Hygroscopic growth of aerosol scattering coefficient： A comparative analysis between urban and suburban sites at winter in Beijing

A humidity controlled inlet system was developed to measure the hygroscopic growth of aerosol scattering coefficient in conjunction with nephelometry at an urban site of Chinese Academy of Meteorological Sciences （CAMS） in Beijing and a rural site at Shangdianzi Regional Background Air Pollution Monitoring Station （SDZ） outside Beijing during winter, from December 2005 to January 2006. Measurements were carded out at a wavelength of 525 nm with an Ecotech M9003 nephelometer. The hygroscopic growth function （or factor） of the aerosol scattering coefficientf（RH） increased continuously with increasing relative humidity （RH） and showed no obvious ＂step-like＂ deliquescent behavior at both sites during the experiment. The average growth factorf（RH） at the SDZ site could reach 1.5 when RH increased from less than 40% to 92%, and to 2.1 at the CAMS site when RH increased from less than 40% to 93%. The average hygroscopic growth factor at a relative humidity of 80%, f（RH = 80 ± 1%）, was found to be about 1.26 ±0.15 at CAMS and 1.24 ±0.11 at SDZ. Further analysis indicated that under relatively polluted conditions, the average hygroscopic growth factor was higher at the CAMS site than that at the SDZ site. However, under relatively clean air conditions, the difference between the two sites was small, showing a hygroscopic growth behavior similar to those of burning biomass or blowing dust. These results reflected the different characteristics of aerosol types at the two sites.     

Effect of mixing structure on the hygroscopic behavior of ultrafine ammonium sulfate particles mixed with succinic acid and levoglucosan

Understanding the interactions between water and atmospheric aerosols is critical for estimating their impact on the radiation budget and cloud formation. The hygroscopic behavior of ultrafine (<100 nm) ammonium sulfate particles internally mixed with either succinic acid (slightly soluble) or levoglucosan (soluble) in different mixing structures (core-shell vs. well-mixed) were measured using a hygroscopicity tandem differential mobility analyzer (HTDMA). During the hydration process (6–92% relative humidity (RH)), the size of core-shell particles (ammonium sulfate and succinic acid) remained unchanged until a slow increase in particle size occurred at 79% RH; however, an abrupt increase in size (i.e., a clear deliquescence) was observed at ∼72% RH for well-mixed particles with a similar volume fraction to the core-shell particles (80:20 by volume). This increase might occur because the shell hindered the complete dissolution of the core-shell particles below 92% RH. The onset RH value was lower for the ammonium sulfate/levoglucosan core-shell particles than the ammonium sulfate/succinic acid core-shell particles due to levoglucosan's higher solubility relative to succinic acid. The growth factor (GF) of the core-shell particles was lower than that of the well-mixed particles, while the GF of the ammonium sulfate/levoglucosan particles was higher than that of ammonium sulfate/succinic acid particles with the same volume fractions. As the volume fraction of the organic species increased, the GF decreased. The data suggest that the mixing structure is also important when determining hygroscopic behavior of the mixed particles.     

环境湿度对碳/铜滑动接触副载流摩擦学行为的影响

弓网系统依靠受电弓滑板与接触网导线间的滑动电接触为电力列车输送电能,作为1个开放的摩擦学系统,外界环境对其服役行为具有显著影响. 本文中利用往复式载流摩擦磨损试验机,通过加装湿度控制模块,在滑动电接触条件下,以碳棒和铜棒为摩擦配副,研究了环境湿度对碳/铜载流滑动接触副摩擦学行为的影响. 结果表明:载流条件下的摩擦系数高于无电流工况;无电流工况下,平均摩擦系数均随环境湿度的增加而单调降低;但由于累积电弧放电能量、平均接触电阻与相对湿度的正相关性,导致载流条件下在35% RH后的摩擦系数几乎不受环境湿度的影响. 进一步发现,无电流工况下,碳棒上的黏着磨损和氧化磨损随相对湿度的增加逐步减缓,载流工况下,存在1个黏着磨损程度最低的最佳湿度值,出现在55% RH附近. 高湿环境下,加速了碳/铜载流滑动过程中碳棒磨损表面分子结构的变化.      

