 1.44 mu g/m(3), and 11.6 +/- 5.72 and 4.01 +/- 1.72 mu g/m(3). The OC and EC concentrations in PM1, PM2.5, and PM10 had similar seasonal trends, with higher values in winter due to the favorable meteorology for accumulating pollutants and urban-increased emissions from heating. Precipitation played a key role in scavenge pollutants, resulting in lower OC and EC concentrations in summer. The OC/EC ratios and principal component analysis (PCA) showed that the dominant pollution sources of carbon components in the PMs in Lanzhou were biomass burning, coal combustion, and diesel and gasoline vehicle emissions; and the backward trajectory and concentration weight trajectory (CWT) analysis further suggested that the primary pollution source of EC in Lanzhou was local fossil fuel combustion.

According to the monitoring data of the optical and microphysical characteristics of smoke aerosol at AERONET stations during forest fires in the summer of 2019 in Alaska, the anomalous selective absorption of smoke aerosol has been detected in the visible and near-infrared spectral range from 440 to 1020 nm. With anomalous selective absorption, the imaginary part of the refractive index of smoke aerosol reached 0.315 at a wavelength of 1020 nm. A power-law approximation of the spectral dependence of the imaginary part of the refractive index with an exponent from 0.26 to 2.35 is proposed. It is shown that, for anomalous selective absorption, power-law approximations of the spectral dependences of the aerosol optical extinction and absorption depths are applicable with an angstrom ngstrom exponent from 0.96 to 1.65 for the aerosol optical extinction depth and from 0.97 to -0.89 for the aerosol optical absorption depth, which reached 0.72. Single scattering albedo varied from 0.62 to 0.96. In the size distribution of smoke aerosol particles with anomalous selective absorption, the fine fraction of particles of condensation origin dominated. The similarity of the fraction of particles distinguished by anomalous selective absorption with the fraction of tar balls (TBs) detected by electron microscopy in smoke aerosol, which, apparently, arise during the condensation of terpenes and their oxygen-containing derivatives, is noted.

As the basic units of soil structure, soil aggregate is essential for maintaining soil stability. Intensified freeze-thaw cycles have deeply affected the size distribution and stability of aggregate under global warming. To date, it is still lacking about the effects of freeze-thaw cycles on aggregate in the permafrost regions of the Qinghai-Tibetan Plateau (QTP). Therefore, we investigated the effects of diurnal and seasonal freeze-thaw processes on soil aggregate. Our results showed that the durations of thawing and freezing periods in the 0-10 cm layer were longer than in the 10-20 cm layer, while the opposite results were observed during completely thawed and frozen periods. Freeze-thaw strength was greater in the 0-10 cm layer than that in the 10-20 cm layer. The diurnal freeze-thaw cycles have no significant effect on the size distribution and stability of aggregate. However, 0.25 mm) and reduced aggregate stability. Our study has scientific guidance for evaluating the effects of freeze-thaw cycles on soil steucture and provides a theoretical basis for further exploration on soil and water conservation in the permafrost regions of the QTP.

East Africa (EA) suffers from the inadequate characterization of atmospheric aerosols, with far-reaching consequences of its inability to quantify precisely the impacts of these particles on regional climate. The current study aimed at character-izing absorption and radiative properties of aerosols using the long-term (2001-2018) AErosol RObotic NETwork (AERONET) and Modern-Era Retrospective analysis for Research and Applications (MERRA-2) data over three environ-mentally specific sites in EA. The annual mean absorption aerosol optical depth (AAOD440 nm), absorption Angstrom Ex-ponent (AAE440-870 nm), total effective radius (REff), and total volume concentration (mu m3/mu m2) revealed significant spatial heterogeneity over the domain. The study domain exhibited a significant contribution of fine-mode aerosols com-pared to the coarse-mode particles. The monthly variation in SSA440 nm over EA explains the strength in absorption aero-sols that range from moderate to strong absorbing aerosols. The aerosols exhibited significant variability over the study domain, with the dominance of absorbing fine-mode aerosols over Mbita accounting for similar to 40 to similar to 50 %, while weakly absorbing coarse-mode particles accounted for similar to 8.2 % over Malindi. The study conclusively determined that Mbita was dominated by AAOD mainly from biomass burning in most of the months, whereas Malindi was coated with black carbon. The direct aerosol radiative forcing (DARF) retrieved from both the AERONET and MERRA-2 models showed strong cooling at the top of the atmosphere (TOA; -6 to -27 Wm-2) and the bottom of the atmosphere (BOA, -7 to -66 Wm-2). However, significant warming was noticed within the atmosphere (ATM; +14 to +76 Wm-2), an indica-tion of the role of aerosols in regional climate change. The study contributed to understanding aerosol absorption and ra-diative characteristics over EA and can form the basis of other related studies over the domain and beyond.

