Glacial changes are crucial to regional water resources and ecosystems in the Sawir Mountains. However, glacial changes, including the mass balance and glacial meltwater of the Sawir Mountains, have sparsely been reported. Three model calibration strategies were constructed including a regression model based on albedo and in-situ mass balance of Muz Taw Glacier (A-Ms), regression model based on albedo and geodetic mass balance of valley, cirque, and hanging glaciers (A-Mr), and degree-day model (DDM) to obtain a reliable glacier mass balance in the Sawir Mountains and provide the latest understanding in the contribution of glacial meltwater runoff to regional water resources. The results indicated that the glacial albedo reduction was significant from 2000 to 2020 for the entire Sawir Mountains, with a rate of 0.015 (10a)- 1, and the spatial pattern was higher in the east compared to the west. Second, the three strategies all indicated that the glacier mass balance has been continuously negative during the past 20 periods, and the average annual glacier mass balance was -1.01 m w.e. Third, the average annual glacial meltwater runoff in the Sawir Mountains from 2000 to 2020 was 22 x 106 m3, and its

A comprehensive global investigation on the impact of reduction (changes) in aerosol emissions due to Coronavirus disease-2019 (COVID-19) lockdowns on aerosol single scattering albedo (SSA) utilizing satellite observations and model simulations is conducted for the first time. The absolute change in Ozone Monitoring Instrument (OMI) retrieved, and two highly-spatially resolved models (Modern-Era Retrospective Analysis for Research and Applications-2 (MERRA-2) and Copernicus Atmosphere Monitoring Service (CAMS)) simulated SSA is <4% (<0.04-0.05) globally during COVID (2020) compared to normal (2015-2019) period. Change in SSA during COVID is not significantly different from long-term and year-to-year variability in SSA. A small change in SSA indicates that significant reduction in anthropogenic aerosol emissions during COVID-19 induced lockdowns has a negligible effect in changing the net contribution of aerosol scattering and/or absorption to total aerosol extinction. The changes in species-wise aerosol optical depth (AOD) are examined in detail to explain the observed changes in SSA. Model simulations show that total AOD decreased during COVID-19 lockdowns, consistent with satellite observations. The respective contributions of sulfate and black carbon (BC) to total AOD increased, which resulted in a negligible change in SSA during the spring and summer seasons of COVID over South Asia. Europe and North America experience a small increase in SSA (<2%) during the summer season of COVID due to a decrease in BC contribution. The change in SSA (2%) is the same for a small change in BC AOD contribution (3%), and for a significant change in sulfate AOD contribution (20%) to total AOD. Since, BC SSA is 5-times lower (higher absorption) than that of sulfate SSA, the change in SSA remains the same. For a significant change in SSA to occur, the BC AOD contribution needs to be changed significantly (4-5 times) compared to other aerosol species. A sensitivity analysis reveals that change in aerosol radiative forcing during COVID is primarily dependent on change in AOD rather than SSA. These quantitative findings can be useful to devise more suitable future global and regional mitigation strategies aimed at regulating aerosol emissions to reduce environmental impacts, air pollution, and public health risks.

The light absorption enhancement (E-abs) of black carbon (BC) coated with non-BC materials is crucial in the assessment of radiative forcing, yet its evolution during photochemical aging of plumes from biomass burning, the globe's largest source of BC, remains poorly understood. In this study, plumes from open burning of corn straw were introduced into a smog chamber to explore the evolution of E-abs during photochemical aging. The light absorption of BC was measured with and without coating materials by using a thermodenuder, while the size distributions of aerosols and composition of BC coating materials were also monitored. E-abs was found to increase initially, and then decrease with an overall downward trend. The lensing effect dominated in E-abs at 520 nm, with an estimated contribution percentages of 47.5%-94.5%, which is far greater than light absorption of coated brown carbon (BrC). The effects of thickening and chemical composition changes of the coating materials on E-abs were evaluated through comparing measured E-abs with that calculated by the Mie theory. After OH exposure of 1 x 10(10) molecules cm(-3) s, the thickening of coating materials led to an E-abs increase by 3.2% +/- 1.6%, while the chemical composition changes or photobleaching induced an E-abs decrease by 4.7% +/- 0.6%. Simple forcing estimates indicate that coated BC aerosols exhibit warming effects that were reduced after aging. The oxidation of light-absorbing CxHy compounds, such as polycyclic aromatic hydrocarbons (PAHs), to CxHyO and CxHyO>1 compounds in coating materials may be responsible for the photobleaching of coated BrC. Plain Language Summary Understanding how black carbon (BC) coated with non-BC materials affects light absorption is crucial for assessing its impact on the Earth's climate. However, there is limited knowledge about how this process changes when BC, particularly from biomass burning, is exposed to light. Biomass burning is a significant global source of BC. This study investigated the changes in light absorption of BC from burning corn straw as it aged in a controlled environment. We measured the light absorption of BC with and without its coating materials. Our results showed that the main cause of increased light absorption was the lensing effect of the coating materials, which was more significant than the light absorption by the coating materials themselves. We also discovered that as the coating materials thickened, BC absorbed more light. However, changes in the chemical composition of the coating materials led to a decrease in total absorption. These findings suggest that while coated BC initially has a warming effect on the climate, this effect diminished as the BC ages. The decrease is likely due to the breakdown of light-absorbing compounds in the coating materials, such as polycyclic aromatic hydrocarbons (PAHs).

