Photochemical Formation of C₁–C₅ Alkyl Nitrates in Suburban Hong Kong and over the South China Sea

Alkyl nitrates (RONO₂) are important reservoirs of atmospheric nitrogen, regulating nitrogen cycling and ozone (O₃) formation. In this study, we found that propane and <i>n</i>-butane were significantly lower at the offshore site (WSI) in Hong Kong (<i>p</i> < 0.05), whereas C₃–C₄ RONO₂ were comparable to the suburban site (TC) (<i>p</i> > 0.05). Stronger oxidative capacity at WSI led to more efficient RONO₂ formation. Relative incremental reactivity (RIR) was for the first time used to evaluate RONO₂–precursor relationships. In contrast to a consistently volatile organic compounds (VOC)-limited regime at TC, RONO₂ formation at WSI switched from VOC-limited regime during O₃ episodes to VOC and nitrogen oxides (NO_<i>x</i>) colimited regime during nonepisodes. Furthermore, unlike the predominant contributions of parent hydrocarbons to C₄–C₅ RONO₂, the production of C₁–C₃ RONO₂ was more sensitive to other VOCs like aromatics and carbonyls, which accounted for ∼40–90% of the productions of C₁–C₃ alkylperoxy (RO₂) and alkoxy radicals (RO) at both sites. This resulted from the decomposition of larger RO₂/RO and the change of OH abundance under the photochemistry of other VOCs. This study advanced our understanding of the photochemical formation of RONO₂, particularly the relationships between RONO₂ and their precursors, which were not confined to the parent hydrocarbons

Ultrasonic Spray Pyrolysis Fabrication of Solid and Hollow PbWO₄ Spheres with Structure-Directed Photocatalytic Activity

Solid and hollow PbWO4 spheres were fabricated by a one-step and template-free ultrasonic spray pyrolysis (USP) using lead nitrate and ammonium metatungstate hydrate as precursors. The characteristics of the resulting samples were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption/desorption, and UV−vis diffuse reflectance spectroscopy in detail. The addition of citric acid (CA) to the precursor solution played a crucial role in producing hollow structured spheres. The hollow PbWO4 spheres were composed of single-crystal nanoparticles. On the basis of the characterization and experimental observations, a possible mechanism on the formation of solid and hollow PbWO4 spheres was proposed. Gaseous products generated due to the decomposition of CA in the pyrolysis process shaped the final hollow morphology. The results also indicated that the CA addition could decrease the crystal size of hollow PbWO4. The specific surface areas and pore volume of hollow PbWO4 spheres were increased simultaneously due to the CA decomposition compared with solid PbWO4 spheres produced without CA addition. The PbWO4 spheres were tested as photocatalyst for NO removal in air. The hollow structured PbWO4 spheres were found to exhibit superior photocatalytic activity to solid spheres due to the differences in microstructure and morphology. The result acquired may shed light on general fabrication strategy for designing hollow structured materials by USP

Metagenomic Analysis Revealing Antibiotic Resistance Genes (ARGs) and Their Genetic Compartments in the Tibetan Environment

Comprehensive profiles of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in a minimally impacted environment are essential to understanding the evolution and dissemination of modern antibiotic resistance. Chemical analyses of the samples collected from Tibet demonstrated that the region under investigation was almost devoid of anthropogenic antibiotics. The soils, animal wastes, and sediments were different from each other in terms of bacterial community structures, and in the typical profiles of ARGs and MGEs. Diverse ARGs that encoded resistance to common antibiotics (e.g., <i>beta</i>-lactams, fluoroquinolones, etc.) were found mainly via an efflux mechanism completely distinct from modern antibiotic resistome. In addition, a very small fraction of ARGs in the Tibetan environment were carried by MGEs, indicating the low potential of these ARGs to be transferred among bacteria. In comparison to the ARG profiles in relatively pristine Tibet, contemporary ARGs and MGEs in human-impacted environments have evolved substantially since the broad use of anthropogenic antibiotics