A novel potential cause of extreme precipitation in the northwest China.

The northwest China is a climate change-sensitive and ecologically vulnerable area. Under the backdrop of global warming, this region exhibits clear characteristics of warming and wetting. In recent years, the causes of climate change in the northwest China has become a widely-focused topic. Previous research has mainly attributed the increase in precipitation to changes in the westerly belt and enhanced local convective activity caused by global warming. South Asia, beside the Tibetan Plateau from the northwest China, is one of the regions with the fastest growth in global atmospheric pollutant emissions. This study utilizes reanalysis data such as ERA5 and MERRA-2. Statistical methods, including Theil-Sen Median trend analysis and Singular Value Decomposition analysis, are employed to analyze the spatiotemporal characteristics of South Asian aerosols, extreme precipitation in the northwest China, and the correlation between the two. The study reveals the existence of two key aerosol-precipitation response areas. Synthetic analysis of the meteorological elements of the response events in both regions is conducted to explore the possible physical mechanisms behind the correlation between South Asian aerosols and precipitation in the northwest China. The result of this study is to provide a new perspective on the causes of extreme precipitation in the arid region of northwest China.

Dark-Channel Soft-Constrained and Object-Perception-Enhanced Deep Dehazing Networks Used for Road Inspection Images.

Haze seriously affects the visual quality of road inspection images and contaminates the discrimination of key road objects, which thus hinders the execution of road inspection work. The basic assumptions of the classical dark-channel prior are not suitable for road images containing light-colored lane lines and vehicles, while typical deep dehazing networks lack physical model interpretability, and they focus on global dehazing effects, neglecting the preservation of object features. For this reason, this paper proposes a Dark-Channel Soft-Constrained and Object-Perception-Enhanced Deep Dehazing Network (DCSC-OPE-Net) for the information recovery of road inspection images. The network is divided into two modules: a dark-channel soft-constrained dehazing module and a near-view object-perception-enhanced module. Unlike the traditional dark-channel algorithms that impose strong constraints on dark pixels, a dark-channel soft-constrained loss function is constructed to ensure that the features of light-colored vehicles and lane lines are effectively maintained. To avoid resolution loss due to patch-based dark-channel processing for image dehazing, a resolution enhancement module is used to strengthen the contrast of the dehazed image. To autonomously perceive and enhance key road features to support road inspection, edge enhancement loss combined with a transmission map is embedded into the network to autonomously discover near-view objects and enhance their key features. The experiments utilize public datasets and real road inspection datasets to validate the performance of the proposed DCSC-OPE-Net compared with typical networks using dehazing evaluation metrics and road object recognition metrics. The experimental results demonstrate that the proposed DCSC-OPE-Net can obtain the best dehazing performance, with an NIQE score of 4.5 and a BRISQUE score of 18.67, and obtain the best road object recognition results (i.e., 83.67%) among the comparison methods.

Warming and Wetting will continue over the Tibetan Plateau in the Shared Socioeconomic Pathways.

We have used bias-corrected data from CMIP6 models to drive a regional climate model and project climate on the Tibetan Plateau (TP) in the 21st century. Changes in two background fields, namely, 2-meter air temperature and total precipitation, were analyzed. The results show that the WRF simulations capture the terrain effect that cannot be represented in low-resolution models. The simulation of temperature is better in summer than in winter, while the simulated precipitation is the opposite. By the end of the 21st century, the entire TP region experiences significant warming, with an average warming of 3°C and 7°C in the SSP245 and SSP585 scenarios, respectively. The western region shows a greater warming amplitude, with a maximum of more than 10°C in the SSP585 scenario. Most regions of the TP had significant increases in precipitation by the end of the 21st century, with precipitation increasing by 90 mm and 200 mm in the two scenarios, respectively. However, in the low-altitude areas of southeastern TP, total winter precipitation is significantly reduced in the SSP585 scenario. The strengthening of the East Asian summer monsoon and westerly disturbances collectively leads to a significant increase in precipitation within the TP region. By the end of the 21st century, the average annual precipitation in the TP is projected to reach approximately 600 millimeters.

