ALBERT

Description: Indoor air pollution (IAP) is one of the leading risk factors for various adverse health outcomes including premature deaths globally. Even though research related to IAP has been carried out, bibliometric studies with particular emphasis on this topic have been lacking. Here, we investigated IAP research from 1990 to 2019 retrieved from the Web of Science database through a comprehensive and systematic scientometric analysis using the CiteSpace 5.7.R2, a powerful tool for visualizing structural, temporal patterns and trends of a scientific field. There was an exponential increase in publications, however, with a stark difference between developed and developing countries. The journals publishing IAP related research had multiple disciplines; ‘Indoor Air’ journal that focuses solely on IAP issues ranked fifth among top-cited journals. The terms like ‘global burden’, ‘comparative risk assessment,’ ‘household air pollution (HAP)', ‘ventilation’, ‘respiratory health’, ‘emission factor’, ‘impact,’ ‘energy’, ‘household’, ‘India’ were the current topical subject where author Kirk R. Smith was identified with a significant contribution. Research related to rural, fossil-fuel toxicity, IAP, and exposure-assessment had the highest citation burst signifying the particular attention of scientific communities to these subjects. Overall, this study examined the evolution of IAP research, identified the gaps and provided future research directions.

Description: Thaw consolidation of degrading permafrost is a serious hazard to the safety and operation of infrastructure. Monitoring thermal changes in the active layer (AL), the proportion of the soil above permafrost that thaws and freezes periodically, is critical to understanding the conditions of the top layer above the permafrost and regulating the construction, operation, and maintenance of facilities. However, this is a very challenging task using ground-based methods such as ground-penetrating radar (GPR) or temperature sensors. This study explores the integration of interferometric measurements from high-resolution X-band Synthetic Aperture Radar (SAR) images and volumetric water content (VWC) data from SoilGrids to quantify detailed spatial variations in active layer thickness (ALT) in Iqaluit, the territorial capital of Nunavut in Canada. A total of 21 SAR images from COSMO Sky-Med (CSK) were first analyzed using the freely connected network interferometric synthetic aperture radar (FCNInSAR) method to map spatial and temporal variations in ground surface subsidence in the study area. Subsequently, we built an ALT retrieval model by introducing the thaw settlement coefficient, which takes soil properties and saturation state into account. The subsidence measurements from InSAR were then integrated with VWC extracted from the SoilGrids database to estimate changes in ALT. For validation, we conducted a comparison between estimated ALTs and in situ measurements in the airport sector. The InSAR survey identifies several sites of ground deformation at Iqaluit, subsiding at rates exceeding 80 mm/year. The subsidence rate changes along the runway coincide with frost cracks and ice-wedge furrows. The obtained ALTs, ranging from 0 to 5 m, vary significantly in different sediments. Maximum ALTs are found for rock areas, while shallow ALTs are distributed in the till blanket (Tb), the intertidal (Mi) sediments, and the alluvial flood plain (Afp) sediment units. The intersection of taxiway and runway has an AL thicker than other parts in the glaciomarine deltaic (GMd) sediments. Our study suggests that combining high-resolution SAR imagery with VWC data can provide more comprehensive ALT knowledge for hazard prevention and infrastructure operation in the permafrost zone.

Description: As the result of changes in ice dynamics and weather-driven changes on the surface, surface elevation changes over ice sheets are sensitive to climate forcing. Thus, long-term surface elevation changes over ice sheets of Greenland and Antarctica are of essential to assess the impact of climate change. Here, a dataset of monthly surface elevation time series over ice sheets of Greenland and Antarctica at 5km grid resolution using ERS-1, ERS-2, Envisat, and CryoSat-2 radar altimeter observations from August 1991 to December 2020. An updated plane-fitting least-squares regression strategy and Empirical orthogonal function (EOF) reconstruction were applied to ensure the accuracy and self-consistency of the merged elevation time series in the data processing. In addition, the cross-comparison with the IceBridge airborne laser altimeter observations confirmed that our merged dataset is reliable. Benefiting from its high temporal and spatial resolutions, the evolution processes on multiple temporal (up to 30 years) of ice loss from the main outflow glaciers in Greenland and Antarctica can be derived in detail. The spatiotemporal patterns of accelerating or decelerating surface elevation changes over ice sheet related to ENSO (for the Antarctic Ice sheet) and NAO (for the Greenland Ice sheet) indicated that climate forcing shifts oceanic forcing or atmospheric forcing in some way to affect ice sheet changes. Our merged time series provide a vital dataset for exploring the processes of climate forcing driving ice sheet change.

