ALBERT

Description: In order to evaluate impacts of different source emission on marine atmospheric particles over the South China Sea (SCS), major inorganic ionic concentrations (Na+, Cl−, SO42−, Ca2+, Mg2+, K+, NH4+ and NO3−) were determined in total suspended particulates (TSPs) at Yongxing Island, from March 2014 to February 2015. The annual average concentration of TSPs was 89.6 ± 68.0 µg m−3, with 114.7 ± 82.1, 60.4 ± 27.0 and 59.5 ± 25.6 µg m−3 in cool, warm and transition seasons, respectively. Cl− had the highest concentration, with an annual average of 7.73 ± 5.99 µg m−3, followed by SO42− (5.54 ± 3.65 µg m−3), Na+ (4.00 ± 1.88 µg m−3), Ca2+ (2.15 ± 1.54 µg m−3), NO3− (1.95 ± 1.34 µg m−3), Mg2+ (0.44 ± 0.33 µg m−3), K+ (0.33 ± 0.22 µg m−3) and NH4+ (0.07 ± 0.07 µg m−3). Concentrations of TSPs and the major ions showed seasonal variations, which were higher in the cool season and lower in the warm and transition seasons. Factors of influence were wind speed, temperature, relatively humidity, rain and air mass source region. Back trajectories, concentration-weighted trajectories (CWTs), and positive matrix factorization (PMF) of chemical compositions were analyzed for source apportionment, source contribution and spatiotemporal variation of major ions. Back trajectories and CWTs showed that air masses at Yongxing Island were mainly from the northeast, southwest and southeast in the cool, warm and transition seasons, respectively. The PMF results showed that 77.4 % of Na+ and 99.3 % of Cl− were from sea salt; 60.5 % of NH4+ was from oceanic emission. Anthropogenic sources were very important for atmospheric aerosols over the island. Secondary inorganic aerosol of SO2 and NOx from fossil fuel combustion (especially coal in Chinese coastal regions) was the dominant source of NO3− (69.5 %) and SO42− (57.5 %).

Description: Major inorganic chemical ionic concentrations (Na+, Cl−, SO42−, Ca2+, Mg2+, K+, NH4+, NO3−) were determined in total suspended particulates (TSP) at Yongxing Island in the South China Sea (SCS), from March 2014 to February 2015. The annual average concentration of TSP was 89.6 ± 68.0 μg/m3, with 114.7 ± 82.1, 60.4 ± 27.0, and 59.5 ± 25.6 μg/m3 in cool, warm, and transition seasons, respectively. Cl− had the highest concentration, with an annual average of 7.73 ± 5.99 μg/m3, followed by SO42− (5.54 ± 3.65 μg/m3), Na+ (4.00 ± 1.88 μg/m3), Ca2+ (2.15 ± 1.54 μg/m3), NO3− (1.95 ± 1.34 μg/m3), Mg2+ (0.44 ± 0.33 μg/m3), K+ (0.33 ± 0.22 μg/m3), and NH4+ (0.07 ± 0.07 μg/m3). Concentrations of TSP and the major ions showed seasonal variations, higher in the cool season and lower in the warm and transition seasons, which were influenced by wind speed, temperature, relatively humidity, rain, and air masses. Back trajectories, concentration weighted trajectories (CWT), and positive matrix factorization (PMF) of chemical compositions were analyzed for source apportionment, source contribution, and spatio-temporal variation of major ions. Back trajectories and CWTs showed that air masses at Yongxing Island were mainly from the northeast, southwest, and southeast in the cool, warm, and transition seasons, respectively. Na+ and Cl− were mainly from sea salt, which made up 74 % and 82 %, respectively. Asian dust contributed 50 % of Ca2+ to the marine aerosols. Anthropogenic sources were very important for atmospheric aerosols over the island. Fossil fuel combustion (especially coal in Chinese coastal regions) was the important sources of NO3− (56 %) and SO42− (22 %). Biomass burning in Asia accounted for 41 % of K+. 69 % of NH4+ and 38 % of SO42− were of marine biogenic sources.

