The influence of COVID-19 pandemic on PM2.5 air quality in Northern Taiwan from Q1 2020 to Q2 2021.

The study aimed to investigate the PM2.5 variations in different periods of COVID-19 control measures in Northern Taiwan from Quarter 1 (Q1) 2020 to Quarter 2 (Q2) 2021. PM2.5 sources were classified based on long-range transport (LRT) or local pollution (LP) in three study periods: one China lockdown (P1), and two restrictions in Taiwan (P2 and P3). During P1 the average PM2.5 concentrations from LRT (LRT-PM2.5-P1) were higher at Fuguei background station by 27.9% and in the range of 4.9-24.3% at other inland stations compared to before P1. The PM2.5 from LRT/LP mix or pure LP (Mix/LP-PM2.5-P1) was also higher by 14.2-39.9%. This increase was due to higher secondary particle formation represented by the increase in secondary ions (SI) and organic matter in PM2.5-P1 with the largest proportion of 42.17% in PM2.5 from positive matrix factorization (PMF) analysis. A similar increasing trend of Mix/LP-PM2.5 was found in P2 when China was still locked down and Taiwan was under an early control period but the rapidly increasing infected cases were confirmed. The shift of transportation patterns from public to private to avoid virus infection explicated the high correlation of the increasing infected cases with the increasing PM2.5. In contrast, the decreasing trend of LP-PM2.5-P3 was observed in P3 with the PM2.5 biases of ∼45% at all the stations when China was not locked down but Taiwan implemented a semi-lockdown. The contribution of gasoline vehicle sources in PM2.5 was reduced from 20.3% before P3 to 10% in P3 by chemical signatures and source identification using PMF implying the strong impact of strict control measures on vehicle emissions. In summary, PM2.5 concentrations in Northern Taiwan were either increased (P1 and P2) or decreased (P3) during the COVID-19 pandemic depending on control measures, source patterns and meteorological conditions.

Characteristics and sources of oxygenated VOCs in Hong Kong: Implications for ozone formation.

To investigate the characteristics of oxygenated volatile organic compounds (OVOCs) and their potential contribution to ozone (O3) generation, we conducted 3-h high-resolution observations during the summertime of 2022 and the wintertime of 2021. This study focused on a total of 28 OVOCs in five different chemical classes, which were encompassed at two representative sites in Hong Kong, including a roadside and an urban area. During the summertime, the total concentrations of quantified OVOCs (∑OVOCs) were 45 ± 12 and 63 ± 20 µg m-3 at the roadside and urban sites, respectively, whereas the ∑OVOCs decreased by 31 ± 11 % and 38 ± 13 %, respectively, during the wintertime. Among the classes of OVOCs, carbonyls and alcohols were the two predominant at both sites, with relatively higher concentration levels of acetone, methanol, butanaldehyde, and acrolein. The sources of OVOCs have significant spatial and temporal characteristics. Spatially, OVOCs were predominately attributed to primary emission and background at the roadside site, whereas they were a combination of primary emission, secondary formation, and background at the urban site. Temporally, background sources dominated the summertime OVOCs, while the contribution of primary emissions increased for the wintertime OVOCs. The O3 formation potential (OFP) for the OVOCs was calculated. The OFPs were 67 ± 16 and 119 ± 31 µg m-3 at the roadside and urban sites during the summertime, whereas the winter OFPs declined 30 % at the roadside and 38 % at the urban site. The background sources of carbonyls and alcohols at the roadside and of carbonyls and acrylates in the urban area were the major contributors to the summer OFP. Controlling the OVOC sources from local non-combustion sources such as gasoline-fuel evaporation and volatile chemical-containing products could lead to a reduction of OVOCs in the background and subsequently mitigate the OFP. This is beneficial for local O3 reduction in Hong Kong and surrounding regions.

Spatial distribution, ecological risk, and human health assessment of heavy metals in lake surface sections - a case study of Qinghai Lake, China.