ANALYSIS OF PARTICULATE MASS CONCENTRATION, AEROSOL NUMBER CONCENTRATION AND VISIBILITY IN BEIJING

1.IntroductionAtmosphericaerosolsplayanimportantroleinatmos-phericvisibility,irradiationbalanceandclimate.Thenum-berconcentrationofsmallparticulatesisusuallyveryhigh,butitsmassconcentrationisrelativelylow.Buzoriusetal.(1999)andPetersetal.(1997)havereportedthatparticu-latehealtheffectsmaybemoresensitivetothenumberthantothemassconcentration.Thispaperstudiestheaverageddiurnalvariationsofparticulatemassconcentra-tion,numberconcentration,atmosphericvisibility,andtheaerosolsizedistribution,n(r),und…     

磁控溅射NbSe2和MoS2薄膜不同湿度下的摩擦学行为

针对MoS₂在潮湿环境易氧化和润滑失效的问题,从增强离子键强度的角度探索改善其抗氧化以及润滑湿度适应性. 选择了离子键更强的NbSe₂进行对比,采用磁控溅射法分别制备了NbSe₂和MoS₂薄膜,研究了两种薄膜在不同湿度下的摩擦学性能,对比其在摩擦稳定阶段的结构和化学组成,探讨了NbSe₂在大气高湿度环境下的优势与作用机理. 结果表明:NbSe₂薄膜在大气环境下的摩擦表现出更佳的湿度适应性,在20% RH、35% RH和55% RH下摩擦系数稳定在0.08左右,直到75% RH下摩擦系数才开始增大,而MoS₂薄膜在35% RH下面临润滑性能快速失效的问题,进一步结合XPS和XRD等表征结果发现:相较于MoS₂,NbSe₂在大气摩擦条件下更难氧化,其层层滑移状态能较好维持,能保持长时间的润滑性能,这为大气高湿度服役润滑材料的改进提供了新的思路.      

Effect of COVID-19 lockdown on the characterization and mixing state of carbonaceous particles in the urban atmosphere of Liaocheng,the North China Plain

To investigate the effect of COVID-19 control measures on aerosol chemistry, the chemical compositions, mixing states, and formation mechanisms of carbonaceous particles in the urban atmosphere of Liaocheng in the North China Plain (NCP) were compared before and during the pandemic using a single particle aerosol mass spectrometry (SPAMS). The results showed that the concentrations of five air pollutants including PM_2.5, PM₁₀, SO₂, NO₂, and CO decreased by 41.2%–71.5% during the pandemic compared to those before the pandemic, whereas O₃ increased by 1.3 times during the pandemic because of the depressed titration of O₃ and more favorable meteorological conditions. The count and percentage contribution of carbonaceous particles in the total detected particles were lower during the pandemic than those before the pandemic. The carbonaceous particles were dominated by elemental and organic carbon (ECOC, 35.9%), followed by elemental carbon-aged (EC-aged, 19.6%) and organic carbon-fresh (OC-fresh, 13.5%) before the pandemic, while EC-aged (25.3%), ECOC (17.9%), and secondary ions-rich (SEC, 17.8%) became the predominant species during the pandemic. The carbonaceous particle sizes during the pandemic showed a broader distribution than that before the pandemic, due to the condensation and coagulation of carbonaceous particles in the aging processes. The relative aerosol acidity (R_ra) was smaller before the pandemic than that during the pandemic, indicating the more acidic particle aerosol during the pandemic closely related to the secondary species and relative humidity (RH). More than 95.0% and 86.0% of carbonaceous particles in the whole period were internally mixed with nitrate and sulfate, implying that most of the carbonaceous particles were associated with secondary oxidation during their formation processes. The diurnal variations of oxalate particles and correlation analyses suggested that oxalate particles before the pandemic were derived from aqueous oxidation driven by RH and liquid water content (LWC), while oxalate particles during the pandemic were originated from O₃-dominated photochemical oxidation.     