Description: Chemistry plays an indispensable role in investigations of the atmosphere; however, many climate models either ignore or greatly simplify atmospheric chemistry, limiting both their accuracy and their scope. We present the development and evaluation of the online global atmospheric chemical model BCC-GEOS-Chem v1.0, coupling the GEOS-Chem chemical transport model (CTM) as an atmospheric chemistry component in the Beijing Climate Center atmospheric general circulation model (BCC-AGCM). The GEOS-Chem atmospheric chemistry component includes detailed tropospheric HOx–NOx–volatile organic compounds–ozone–bromine–aerosol chemistry and online dry and wet deposition schemes. We then demonstrate the new capabilities of BCC-GEOS-Chem v1.0 relative to the base BCC-AGCM model through a 3-year (2012–2014) simulation with anthropogenic emissions from the Community Emissions Data System (CEDS) used in the Coupled Model Intercomparison Project Phase 6 (CMIP6). The model captures well the spatial distributions and seasonal variations in tropospheric ozone, with seasonal mean biases of 0.4–2.2 ppbv at 700–400 hPa compared to satellite observations and within 10 ppbv at the surface to 500 hPa compared to global ozonesonde observations. The model has larger high-ozone biases over the tropics which we attribute to an overestimate of ozone chemical production. It underestimates ozone in the upper troposphere which is likely due either to the use of a simplified stratospheric ozone scheme or to biases in estimated stratosphere–troposphere exchange dynamics. The model diagnoses the global tropospheric ozone burden, OH concentration, and methane chemical lifetime to be 336 Tg, 1.16×106 molecule cm−3, and 8.3 years, respectively, which is consistent with recent multimodel assessments. The spatiotemporal distributions of NO2, CO, SO2, CH2O, and aerosol optical depth are generally in agreement with satellite observations. The development of BCC-GEOS-Chem v1.0 represents an important step for the development of fully coupled earth system models (ESMs) in China.

Description: Cloud cover estimates of single-layer shallow cumuli obtained from narrow field-of-view (FOV) lidar–radar and wide-FOV total sky imager (TSI) data are compared over an extended period (2000–2017 summers) at the established United States Atmospheric Radiation Measurement mid-continental Southern Great Plains site. We quantify the impacts of two factors on hourly and sub-hourly cloud cover estimates: (1) instrument-dependent cloud detection and data merging criteria and (2) FOV configuration. Enhanced observations at this site combine the advantages of the ceilometer, micropulse lidar (MPL) and cloud radar in merged data products. Data collected by these three instruments are used to calculate narrow-FOV cloud fraction (CF) as a temporal fraction of cloudy returns within a given period. Sky images provided by TSI are used to calculate the wide-FOV fractional sky cover (FSC) as a fraction of cloudy pixels within a given image. To assess the impact of the first factor on CF obtained from the merged data products, we consider two additional subperiods (2000–2010 and 2011–2017 summers) that mark significant instrumentation and algorithmic advances in the cloud detection and data merging. We demonstrate that CF obtained from ceilometer data alone and FSC obtained from sky images provide the most similar and consistent cloud cover estimates; hourly bias and root-mean-square difference (RMSD) are within 0.04 and 0.12, respectively. However, CF from merged MPL–ceilometer data provides the largest estimates of the multiyear mean cloud cover, about 0.12 (35 %) and 0.08 (24 %) greater than FSC for the first and second subperiods, respectively. CF from merged ceilometer–MPL–radar data has the strongest subperiod dependence with a bias of 0.08 (24 %) compared to FSC for the first subperiod and shows no bias for the second subperiod. The strong period dependence of CF obtained from the combined ceilometer–MPL–radar data is likely results from a change in what sensors are relied on to detect clouds below 3 km. After 2011, the MPL stopped being used for cloud top height detection below 3 km, leaving the radar as the only sensor used in cloud top height retrievals. To quantify the FOV impact, a narrow-FOV FSC is derived from the TSI images. We demonstrate that FOV configuration does not modify the bias but impacts the RMSD (0.1 hourly, 0.15 sub-hourly). In particular, the FOV impact is significant for sub-hourly observations, where 41 % of narrow- and wide-FOV FSC differ by more than 0.1. A new “quick-look” tool is introduced to visualize impacts of these two factors through integration of CF and FSC data with novel TSI-based images of the spatial variability in cloud cover. The influence of cloud field organization, such cloud streets parallel to the wind direction, on narrow- and wide-FOV cloud cover estimates can be visually assessed.

Description: Accurately assessing the impact of groundwater exploitation on land subsidence can provide scientific support for decision-makers. This article establishes a groundwater–subsidence model in a typical area using the land subsidence characteristics of Tongzhou, China, and subsequently classifies a land subsidence early warning zone based on the land subsidence rate. Results show that land subsidence occurred throughout the whole Tongzhou District. The land subsidence that developed to the west of Liuzhuang, Tongzhou city and Taihu was the most serious The maximum annual subsidence rate reached 120 mm a−1 under the current groundwater extraction conditions, and the early warning level for land subsidence reached its highest level. If the pumping of groundwater was reduced by 50 % in the second and the fourth aquifers and by 60 % in the third aquifer, the land subsidence early warning level would be largely reduced and would meet the requirements for land subsidence control.