Description: PPP-RTK, a synthesis of the well-known precise point positioning (PPP) and real-time kinematic (RTK) techniques, requires precise satellite-related products and atmospheric corrections estimated in a global navigation satellite system (GNSS) network. For generating these products, one commonly sends all network data to a computation center and conducts a centralized processing scheme. However, this centralized algorithm faces considerable challenges in computational efficiency and model formulation with expanding network coverage and increasing number of receivers. This work proposes a decentralized algorithm that generates PPP-RTK products in three steps: subnetwork processing, satellite-related product integration, and atmospheric correction update. The first step divides the whole network into several subnetworks where we can guarantee common satellite visibility at all receivers to estimate continuous satellite phase biases and impose ionosphere-weighted constraints to improve the precision of ionospheric estimates. The second step integrates subnetwork-dependent satellite clocks and biases and aligns the underlying datum. The final step updates the estimated atmospheric delays by considering the covariances between satellite-related products and atmospheric delays. For numerical evaluation, we collected one-week dual-frequency global positioning system (GPS) data from 82 stations to generate network products and conduct user positioning. The results show, on the network side, that the decentralized PPP-RTK generates products with the same precision as that of centralized PPP-RTK and reduces the computation time by 50%. On the user side, the decentralized PPP-RTK performs as well as the centralized PPP-RTK, and the time-to-first-fix and three-dimensional root-mean-square (RMS) is less than 3 epochs and 1.59 cm on average, respectively.

Description: Here we presented a combination study of PM〈sub〉2.5〈/sub〉 water-soluble ionic composition and PM〈sub〉2.5〈/sub〉 acidity of aerosol samples collected from urban site (CNEMC) in Beijing, China, from 2016-2020, to assess the response of secondary inorganic species in PM〈sub〉2.5〈/sub〉 to the emission reduction and reveal the characteristics and main driving factors of aerosol pH variation. The averaged SO〈sub〉4〈/sub〉〈sup〉2-〈/sup〉, NO〈sub〉3〈/sub〉〈sup〉-〈/sup〉, and NH〈sub〉4〈/sub〉〈sup〉+〈/sup〉 concentration was 8.9, 16.6 and 8.2 μg m〈sup〉-3〈/sup〉 at CNEMC site during autumn-winter seasons, driving the rapid increase of PM〈sub〉2.5〈/sub〉 during pollution. The ISORROPIA II model was employed to predict PM〈sub〉2.5〈/sub〉 pH in autumn-winter seasons, with an average of 3.9 (1.4~6.9) and 4.4 (2.4~6.9) during pollution and non-polluted periods, all acidic. Based on the continuous observations and simulation throughout 2020, PM〈sub〉2.5〈/sub〉 pH showed a significant seasonal cycle pattern. Aerosols in summer were more acidic (pH range: 1-3), while aerosols in winter were less acidic (pH range: 3-6) and fluctuated more violently. We also conducted a sensitivity analysis of PM〈sub〉2.5〈/sub〉 pH to changing meteorological parameters and SNA levels. Overall, temperature was found to be the main factor driving the seasonal and interannual variations in aerosol pH. This result may provide a scientific basis for formulating regional air quality improvement strategies, and provide a new perspective for exploring the influence of meteorological factors on atmospheric chemical processes.

Description: Aims. For decades now, researchers have been looking for a way to tie the kinematic and dynamic reference frames. Certain worldwide organizations have looked to using co-location in space, combining various techniques. Given the long list of possible applications of the Global Navigation Satellite System (GNSS), it is worthwhile investigating the connection between the most accurate and stable International Celestial Reference Frame (ICRF) and the Earth-centered Celestial Inertial reference frame (ECI) used in GNSS data processing. Methods. We simulated phase-referencing observations of GNSS satellites and nearby radio source calibrators to realize the connection between the two celestial reference frames. We designed two schemes for observation plans. One scheme is to select the satellite target when it can be observed by the greatest number of stations in order to obtain high-precision positioning. During each scan, we employ four regional networks to simultaneously track four chosen satellites. The alternative scheme is to observe satellite orbits of as many satellites as possible on different daily observations. In addition, to test the two schemes, we used Monte Carlo methods to generate 1000 groups of random errors in the simulation. Results. Finally, we estimate the right ascension and declination offsets (∆α, ∆δ) of GNSS satellites in the ICRF, and then derive frame tie parameters based on those results: three global rotation angles (A1, A2, A3). The celestial angular offset results assessed from the former scheme show that this scheme leads to high precision of namely 1 mas, while the parameters of the frame tie determined from the second scheme can achieve an improved precision of better than 1.3 µas.