The Significant Contribution of Small-Sized and Spherical Aerosol Particles to the Decreasing Trend in Total Aerosol Optical Depth over Land from 2003 to 2018

The optical and microphysical properties of aerosols remain one of the greatest uncertainties associated with evaluating the climate forcing attributed to aerosols.Although the trends in aerosol optical depth(AOD)at global and regional scales have been widely examined,little attention has been paid to the trends in type-dependent AODs related to aerosol particle properties.Here,using the aerosol optical component dataset from the Multi-angle Imaging SpectroRadiometer(MISR)instrument,we investigate decadal-scale trends in total aerosol loading as well as AODs for five aerosol components by particle size and morphology during 2003–2018 over land.Relationships between the total AOD(TAOD)trends and type-dependent AOD changes were examined,and the relative contribution of each type-dependent AOD to the overall TAOD trends was quantified.By dividing the TAOD values into four different aerosol pollution levels(APLs)with splits at 0.15,0.40,and 0.80,we further explored the relationships between TAOD changes and interannual variations in the frequency-of-occurrences(FoOs)of these APLs.Long-term trends in FoOs in the different APLs show that there was a significant improvement in air quality between 2003 and 2018 in most land areas,except South Asia,corresponding to a shift from lightly polluted to clean conditions.However,the effects of different APLs on TAOD changes are regionally dependent and their extent of correlation varied spatially.Moreover,we observed that the annual mean TAOD has decreased by 0.47%.a^(-1)over land since 2003(P<0.05).This significant reduction was mainly attributed to the continued reduction in small-sized(<0.7 mm diameter)AOD(SAOD)(-0.74%.a^(-1))and spherical AOD(SPAOD)(-0.46%.a^(-1)).Statistical analysis shows that SAOD and SPAOD respectively accounted for 57.5%and 89.6%of the TAOD,but contributed 82.6%and 90.4%of the trend in TAOD.Our study suggests that small-sized and spherical aerosols composed of sulfate,organic matter,and black carbon play a dominant role in determining interannual variability in land TAOD.

超强金属/高熵合金纳米叠层材料:利用相变的尺寸约束效应

本文通过磁控溅射制备了具有相同组元层厚度(h=5-150 nm)的Cu/Fe_(50)Mn_(30)Co_(10)Cr_(10)和Cu/Fe_(50)Mn_(30)Co_(10)Ni_(10)金属/高熵合金纳米多层膜,对比研究了强约束条件下非等原子比Fe_(50)Mn_(30)Co_(10)Cr_(10)和Fe50Mn30-Co10Ni10高熵合金的相稳定性及其对力学性能的影响.沉积过程中由于组元Cu层的约束与模板效应,组元Fe_(50)Mn_(30)Co_(10)Cr_(10)层在层厚小于25 nm时发生了尺寸驱动的HCP到FCC相变.与此同时,由于堆垛层错可以作为相变的形核质点,Cu/Fe_(50)Mn_(30)Co_(10)Cr_(10)多层膜在压入变形过程中也发生了应力驱动的HCP到FCC相变.相比之下,Cu/Fe_(50)Mn_(30_)-Co_(10)Ni_(10)多层膜组织稳定,没有发生尺寸/应力驱动的相变行为.随层厚减小,两种Cu/高熵合金纳米多层膜均表现出了从层厚无关转变为层厚相关的超高硬度,这源于偏位错形核主导的强化机制.尤为特别的是,Cu/Fe_(50)Mn_(30)Co_(10)Cr_(10)多层膜的归一化硬度(实测硬度与混合法则预测硬度的比值)远高于传统的Cu基双金属多层膜.本文研究结果从调控高熵合金相变行为的角度为提高复合材料的强度和塑性提供了新思路.