Description: To analyze the generation of different ground fissure disasters, two typical ground fissures were selected. With geological survey and exploration data, the spatial characteristics of the Songzhuang and Gaoliying fissures were investigated. The different occurrence factors for the Songzhuang and Gaoliying fissures were analyzed based on geological structure and groundwater. The conclusions contain are as follows. The affected body of the Songzhuang fissure exhibits obvious tensile deformation, and it is not contact with buried faults. The fracture-affected body of the Gaoliying fissure shows obvious vertical dislocation and shear, and this is compounded with buried faults. The distribution characteristic of the Songzhuang fissure was controlled by the tectonics and the normal fault, while the buried fault not only control the distribution feature of the Gaoliying fissure but also controlled its deformation characteristic. A buried fault is the geological background for the formation of the Gaoliying fissure. The long-term exploitation of groundwater has caused the horizontal deformation of the soil and the rigid rotation of stratum in the subsidence edge. Both of them are the reason for the tensile deformation. Due to the activities of buried faults and differential subsidence in small areas, the affected bodies of the Gaoliying fissure showed vertical dislocation and shear deformation.

Description: It is of great significance to reveal the mechanism of land subsidence to further find out the mechanism of leakage flow in multi-layer aquifer systems and the water-release compression of weak aquifers. In this paper, conditions of groundwater leakage flow are expounded, and the initial hydraulic gradient calculation formula in the aquitards are deduced. The data of Tianzhu Land Subsidence Monitoring Station are selected to preliminarily discuss the leakage flow mechanism of the multi-layer groundwater system and water-release compression of weak aquifers. The results show that, firstly the weak aquifer layers in the shallow strata above 91.32 m in Tianzhu Land Subsidence Station are all in the state of unidirectional drainage consolidation, and the water heads in the upper strata are higher than those in the lower strata. However, the hydraulic gradient between the two adjacent aquifers is smaller than the initial hydraulic gradient in the weak aquifer layer, so no leakage recharge effect is generated. Secondly, the water level of the two adjacent aquifers in the deep formation below 91.32 m shows a continuous downward trend, among which the weak aquifer is drained and consolidated on both sides, and the pore water head in the middle of the weak aquifer is the lowest. Although the strata has a large amount of compression, no leakage recharge phenomenon occurs. Thirdly, in a multi-layer aquifer system, when the head difference between adjacent aquifers is small and there is a thick viscous layer between them, it is difficult for the upper aquifer to overcome the shear strength of the bound water in the weak aquifer below, leaking recharge barely occurs.

Description: Land subsidence is a worldwide geohazard caused by various factors, and its direct impact is loss of elevation, which is especially severe in coastal areas due to sea level rise. Quantifying contributions of compressed strata is significant for evaluating the subsidence. In this paper, we used distributed fiber optic sensing (DFOS) with Brillouin scattering to monitor the strain distribution along optical cables embedded in a borehole located in Tianjin, China. The novel technique revealed that the land subsidence rate was 21.2 mm a−1 from 2017 to 2019. The strata contributed to the subsidence have been identified in the range of 3 to 35 m. The results showed good agreement with those obtained by a group of extensometers. We demonstrated that DFOS could be a supplement to land subsidence monitoring technologies in coastal areas.

Description: The high contribution of secondary organic aerosol to the loading of fine particle pollution in China highlights the roles of volatile organic compound (VOC) oxidation. In this respect, particulate active metallic oxides in dust, like TiO2 and Fe ions, were proposed to influence the photochemical reactions of ambient VOCs. A case study was conducted at an urban site in Xi'an, northwest China, to investigate the origin and transformation of VOCs during a windblown dust-to-haze pollution episode, and the assumption that dust would enhance the oxidation of VOCs was verified. Local vehicle exhaust (25 %) and biomass burning (18 %) were found to be the two largest contributors to ambient VOCs. In the dust pollution period, a sharp decrease in the loading of VOCs and the aging of their components were observed. Simultaneously, the secondary oxygenated VOC fraction (i.e., methylglyoxal) increased. Source strength, physical dispersion, and regional transport were eliminated as major factors for the variation of ambient VOCs. In another aspect, about a 2- to 3-fold increase in the loading of iron (Fe) and titanium (Ti) was found in the airborne particles, together with a fast decrease in trans-/cis-2-butene ratios, which demonstrated that dust can accelerate the oxidation of ambient VOCs and the formation of secondary organic aerosol (SOA) precursors.

Description: This study examines how cone penetration test (CPT) parameters, such as cone tip resistance and friction sleeve resistance, can be used to assess the compressibility of fine-grained soils across the Netherlands based on a database of 286 paired CPTs and oedometer tests from across the country. This is done with the aim of refining and simplifying the parameterisation of the Koppejan consolidation coefficients, a procedure which can yield significant error and is prone to misinterpretation. It was found that there is significant potential in using gradient boosting methods to obtain a relationship between the CPT parameters and the Koppejan parameters, with further investigation required into the noise within the dataset and the acquisition of additional high-quality samples. The use of such methods will offer a means of reducing the influence of human error or misinterpretation on the prediction of settlement and provide further confidence in the use of machine learning methods in engineering practice.