Black carbon (BC) is an important aerosol species due to its strong heating of the atmosphere accompanied by cooling of the Earth's surface, but its radiative forcing is poorly constrained by different regional size distributions due to uncertain reproductions of a morphologically simplified model. Here, we quantify the BC morphological effect on measuring the particle size using an aggregate model. We show that the size distributions of loose BC particles could account for up to 45% underestimation by morphological simplification, leading to up to 25% differences, by relying on a simplified model to estimate radiative forcing. We find that the BC particle size is remarkably amplified for looser and larger BC aggregates by angular scattering observations. We suggest that the BC morphological diversity can be neglected in forward scattering angles (<30 degrees), which is a useful supplement to reduce the uncertainty of radiative forcing assessment.

The study on the light absorption of carbonaceous components is a research hotspot in the field of aerosol optical. Size distribution and lensing effect have great influence on the absorption of elemental carbon (EC) and brown carbon (BrC). However, few studies were conducted on the spatial variations of BC and BrC absorption with different size ranges in different regions. In this study, the mass concentration, absorption coefficient and mass absorption efficiency (MAE) of size-resolved carbonaceous components in three functional areas of Nanjing were compared based on offline sampling and experimental analysis. Bimodal and unimodal size distributions were found for EC and BrC mass concentrations at the three sites, respectively. Affected by the emission of diesel vehicles and aggregation condensation, high EC concentration in the size range of 0.56-1 mu m was found at the suburban site. Due to the secondary formation from VOCs, high BrC concentration in the size range of 0.18-0.32 mu m was observed at the industrial site. High EC concentration in the size range of 0.18-0.32 mu m caused by diesel emission was the main reason for the high EC absorption in the regional area. Compared with vehicle emissions, the absorption capacity of secondary BrC was weaker. The variation of MAE values caused by various sources was the key factor leading to BrC absorption, which varied greatly in different regions. This study is helpful to understand the variation of light absorption of carbonaceous component and its source influence in a typical polluted city in the Yangtze River Delta, which provides important data support for the comprehensive evaluation of the role of aerosol light absorption in the change of radiative forcing in different regions.

Dust aerosol has an impact on both the regional radiation balance and the global radiative forcing estimation. The Taklimakan Desert is the focus of the present research on the optical and micro-physical characteristics of the dust aerosol characteristics in Central Asia. However, our knowledge is still limited regarding this typical arid region. The DAO-K (Dust Aerosol Observation-Kashgar) campaign in April 2019 presented a great opportunity to understand further the effects of local pollution and transported dust on the optical and physical characteristics of the background aerosol in Kashgar. In the present study, the consistency of the simultaneous observations is tested, based on the optical closure method. Three periods dominated by the regional background dust (RBD), local polluted dust (LPD), and Taklimakan transported dust (TTD), are identified through the backward trajectories, combined with the dust scores from AIRS (Atmospheric Infrared Sounder). The variations of the optical and micro-physical properties of dust aerosols are then studied, while a direct comparison of the total column and near surface is conducted. Generally, the mineral dust is supposed to be primarily composed of silicate minerals, which are mostly very weakly absorbing in the visible spectrum. Although there is very clean air (with PM2.5 of 21 mu g/m(3)), a strong absorption (with an SSA of 0.77, AAE of 1.62) is still observed during the period dominated by the regional background dust aerosol. The near-surface observations show that there is PM2.5 pollution of similar to 98 mu g/m(3), with strong absorption in the Kashgar site during the whole observation. Local pollution can obviously enhance the absorption (with an SSA of 0.72, AAE of 1.58) of dust aerosol at the visible spectrum. This is caused by the increase in submicron fine particles (such as soot) with effective radii of 0.14 mu m, 0.17 mu m, and 0.34 mu m. The transported Taklimakan dust aerosol has a relatively stable composition and strong scattering characteristics (with an SSA of 0.86, AAE of similar to 2.0). In comparison to the total column aerosol, the near-surface aerosol has the smaller size and the stronger absorption. Moreover, there is a very strong scattering of the total column aerosol. Even the local emission with the strong absorption has a fairly minor effect on the total column SSA. The comparison also shows that the peak radii of the total column PVSD is nearly twice as high as that of the near-surface PVSD. This work contributes to building a relationship between the remote sensing (total column) observations and the near-surface aerosol properties, and has the potential to improve the accuracy of the radiative forcing estimation in Kashgar.