The impact of meteorological changes from 2013 to 2017 on PM2.5 mass reduction in key regions in China

In 2013,China issued the"Action Plan for the Prevention and Control of Air Pollution"("Ten Statements of Atmosphere")and implemented a series of pollution reduction measures from 2013 to 2017.In key regions of China,the mass concentrations of particulate matter with aerodynamic equivalent diameters less than 2.5μm(PM2.5)have dropped significantly.However,the contributions of meteorological changes to PM2.5 reduction are largely uncertain,which has attracted particular concern from the government and the public.Here,we investigated the impact of large-scale and boundary layer(BL)meteorological conditions on aerosol pollution and estimated the contributions of meteorological changes to PM2.5 reduction based on in-depth analysis and diagnosis of various observed meteorological elements and an integrated pollution-linked meteorological index(PLAM,which is approximately and linearly related to PM mass concentration).In this study,we found that the meteorological conditions worsened in 2014 and 2015 and improved in 2016 and 2017 relative to those in 2013 in key regions in China.In 2017 relative to 2013,only^5%(approximately 13%of the total PM2.5 decline)of the 39.6%reduction in PM2.5 mass concentrations can be attributed to meteorological changes in the Beijing-Tianjin-Hebei(BTH)region,and only^7%(approximately 20%of the total PM2.5 decline)of the 34.3%reduction can be attributable to meteorological changes in the Yangtze River Delta(YRD)region.Overall,the PM2.5 reduction due to meteorological improvement is much lower than the observed PM2.5 reduction in these areas,which indicates that emission reduction during the five-year implementation of the"Ten Statements of Atmosphere"is the dominant factor in the improvement in air quality.The changes in meteorology and climate are conducive to PM2.5 reduction but do not dominate the substantial improvement in air quality.Similar to the above regions,in the Pearl River Delta(PRD)region,the impact of meteorological changes on the annual averaged PM2.5 concentration from 2013 to2017 was relatively weak,and the PM2.5 reduction was mainly due to emission reductions.During winter 2017(January,February,and December of this year),the meteorological conditions improved-20%in the BTH region(observed total PM2.5reduction:40.2%)and-30%in the YRD region(observed total PM2.5 reduction:38.2%)relative to those in 2013,showing the meteorological factors played more important role in the decrease of PM2.5 in winter of these years in the two regions,respectively.The meteorological conditions in winter 2016 were 14%better than those in winter 2017,but the PM2.5 reduction in winter 2016 was still less than that in winter 2017,reinforcing the significant contributions of the increasing efforts to reduce PM2.5 emissions in 2017.The substantial progress of strict emission measures was also confirmed by a comparison of several persistent heavy aerosol pollution episodes(HPEs)with similar meteorological conditions.It is found that the decrease of PM2.5mass caused by emission reduction increases year by year,especially the decrease of PM2.5 concentration in 2016 and 2017.In China,HPEs mainly occur in winter,when meteorological conditions are approximately 40-100%worse than in other seasons.This worsening is partly due to the harbor effect of high topography,including downdrafts and the weak wind zone,and partly due to the increasingly stable regional BL structure caused by climate warming.For the formation of HPEs,it occurred under regional stagnant and stable conditions associated with upper-level circulation patterns,including the zonal westerly winds type and high-pressure ridges.After pollution formation,PM2.5 with mass accumulated to a certain degree can further worsen the BL meteorological conditions.The feedback effect associated with worsening conditions dominates PM2.5 mass explosive growth.In the context of high air pollutant emissions in China,unfavorable meteorological conditions are the necessary external conditions for the formation and accumulation of HPEs.Therefore,reducing aerosol pollution significantly during the earlier transport stage is critical in reducing persistent HPEs.Currently,even under favorable meteorological conditions,allowing emissions without restriction is also not advisable because aerosol pollution allowed to accumulate to a certain extent will significantly worsen the BL meteorological conditions and close the"meteorological channels"available for pollution dispersion.

