Air quality in Bangladesh has depreciated over the years owing to substantial local and regional aerosol emissions. This study investigates the impact of anthropogenic aerosol emissions, aerosol radiative forcing, and socioeconomic factors on aerosol optical depth (AOD) over Bangladesh. The research focuses on the capital city Dhaka and the coastal island Bhola, using data from the ground-based AERONET, MODIS satellite, and MERRA-2 reanalysis model. AOD exhibited increasing trends over Bangladesh (0.004-0.010/years) and showed significant annual cycles. Northwestern regions of the country experienced extremely high concentrations of anthropogenic black carbon (BC) and organic carbon (OC) aerosols, whereas the central regions exhibited elevated anthropogenic SO2 and SO4 concentrations. The dominance of anthropogenic aerosols (SO4, BC, and OC) over Dhaka (similar to 75%) and natural aerosols (sea salt and dust) over Bhola (similar to 63%) were calculated. SO4 aerosol was the primary driving force over Dhaka contributing 47.60% of the total AOD, while sea salt aerosol was the dominant species (45.78%) over Bhola. High aerosol radiative forcing at the atmosphere (ARF(ATM)) values were calculated for both Dhaka and Bhola. Average heating rate (HR) at Dhaka was 2.05 +/- 0.75 K day(-1), and at Bhola was 1.54 +/- 0.58 K day(-1) indicating the presence of light-absorbing aerosols over Bangladesh. All the socioeconomic factors were positively correlated with AOD except population growth and agriculture land indicating the substantial impact of socioeconomic development on AOD. The findings of this study will have notable influences on long-term air quality management in Bangladesh as well as in Southeast Asia.

Soil organic carbon (SOC) rapidly accumulates during ecosystem primary succession in glacier foreland. This makes it an ideal model for studying soil carbon sequestration and stabilization, which are urgently needed to mitigate climate change. Here, we investigated SOC dynamics in the Kuoqionggangri glacier foreland on the Tibetan Plateau. The study area along a deglaciation chronosequence of 170-year comprising three ecosystem succession stages, including barren ground, herb steppe, and legume steppe. We quantified amino sugars, lignin phenols, and relative expression of genes associated with carbon degradation to assess the contributions of microbial and plant residues to SOC, and used FT-ICR mass spectroscopy to analyze the composition of dissolved organic matter. We found that herbal plant colonization increased SOC by enhancing ecosystem gross primary productivity, while subsequent legumes development decreased SOC, due to increased ecosystem respiration from labile organic carbon inputs. Plant residues were a greater contributor to SOC than microbial residues in the vegetated soils, but they were susceptible to microbial degradation compared to the more persistent and continuously accumulating microbial residues. Our findings revealed the organic carbon accumulation and stabilization process in early soil development, which provides mechanism insights into carbon sequestration during ecosystem restoration under climate change.

Our understanding of tundra fire effects in Northern Alaska is limited because fires have been relatively rare. We sampled a 70+ year -old burn visible in a 1948 aerial photograph for vegetation composition and structure, soil attributes, terrain rugosity, and thermokarst pit density. Between 1948 and 2017 the burn initially became wetter as ice wedges melted but then drained and dried as the troughs became hydrologically connected. The reference tundra has become wetter over the last few decades and appears to be lagging through a similar sequence. The burn averaged 2.5 degrees C warmer than the reference tundra at 30 cm depth. Thinning of organic soil following fire appears to dramatically accelerate the background degradation of ground-ice features in response to climate change and promotes a plant community that is distinct in terms of taxa and structure, dominated by tall willows and other competitive, rather than cold-tolerant, species. The cover of sedges and mosses is low while that of willows and grass is high relative to the reference tundra. The changes in plant community composition and structure, increasing ground temperature, and thermokarst lead us to expect the observed biophysical changes to the tundra will persist centuries into the future.