South Asian black carbon is threatening the water sustainability of the Asian Water Tower.

Long-range transport of black carbon from South Asia to the Tibetan plateau and its deposition on glaciers directly enhances glacier melt. Here we find South Asian black carbon also has an indirect effect on the plateau's glaciers shrinkage by acting to reduce the water supply over the southern Tibetan plateau. Black carbon enhances vertical convection and cloud condensation, which results in water vapor depletion over the Indian subcontinent that is the main moisture flux source for the southern Tibetan plateau. Increasing concentrations of black carbon causes a decrease in summer precipitation over the southern Tibetan plateau, resulting in 11.0% glacier deficit mass balance on average from 2007 to 2016; this loss rises to 22.1% in the Himalayas. The direct (accelerated melt) and indirect (mass supply decrease) effects of black carbon are driving the glacial mass decline of the so-called "Asian Water Tower".

Temperature Induced Dimensional Tuning and Anomalous Deformation of Micro/Nanopores.

Artificial nanopores have become a common toolbox in nanotechnologies, with dimension and geometry as predominant factors. Most fabrication technologies determine the pore size beforehand, but few exist that enable size-tuning post-manufacturing. In this work, we reported a type of ion track etched micro/nanopores on uniaxially drawn PET foils that enable irreversible thermal shrinkage, thus tuning the pore dimensions by increasing ambient temperatures. Importantly, we found a complex pore deformation process, which for a specific range of pore sizes and temperatures resulted in a peculiar "eye"-shaped appearance of the pore openings. We analyzed the mechanical stresses and theoretically illustrated the complex deformation process by a phase diagram. Temperature-induced dimensional tuning nanopores reduced maximally over 98% of ionic conduction in a single nanopore and 99% of pressure-driven flow in a pore-array membrane within few seconds at 90 °C, which is useful for temperature-modulated mass transport in nanotechnology and energy applications.

Contribution of South Asian biomass burning to black carbon over the Tibetan Plateau and its climatic impact.

This study used a regional climate-chemistry transport model, WRF-Chem v3.9.1, to evaluate the impact of South Asian biomass burning on black carbon (BC) over the Tibetan Plateau (TP) and its climatic effects for an entire year. The simulation, which was validated by comparing surface meteorological parameters and BC concentration against in-situ observations over South Asia and the TP, provided a perspective on the seasonal variations and regional spatial patterns of BC concentration. Using a sensitivity simulation where BC emissions from biomass burning were removed from South Asia, this study found South Asian biomass burning emissions contributed up to 90% of BC mass over the TP during the pre-monsoon season, specifically emissions from western India for the simulated year. The emissions led to reduced surface radiative forcing, causing the temperature to decrease accordingly. However, column cloud water was increased. This study suggested that the biomass burning emissions from South Asia have significant impact on atmospheric BC over the TP, especially during the pre-monsoon season. Therefore, reducing biomass burning emissions from South Asia is potentially important for alleviating the effects of BC on climatic and environmental conditions over the TP and surrounding regions.

Investigation of black carbon climate effects in the Arctic in winter and spring.

Black carbon (BC) exerts a potential influence on climate, especially in the Arctic, where the environment is very sensitive to climate change. Therefore, the study of climate effects of BC in this region is particularly important. In this study, numerical simulations were performed using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) in the Arctic in winter and spring for two years to investigate the atmospheric BC causing changes in surface radiation, meteorology, and atmospheric stability. Generally, WRF-Chem well reproduced the temporal variations of meteorological variables and BC concentration. Numerical simulations showed that BC concentrations in the Arctic in winter were mostly higher than those in spring, and the BC-induced near-surface temperature changes were also stronger. The effects of BC on near-surface water vapor mixing ratio were consistent with the spatial pattern of near-surface temperature changes. That was probably the result of the regional circulation anomaly due to the temperature changes. Additionally, the distributions of near-surface temperature changes and horizontal wind changes also reflected in the distribution of planetary boundary layer height. Ultimately, this study revealed that the downward longwave radiation related to cloudiness changes played an important role for driving near-surface temperature in the Arctic in winter. While in spring, the relatively less changes in near-surface temperature may be the result of the mutual compensation between the surface longwave and shortwave radiation effects.