Relative Contributions of Boundary-Layer Meteorological Factors to the Explosive Growth of PM2.5 during the Red-Alert Heavy Pollution Episodes in Beijing in December 2016

Based on observations of urban mass concentration of fine particulate matter smaller than 2.5 μm in diameter （PM2.5）, ground meteorological data, vertical measurements of winds, temperature, and relative humidity （RH）, and ECMWF reanalysis data, the major changes in the vertical structures of meteorological factors in the boundary layer （BL） during the heavy aerosol pollution episodes （HPEs） that occurred in winter 2016 in the urban Beijing area were analyzed. The HPEs are divided into two stages： the transport of pollutants under prevailing southerly winds, known as the transport stage （TS）, and the PM2.5 explosive growth and pollution accumulation period characterized by a temperature inversion with low winds and high RH in the lower BL, known as the cumulative stage （CS）. During the TS, a surface high lies south of Beijing, and pollutants are transported northwards. During the CS, a stable BL forms and is characterized by weak winds, temperature inversion, and moisture accumulation. Stable atmospheric stratifica- tion featured with light/calm winds and accumulated moisture （RH 〉 80%） below 250 m at the beginning of the CS is closely associated with the inversion, which is strengthened by the considerable decrease in near-surface air temperat- ure due to the interaction between aerosols and radiation after the aerosol pollution occurs. A significant increase in the PLAM （Parameter Linking Aerosol Pollution and Meteorological Elements） index is found, which is linearly re- lated to PM mass change. During the first 10 h of the CS, the more stable BL contributes approximately 84% of the explosive growth of PM2.5 mass. Additional accumulated near-surface moisture caused by the ground temperature de- crease, weak turbulent diffusion, low BL height, and inhibited vertical mixing of water vapor is conducive to the sec- ondary aerosol formation through chemical reactions, including liquid phase and heterogeneous reactions, which fur- ther increases the PM2.5 concentration levels. The contribution of these reaction mechanisms to the explosive growth of PM2,5 mass during the early CS and subsequent pollution accumulation requires further investigation.

Aerosol Hygroscopicity during the Haze Red-Alert Period in December 2016 at a Rural Site of the North China Plain

A humidification system was deployed to measure aerosol hygroscopicity at a rural site of the North China Plain during the haze red-alert period 17–22 December 2016. The aerosol scattering coefficients under dry [relative humidity（RH） 〈 30%] and wet（RH in the range of 40%–85%） conditions were simultaneously measured at wavelengths of450, 550, and 700 nm. It is found that the aerosol scattering coefficient and backscattering coefficient increased by only 29% and 10%, respectively when RH went up from 40% to 80%, while the hemispheric backscatter fraction went down by 14%, implying that the aerosol hygroscopicity represented by the aerosol scattering enhancement factor f（RH） is relatively low and RH exerted little effects on the aerosol light scattering in this case. The scattering enhancement factors do not show significant differences at the three wavelengths, only with an approximate 2% variation, suggesting that the aerosol hygroscopicity is independent of the wavelength. Aerosol hygroscopicity is highly dependent on the aerosol chemical composition. When there is a large mass fraction of inorganics and a small mass fraction of organic matter, f（RH） reaches a high value. The fraction of NO3^- was strongly correlated with the aerosol scattering coefficient at RH = 80%, which suggests that NO3^- played an important role in aerosol hygroscopic growth during the heavy pollution period.

Cu/NbMoTaW纳米叠层材料具有尺寸效应的力学性能及变形机制（英文）

高熵合金(HEA)由于其在恶劣环境中优异的力学性能引起了研究者的广泛关注.我们将高熵合金NbMoTaW引入到纳米叠层材料中,制备出等层厚的Cu/HEA纳米多层膜,综合研究了其具有尺寸效应的力学性能及变形行为.实验表明,Cu/HEA纳米多层膜的硬度随着层厚h的减小而增加,随后在h≤50 nm的区域到达一个平台,而应变速率敏感性出现了一个最大值,这是由于Cu和HEA两相对应变速率敏感性的影响从协同转变为竞争.在层厚较大时,非共格界面导致Cu/HEA多层膜在变形后出现了剪切带,并且软相Cu层主导变形.