Qinghai Lake is the largest inland saltwater lake in China, with a drainage area of 29,661 km2. This study sought to conduct an ecological and human health risk assessment of metals and heavy metals, including copper, as well as investigate their concentration, distribution, and source distribution. In terms of seasonal variation, the increases in Fe, Cr, As, Pb, and Hg were relatively large, and the spatial distribution of metals presented a three-level stepped distribution trend, gradually increasing from east to west. By further exploring the source and migration path of pollutants, our study found that the source of metals in the sediments of Qinghai Lake is mainly controlled by five rivers entering the lake. Enrichment factor (EF) calculations indicated that the metal accumulation or enrichment capacity of the three central points in Qinghai Lake Basin was strong. Interestingly, the enrichment capacity of Cu and Zn was the strongest among all metals but occurred at low and medium concentration levels, respectively. The Igeo and [Formula: see text] ecological risk assessment results indicated that the individual metals posed little to no ecological risks to the Qinghai Lake Basin. However, the multi-element environmental risk comprehensive index (RI) indicated that Hg (RI = 147.97) represented a slight ecological hazard, Mn (RI = 181.13) posed moderate ecological hazards, and Zn (RI = 386.66) posed strong ecological hazards. The human health risk assessment results showed that the heavy metals in the surface sediments of Qinghai Lake currently do not pose a threat to human health. This information may facilitate the implementation of more stringent monitoring programs in the aquatic ecosystem by the relevant regulatory authorities.

Characteristics of Dissolved Organic Matter Impacted by Different Land Use in Haihe River Watershed, China.

It is important to explore characteristics of dissolved organic matter (DOM) in the riverine system due to its critical role in the carbon cycle. This study investigated the distribution characteristics and sources of DOM based on excitation emission matrix three-dimensional fluorescence technology and parallel factor (EEM-PARAFAC) analysis at two rivers in northern China strongly impacted by human activities. The results show that the fluorescence intensity of terrestrial humic-like substances increased during summer in Haihe River. The intensity was significantly higher than in spring due to terrestrial detritus from runoff conveyance. The fluorescence intensity of protein-like substances in spring was the highest and decreased in summer. This feature of DOM in the Duliujian River was related to the increase in precipitation and surface runoff in the wet season and the rapid degradation of mixed DOM in the dry season. An analysis of HIX, BIX and FI showed a low degree of DOM humification and more endogenous contributions from microbial and phytoplankton degradation. Seasonal variations of dissolved organic carbon (DOC) and chromophoric DOM (CDOM, a335, thereinto C1) suggest that chromophores, particularly terrestrial substances, regulate the temporal patterns of DOM in the two rivers. Combined with the analysis of the proportion of land use types in riparian buffers, tillage had a great impact on DOM content and hydrophobicity in Haihe River watershed. Domestic wastewater and industrial sewage discharge contribute more DOM to Duliujian River watershed, which was indicated by more abundant protein-like components (212.17 ± 94.63 QSU in Duliujian River;186.59 ± 238.72 QSU in Haihe River). This study highlights that different land use types resulted in distinctive sources and seasonal dynamics of DOM in rivers. Meanwhile, it should be considered that the estimation of carbon cycling should involve monitoring and evaluating anthropogenic inputs into rivers.

Improving Bayesian radiological profiling of waste drums using Dirichlet priors, Gaussian process priors, and hierarchical modeling.

We present three methodological improvements of our recently proposed approach for Bayesian inference of the radionuclide inventory in radioactive waste drums, from radiological measurements. First we resort to the Dirichlet distribution for the prior distribution of the isotopic vector. The Dirichlet distribution possesses the attractive property that the elements of its vector samples sum up to 1. Second, we demonstrate that such Dirichlet priors can be incorporated within an hierarchical modeling of the prior uncertainty in the isotopic vector, when prior information about isotopic composition is available. Our used Bayesian hierarchical modeling framework makes use of this available information but also acknowledges its uncertainty by letting to a controlled extent the information content of the indirect measurement data (i.e., gamma and neutron counts) shape the actual prior distribution of the isotopic vector. Third, we propose to regularize the Bayesian inversion by using Gaussian process (GP) prior modeling when inferring 1D spatially-distributed mass or, equivalently, activity distributions. As of uncertainty in the efficiencies, we keep using the same stylized drum modeling approach as proposed in our previous work to account for the source distribution uncertainty across the vertical direction of the drum. A series of synthetic tests followed by application to a real waste drum show that combining hierarchical modeling of the prior isotopic composition uncertainty together with GP prior modeling of the vertical Pu profile across the drum works well. We also find that our GP prior can handles both cases with and without spatial correlation. Of course, our GP prior modeling framework only makes sense in the context of spatial inference. Furthermore, the computational times involved by our approach are on the order of a few hours, say about 2, to provide uncertainty estimates for all variables of interest in the considered inverse problem. This warrants further investigations to speed up the inference.