Bioinspired Dual-Responsive Nanofluidic Diodes by Poly-l-lysine Modification.

A smart nanofluidic device attracts attention as it enables to control the physicochemical properties and transportation phenomena, by using stimuli-responsive materials. This work reports a bioinspired modification of a conical ion track-etched polyethylene terephthalate nanopore surface by coating a layer of poly-l-lysine (PLL), which is a commonly used coating in biotechnology to achieve a dual-responsive nanofluidic channel by pH or temperature. The rectification of ionic transportation can be reversed by assembling PLL because of the change of surface bonds from the carboxyl to amine group. The PLL-modified nanopore becomes nonconductive as an "OFF" state at pH 11.5 and at a temperature of 70 °C in solution. The ionic transport in nanopores can be switched to the "ON" (conductive) state, by either decreasing pH or temperature. The transitions between "ON" and "OFF" states present excellent reversibility, which make the PLL-modified nanopores a promising smart nanofluidic device that can be used for drug delivery or biomimic ion/mass transport in future, besides the good biocompatibility and ease of use of PLL modification.

Investigating air pollutant concentrations, impact factors, and emission control strategies in western China by using a regional climate-chemistry model.

In this study, in situ observations were conducted for six criteria air pollutants (PM2.5, PM10, SO2, NO2, CO, and O3) at 23 sites in western China for 1 year. Subsequently, the detailed Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) results for the pollutants were determined. The WRF-Chem model provided a clear perspective on the spatiotemporal distribution of air pollutants. High pollutant concentrations were mainly observed over highly populated mega-city regions, such as Sichuan and Guanzhong basins, whereas low concentration levels were observed over the Tibetan Plateau (TP). The TP also showed an increased concentration of O3. Seasonally, all six pollutants except O3 exhibited high concentration values during winter and low values during summer. O3 concentrations exhibited an opposite seasonal variation in low-altitude regions. Unlike other pollutants that exhibited gradually decreasing concentrations with an increase in altitude, O3 concentrations revealed an increasing trend. Furthermore, NO2 concentrations gradually increased in the upper atmosphere possibly due to lighting and stratospheric transmission. Atmospheric pollution is closely related to emissions and meteorological variations in western China. Meteorological conditions in the summer are conducive to pollutant dispersion and wet scavenging; however, unfavourable weather conditions (high pressure as well as a low planetary boundary layer height and precipitation level) in the winter can further worsen air pollution. Atmospheric pollutants from various emission sectors generally exhibited varying monthly profiles. In six typical cities, pollutants were positively correlated with multiple emission sources except for industrial emissions. Further sensitivity simulations indicated that eliminating residential emissions resulted in the largest decrease (up to 70%) in PM2.5 and PM10 concentrations. The most significant reductions in the concentrations of SO2 and NO2 were achieved by eliminating industrial and transportation emissions, respectively. The outcomes of this study could be helpful for future studies on pollution formation mechanisms as well as environmental and health risk assessments in western China.

Critical contribution of south Asian residential emissions to atmospheric black carbon over the Tibetan plateau.

