Model Performance Differences in Fine-Mode Nitrate Aerosol during Wintertime over Japan in the J-STREAM Model Inter-Comparison Study

In this study, the results for nitrate (NO3−) aerosol during winter from the first-phase model inter-comparison study of Japan’s Study for Reference Air Quality Modeling (J-STREAM) were analyzed. To investigate the models’ external and internal settings, the results were limited to Community Multiscale Air Quality (CMAQ) models. All submitted models generally underestimated NO3− over the urban areas in Japan (e.g., Osaka, Nagoya, and Tokyo); however, some model settings showed distinct behavior. The differences due to the model external settings were larger than the model internal settings. Emissions were an important factor, and emissions configured with lower NOx emissions and higher NH3 emissions led to a higher NO3− concentration as the NH3 was consumed under NH3-rich conditions. The model internal settings of the chemical mechanisms caused differences over China, and this could affect western Japan; however, the difference over Tokyo was lower. To obtain a higher NO3− concentration over the urban areas in Japan, the selection of the HONO option for the heterogenous reaction and the inline calculation of photolysis was desired. For future studies, the external settings of the boundary condition and the meteorological field require further investigation.

Using WRF-Chem Volcano to model the in-plume halogen chemistry of Etna’s 2018 eruption

<p>Volcanic eruptions emit halogen-containing species in varying quantities, with their emission ratio to tracer species such SO<sub>2</sub> varying between volcanoes, eruptions, and even phases of an eruptive event.</p><p>The bromine explosion is known to occur within volcanic plumes, converting bromine from HBr – the primary form in which it is emitted – to other forms, including the spectroscopically detectable BrO. Measurements of BrO have been made in the plumes of many volcanoes from both ground-based and satellite-based instruments. There also exist a small number of measurements of OClO.</p><p>We present results from WRF-Chem Volcano (WCV), a modified version of the three-dimensional regional atmospheric chemistry and transport model WRF-Chem and associated utilities. We have simulated the Christmas 2018 eruptive event of Mount Etna using a nested implementation the model at maximum lateral resolution of 1km, as well as a weaker emission plume representing Etna’s more common quiescent degassing state. The plume of this 2018 eruption was observed remotely by the TROPOMI instrument.</p><p>WCV is able to model the transport and dispersion of the plume. We compare these model outputs to the satellite observations and use this to estimate the volcanic emission column height.</p><p>In terms of chemistry, WCV is able to reproduce the bromine explosion and the major features of the satellite observation – including a cross-plume variation in the BrO/SO<sub>2</sub> column ratio. We find that variations in the BrO/SO<sub>2</sub> ratio are primarily caused by variations in the concentration of ozone. Ozone is consumed by bromine chemistry and is replenished by the mixing in of ozone-rich background air. This creates a zone of low ozone in the core of the plume which is consequently low in BrO and surrounded by a higher-ozone edge with a higher BrO/SO2 ratio.</p><p>For the temporal evolution of the plume, we find that the bromine-chemistry of a concentrated emission plume can be divided into four phases, also governed by ozone availability. In the last phase ozone limitation is minimal and the proportion of bromine in the form of BrO (and the BrO/SO2 ratio) is approximately stable. We find this stable regime also with a simulation of a weaker emission plume. These results could facilitate the use of remote-sensing BrO measurements as a means of quantifying total bromine emissions from volcanoes.</p><p>Oxidized forms of chlorine are modelled to be formed within the plume due to the heterogenous reaction of HOBr with HCl, forming BrCl that photolyzes and produces Cl radicals. We also investigate the extent to which mercury could be oxidized by halogens within the plume.</p>

Measurements of I/SVOCs in biomass-burning smoke using solid-phase extraction disks and two-dimensional gas chromatography

Biomass-burning organic-aerosol (OA) emissions are known to exhibit semi-volatile behavior that impacts OA loading during plume transport. Because such semi-volatile behavior depends in part on OA composition, improved speciation of intermediate and semi-volatile organic compounds (I/SVOCs) emitted during fires is needed to assess the competing effects of primary OA volatilization and secondary OA production. In this study, 18 laboratory fires were sampled in which a range of fuel types were burned. Emitted I/SVOCs were collected onto Teflon filters and solid-phase extraction (SPE) disks to qualitatively characterize particulate and gaseous I/SVOCs, respectively. Derivatized filter extracts were analyzed using comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GC × GC-TOFMS). Quality control tests were performed using biomass-burning relevant standards and demonstrate the utility of SPE disks for untargeted analysis of air samples. The observed chromatographic profiles of I/SVOCs in coniferous fuel-derived smoke samples were well correlated with each other, but poorly correlated with other fuel types (e.g., herbaceous and chaparral fuels). Emissions of benzenediol isomers were also shown to be fuel dependent. The combined Teflon and SPE filter data captured differences in gas-particle partitioning of the benzenediol isomers, with hydroquinone having a significantly higher particle-phase fraction than catechol due to its lower volatility. Additionally, the speciated volatility distribution of I/SVOCs in smoke from a rotten-log fire was estimated to evaluate the composition of potentially volatilized primary OA, which was entirely attributed to oxygenated (or other heteroatomic) compounds. The isomer-dependent partitioning and the speciated volatility distributions both suggest the need for better understanding of gas-phase and heterogenous reaction pathways of biomass-burning-derived I/SVOCs in order to represent the atmospheric chemistry of smoke in models.

Reduction of the Ni(II) ion at the dropping mercury electrode from amoxicillin water solution

The nature of polarographic precurrents of Ni(II) ion in the presence of amoxicillin as well as the behaviour of amoxicillin in the electrical double layer has been investigated. It has been established the formation of the mono complex of Ni(II) ion with amoxicillin adsorbed at the mercury. The reduction mechanism of the complex has been proposed. Taking into account the effect of the double layer on the kinetics, the rate constant of the heterogenous reaction of the complex formation has been found to be 5.8 · 103 l mol-1 s -1.