CHARACTERISTICS OF CLAY MINERALS IN ASIAN DUST AND THEIR ENVIRONMENTAL SIGNIFICANCE

The objectives of this research were to characterise the clay minerals composition of soil-derived dust in Northern China and to set up a mineralogical signature to trace their origin. Mineral composition of aerosol particles was investigated at Aksu, Dunhuang, Yulin, Tongliao and Changwu during an intensive field campaign period of ACE-Asia. The results show that the kaolinite （K） to chlorite （C） ratio is sensitive to the regional origin of Asian dust. Western source areas （represented by Aksu） displayed the lowest K/C ratio of 0.3 （average）, while it was found to increase up to 0.70 （average） upon moving towards northern source areas （represented by Yulin）. By studying transported dust in a deposition area representative of the Chinese Loess Plateau, the usefulness of the K/C ratio, when associated with back air-mass trajectories, was found to lie in revealing the origin of the dust. Comparison of the mineralogical data between Asian dust and Sahara dust, shows that the K/C ratio is also an effective signature to identify the source areas on a hemisphere scale.

Chemical Components, Variation, and Source Identification of PM1 during the Heavy Air Pollution Episodes in Beijing in December 2016

Air pollution is a current global concern. The heavy air pollution episodes（HPEs） in Beijing in December 2016 severely influenced visibility and public health. This study aims to survey the chemical compositions, sources, and formation processes of the HPEs. An aerodyne quadruple aerosol mass spectrometer（Q-AMS） was utilized to measure the non-refractory PM1（NR-PM1） mass concentration and size distributions of the main chemical components including organics, sulfate, nitrate, ammonium, and chloride in situ during 15–23 December 2016. The NR-PM1 mass concentration was found to increase from 6 to 188 μg m–3 within 5 days. During the most serious polluted episode, the PM1 mass concentration was about 2.6 times that during the first pollution stage and even 40 times that of the clean days. The formation rates of PM2.5 in the five pollution stages were 26, 22, 22, 32, and 67 μg m^（–3） h–1, respectively. Organics and nitrate occupied the largest proportion in the polluted episodes, whereas organics and sulfate dominated the submicron aerosol during the clean days. The size distribution of organics is always broader than those of other species, especially in the clean episodes. The peak sizes of the interested species grew gradually during different HPEs. Aqueous reaction might be important in forming sulfate and chloride, and nitrate was formed via oxidization and condensation processes. PMF（positive matrix factorization） analysis on AMS mass spectra was employed to separate the organics into different subtypes. Two types of secondary organic aerosol with different degrees of oxidation consisted of 43% of total organics. By contrast, primary organics from cooking, coal combustion, and traffic emissions comprised 57% of the organic aerosols during the HPEs.

The metastable constituent effects on size-dependent deformation behavior of nanolaminated micropillars: Cu/FeCoCrNi vs Cu/CuZr

Metastable high entropy alloys(HEAs) and amorphous metallic glasses(MGs), with the chemical disordered character, are intensively studied due to their excellent performance. Here, we introduce Cu to separately constrain these two metastable materials and comparatively investigate their deformation behaviors and mechanical properties of Cu/HEA Fe Co Cr Ni and Cu/MG Cu Zr nanolaminated micropillars in terms of intrinsic layer thickness h and extrinsic pillar diameter D. The metastable HEA layers, as the hard phase in Cu/HEA micropillars, are stable and dominate the deformation, while transformation(crystallization) occurs in MG which plays a minor role in deformation of Cu/MG micropillars. The h-controlled deformation mode transits from the D-independent homogenous-like deformation at large h to the Ddependent shear banding at small h in both Cu/HEA and Cu/MG micropillars. Although both Cu/HEA and Cu/MG micropillars exhibit a maximum strain hardening capability controlled by h, the former manifests much lower hardening capability compared with the latter. The intrinsic size h and extrinsic size D have a strong coupling effect on the strength of Cu/HEA and Cu/MG micropillars. The strength of strength of Cu/HEA micropillars exhibits the D-dependent transition from "smaller is stronger" to "smaller is weaker"with increasing h. By contrast, the strength of Cu/MG micropillars exhibits the transition from bulk-like D-independent behavior at large h to small volume D-dependent behavior(smaller is stronger) at small h.