Black carbon (BC) over the Tibetan Plateau (TP), both in the air and deposited on the surface of snow and ice, has been shown to accelerate the retreat of mountain glaciers. Previous study indicated that South Asian anthropogenic emissions primarily contributed to atmospheric loading of BC over the TP, it is essential to further identify the major sector in South Asia and provide guidance for potential mitigation strategies. In this study, the regional atmospheric chemistry model WRF-Chem was run for an entire year. The results suggested that residential BC emissions from South Asia contributed the largest (25.8% in summer and 44.8% in winter) to BC concentrations over the TP compared to other anthropogenic emission sectors in the region. Furthermore, significant seasonal variability existed in the transport process of residential BC from South Asia to the TP. The South Asia monsoon during summer and the mountain-valley wind system during spring could transport South Asian residential BC across the Himalayas to the TP. However, the higher transportation flux along 30°N indicated that the transport was mainly influenced by westerly winds, implying that residential emissions from northern India were the critical source of BC aerosols over the TP. A further assessment of emission control strategies suggested that reducing emissions from South Asian residential sources can effectively reduce BC concentrations over the TP, which may potentially alleviate the TP's accelerating glacier melting.

Geometry-on-demand fabrication of conductive microstructures by photoetching and application in hemostasis assessment.

Photo-corrosion is a common phenomenon observed in the photocatalytic semiconductor materials, which can seriously harm the photoelectric properties and performances in the energy applications. However, in this paper, we demonstrated that the photo-corrosion effects can be used for the microfabrication of conductive structures on a photocatalytic film like zinc oxide (ZnO), named as "photoetching". Our results demonstrated that microstructures can be prepared within seconds with a precision at an order of tens of micrometers using our current devices. Different from the previous work, the etching process was achieved free of conducting layer under the ZnO film, avoiding the short-circuit of the conductive micro-patterns and enabling the use for the impedance sensing. We demonstrated the fabricated ZnO microelectrode pairs can work for the electrochemical impedance measurements like assessment of hemostasis integrated with a microfluidic chip. Compared to the noble metal microelectrodes, the ZnO conductive microelectrodes can be fabricated within seconds and the low costs make it possible as a disposable diagnostic device. Besides, the photoetching technique can be performed without a cleanroom reducing the technical barriers, possibly helpful for the low resources areas. We believe the simplicity of device, low costs and fast fabrication can be useful in the relevant fields such as biomedical and energy harvesting, especially for low resources areas.

Nitrogen Speciation and Isotopic Composition of Aerosols Collected at Himalayan Forest (3326 m a.s.l.): Seasonality, Sources, and Implications.

Nitrogenous aerosols are ubiquitous in the environment and thus play a vital role in the nutrient balance as well as the Earth's climate system. However, their abundance, sources, and deposition are poorly understood, particularly in the fragile and ecosensitive Himalayan and Tibetan Plateau (HTP) region. Here, we report concentrations of nitrogen species and isotopic composition (δ15N) in aerosol samples collected from a forest site in the HTP (i.e., Southeast Tibet). Our results revealed that both organic and inorganic nitrogen contribute almost equally with high abundance of ammonium nitrogen (NH4+-N) and water-insoluble organic nitrogen (WION), contributing ∼40% each to aerosol total nitrogen (TN). The concentrations and δ15N exhibit a significant seasonality with ∼2 times higher in winter than in summer with no significant diurnal variations for any species. Moreover, winter aerosols mainly originated from biomass burning emissions from North India and East Pakistan and reached the HTP through a long-range atmospheric transport. The TN dry deposition and total deposition fluxes were 2.04 kg ha-1 yr-1 and 6.12 kg ha-1 yr-1 respectively. Our results demonstrate that the air contamination from South Asia reach the HTP and is most likely impacting the high altitude ecosystems in an accepted scenario of increasing emissions over South Asia.

Spatiotemporal variations of air pollutants in western China and their relationship to meteorological factors and emission sources.

