Abstract. Isocyanic acid (HNCO) is a chemical constituent suspected to be harmful to humans if ambient concentrations exceed ∼1 ppbv. HNCO is mainly emitted by combustion processes but is also inadvertently released by NOx mitigation measures in flue gas treatments. With increasing biomass burning and more widespread usage of catalytic converters in car engines, good prediction of HNCO atmospheric levels with global models is desirable. Little is known directly about the chemical loss processes of HNCO, which limits the implementation in global Earth system models. This study aims to close this knowledge gap by combining a theoretical kinetic study on the major oxidants reacting with HNCO with a global modelling study. The potential energy surfaces of the reactions of HNCO with OH and NO3 radicals, Cl atoms, and ozone were studied using high-level CCSD(T)/CBS(DTQ)//M06-2X/aug-cc-pVTZ quantum chemical methodologies, followed by transition state theory (TST) theoretical kinetic predictions of the rate coefficients at temperatures of 200–3000 K. It was found that the reactions are all slow in atmospheric conditions, with k(300K)≤7×10-16 cm3molecule-1s-1, and that product formation occurs predominantly by H abstraction; the predictions are in good agreement with earlier experimental work, where available. The reverse reactions of NCO radicals with H2O, HNO3, and HCl, of importance mostly in combustion, were also examined briefly. The findings are implemented into the atmospheric model EMAC (ECHAM/MESSy Atmospheric Chemistry) to estimate the importance of each chemical loss process on a global scale. The EMAC predictions confirm that the gas-phase chemical loss of HNCO is a negligible process, contributing less than 1 % and leaving heterogeneous losses as the major sinks. The removal of HNCO by clouds and precipitation contributes about 10 % of the total loss, while globally dry deposition is the main sink, accounting for ∼90 %. The global simulation also shows that due to its long chemical lifetime in the free troposphere, HNCO can be efficiently transported into the UTLS by deep convection events. Daily-average mixing ratios of ground-level HNCO are found to regularly exceed 1 ppbv in regions dominated by biomass burning events, but rarely exceed levels above 10 ppt in other areas of the troposphere, though locally instantaneous toxic levels are expected.

Terpenoids are an important class of multi-unsaturated volatile organic compounds emitted to the atmosphere. During their oxidation in the troposphere, unsaturated peroxy radicals are formed, which may undergo ring closure...

Nowadays, urban development associated with sustainable development goals is a global trend, in which the Eco-city paradigm is considered a central paradigm of a sustainable city. Faced with environmental crises and ecological imbalance problems taking place in some cities today, the Eco-city paradigm will be an appropriate solution, overcoming the limitations of modern cities, is especially meaningful, and important for developing countries. Eco-city with its strategies and structure will minimize the environmental and social consequences, while minimizing the impact on the ecosystem, helping the city develop in balance and harmony between the ecological system and urban social system. Based on the analysis of theories on Eco-city, Eco2-cities, and planning methods based on socio-ecosystem (SES). From there, the article presents research results on principles of Eco-city planning, Eco-city structure paradigm; and discusses the possibility of applying the Eco-city paradigm in the practical conditions of Vietnam. The research and proposals in this article aim to contribute to the scientific basis of Eco-cities, thereby promoting the research, planning, implementation, and management of Eco-cities in Vietnam, with the expectation of creating healthy and liveable living environments with minimal need for resources, minimizing environmental impacts; enhancing urban resilience; towards the goal of sustainable development, adapting to climate change, and conservation of biodiversity.

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<p>The oxidation of most organic matter emitted to the atmosphere proceeds by radical reaction steps, where peroxy radicals, ROO<sup>•</sup>, are critical intermediates formed by addition of O<sub>2</sub> molecules to carbon-based radicals. The chemistry of these RO<sub>2</sub> radicals in high-NOx conditions is well-known, forming alkoxy radicals and NO<sub>2</sub>. In low-NOx and pristine conditions, the RO<sub>2</sub> radicals react with HO<sub>2</sub> and other R'O<sub>2</sub> radicals, but can have a sufficiently long lifetime to also undergo unimolecular reactions. Hydrogen atom migration, forming a hydroperoxide (-OOH) and a new peroxy radical site after addition of an additional O<sub>2</sub> on the newly formed radical site, has been studied extensively in some compounds, such as isoprene where it was shown to be the a critical step in OH radical regeneration. RO<sub>2</sub> ring closure reactions have likewise been studied, where for β-pinene it has been shown to be a critical step governing the yield of the decomposition products such as acetone and nopinone.</p> <p>Despite the interest in RO<sub>2</sub> unimolecular reactions, and the potential impact on atmospheric chemistry, no widely applicable structure-activity relationships (SARs) have been proposed to allow systematic incorporation of such unimolecular reactions in gas phase atmospheric kinetic models. In this work, we present a series of systematic theoretical predictions on the site-specific rate coefficients for such reactions for a wide range of molecular substitutions. Combined with extensive literature data this allows for the formulation of a SAR for RO<sub>2</sub> unimolecular reactions, covering aliphatic, branched, and unsaturated RO<sub>2</sub> with oxo, hydroxy, hydroperoxy, nitrate, carboxylic acid, and ether substitutions.</p> <p>The predictions are compared to experimental and theoretical data, including multi-functionalized species. Though some molecular classes are well represented in the training set (e.g. aliphatic RO<sub>2</sub>), other classes have little data available and additional work is needed to enhance and validate the reliability of the SAR. Direct experimental data is scarce for all RO<sub>2</sub> classes. The fastest H-migrations are found to be for unsaturated RO<sub>2</sub>, with the double bond outside the H-migration TS ring. Ring closure of unsaturated RO<sub>2</sub> are likewise fast if the product radical carbon is exocyclic to the newly formed peroxide ring.</p>