Mineralogical characteristics of soil dust from source regions in northern China

Mineral compositions of aerosol particles were investigated at four sites （Aksu, Dunhuang, Zhenbeitai, and Tongliao） in desert regions of northern China from March to May in 2001 and 2002 during the intensive field campaign period of ACE-Asia （Aerosol Characterization Experiments-Asia）. The X-ray diffraction （XRD） results show the main minerals for Asian dust are illite, chlorite, kaolinite, quartz, feldspar, calcite, and dolomite. Gypsum, hornblende, and halite are also detected in several samples. Semi-quantitative mineralogical data of aerosol samples show that carbonate content decreases from western to eastern source areas; that is, soil dust collected at western source area sites of Dunhuang and Aksu are enriched with carbonate, while northeastern source area site of Tongliao is associated with low carbonate content. But the spatial distribution of feldspar exhibits a different pattern as compared to carbonate, increasing from the western to the eastern sources. The total clay content is significantly higher （73% in average） at the deposition site of Changwu than those at source areas. Air-mass back trajectory studies for the three dust storm events observed at Changwu, showed that soil dust transport pathways were as expected from carbonate content for the source identification, further demonstrating that carbonate was a useful tracer for eolian dust on regional scale in northern China.     

氧化硼的纳米磨损特性研究

利用原子力显微镜和将纳米力学性能测试仪研究了室温及不同湿度环境下,氧化硼表面上硼酸的形成规律,分析了表面形貌,表面力学性能及微观磨损特性,研究表明,氧化硼表面生成硼酸时,体积发生膨胀,硼酸的形成受环境湿度的影响,而氧化硼的微观磨损率与硼酸的生长速度呈对应关系,硼酸的生长使氧化硼表面软化,强度降低。     

Aerosol composition,sources, and secondary processing during autumn at a regional site in the Beijing–Tianjin–Hebei region

Air pollution is serious during autumn in the Beijing–Tianjin–Hebei (BTH) region, but there are few studies that have utilized real-time observations and source apportionment of the autumn submicron aerosols in this region. In this study, a quadrupole aerosol chemical speciation monitor (Q-ACSM) was deployed for the real-time measurement of the non-refractory compositions of submicron aerosols (NR-PM₁) at a regional site (Xianghe) from October 3 to November 14, 2017. The results showed that nitrate was the largest inorganic aerosol, and the oxygenated organic aerosol (OOA) was the largest organic aerosol in Xianghe. Hydrocarbon-like OA (HOA) was the largest organic aerosol When the NR-PM₁ mass concentrations increased from the lowest to the highest bins, nitrate and biomass burning OA (BBOA) showed increasing trends in the suburban area. Enhanced nitrate formation during the pollution episodes resulted from both photochemical and aqueous processing. To reduce the particulate matter (PM_2.5) concentrations and eliminate heavy pollution episodes, control measures should focus on reducing NO_x, NH₃, and volatile organic compound (VOC_s) emissions.     

Validation of MODIS and Deep Blue aerosol optical depth retrievals in an arid/semi-arid region of northwest China

The global aerosol optical depth (AOD or τ) has been retrieved using the Dark Target algorithm (the C004 and C005 products) and the Deep Blue algorithm (DB product). Few validations have thus far been performed in arid/semi-arid regions, especially in northwest China. The ground-based remote sensing of AOD from sun photometers at four sites in Xinjiang during the years 2002–2003 is used to validate aerosol products, including C004, C005 and DB of the Moderate Resolution Imaging Spectroradiometer (MODIS). The results show substantial improvement in the C005 aerosol product over the C004 product. The average correlation coefficient of regression with ground measurements increased from 0.59 to 0.69, and the average offset decreased from 0.28 to 0.13. The slopes of the linear regressions tended to be close to unity. The percentage of AODs falling within the retrieval errors of 30% (or △τ = ±0.1 ± 0.2τ) increased from 16.1% to 45.6%. The best retrievals are obtained over an oasis region, whereas the worst are obtained over urban areas. Both the MODIS C004 and C005 products overestimate AOD, which is likely related to improper assumptions of the aerosol model and of the estimation of surface reflectance. An encouraging result has been derived with regard to validation of the DB AOD. Overall, the average offset, slope and correlation coefficient of regression with sun-photometer measurements are ?0.04, 0.88 and 0.85, respectively. Approximately 73% of the DB AOD retrievals fall within the expected error of 30%. Underestimation of the AOD by the DB products is observed. The aerosol model and estimations of surface reflectance in this region require further improvements.     