We have carried out a comprehensive analysis of six air pollutants (particles with an aerodynamic diameter less than 2.5 µm (PM2.5) and less than 10 µm (PM10), carbon monoxide (CO), sulfur dioxide (SO2), nitrogen dioxide (NO2), and ozone (O3)) in western China, including the spatiotemporal characteristics of air pollutants, their relationship with meteorological factors and emission sources, and the efficiency of emission control strategies for the region. Based hourly observations at 23 sites in western China from June 2016 to May 2017, concentrations of most pollutants were higher outside the Tibetan Plateau, lowest in summer and highest in winter, the exception being O3. This was partially because meteorological conditions in winter were found to the most unfavorable to pollutant dispersion and dilution than other seasons. Pollutant concentrations at most sites were correlated with the residential emissions which were higher in winter, but anti-correlated with the industrial emissions which were lower during the winter holiday period. The Weather Research and Forecasting with Chemistry (WRF-Chem) simulations of four pollution control strategies indicated that reduction of residential emissions is crucial to alleviate PM2.5, PM10, and CO pollution in western China, although reduction of industrial and transport emissions can reduce SO2 and NO2, respectively. Since PM2.5 and PM10 were also found to be the species most and next frequently responsible for extremely serious pollution in western China, respectively, we recommend pollution control regulations that target residential emissions.

Carbonaceous aerosol characteristics on the Third Pole: A primary study based on the Atmospheric Pollution and Cryospheric Change (APCC) network.

Carbonaceous aerosols (CAs) scatter and absorb incident solar radiation in the atmosphere, thereby influencing the regional climate and hydrological cycle, particularly in the Third Pole (TP). Here, we present the characteristics of CAs at 19 observation stations from the Atmospheric Pollution and Cryospheric Change network to obtain a deep understanding of pollutant status in the TP. The organic carbon (OC) and elemental carbon (EC) concentrations decreased noticeably inwards from outside to inland of the TP, consistent with their emission load and also affected by transport process and meteorological condition. Urban areas, such as Kathmandu, Karachi, and Mardan, exhibited extremely high OC and EC concentrations, with low and high values occurring in the monsoon and non-monsoon seasons, respectively. However, remote regions inland the TP (e.g., Nam Co and Ngari) demonstrated much lower OC and EC concentrations. Different seasonal variations were observed between the southern and northern parts of the TP, suggesting differences in the patterns of pollutant sources and in distance from the sources between the two regions. In addition to the influence of long-range transported pollutants from the Indo-Gangetic Plain (IGP), the TP was affected by local emissions (e.g., biomass burning). The OC/EC ratio also suggested that biomass burning was prevalent in the center TP, whereas the marginal sites (e.g., Jomsom, Dhunche, and Laohugou) were affected by fossil fuel combustion from the up-wind regions. The mass absorption cross-section of EC (MACEC) at 632 nm ranged from 6.56 to 14.7 m2 g-1, with an increasing trend from outside to inland of the TP. Urban areas had low MACEC values because such regions were mainly affected by local fresh emissions. In addition, large amount of brown carbon can decrease the MACEC values in cities of South Asia. Remote sites had high MACEC values because of the coating enhancement of aerosols. Influenced by emission, transport process, and weather condition, the CA concentrations and MACEC presented decreasing and increasing trends, respectively, from outside to inland of the TP.

Linking atmospheric pollution to cryospheric change in the Third Pole region: current progress and future prospects.

The Tibetan Plateau and its surroundings are known as the Third Pole (TP). This region is noted for its high rates of glacier melt and the associated hydrological shifts that affect water supplies in Asia. Atmospheric pollutants contribute to climatic and cryospheric changes through their effects on solar radiation and the albedos of snow and ice surfaces; moreover, the behavior and fates within the cryosphere and environmental impacts of environmental pollutants are topics of increasing concern. In this review, we introduce a coordinated monitoring and research framework and network to link atmospheric pollution and cryospheric changes (APCC) within the TP region. We then provide an up-to-date summary of progress and achievements related to the APCC research framework, including aspects of atmospheric pollution's composition and concentration, spatial and temporal variations, trans-boundary transport pathways and mechanisms, and effects on the warming of atmosphere and changing in Indian monsoon, as well as melting of glacier and snow cover. We highlight that exogenous air pollutants can enter into the TP's environments and cause great impacts on regional climatic and environmental changes. At last, we propose future research priorities and map out an extended program at the global scale. The ongoing monitoring activities and research facilitate comprehensive studies of atmosphere-cryosphere interactions, represent one of China's key research expeditions to the TP and the polar regions and contribute to the global perspective of earth system science.