Temporal Variation and Source Identification of Black Carbon at Lin'an and Longfengshan Regional Background Stations in China

Black carbon （BC） is a component of fine particulate matter （PM2.5）, associated with climate, weather, air quality, and people＇s health. However, studies on temporal variation of atmospheric BC concentration at background stations in China and its source area identification are lacking. In this paper, we use 2-yr BC observations from two background stations, Lin＇an （LAN） and Longfengshan （LFS）, to perform the investigation. The results show that the mean diurnal variation of BC has two significant peaks at LAN while different characteristics are found in the BC vari- ation at LFS, which are probably caused by the difference in emission source contributions. Seasonal variation of monthly BC shows double peaks at LAN but a single peak at LFS. The annual mean concentrations of BC at LAN and LFS decrease by 1.63 and 0.26 μg m 3 from 2009 to 2010, respectively. The annual background concentration of BC at LAN is twice higher than that at LFS. The major source of the LAN BC is industrial emission while the source of the LFS BC is residential emission. Based on transport climatology on a 7-day timescale, LAN and LFS stations are sensitive to surface emissions respectively in belt or approximately circular area, which are dominated by summer monsoon or colder land air flows in Northwest China. In addition, we statistically analyze the BC source regions by using BC observation and FLEXible PARTicle dispersion model （FLEXPART） simulation. In summer, the source regions of BC are distributed in the northwest and south of LAN and the southwest of LFS. Low BC concentration is closely related to air mass from the sea. In winter, the source regions of BC are concentrated in the west and south of LAN and the northeast of the threshold area of stot at LFS. The cold air mass in the northwest plays an important role in the purification of atmospheric BC. On a yearly scale, sources of BC are approximately from five provinces in the northwest/southeast of LAN and the west of LFS. These findings are helpful in reducing BC emission and con- trolling air pollution.

Optical and Radiative Properties of Aerosols during a Severe Haze Episode over the North China Plain in December 2016

The optical and radiative properties of aerosols during a severe haze episode from 15 to 22 December 2016 over Beijing, Shijiazhuang, and Jiaozuo in the North China Plain were analyzed based on the ground-based and satellite data, meteorological observations, and atmospheric environmental monitoring data. The aerosol optical depth at 500 nm was 〈 0.30 and increased to 〉 1.4 as the haze pollution developed. The Angstr6m exponent was 〉 0.80 for most of the study period. The daily single-scattering albedo was 〉 0.85 over all of the North China Plain on the most polluted days and was 〉 0.97 on some particular days. The volumes of fine and coarse mode particles during the haze event were approximately 0.05-0.21 and 0.01-0.43 μm^3, respectively-that is, larger than those in the time without haze. The daily absorption aerosol optical depth was about 0.01-0.11 in Beijing, 0.01-0.13 in Shijiazhuang, and 0.01-0.04 in Jiaozuo, and the average absorption Angstrom exponent varied between 0.6 and 2.0. The aerosol radiative forcing at the bottom of the atmosphere varied from -23 to -227, -34 to -199, and -29 to -191 W m^-2 for the whole haze period, while the aerosol radiative forcing at the top of the atmosphere varied from -4 to -98, -10 to -51, and -21 to -143 W m^-2 in Beijing, Shijiazhuang, and Jiaozuo, respectively. Satellite observations showed that smoke, polluted dust, and polluted continental components of aerosols may aggravate air pollution during haze episodes. The analysis of the potential source contribution function and concentration-weighted trajectory showed that the contribu- tion from local emissions and pollutants transport from upstream areas were 190-450 and 100-410 btg m-3, respectively.

Comparison of Submicron Particles at a Rural and an Urban Site in the North China Plain during the December 2016 Heavy Pollution Episodes

An extensive field experiment for measurement of physical and chemical properties of aerosols was conducted at an urban site in the Chinese Academy of Meteorological Sciences（CAMS） in Beijing and at a rural site in Gucheng（GC）, Hebei Province in December 2016. This paper compares the number size distribution of submicron particle matter（PM1, diameter 〈 1 μm） between the two sites. The results show that the mean PM1 number concentration at GC was twice that at CAMS, and the mass concentration was three times the amount at CAMS. It is found that the accumulation mode（100–850 nm） particles constituted the largest fraction of PM1 at GC, which was significantly correlated with the local coal combustion, as confirmed by a significant relationship between the accumulation mode and the absorption coefficient of soot particles. The high PM1 concentration at GC prevented the occurrence of new particle formation（NPF） events, while eight such events were observed at CAMS. During the NPF events, the mass fraction of sulfate increased significantly, indicating that sulfate played an important role in NPF. The contribution of regional transport to PM1 mass concentration was approximately 50% at both sites, same as that of the local emission. However, during the red-alert period when emission control took place, the contribution of regional transport was notably higher.