Insight into the interaction between water and surfactant aerosol particles based on molecular dynamics simulations

The ubiquitous surfactant significantly influences the hygroscopic growth of atmospheric aerosol particles. However, knowledge on the morphology of surfactant particles after the adsorption of water is insufficient. In this study, the interaction between water and particles composed of surface active malonic acid (MA) or adipic acid (AA) are simulated based on the molecular dynamics method. The key point is the combined effect of temperature and water content on the structural properties of particles and the surface propensity of surfactants at the equilibrium state. Results show that demixed structure 1 with the adsorption of water clusters on acid grain, mixed structure and demixed structure 2 with acids coating on water droplet can be observed. With temperature increasing from 160 K to 330 K the surface propensity of MA and AA increases first and then weakens. Near the standard atmospheric temperature (280–330 K), the surface propensity of MA and AA increases with increasing water content and alkyl group, and its sensitivity to temperature and water content varies regularly. Moreover, all surfactants at the particle surface orient their hydrophobic groups toward the gas. These findings improve our insight into the surfactant partitioning and further assist in more accurate prediction of the particle hygroscopic growth.     

氧化硼的纳米磨损特性研究

Nanoscale tribological andmechanical properties o f boric acid were studied by Atomic Force Microscopy (AFM) and Nanomechanical Te stingSystem. The surface morphology, mechanical properties, and wear properties of boric acid on bulk boron oxide substrates inair at room temperature and var ious relative humidity (RH) were examined. It is shown that the growth of bo ric acid filmis dependent on RH, and the growth rate of H₃BO₃ correlate s with the micro-wear rate of B₂O₃. Thesurface of B₂O₃ became soft wit h the growth of boric acid film.     

NUMERICAL STUDY ON THE GROWTH PROCESS OF SECONDARY AEROSOL IN THE FOG

雾环境气溶胶之间的碰撞和凝并是气溶胶迁移、生长的动力学基础. 基于颗粒群平衡方程和多重蒙特卡洛方法,针对雾环境中二次液态气溶胶生长过程开展数值研究,着重分析了湍流和布朗作用机制对单分散和指数分布的二次气溶胶碰撞凝并的影响. 结果表明:雾环境气溶胶之间的碰撞凝并使得颗粒的总数目减少,颗粒平均体积逐渐增大. 对于初始尺度为自由分子区、单分散的气溶胶,布朗运动时间为600 s时,二次气溶胶平均尺度增大至初始的202.7倍左右,数目降至初始的0.006. 对于湍流作用下有布朗运动的二次气溶胶,在较短的时间内(如100 s)气溶胶尺度增至初始的163倍,颗粒数目降至初始的0.025倍, 说明雾环境流场的湍流运动引起二次气溶胶较强的输运和聚集,导致颗粒碰撞凝并概率增加,颗粒尺度增大.     

Effects of humidity and temperature on subcritical crack growth in sandstone

In order to ensure long-term stability of structures in a rock mass, the study of time-dependent fracturing is essential. The influences of the surrounding environmental conditions and rock fabric on subcritical crack growth in sedimentary rocks in air are yet to be clarified, while the nature of subcritical crack growth in igneous rocks has been studied well. In this study, the influences of temperature and relative humidity on subcritical crack growth in Berea sandstone, Shirahama sandstone and Kushiro sandstone were investigated in air. The load relaxation method of Double Torsion (DT) testing method was used to measure both crack velocity and stress intensity factor under a controlled temperature and relative humidity.Results show that the change of the crack velocity at a given stress intensity factor was unclear when the temperature increased under a constant relative humidity in air. On the other hand, we show that the crack velocity increased by several orders of magnitude when the relative humidity increased threefold or fourfold under a constant temperature at a given stress intensity factor. This increase is much larger than that expected from the conventional concept based on the theory of stress corrosion. It is therefore necessary to consider the additional mechanisms for subcritical crack growth in sandstone. The increase of the crack velocity was larger for sandstone which contained larger amount of clays. We conclude that subcritical crack growth in sandstone in air is affected remarkably by the relative humidity and the amount of clays in rock.     