High uncertainty in optical properties of black carbon (BC) involving heterogeneous chemistry has recently attracted increasing attention in the field of atmospheric climatology. To fill the gap in BC optical knowledge so as to estimate more accurate climate effects and serve the response to global warming, it is beneficial to conduct site-level studies on BC light absorption enhancement (E-abs) characteristics. Real-time surface gas and particulate pollutant observations during the summer and winter over Wuhan were utilized for the analysis of E-abs simulated by minimum R squared (MRS), considering two distinct atmospheric conditions (2015 and 2017). In general, differences in aerosol emissions led to E-abs differential behaviors. The summer average of E-abs (1.92 +/- 0.55) in 2015 was higher than the winter average (1.27 +/- 0.42), while the average (1.11 +/- 0.20) in 2017 summer was lower than that (1.67 +/- 0.69) in winter. E-abs and R-BC (representing the mass ratio of non-refractory constituents to elemental carbon) constraints suggest that E-abs increased with the increase in R-BC under the ambient condition enriched by secondary inorganic aerosol (SIA), with a maximum growth rate of 70.6% in 2015 summer. However, E-abs demonstrated a negative trend against R-BC in 2017 winter due to the more complicated mixing state. The result arose from the opposite impact of hygroscopic SIA and absorbing OC/irregular distributed coatings on amplifying the light absorbency of BC. Furthermore, sensitivity analysis revealed a robust positive correlation (R > 0.9) between aerosol chemical compositions (including sulfate, nitrate, ammonium and secondary organic carbon), which could be significantly perturbed by only a small fraction of absorbing materials or restructuring BC through gaps filling. The above findings not only deepen the understanding of BC, but also provide useful information for the scientific decision-making in government to mitigate particulate pollution and obtain more precise BC radiative forcing.

Global warming in tandem with surface albedo reduction caused by black carbon (BC) deposition on glaciers accelerated glacier melting; however, their respective contributions remain unclear. Glaciers in the Qilian Mountains are crucial for the development of oases in the Hexi Corridor; however, their area has decreased by more than 20% over the past half-century. Thus, this study developed a dynamic deposition model for light-absorbing particles (LAPs), coupled with a surface energy and mass balance model. We comprehensively assessed the effects of BC and warming on the melting of a typical glacier in the Qilian Mountains based on the coupled model. BC on the glacier surface caused 13.1% of annual glacier-wide melting, of which directly deposited atmospheric BC reduced the surface albedo by 0.02 and accounted for 9.1% of glacier melting. The air temperature during 2000-2010 has increased by 1.5 degrees C relative to that during the 1950s, accounting for 51.9% of current glacier melting. Meanwhile, BC emission have increased by 4.6 times compared to those of the early Industrial Revolution recorded in an ice core, accounting conservatively for 6.3% of current glacier melting. Mitigating BC emissions has a limited influence on current glacier melting; however, in the long-term, mitigation should exert a noteworthy impact on glacier melting through the self-purification of glaciers.

A critical comprehension of the impact of snow cover on urban bidirectional reflectance is pivotal for precise assessments of energy budgets, radiative forcing, and urban climate change. This study develops a numerical model that employs the Monte Carlo ray-tracing technique and a snow anisotropic reflectance model (ART) to simulate spectral albedo and bidirectional reflectance, accounting for urban structure and snow anisotropy. Validation using three flat surfaces and MODIS data (snow-free, fresh snow, and melting snow scenarios) revealed minimal errors: the maximum domain-averaged BRDF bias was 0.01% for flat surfaces, and the overall model-MODIS deviation was less than 0.05. The model's performance confirmed its accuracy in reproducing the reflectance spectrum. A thorough investigation of key factors affecting bidirectional reflectance in snow-covered urban canyons ensued, with snow coverage found to be the dominant influence. Urban coverage, building height, and soot pollutant concentration significantly impact visible and infrared reflectance, while snow grain size has the greatest effect on shortwave infrared. The bidirectional reflectance at backward scattering angles (0.5-0.6) at 645 nm is lower than forward scattering (around 0.8) in the principal plane as snow grain size increases. These findings contribute to a deeper understanding of snow-covered urban canyons' reflectance characteristics and facilitate the quantification of radiation interactions, cloud-snow discrimination, and satellite-based retrieval of aerosol and snow parameters.

