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Determining the chemical characteristics of atmospheric precipitation and its source contributions is critical for improving atmospheric environmental quality and water security. In this study, we analyzed the pH, Electrical Conductivity (EC), and major ion concentrations of precipitation from 2000 to 2021 at 29 monitoring stations in the Pearl River Delta (PRD), which typically experiences acid rain. Correlation analysis, the Positive Matrix Factorization (PMF) model, and other statistical methods were used to analyze the correlations between the major ion concentrations and their source contributions. The results indicate that the pH, EC, and Fractional Acidity (FA) of precipitation from 2000 to 2021 ranged from 4.66 ± 0.18 to 5.91 ± 0.45, from 1.63 ± 0.59 to 5.49 ± 1.62 mS/m, and from 0.05 ± 0.06 to 0.19 ± 0.13, respectively. The pH exhibited interannual variations (first decreasing and then increasing), whereas EC and FA exhibited the opposite trend. The total ion concentrations in precipitation ranged from 166.63 ± 46.56 to 631.48 ± 212.83 μeq/L, which first increased and then decreased. The weighted equivalent ion concentrations were in order of SO42- > Ca2+ > NH4+ > NO3- > Cl- > Na+ > K+ > Mg2+ > F-. SO42-, NO3-, Ca2+, and NH4+ were the main ions, accounting for 72.98% of the total concentration. The ratio of the SO42- concentration to the total concentration decreased from 32.71% in 2000 to 14.33% in 2021, whereas NO3- increased from 9.03% to 13.74% during the same period. The ratio of SO42- to NO3- concentrations (SO42-/NO3-) decreased by 65.95% from 2000 to 2021. After 2008, the SO42-/NO3- values ranged from 0.5 to 3, and precipitation shifted from a sulfuric acid type to a mixed sulfuric-nitric acid type. This change indicates that increased NOx emissions in the PRD under urbanization and agricultural intensification altered the structure of precipitation pollution and further increased the complexity of regional air pollution. The ions were highly significantly positively correlated, of which NO3- and SO42- had the strongest positive correlation (r=0.69‒0.74). Generally, NOx and SO2 are emitted together and enter precipitation via overlapping pathways. Of the six ion sources, coal combustion had the highest contribution rates (a>60%) to SO42- and F-, while secondary inorganic salts contributed 82.30% of the NO3-. Agriculture, sea salt, biomass combustion, and dust contributed > 70% of the NH4+, Na+, K+, and Ca2+. The contribution rates of secondary inorganic salts to SO42-, Cl-, and NH4+ were also greater than 25%. Owing to the increase in motor vehicles driven by urbanization, the impacts of secondary inorganic salt sources on ions in precipitation have become more extensive, and controlling NOx emissions to effectively control secondary pollution sources is urgently required.

Reservoir-type drinking water sources in the Pearl River Delta ensure a safe urban water supply; thus, land-use changes are important factors affecting these aquatic environments. In this study, we investigated the water source areas of medium and large reservoirs in the Pearl River Delta to determine the contributions and trends of land-use changes within reservoir drinking water source areas to the reservoir water quality. First, we analyzed dynamic land-use changes in reservoir-type water sources in the Pearl River Delta region from 1980 to 2020. We then used the gray relational analysis method to determine the relationship between land use and water quality changes. We analyzed changes in the main water quality factors in the Dajingshan Reservoir (Zhuhai) and determined the relationship between changes in land use and the reservoir water quality index over the past 20 years using correlation and redundancy analyses. The results indicate that paddy fields, dry land, forest land, and water areas were the main land-use types around reservoir-type drinking water sources in the Pearl River Delta. Although construction land and water areas expanded, paddy fields, dry land, and forest land areas decreased. The land transfer trend was mainly from forest and cultivated land to production and living land (e.g.1980-2020), construction land) and water areas. With the implementation of the policy, the aforementioned land-use transformation began to slow. Regionally, the risk sources of non-point source pollution in the study area gradually decreased, but still accounted for 9.48% of total land use in 2020. The water quality of reservoir sources in the Pearl River Delta improved; however, nitrogen pollution remains problematic. Gray relational analysis indicates that land-use changes and water quality were correlated (in order of decreasing strength): construction land > agricultural land > forest land. Non-point source pollution caused by land use remains an important influencing factor. The Dajingshan Reservoir water quality is seriously polluted, as the total nitrogen exceeded the standard during several months, and nitrogen and phosphorus pollution gradually increased over time. Nitrogen and phosphorus were the main pollutants in the reservoir. Big mountain reservoir redundancy, correlation, and partial least squares regression analyses indicate that the land use type and water quality index were correlated, forest land and the nitrogen/phosphorus water quality index were negatively correlated, and construction and agricultural land were significantly positively correlated, which had a positive effect on the total nitrogen concentration. The influence of land-use patterns on non-point source pollution remains an uncontrollable factor. The specific effects of land-use changes on water quality are complex; therefore, further modeling should investigate the mechanism by which the water supply quality is influenced to improve reservoir water quality, ensure the safety of the regional water supply, and provide support for ecological restoration measures in protected areas.

Quantitative studies of mangrove leaf functional traits will help us understand the adaptive evolutionary strategies of mangrove plants and the relationship between mangrove biodiversity and ecosystem functions. Because of the special environment of the intertidal zone where mangroves are located, it is very difficult to obtain the functional traits of mangrove canopies from the ground, and relevant studies are lacking. The maturity of Unmanned Aerial Vehicle (UAV) hyperspectral remote sensing technology provides a new means of conducting such research. This study considered mangroves on Qi'ao Island, Zhuhai, as the research object. Based on UAV hyperspectral data, two UAV hyperspectral data processing methods, which combined Partial Least Squares Regression with Normalized Difference Vegetation Index (PLSR+NDVI) and Partial Least Squares Regression with Continuous Wavelet Transform (PLSR+CWT), were used to estimate the 10 canopy leaf functional traits of mangroves on Qi'ao Island. The results showed that the PLSR + NDVI method was more suitable for the inversion of mangrove canopy-specific leaf weight (LMA), phosphorus content per unit mass (Pmass), and nitrogen content per unit area (Narea), whereas the PLSR + CWT method was more suitable for the estimation of the nitrogen/phosphorus ratio (N/P), chlorophyll content (Cab), and carotenoid content (Cxc). However, the results of the above two methods for retrieving the nitrogen content per unit mass (Nmass), potassium content per unit mass (Kmass), phosphorus content per unit area (Parea), and potassium content per unit area (Karea) were not ideal (R2

For studying the effect of methanol gasoline on the corrosion and mechanical properties of rubber parts in vehicles, an immersion test of several currently used rubber parts in methanol gasoline is conducted to observe the variation relationship between the deformation and acting force of rubber parts and to analyze the cause of change of rubber parts after immersion. The results show that the black precipitate of solution, in which rubber parts are immersed, contains carbon black; the rubber tube made of NBR + CR or FKM + braided layer + ECO are rather significantly subjected to the effects of methanol concentration of methanol gasoline, leading to marked deterioration in mechanical performance; multi-layered PA12 is also greatly subjected to the effects of methanol but is not sensitive to the proportion of methanol added; while methanol has no apparent effects on the oil seals for intake and exhaust valves. [ABSTRACT FROM AUTHOR]