Analysis of the causes of heavy aerosol pollution in Beijing,China: A case study with the WRF-Chem model

The causes and variability of a heavy haze episode in the Beijing region was analyzed. During the episode, the PM_2.5 concentration reached a peak value of 450 μg/kg on January 18, 2013 and rapidly decreased to 100 μg/kg on January 19, 2013, characterizing a large variability in a very short period. This strong variability provides a good opportunity to study the causes of the haze formation. The in situ measurements (including surface meteorological data and vertical structures of the winds, temperature, humidity, and planetary boundary layer (PBL)) together with a chemical/dynamical regional model (WRF-Chem) were used for the analysis. In order to understand the rapid variability of the PM_2.5 concentration in the episode, the correlation between the measured meteorological data (including wind speed, PBL height, relative humidity, etc.) and the measured particle concentration (PM_2.5 concentration) was studied. In addition, two sensitive model experiments were performed to study the effect of individual contribution from local emissions and regional surrounding emissions to the heavy haze formation. The results suggest that there were two major meteorological factors in controlling the variability of the PM_2.5 concentration, namely, surface wind speed and PBL height. During high wind periods, the horizontal transport of aerosol particles played an important role, and the heavy haze was formed when the wind speeds were very weak (less than 1 m/s). Under weak wind conditions, the horizontal transport of aerosol particles was also weak, and the vertical mixing of aerosol particles played an important role. As a result, the PBL height was a major factor in controlling the variability of the PM_2.5 concentration. Under the shallow PBL height, aerosol particles were strongly confined near the surface, producing a high surface PM_2.5 concentration. The sensitivity model study suggests that the local emissions (emissions from the Beijing region only) were the major cause for the heavy haze events. With only local emissions, the calculated peak value of the PM_2.5 concentration was 350 μg/kg, which accounted for 78% of the measured peak value (450 μg/kg). In contrast, without the local emissions, the calculated peak value of the PM_2.5 concentration was only 100 μg/kg, which accounted for 22% of the measured peak value.     

Aerosol optical properties and its direct radiative forcing over Tibetan Plateau from 2006 to 2017

Studies on optical properties of aerosols can reduce the uncertainty for modelling direct radiative forcing (DRF) and improve the accuracy for discussing aerosols effects on the Tibetan Plateau (TP) climate. This study investigated the spatiotemporal variation of aerosol optical and microphysical properties over TP based on OMI and MERRA2, and assessed the influence of aerosol optical properties on DRF at NamCo station (30°46.44′N, 90°59.31′E, 4730 m) in the central TP from 2006 to 2017 based on a long measurement of AERONET and the modelling of SBDART model. The results show that aerosol optical depth (AOD) exhibits obvious seasonal variation over TP, with higher AOD_500nm (>0.75) during spring and summer, and lower value (<0.25) in autumn and winter. The aerosol concentrations show a fluctuated rising from 1980 to 2000, significant increasing from 2000 to 2010 and slight declining trend after 2013. Based on sensitivity experiments, it is found that AOD and single scattering albedo (SSA) have more important impact on the DRF compared with α values and ASY. When AOD_440nm increases by 60%, DRF at the TOA and ATM is increased by 57.2% and 60.2%, respectively. When SSA_440nm increases by 20%, DRF at the TOA and ATM decreases by 121% and 96.7%, respectively.     