This study explores the carbon stability in the Arctic permafrost following the sea-level transgression since the Last Glacial Maximum (LGM). The Arctic permafrost stores a significant amount of organic carbon sequestered as frozen particulate organic carbon, solid methane hydrate and free methane gas. Post-LGM sea-level transgression resulted in ocean water, which is up to 20 degrees C warmer compared to the average annual air mass, inundating, and thawing the permafrost. This study develops a one-dimensional multiphase flow, multicomponent transport numerical model and apply it to investigate the coupled thermal, hydraulic, microbial, and chemical processes occurring in the thawing subsea permafrost. Results show that microbial methane is produced and vented to the seawater immediately upon the flooding of the Arctic continental shelves. This microbial methane is generated by the biodegradation of the previously frozen organic carbon. The maximum seabed methane flux is predicted in the shallow water where the sediment has been warmed up, but the remaining amount of organic carbon is still high. It is less likely to cause seabed methane emission by methane hydrate dissociation. Such a situation only happens when there is a very shallow (similar to 200 m depth) intra-permafrost methane hydrate, the occurrence of which is limited. This study provides insights into the limits of methane release from the ongoing flooding of the Arctic permafrost, which is critical to understand the role of the Arctic permafrost in the carbon cycle, ocean chemistry and climate change. Arctic permafrost stores similar to 1,700 billion tons of organic carbon. If just a fraction of that melts, the escaping methane would become one of the world's largest sources of greenhouse gas and would severely impact the environment and the climate. Over the last similar to 18,000 years, a quarter of the stored organic carbon in the Arctic permafrost has been flooded by the rising, warm seas. This has melted the ice and degraded the permafrost. But what happens to the carbon pools? This study investigates the stability of the carbon in the Arctic permafrost following the flooding using a newly developed numerical model. Results show that microbial methane is generated and emitted to the seawater immediately following the flooding. This methane is produced by the biodegradation of the previously frozen organic carbon near the seafloor. The maximum methane emission is predicted in the shallow water near the coast where the sediment has been warmed up, but the remaining amount of organic carbon is still high. This study provides insights into the limits of methane release from the ongoing flooding of the Arctic permafrost, which is critical to understand the role of the Arctic permafrost in the carbon cycle, ocean chemistry and climate change. A numerical model is developed to simulate the coupled thermal, hydraulic, microbial and chemical processes in the thawing subsea permafrost The biodegradation of the ancient organic carbon in the thawing subsea permafrost results in seabed microbial methane emission Seabed methane emission is less likely to be caused by methane hydrate dissociation at the Arctic continental shelves

Many studies have focused on elevation-dependent warming (EDW) across high mountains, but few studies have examined both EDW and LDW (latitude-dependent warming) on Antarctic warming. This study analyzed the Antarctic amplification (AnA) with respect to EDW and LDW under SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5 from Coupled Model Intercomparison Project Phase 6 (CMIP6) during the period 2015-2100. The results show that the AnA appears under all socioeconomic scenarios, and the greatest signal appears in austral autumn. In the future, Antarctic warming is not only elevation-dependent, but also latitude-dependent. Generally, positive EDW of mean temperature (T-mean), maximum temperature (T-max) and minimum temperature (T-min) appear in the range of 1.0-4.5 km, and the corresponding altitudinal amplification trends are 0.012/0.012/0.011 (SSP1-2.6)- 0.064/0.065/0.053 (SSP5-8.5) degrees C decade(-1)center dot km(-1). Antarctic EDW demonstrates seasonal differences, and is strong in summer and autumn and weak in winter under SSP3-7.0 and SSP5-8.5. For T(mea)n, T-max and T-min, the feature of LDW is varies in different latitude ranges, and also shows seasonal differences. The strongest LDW signal appears in autumn, and the warming rate increases with increasing latitude at 64-79 degrees S under SSP1-2.6. The similar phenomenon can be observed at 68-87 degrees S in the other cases. Moreover, the latitude component contributes more to the warming of T-mean and T-max relative to the corresponding altitude component, which may relates to the much larger range of latitude (similar to 2600 km) than altitude (similar to 4.5 km) over Antarctica, while the EDW contributes more warming than LDW in the changes in T-min in austral summer. Moreover, surface downwelling longwave radiation, water vapor and latent heat flux are the potential factors influencing Antarctic EDW, and the variation in surface downwelling longwave radiation can also be considered as an important influencing factor for Antarctic LDW. Our results provide preliminary insights into EDW and LDW in Antarctica.