Sensing Shallow Structure and Traffic Noise with Fiber-optic Internet Cables in an Urban Area.

Abstract: Distributed acoustic sensing (DAS) is a novel seismic observation system developed in recent years that can realize ultrahigh density observations and has attracted extensive attention in the field of seismology. DAS uses fiber-optic cables as sensing units, which are easy to incorporate with urban telecommunication fiber-optic cables for seismological observations. Compared with seismometers, DAS has the advantages of being rapidly deployed and recyclable, being able to acquire dense observations at low cost, and convenient data collection. In this study, a 5.2 km long telecom fiber-optic internet cable was utilized as a DAS array in an urban area to record ambient noise, and the noise cross-correlation function (NCF) was calculated. There are two different distribution types of ambient noise sources along the cable, regular along-road trucks (Taihe Road) and complex ambient noise, including human activities and traffic sources along and across the Jinniu road. In the first case, we constructed a 2D S-wave velocity model down to 100 m depth and a low-velocity zone was revealed. The S-wave model well explained the traffic signal along the Taihe road and the low-velocity zone is also consistent with the results obtained from co-located geophone arrays. In the second case, due to the complexity of the traffic noise distribution, empirical Green's functions were barely achieved. Therefore, we performed a synthetic test obtaining different NCFs with different source distributions, and two specific cases that dominate the NCF results were matched. Finally, we obtained the traffic noise distribution along the road, which is consistent with the power spectra density of the ambient noise. In conclusion, by combining DAS and urban fiber-optic internet cables with urban traffic noise, we can effectively reveal the traffic activities and image shallow structures with high resolution, which could offer a reference for urban construction and disaster prevention. Article Highlights: DAS turns the urban fiber-optic internet cables into ultra-dense permanent seismic observation arraysWe revealed a high-resolution shallow structure using urban fiber-optic internet cablesWe obtained the distribution of traffic activities along the road.

Bayesian inference of 1D activity profiles from segmented gamma scanning of a heterogeneous radioactive waste drum.

We present a Bayesian approach to probabilistically infer vertical activity profiles within a radioactive waste drum from segmented gamma scanning (SGS) measurements. Our approach resorts to Markov chain Monte Carlo (MCMC) sampling using the state-of-the-art Hamiltonian Monte Carlo (HMC) technique and accounts for two important sources of uncertainty: the measurement uncertainty and the uncertainty in the source distribution within the drum. In addition, our efficiency model simulates the contributions of all considered segments to each count measurement. Our approach is first demonstrated with a synthetic example, after which it is used to resolve the vertical activity distribution of 5 nuclides in a real waste package.

Assessing the Spatial Distribution of Soil PAHs and their Relationship with Anthropogenic Activities at a National Scale.

Soil polycyclic aromatic hydrocarbon (PAH) pollution is a major concern due to its negative impact on soil quality around the world. In China, accurate data on soil PAHs and information on the relationship with anthropogenic activities are limited. In this study, about 30,800 samples from 1833 soil sample sites were reviewed from 306 published reports to build a soil PAHs database. Based on the data obtained, the results demonstrated that 24.11% of surface soils in China are heavily contaminated. Meanwhile, the concentration of soil PAHs varied, in the order of independent mining and industrial areas (IMIA) > urban areas > suburban areas > rural areas, and the spatial distribution in China demonstrated a descending trend from north to south. Moreover, the characteristic ratio and PCA-MLR (principal component analysis-multiple linear regression) analysis demonstrated that coal combustion and vehicular exhaust emissions were the main sources of soil PAH pollution in China. On the other hand, provincial total Σ16PAHs in surface soil were significantly correlated with the per square kilometer GDP (gross domestic product) of industrial land, the per capita GDP, as well as the production and consumption of energy. These results indicate that anthropogenic factors have greatly affected the levels of soil PAHs in China. This study improves our understanding on the status and sources of soil PAH contamination in China, thereby facilitating the implementation of strategies of prevention, control, and remediation of soils.