Characteristics of organic and elemental carbon in atmospheric fine particles in Tianjin, China

PM2.5 samples were collected at urban, industrial and coastal sites in Tianjin during winter, spring and summer in 2007. Concentrations of elemental carbon （EC） and organic carbon （OC） were analyzed using the IMPROVE thermal-optical reflectance （TOR） method. Both OC and EC exhibited a clear seasonal pattern with higher concentrations observed in the winter than in the spring and summer, due to cooperative effect of changes in emission rates and seasonal meteorology. The concentrations of carbonaceous species were also influenced by the local factors at different sampling sites, ranking in the order of industrial〉 urban 〉 coastal during winter and spring. In the summer, the port emissions, enriched with EC, had a significant impact on carbonaceous aerosols at the coastal site. Total carbonaceous aerosol accounted for 40.0% in winter, 33.8% in spring and 31.4% in summer of PM2.5 mass. Good correlation （R = 0.84-0.93） between OC and EC indicated that they had common dominant sources of combustion such as coal burning and traffic emissions. The daily average OC/EC ratios ranged from 2.1 to 9.1, the elevated OC/EC ratios being found in the winter. The estimated secondary organic carbon （SOC） accounted for 46.9%, 35.3% and 40.2% of the total OC in the winter, spring and summer, respectively, indicating that SOC may be an important contributor to fine organic aerosol in Tianjin.     

Defining the effects of ambient conditions in large-scale fire tests

The paper documents the results of an analysis of the effects of ambient conditions, temperature and relative humidity, on the development of large-scale fires during their initial growth. While the study has focused on the behavior of hygroscopic cartoned commodities, because their burning behavior is greatly affected by propensity to absorb ambient moisture, non-hygroscopic materials and their reduced sensitivity to ambient humidity could also be considered. The analysis introduces the heat release rate at the time of first sprinkler activation as a meaningful measure to represent the impact of ambient conditions on the development of a free-burning fire. The next step of estimating the behavior under extinguishment conditions is not possible at this time, though general considerations on expected trends are offered on the basis of the results obtained from another research program. The practical output of the work is in the form of the identification of the desirable range of operating conditions for ambient temperature and relative humidity in large-scale fire testing.     

扭动微动条件下含水气氛对氧化行为的影响

对7075铝合金/GCr15摩擦副在不同湿度条件下扭动微动的损伤行为、氧化行为进行了研究.建立了7075铝合金在不同湿度条件下的扭动微动运行工况微动图.采用SEM、XPS对不同湿度环境下的磨损机制、氧化行为及其影响因素进行了分析.结果表明:湿度对7075的扭动微动运行存在显著影响,随着湿度的增加,摩擦扭矩明显降低;部分滑移区的磨损发生在接触边缘,损伤轻微;混合区和滑移区发生强烈的塑性变形,损伤严重,其主要磨损机制是磨粒磨损和剥层;潮湿空气增加了界面滑移,反应生成的氧化磨屑起到了润滑剂的作用,减轻了磨损.     

Decoupling of Autogenous Shrinkage and Tensile Creep Strain in High Strength Concrete at Early Ages

Appropriately interpreting the measured creep strain is critical for obtaining the actual creep strain, especially for high-strength concretes characterized by a low water/cement ratio (w/c) because autogenous shrinkage is significant in such concrete at early ages. To investigate the interaction between the autogenous shrinkage and tensile creep of concrete at early ages, various tests were conducted on concretes with water/cement (w/c) ratios =0.3 and 0.4, including basic tensile creep, strength, autogenous shrinkage, and the internal relative humidity (RH) measurements. The load was applied at the ages of 1 and 7 days at the stress/strength levels of 40% and 70%, respectively. It was found that the measured early-age tensile creep strain becomes negative due to the large autogenous shrinkage involved. The principle of superposition can be used for creep-autogenous shrinkage decoupling to obtain the actual basic tensile creep, as there is virtually no additional RH reduction or stress-induced shrinkage in concrete due to the sustained tensile load at early ages. An average tensile strength gain of 8.2% was found in specimens after sustained tensile loading compared to the unloaded specimens. An exponential function is proposed to quantify the autogenous shrinkage effect on the basic tensile creep in terms of specific creep/autogenous shrinkage ratio.