This study reports day-night and seasonal variations of aqueous brown carbon (BrCaq) and constituent humic-like substances (HULIS) (neutral and acidic HULIS: HULIS-n and HULIS-a) from the eastern Indo-Gangetic Plain (IGP) of India during 2019-2020. This is followed by the application of the receptor model positive matrix factorization (PMF) for optical source apportionment of BrCaq and the use of stable isotopic ratios (813C and 815N) to understand atmospheric processing. Nighttime BrCaq absorption and mass absorption efficiencies (MAE) were enhanced by 40-150 % and 50-190 %, respectively, compared to the daytime across seasons, possibly as a combined effect from daytime photobleaching, dark-phase secondary formation, and increased nighttime emissions. MAE250 nm/MAE365 nm (i.e., E2/E3) ratios and Angstrom Exponents revealed that BrCaq and HULIS-n were relatively more aromatic and conjugated during the biomass burning-dominated periods while BrCaq and HULIS-a were comprised mostly of nonconjugated aliphatic structures from secondary processes during the photochemistry-dominated summer. The relative radiative forcing of BrCaq with respect to elemental carbon (EC) was 10-12 % in the post-monsoon and winter in the 300-400 nm range. Optical source apportionment using PMF revealed that BrCaq absorption at 300, 365 and 420 nm wavelengths in the eastern IGP is mostly from biomass burning (60-75 %), followed by combined marine and fossil fuel-derived sources (24-31 %), and secondary processes (up to 10 %). Source-specific MAEs at 365 nm were estimated to be the highest for the combined marine and fossil fuel source (1.34 m2 g-1) followed by biomass burning (0.78 m2 g-1) and secondary processing (0.13 m2 g-1). Finally, 813C and 815N isotopic analysis confirmed the importance of summertime photochemistry and wintertime NO3--dominated chemistry in constraining BrC characteristics. Overall, the quantitative apportionment of BrCaq sources and processing reported here can be expected to lead to targeted source-specific measurements and a better understanding of BrC climate forcing in the future.

Climate and health in the pristine Himalayan region are largely impacted by the transport of carbonaceous aerosols from the polluted regions of Asia and Europe. Yet, there is a scarcity of source apportionment studies that can explain diurnal scale phenomena concerning various emission sources and radiative forcing. Here, we report the first simultaneous high-resolution delineation of primary organic carbon (POC) and secondary organic carbon (SOC) content and quantify the contributions of fossil fuel combustion and biomass burning over the Central Himalayas using four-year (2014-2017) online observations. Four different methods are employed to deconvolute organic carbon (OC) into POC and SOC. Unlike SOC, POC exhibits significant unimodal diurnal variations with higher values during daytime in all four methods. These methods show intra-annual variations in POC (56-80%) and SOC (20-44%) concentrations but they agree that overall POC (4.7-8 & mu;g m-3) dominates over SOC (2.4-3.9 & mu;g m-3). The role of crop residue burning in northern India and forest fires is shown to be dominant in spring while local heatingpurpose emissions dominate in winter. Further, we show that the contribution of fossil fuel combustion (eBCff) is 3.5 times greater than that of biomass burning (eBCbb). Monthly variations in mean diurnal amplitudes of eBCff and eBCbb reveal that the differences in their amplitudes (9- 32%) is smallest during April-May, depicting the relative importance of biomass emissions at the diurnal scale during spring. The estimated daily radiative forcing shows that eBCff contributes more (16.4%) atmospheric forcing than eBCbb. Atmospheric forcing from both eBCff and eBCbb are higher (19.8 and 13.0 W m-2, respectively) in the afternoon than morning. These findings underscore the need for high-resolution data when researching aerosol-radiation interaction over the Himalayan area and are vital for developing aerosol mitigation plans.