Vital contribution of residential emissions to atmospheric fine particles (PM2.5) during the severe wintertime pollution episodes in Western China.

To mitigate severe wintertime pollution events in Western China, identifying the source of atmospheric fine particles with an aerodynamic diameter of ≤2.5 µm (PM2.5) is a crucial step. In this study, we first analyzed the meteorological and emission factors that caused a considerable increase in the PM2.5 concentration in December 2016. This severe pollution episode was found to be related with unfavorable meteorological conditions and increased residential emissions. The WRF-Chem simulations were used to calculate the residential contribution to PM2.5 through a hybrid source apportionment method. From the validation that used grid data and in situ observations in terms of meteorological elements, PM2.5 and its compounds, the simulated results indicated that the residential sector was the largest single contributor to the PM2.5 concentration (60.2%), because of its predominant contributions to black carbon (BC, 62.1%) and primary organic aerosol (POA, 86.5%), with these two primary components accounting for 70.7% of the PM2.5 mass. Compared with the remote background (RB) region covering the central part of the Tibetan Plateau, the residential sector contributed 11.3% more to PM2.5 in the highly populated mega-city (HM) region, including the Sichuan and Guanzhong Basins, due to greater contribution to the concentrations of primary PM2.5 components. As the main emission source of sulfur dioxide (SO2), nitrogen oxides (NOx), and secondary organic aerosol (SOA), the industrial sector was the second largest contributor to the PM2.5 concentration in the HM region. However, in the RB region, the dominating emissions of NOx, SOA, and BC were from the transport sector; thus, it was the next largest contributor to total PM2.5. An evaluation of the emission control experiment suggested that mitigation strategies that reduce emissions from residential sources can effectively reduce the PM2.5 concentration during heavy pollution periods.

Characteristics and sources of polycyclic aromatic hydrocarbons in atmospheric aerosols in the Kathmandu Valley, Nepal.

The Kathmandu Valley in the foothills of the Himalayas, where the capital city of Nepal is located, has one of the most serious air pollution problems in the world. In this study, total suspended particle (TSP) samples collected over a year (April 2013-March 2014) in the Kathmandu Valley were analyzed for determining the concentrations of 15 priority particle-bound polycyclic aromatic hydrocarbons (PAHs). The TSP and PAH concentrations were extremely high, with annual average concentration being 199±124µg/m(3) and 155±130ng/m(3), respectively, which are comparable to those observed in Asian cities such as Beijing and Delhi. The TSP and PAH concentrations varied considerably, with the seasonal average concentration being maximal during the post-monsoon season followed by, in descending order, the winter, pre-monsoon, and monsoon seasons. In the winter and pre-monsoon seasons, ambient TSP and PAH concentrations increased because of emissions from brick kilns and the use of numerous small generators. Moreover, in the pre-monsoon season, forest fires in the surrounding regions influenced the TSP and PAH concentrations in the valley. PAHs with 4 to 6 rings constituted a predominant proportion (92.3-93.3%) of the total PAHs throughout the year. Evaluation of diagnostic molecular ratios indicated that the atmospheric PAHs in the Kathmandu Valley originated mainly from diesel and biomass combustion. The toxic equivalent quantity (TEQ) of particle phase PAHs ranged between 2.74 and 81.5ngTEQ/m(3), which is considerably higher than those reported in other South Asian cities, and 2-80 times higher than the World Health Organization guideline (1ngTEQ/m(3)). This suggests that ambient PAH levels in the Kathmandu Valley pose a serious health risk to its approximately 3.5 million residents.