Orchestrated cellular,biochemical,and biomechanical optimizations endow platelet-rich plasma-based engineered cartilage with structural and biomechanical recovery

Recently,biomaterials for cartilage regeneration has been intensively investigated.However,the development of scaffolds that capture regenerated cartilage with biomechanical and structural recovery has rarely been reported.To address this challenge,platelet-rich plasma(PRP)-based cartilage constructs with a well-orchestrated symphony of cellular,biochemical and biomechanical elements were prepared by simultaneously employing chondrogenic progenitor cells(CPCs)as a cell source,optimizing platelet concentration,and adding an enzyme-ion activator.It was shown that this triple-optimized PRP+CPC construct possessed increased biomechanical properties and suitable biochemical signals.The following in vitro study demonstrated that the triple-optimized PRP+CPC constructs generated cartilage-like tissue with higher expression levels of chondrogenic-specific markers,more deposition of cartilage-specific extracellular matrix(ECM),and greater biomechanical values than those of the other constructs.Twelve weeks after the construct was implanted in a cartilage defect in vivo,histological analysis,qPCR,and biomechanical tests collectively showed that the triple-optimized constructs yielded a more chondrocyte-like cell phenotype with a higher synthesis of Col-Ⅱand aggrecan.More importantly,the triple-optimized constructs facilitated cartilage regeneration with better biomechanical recovery than that of the other constructs.These results demonstrate the efficacy of the triple-optimization strategy and highlight the simplicity and potency of this PRP+CPC construct for cartilage regeneration.

Carbide precipitates and mechanical properties of medium Mn steel joint with metal inert gas welding

Medium Mn steel was metal inert gas(MIG)welded with NiCrMo-3 and 307 Si filler wires.The effect of filler wires on the microstructure and mechanical properties of joint was investigated,and the carbide precipitates were contrastively discussed.The results revealed that the microstructure of weld metal,heat-affected zone and base metal are austenite.Obvious grain coarsening occurred in the heat-affected zone(HAZ),and the maximum grain size grew up to 160μm.In HAZ,C and Cr segregated at grain boundaries,the carbides was identified as Cr7 C3.The dispersive(Nb,Mo)C phase was also found in weld metal with NiCrMo-3 filler wire.All the welded joints failed in HAZ during tensile tests.The tensile strength of welded joint with NiCrMo-3 filler wire was 675 MPa,which is much higher than that with307 Si filler wire.In comparison to base metal,higher microhardness and lower impact toughness were obtained in HAZ for these two welded joints,which was attributed to the precipitation of Cr7 C3 phase and grain coarsening.The impact toughness around the fusion line is the worst for these two welded joints.

Development of an integrating sphere calibration method for Cimel sunphotometers in China aerosol remote sensing network

Based on the integrating sphere traced from the National Institute of Standards and Technology （NIST, USA）, a sphere calibration method and protocol for the China aerosol remote sensing network （CARSNET） Cimel sun photometer was established. Four CE318 sun photometers were verified using the proposed cal- ibration method and operational protocol. The calibration results showed that the instrument coefficients differed by less than 3% for visible （-5% for infrared） wavelengths from the original ones stated by Cimel Electronique. In situ validation experiment data showed that radiances at ±6° measured by sun collimator （aureole） were consistent with those measured by sky collimator （sky）, under both almucantar （ALMUC） and principal plane （PPLAN） scenarios. Differences at all wavelengths were less than 1%, indicating that the method and protocol are suitable for CARSNET field sun photometer calibration, and would benefit improvement of data quality and accuracy of network observations.