High-latitude permafrost, including hydrate-bearing frozen ground, changes its properties in response to natural climate change and to impacts from petroleum production. Of special interest is the behavior of thermal conductivity, one of the key parameters that control the thermal processes in permafrost containing gas hydrate accumulations. Thermal conductivity variations under pressure and temperature changes were studied in the laboratory through physical modeling using sand sampled from gas-bearing permafrost of the Yamal Peninsula (northern West Siberia, Russia). When gas pressure drops to below equilibrium at a constant negative temperature (about -6(degrees)C), the thermal conductivity of the samples first becomes a few percent to 10% lower as a result of cracking and then increases as pore gas hydrate dissociates and converts to water and then to ice. The range of thermal conductivity variations has several controls: pore gas pressure, hydrate saturation, rate of hydrate dissociation, and amount of additionally formed pore ice. In general, hydrate dissociation can cause up to 20% thermal conductivity decrease in frozen hydrate-bearing sand. As the samples are heated to positive temperatures, their thermal conductivity decreases by a magnitude depending on residual contents of pore gas hydrate and ice: the decrease reaches similar to 30% at 20-40% hydrate saturation. The thermal conductivity decrease in hydrate-free saline frozen sand is proportional to the salinity and can become similar to 40% lower at a salinity of 0.14%. The behavior of thermal conductivity in frozen hydrate-bearing sediments under a pressure drop below the equilibrium and a temperature increase to above 0 C-degrees is explained in a model of pore space changes based on the experimental results.

Mineral organic carbon interactions (aggregation, organo-mineral associations and organo-metallic complexes) enhance the protection of organic carbon (OC) from microbial degradation in soils. The northern circumpolar permafrost region stores between 1,440 and 1,600 Pg OC of which a significant portion is already thawed or about to thaw in coming years. In the light of this tipping point for climate change, any mechanism that can promote OC stabilization and hence mitigate OC mineralization and greenhouse gas emissions is of crucial interest. Here, we study interactions between metals (Fe, Al, Mn and Ca) and OC in the moist acidic tundra ecosystem of Eight Mile Lake, near Healy, AK, USA. We collected thirteen cores (124 soil samples) in late summer 2019 with shallow and deep active layers (45 to 109 cm deep) and varying water table depths. We find that between 6% and 59% of total OC in Eight Mile Lake tundra soils is mineral-associated (mean 20%), in organomineral associations (association between poorly crystalline oxides and OC) and in organo-metallic complexes (associations between Fe, Mn, Al, Ca polyvalent cations and organic acids). We find that total Fe and Mn concentrations can be used as good proxies to assess the reactive pool of these metals able to form associations with OC, i.e., poorly crystalline oxides or metals complexed with OC. We observe that in the active layer, mineral OC interactions are mostly as organo-metallic complexes with Fe cations, with an accumulation at the water table level acting as a soil redox interface. In waterlogged soils with a water table level above surface, no such accumulation of OC-Fe complexes is found due to the absence of a redox interface below soil surface. In the permafrost layer, we find that a combination of complexed metals and poorly crystalline Fe oxides act as reactive phases towards OC. Knowing that upon permafrost thaw tundra soils will become wetter or drier, the assessment of mineral-bound OC in drier or wetter tundra soils is a needed step to better constrain the changes in the proportion of non-protected OC more likely to contribute to C emissions from tundra soils.

Study region: Upper Yellow River Basin (UYRB), China. Study focus: We provide a comprehensive overview of the changes in the natural social binary water cycle system in the UYRB from the perspectives of the atmosphere, hydrosphere, cryosphere, biosphere, and human society by summarizing previous research results. New hydrological insight for the region: Since the 1980s, the continuous temperature rise led to permafrost thawing, resulting in a decrease in runoff and an increase in groundwater in the UYRB. The ecological protection and high-quality development of human society continuously increase the demand for water resources. Especially the runoff of the river in the human gathering area has significantly decreased and there has been an overexploitation of groundwater, resulting in a serious shortage of water resources. The future water supply and demand situation in the UYRB will be more severe. However, the current understanding of the natural social binary water cycle in the Upper Yellow River Basin is still insufficient, which seriously limits the high-quality development of human society in the UYRB. Among them, some erroneous conclusions can even provide misleading information for policy-making and cause serious manpower and resources loss. Natural social binary water cycle is still in initial stage in the UYRB, that is reflected in a lot of contradictions and shortcomings in past research. We propose four feasible research directions to comprehensively promote hydrometeorological research, providing effective guidance for the formulation of high-quality development policies in the UYRB.