Emerging advanced oxidation processes for the elimination of micro-pollutants

Emerging advanced oxidation processes for the elimination of micro-pollutant

Interaction between succinic acid and sulfuric acid–base clusters

Dicarboxylic acids likely participate in the formation of pre-nucleation clusters to facilitate new particle formation in the atmosphere, but the detailed mechanism leading to the formation of multicomponent critical nuclei involving organic acids, sulfuric acid (SA), base species, and water remains unclear. In this study, theoretical calculations are performed to elucidate the interactions between succinic acid (SUA) and clusters consisting of SA-ammonia (AM)∕dimethylamine (DMA) in the presence of hydration of up to six water molecules. Formation of the hydrated SUA•SA• base clusters is energetically favorable, triggering proton transfer from SA to the base molecule to form new covalent bonds or strengthening the preexisting covalent bonds. The presence of SUA promotes hydration of the SA•AM and SA•AM•DMA clusters but dehydration of the SA•DMA clusters. At equilibrium, SUA competes with the second SA molecule for addition to the SA• base clusters at atmospherically relevant concentrations. The clusters containing both the base and organic acid are capable of further binding with acid molecules to promote subsequent growth. Our results indicate that the multicomponent nucleation involving organic acids, sulfuric acid, and base species promotes new particle formation in the atmosphere, particularly under polluted conditions with a high concentration of diverse organic acids

Formation and optical properties of brown carbon from small α-dicarbonyls and amines

Brown Carbon (BrC) aerosols scatter and absorb solar radiation, directly affecting the Earth’s radiative budget. However, considerable uncertainty exists concerning the chemical mechanism leading to BrC formation and their optical properties. In this work, BrC particles were prepared from mixtures of small α-dicarbonyls (glyoxal and methylglyoxal) and amines (methylamine, dimethylamine, and trimethylamine). The absorption and scattering of BrC particles were measured using a photoacoustic extinctometer (405 and 532 nm), and the chemical composition of the α-dicarbonyl-amine mixtures was analyzed using orbitrap-mass spectrometry and thermal desorption-ion drift-chemical ionization mass spectrometry. The single scattering albedo for methylglyoxal-amine mixtures is smaller than that of glyoxal-amine mixtures and increases with the methyl substitution of amines. The mass absorption cross-section for methylglyoxal-amine mixtures is two times higher at 405 nm wavelength than that at 532 nm wavelength. The derived refractive indexes at the 405 nm wavelength are 1.40–1.64 for the real part and 0.002–0.195 for the imaginary part. Composition analysis in the α-dicarbonyl-amine mixtures reveals N-heterocycles as the dominant products, which are formed via multiple steps involving nucleophilic attack, steric hindrance, and dipole–dipole interaction between α-dicarbonyls and amines. BrC aerosols, if formed from the particle-phase reaction of methylglyoxal with methylamine, likely contribute to atmospheric warming

Reassessing the atmospheric oxidation mechanism of toluene

Photochemical oxidation of aromatic hydrocarbons leads to tropospheric ozone and secondary organic aerosol (SOA) formation, with profound implications for air quality, human health, and climate. Toluene is the most abundant aromatic compound under urban environments, but its detailed chemical oxidation mechanism remains uncertain. From combined laboratory experiments and quantum chemical calculations, we show a toluene oxidation mechanism that is different from the one adopted in current atmospheric models. Our experimental work indicates a larger-than-expected branching ratio for cresols, but a negligible formation of ring-opening products (e.g., methylglyoxal). Quantum chemical calculations also demonstrate that cresols are much more stable than their corresponding peroxy radicals, and, for the most favorable OH (ortho) addition, the pathway of H extraction by O_2 to form the cresol proceeds with a smaller barrier than O_2 addition to form the peroxy radical. Our results reveal that phenolic (rather than peroxy radical) formation represents the dominant pathway for toluene oxidation, highlighting the necessity to reassess its role in ozone and SOA formation in the atmosphere

The Society for Environmental Geochemistry and Health (SEGH): building for the future.

The challenges of sustainable development are ever more pressing, and the skills, interests and capabilities of the SEGH member are well-placed to continue to make more meaningful contributions to the environment, society and well-being. We reflect on the historical development of the society, its response to the dynamic international research landscape and the great opportunities ahead. In 2018, SEGH implemented a new board structure after 2–3 years of consultation, with approval of a new constitution and a new strategy across the large number of international board members. While regions were represented by sections in Europe, Asia/Pacific and the USA, the structure required renewal in order to be more representative of the distribution of members and website traffic that had evolved in preceding years. In addition, the society wanted to improve its position for future growth opportunities across rapidly developing regions

Effect of reducible oxide-metal cluster charge transfer on the structure and reactivity of adsorbed Au and Pt atoms and clusters on anatase TiO2

We carried out density functional theory calculations to study the influence of oxide–metal charge transfers on the structure, energetics, and reactivity of Au and Pt atoms, dimers, and trimers adsorbed on the (101) surface of reduced anatase TiO2. Pt clusters interact much more strongly with the TiO2 support than Au clusters, and, with the exception of single Pt adatoms, generally behave as electron acceptors on reduced TiO2, whereas Au clusters can both accept and donate charge on the reduced surface. The reactivity of the supported clusters was probed by considering their interaction with CO and co-adsorbed O2. The effect of surface reduction on the interaction with CO is particularly significant when the CO adsorption site is an interfacial metal atom directly in contact with the TiO2 surface and/or in the presence of co-adsorbed O2. Pt clusters interact strongly with co-adsorbed O2 and form Pt–O2 complexes that can easily accept electrons from reduced surfaces. In contrast, Au clusters donate charge to co-adsorbed O2 even in the presence of excess electrons from a reduced support. The computed differences in the properties of the supported Pt and Au clusters are consistent with several experimental observations and highlight the important role of excess surface electrons in the behavior of supported metal catalysts on reducible oxides

LONG-TERM ECOSYSTEM CHANGE IN JIAOZHOU BAY AND ITS CATCHMENT: THE DPSIR APPROACH

Jiaozhou Bay is a semi-closed embayment, affected by anthropogenic factors around Qingdao, China. This article illustrates the long-term change in the Bay and its catchment using the driver-pressure-state-impact-response (DPSIR) approach. Under the Chinese national macro-socioeconomic policy, rapid development and massive urbanization occurred in Qingdao that has resulted in the serious reduction and quality deterioration of its arable land and the variation in water resources. The production and consumption pattern changed with population growth and an increasing demand for water and food as well as pollutants emissions. The pressure alteration in the Bay and its catchment has created far-reaching impacts on the ecosystem. These changes include: significant deterioration in water quality of the catchment; decreased river runoff into the bay; shift in the nutrient regime of the Bay; decreased tidal prism in the Bay; increased eutrophication in the Bay; fragmentation of natural habitats and loss of biodiversity. Relevant policies aimed to formulate the promotion of the water quality have been done in the system. However, the deterioration trend has not yet been halted or reversed. Hence new management mechanisms are under discussion to improve the ecosystem in this area