Abstract. Atmospheric brown carbon (BrC) is a collective term for light absorbing organic compounds in the atmosphere. While the identification of BrC and its formation mechanisms is currently a central effort in the community, little is known about the atmospheric removal processes of aerosol BrC. As a result, we report on a series of laboratory studies of photochemical processing of BrC in the aqueous phase, by direct photolysis and OH oxidation. Solutions of ammonium sulfate mixed with glyoxal (GLYAS) or methylglyoxal (MGAS) are used as surrogates for a class of secondary BrC mediated by imine intermediates. Three nitrophenol species, namely 4-nitrophenol, 5-nitroguaiacol and 4-nitrocatechol, were investigated as a class of water-soluble BrC originating from biomass burning. Photochemical processing induced significant changes in the absorptive properties of BrC. The imine-mediated BrC solutions exhibited rapid photo-bleaching with both direct photolysis and OH oxidation, with atmospheric half-lives of minutes to a few hours. The nitrophenol species exhibited photo-enhancement in the visible range during direct photolysis and the onset of OH oxidation, but rapid photo-bleaching was induced by further OH exposure on an atmospheric timescale of an hour or less. To illustrate the atmospheric relevance of this work, we also performed direct photolysis experiments on water-soluble organic carbon extracted from biofuel combustion samples and observed rapid changes in the optical properties of these samples as well. Overall, these experiments indicate that atmospheric models need to incorporate representations of atmospheric processing of BrC species to accurately model their radiative impacts.

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Isothermal compression tests at temperatures ranging from 523 to 723 K and strain rates from 0·01 to 10 s−1 were performed on AZ31 magnesium alloy to reveal the deformation characteristics. The flow stress–strain curves show that the flow stress reaches a peak value and then decreases to steady values, which characterise a dynamic flow softening. The measured flow stress was modified by friction and temperature correction, which reflect the friction corrected flow stresses are lower than the measured ones and the effect of temperature rise on flow stress is obvious at high strain rate (≥1 s−1). The corrected flow curves were employed to develop the constitutive model. The influence of strain was also incorporated in the constitutive equation by considering the effects of strain on material constants, which were identified using sixth order polynomial. The flow stress predicted by the constitutive model shows good agreement with the corrected stress, which confirmed that the proposed model is effective and accurate for the flow stress of AZ31 magnesium alloy.

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The superiority of sharkskin is the consequence of nature selection and self-evolution. The nano/ microhierarchical structure covering over sharkskin can match its living surroundings perfectly, whereas the best drag reducing effect cannot be implemented at all circumstances. Therefore, it is necessary to adjust the size and shape of sharkskin morphology to accommodate more potential flowing conditions. In this paper, the stretching deformed fabrication process of sharkskin surface is explored and investigated, and the super-hydrophobic and hydrodynamic drag reduction effect is inspected. The experimental results in the water tunnel indicate that the stretched sharkskin can expand the speed scope of applications with satisfactory drag reduction effect. Additionally, the drag reduction mechanism is explained and derived comprehensively, which has important significance to apprehend sharkskin effect.