Listeria monocytogenes Source Distribution Analysis Indicates Regional Heterogeneity and Ecological Niche Preference among Serotype 4b Clones.

Biodiversity analysis of the foodborne pathogen Listeria monocytogenes recently revealed four serotype 4b major hypervirulent clonal complexes (CCs), i.e., CC1, CC2, CC4, and CC6. Hypervirulence was indicated by overrepresentation of these clones, and serotype 4b as a whole, among human clinical isolates in comparison to food. However, data on potential source-dependent partitioning among serotype 4b clones in diverse regions are sparse. We analyzed a panel of 347 serotype 4b isolates, primarily from North America, to determine the distribution of clones in humans, other animals, food, and water. CC1, CC2, CC4, and CC6 predominated, but surprisingly, only three clones, i.e., CC2 and the singleton sequence types (STs) ST382 and ST639, exhibited significant source-dependent associations, with higher propensity for food (CC2) or water (ST382 and ST639) than other sources. Pairwise comparisons between human and food isolates identified CC4 as the only serotype 4b clone significantly overrepresented among human isolates. Our analysis also revealed several serotype 4b clones emerging in North America. Two such emerging clones, ST382 (implicated in several outbreaks since 2014) and ST639, were primarily encountered among human and water isolates. Findings suggest that in spite of the ubiquity of CC1, CC2, CC4, and CC6, regional heterogeneity in serotype 4b is substantially larger than previously surmised. Analysis of even large strain panels from one region may not adequately predict clones unique to, and emerging in, other areas. Serotype 4b clonal complexes may differ in ecological niche preference, suggesting the need to further elucidate reservoirs and vehicles, especially for emerging clones.IMPORTANCE In Listeria monocytogenes, serotype 4b strains are leading contributors to human disease, but intraserotype distributions among different sources and regions remain poorly elucidated. Analysis of 347 serotype 4b isolates from four different sources, mostly from North America, confirmed the overall predominance of the major clones CC1, CC2, CC4, and CC6 but found that only CC4 was significantly associated with human disease, while CC2 was significantly associated with food. Remarkably, several emerging clones were identified among human isolates from North America, with some of these also exhibiting a propensity for surface water. The latter included the singleton clones ST382, implicated in several outbreaks in the United States since 2014, and ST639. These clones were noticeably underrepresented among much larger panels from other regions. Though associated with North America for the time being, they may eventually become globally disseminated through the food trade or other venues.

Resting state theta band source distribution and functional connectivity in remitted schizophrenia.

Increased resting theta activity is one consistent observation occurring during all the phases of schizophrenia. However, the resting theta oscillations during the remission phase are yet unclear. We studied resting theta current source density and functional connectivity in remitted schizophrenia and compared with healthy controls. Significantly increased current source density was found in the dominant anterior cingulate cortex. Increased connectivity between the inferior parietal lobe bilaterally and between the left inferior parietal lobe and right middle frontal gyrus was also found. It may be concluded that schizophrenia patients have aberrant regional theta band current source density and functional connectivity even during remission.

Quantitative annular dark-field imaging of single-layer graphene-II: atomic-resolution image contrast.

We have investigated how accurately atomic-resolution annular dark-field (ADF) images match between experiments and simulations to conduct more reliable crystal structure analyses. Quantitative ADF imaging, in which the ADF intensity at each pixel represents the fraction of the incident probe current, allows us to perform direct comparisons with simulations without the use of fitting parameters. Although the conventional comparison suffers from experimental uncertainties such as an amorphous surface layer and specimen thickness, in this study we eliminated such uncertainties by using a single-layer graphene as a specimen. Furthermore, to reduce image distortion and shot noises in experimental images, multiple acquisitions with drift correction were performed, and the atomic ADF contrast was quantitatively acquired. To reproduce the experimental ADF contrast, we used three distribution functions as the effective source distribution in simulations. The optimum distribution function and its full-width at half-maximum were evaluated by measuring the residuals between the experimental and simulated images. It was found that the experimental images could be explained well by a linear combination of a Gaussian function and a Lorentzian function with a longer tail than the Gaussian function.