Aerosol optical properties, including absorption and scattering coefficients (B-abs, and B-scat), extinction coefficient (B-ext), single scattering albedo (SSA), and so forth, are critical metrics to estimate the radiative balance of the atmosphere. However, their ground measurements are sparsely distributed in the world, where Central Asia is void in these measurements. We had been performing the measurements of AOPs and BC with a photoacoustic extinctiometer (PAX) in Jimunai, a border town of China neighboring Kazakhstan, Central Asia, from Aug 2016 to Apr 2019. This three-year study first reported statistically significant trends of B-abs, B-scat, B-ext, SSA, and derived concentrations of BC (Mann-Kendall trend test, p-value 0.05) in the Central-Asian area. B-abs and B-scat show increasing trends and SSA was decreasing determined by the greater increasing pace of B-abs than B-scat. Seasonal and diurnal variations of the AOPs were associated with climate shift and residents' commute activity, respectively. The difference in the magnitudes and trends of AOPs between the measurements and satellites' observations advise that more care should be invested when choosing remote-sensing data to represent the AOPs at a specific site. The increasing trend of derived BC concentrations is reflected in the deposition record of BC in a snowpit of the nearby Muz Taw glacier. We suppose that the dramatically increasing BC particles emitted from Jimunai are significant factors triggering the melting of the adjacent mountain glaciers. The outflow of dust from the neighboring Gurbantiinggiit Desert could occasionally invade into Jimunai and deteriorate the local air quality, as evidenced by a probable dust event captured by the PAX on Feb 15, 2018. Finally, we outlook the future perspectives of measurements in Jimunai as a long-standing station.

To address data scarcity on long-term glacial discharge and inadequacies in simulating and predicting hydrological processes in the Tien Shan, this study analysed the observed discharge at multiple timescales over 1980s-2017 and projected changes within a representative glacierized high-mountain region: eastern Tien Shan, Central Asia. Hydrological processes were simulated to predict changes under four future scenarios (SSP1, SSP2, SSP3, and SSP5) using a classical hydrological model coupled with a glacier dynamics module. Discharge rates at annual, monthly (June, July, August) and daily timescales were obtained from two hydrological gauges: Urumqi Glacier No.1 hydrological station (UGH) and Zongkong station (ZK). Overall, annual and summer discharge increased significantly ( p < 0.05) at both stations over the study period. Their intra-annual variations mainly resulted from differences in their recharge mechanisms. The simulations show that a tipping point in annual discharge at UGH may occur between 2018 and 2024 under the four SSPs scenarios. Glacial discharge is predicted to cease earlier at ZK than at UGH. This relates to glacier type and size, suggesting basins with heavily developed small glaciers will reach peak discharge sooner, resulting in an earlier freshwater supply challenge. These findings serve as a reference for research into glacial runoff in Central Asia and provide a decision-making basis for planning local water-resource projects.

The freezing index (FI) is one of the most important indicators that shows the variation of permafrost. However, the relationship between climate change and the thermal conditions of permafrost is not understood well. This study analyzed the variation of FI based on 5-cm soil temperature derived from 74 meteorological stations from 1977 to 2016 on the Qinghai-Tibet Plateau (QTP). Furthermore, the factors affecting the FI variation and its relationship with permafrost degradation were also discussed. The results showed that FI was much smaller in the interior than other areas of the QTP, and it increased at a rate of 53.0 degrees C d/10a during the 40 years. FI in the main body of the QTP was relatively stable than surrounding areas; it was more stable in the northern part than in the southern part. On average, the FI variation coefficient was larger than 10%, indicating the large fluctuation of FI during the 40 years. FI decreased with the increasing altitude; it was more sensitive to the altitude in the south of 33 degrees N than in the north. The variation of FI was closely related to the maximum freezing depth (MFD) and the active layer thickness (ALT). It was observed that MFD decreased and ALT increased by approximately 1.4 cm and 1.6 cm, respectively, with each 10.0 degrees C d increase in FI. The results exhibited the thermal condition variation of the permafrost in QTP and revealed a degrading trend of the permafrost.

Knowledge of the paleoclimatic record of the northeastern Tibetan Plateau (NETP) can potentially improve our understanding of the evolution of the Asian summer monsoon (ASM). However, the history of climate change and inferred spatial extent of the ASM on the NETP since the last deglaciation remain unclear. Here, we use several environmental proxies from the sediments of Hala Lake (beyond the modern limit of ASM), including chironomids, loss-on-ignition, grain size and element data, to explore the climatic history of the NETP and the northern boundary of the ASM since the last deglaciation. The results document a series of climatic events during the deglaciation, including Heinrich Event 1, the Bolling-Allerod interstadial and the Younger Dryas event. The records also reveal the timing of the megathermal and precipitation maximum, the lake-level maximum, and strongest chemical weathering, which occurred during similar to 10-7 ka. The inferred precipitation maximum during the early Holocene in the Hala Lake basin, which can be verified by the simulated precipitation change, is consistent with that in typical Indian summer monsoon (ISM) regions, suggesting that the ISM has penetrated into Hala Lake basin at that time. The monsoon-dominated climate in the Hala Lake basin during the early Holocene and the westerlies-dominated climate in the arid central Asia indicate that the maximum areal extent of the ASM on the NETP since the last deglaciation lay to the northwest of Hala Lake basin. In combination with other published records, the northernmost boundary of the ASM over China since the last deglaciation has been tentatively delineated, to shed some lights on this long-standing debate.