Continuous long-term monitoring of black carbon (BC) mass concentration and aerosol light scattering coefficient (sigma(SCA)), supplemented by number size distribution and chemical composition, are utilized in this study to understand the temporal changes in aerosol properties, associated source processes and radiative effects at Ny-angstrom lesund (79 degrees N) in the Svalbard Archipelago. A statistically significant decreasing trend in BC (- 24.7 ng m(-3) decade(-1)) is observed during spring of 2010-2019. In contrast, sigma SCA depicted a general increasing trend (5.2 Mm(-1) decade(-1)) during 2011-2016. BC and sigma(SCA) were higher during winter and spring. Aerosol single scattering albedo was highest in May similar to 0.95 (during spring) and lowest in September similar to 0.87 (during summer). Fractional share of BC to total aerosol mass was higher in winter and summer. Anthropogenic SO42- and NO3- (after ssNa(+)) species dominated the summer, when total number and mass concentrations of aerosols were at their minimum. Elemental Carbon (EC) and Organic Carbon (OC) showed higher concentrations in spring with EC-to-OC ratio similar to 0.08 - 0.22. The columnar AOD varied between 0.01 and 0.20 (annual mean similar to 0.09), resulting in aerosol radiative forcing (in the top of the atmosphere) similar to 0.15 - 2.69 Wm(-2) in the month of April (during spring). Potential source contribution function (PSCF) revealed the dominant source areas to be over Europe and Russia in terms of contributing to the seasonal high BC mass concentrations at Ny-angstrom lesund. Our study has also revealed an unusual impact of biomass burning aerosols (advected from the Alaska wildfire) during July 2015.

Since aerosols are an integral part of the Arctic climate system, understanding aerosol radiative properties and the relation of these properties to each other is important for constraining aerosol radiative forcing effects in this remote region where measurements are sparse. In situ measurements of aerosol size distribution, aerosol light scattering and absorption were taken near Eureka (80.05 degrees N, 86.42 degrees W), on Ellesmere Island, in the Canadian High Arctic over three consecutive years to provide insights into radiative properties of Arctic aerosols. During periods of Arctic haze, we find that the single scattering albedo (SSA) at 405 nm is generally higher and more stable than that determined at 870 nm, with values ranging between 0.90-0.99 and 0.79-0.97, respectively. Events with elevated absorption coefficients (B-abs) exhibit generally an absorption Angstrom exponent (AAE) of around 1 suggesting that black carbon (BC) is the dominant absorbing aerosol for the measurement period. AAE values close to 2 occurring with scattering Angstrom exponent (SAE) values near 0 and SAE values below 0 occasionally observed in December indicate a potential contribution from mineral dust aerosols in late fall and early winter. The apparent real and imaginary parts of the complex refractive index at 405 nm have been found to range between 1.6-1.9 and 0.002-0.02, respectively. The low imaginary component indicates very weak intrinsic absorption compared to BC-rich aerosols. Systematic variabilities between different aerosol optical and microphysical properties depend strongly on the given wavelength. SSA at 405 nm shows a strong inverse dependence with B-abs, because B-abs correlates positively with the imaginary component of the refractive index. On the other hand, SSA at 870 nm correlates with scattering coefficient (B-sca) and not with B-abs due to a greater sensitivity to the ambient particle size distribution for 870 nm scattering. Smaller particles with higher SAE that are prevalent during less polluted periods only weakly scatter at 870 nm leading to lower SSA when B-sca is also low. Lastly, FLEXPART back-trajectories show that lower aerosol SSA and higher B-abs correspond to air masses which are more influenced by Eurasian and Alaskan regions, including regions known to have important BC emissions. This work emphasizes the important variability in Arctic aerosol optical properties during winter and spring, which is likely due to changes in source regions.

The temperature and thermal properties of shelf sediments from the East Siberian, Laptev, and Kara Seas were determined from field investigations. The sediments were in an unfrozen cryotic state (ice-free) and showed negative temperatures, ranging from-1.0 to-1.4 degrees C. These temperatures imply the presence of widespread subsea permafrost from the shelf to the continental slope of the East Siberian Arctic Seas, reaching-1000-1500 km off the coast. The thermal conductivity and heat capacity of sediments (up to a depth of 0.5 m) from the Eastern Arctic Seas averaged 0.95 W/(m.K) and 3010 kJ/(m(3).K), respectively. We also conducted temperature and thermal conductivity measurements of the upper sediment horizons of the permafrost in the Laptev Sea shelf (drilling depth of 57 m). The analysis of sediment cores ensured the determination of thermal conductivity with depth. We also analyzed the influence of moisture content, density, particle size distribution, salinity, and thermal state on sediment thermal conductivity. The thermal conductivity of unfrozen cryotic (ice-free) sediments was predominantly dependent on the contents of silt and clay. In general, unfrozen cryotic sandy sediments had a thermal conductivity range 1.7-2.0 W/(m.K), a moisture content of-20%, and a density of 2.0-2.2 g/cm(3). Frozen (ice-containing) sediments showed higher thermal conductivities of 2.5-3.0 W/(m.K), with a density of 1.9-2.0 g/cm(3) and a moisture content exceeding 25-30%. The high thermal conductivity of sand was associated with low salinity (0.1-0.2%), high ice content, and moderate unfrozen water content.