The optimal sex ratio in cooperatively breeding populations

In some cooperatively breeding species,elder siblings remain within their home ranges to assist their parents in raising their younger siblings by providing protection or food.Previous attempts to model the population sex ratios of such species have assumed that helping is cost-free and only involves benefits to parents,resulting in offspring sex ratio biases towards the helping sex.However,parents may also incur costs in maintaining helpers.We incorporated costs and benefits of helping to predict the sex ratio of offspring in a theoretical model.Our model showed that the evolutionary stable strategy(ESS)sex ratio strongly depends on three parameters:(1) the average number of helpers per female;(2) the benefits that a helper brings to its mother's offspring production(MOP);and(3) the cost-benefit ratio of helping.When one sex of elder siblings provides help,the ESS sex ratio is biased towards the helping sex if MOP costs are less than the benefits,(i.e.,the cost-benefit ratio \1).However,the ESS sex ratio becomes biased towards the non-helping sex if MOP costs exceed the benefits(i.e.,the cost-benefit ratio [1).Additionally,our model shows that the ESS sex ratio becomes biased in favor of the more helpful sex when both male and female elder siblings provide help.These results explain why sex ratios may become biased towardsthe helping sex,as well as the non-helping sex,in some species.

2022汤加火山灰羽流的气溶胶光学、微物理和辐射特性

作为21世纪乃至近30年最强的火山喷发之一,2022年汤加火山喷发事件已经引起了广泛关注.研究表明,汤加火山喷发所产生的大量火山灰气溶胶突破对流层进入平流层,形成了一个顶部高度约为25~30 km的火山灰羽流.在喷发后的4天内,火山灰羽流在平流层环流的驱动下迅速向西移动了近10000 km.侵入平流层的火山灰气溶胶导致整个澳大利亚北部的大气气溶胶负荷显著增加,气溶胶光学厚度(AOD)在澳大利亚东北部海岸达到1.5,约为侵入前一日的15倍.此次汤加火山灰羽流主要以半径集中在~0.26μm处的细模态颗粒物为主,同时其体积峰值达到0.25μm^(3)μm^(-2).汤加火山喷发对平流层AOD和辐射平衡的影响显著,卫星观测到的平流层AOD的扰动高达0.6.这种扰动在很大程度上解释了区域性地表(大气层顶)的瞬时短波辐射强迫可达-105.0 W m^(-2)(-65.0 W m^(-2)).

Synergistic control of dual cross-linking strategy toward tailor-made hydrogels

Simple, efficient and accurate controllable systems for materials are becoming more essential, in response to the explosively growing demands in the fields of chemistry and material science. Herein, tailored hydrogels are explored depending on synergistic regulation of p H-responsive chemical networks with an "on/off" function and physical networks with dynamic selfoptimized arrangement. Thiol-disulfide exchange reaction endows hydrogels with controlled architectures while hydrogen bondstrengthened 2-ureido-4[1H]-pyrimidinone(UPy) moieties contributes a significant increase in mechanical strengths. The integration of that dual cross-linking(DC) network ensures the hydrogels with customized structure and enhanced mechanical property. Such controllably strategy is universally applicable and will open a new avenue to flexibly fabricate desired hybrid hydrogels with distinctive features and functions for their potential applications.

RELATIONSHIPS BETWEEN DUST STORMS AND DRYNESS-WETNESS IN MIDDLE–EASTERN CHINA DURING 1470–1950

Based on 481-year records of historical dust storm （DS） and Dryness-Wetness Index （DWI） at 120 sites, spatial distribution characteristics of dryness-wetness （DW） in typical dust storm years （DS years） and in non-dust storm years （non-DS years） were derived for continental China. In DS years, most of the sites were drier than in normal years while in non-DS years wetter than normal, and the variation of DWI in DS years was larger than that in non-DS years. The relative instability and increased regional difference of atmospheric circulation in DS years might have induced more frequent DS events and dry-wet abnormality in continental China. In DS years the latitudinal （north-south） dry-wet difference was larger than that in non-DS years, that is, north China was even much drier than south China. This might be attributed to increased latitudinal differences of thermal and pressure gradients in DS years, resulting in the southward withdrawal of precipitation and increase of DS events.