Smoke aerosols dispersion and transport from the 2013 New South Wales (Australia) bushfires

Environmental monitoring and modelling, especially in the regional context, has seen significant progress with the widely usage of satellite measurement in conjunction with local meteorological and air quality monitoring to understand the atmospheric dispersion and transport of air pollutants. This paper studies the application of these data and modelling tools to understand the environment effects of a major bushfire period in the state of New South Wales (NSW), Australia, in 2013. The bushfires have caused high pollution episodes at many sites in the greater Sydney metropolitan areas. The potential long-range transport of aerosols produced by bushfires to other region and states has been seen by regulators as a major concern. Using data and images collected from satellites, in addition to the results obtained from different simulations carried out using HYSPLIT trajectory model and a regional meteorological model called Conformal Cubic Atmospheric Model (CCAM), we were able to identify at least 2 days on which the smoke aerosols from bush fires in NSW has been transported at high altitude to the northern state of Queensland and the Coral Sea. As a result, widespread high particle concentration in South East Queensland including the Brisbane area, as measured by nearly all the air quality monitoring stations in this region, occurred on the day when the smoke aerosols intruded to lower altitude as indicated by the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) Lidar measurements on the CALIPSO (Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation) satellite. The use of meteorological or air quality modelling to connect the ground-based measurements with satellite observations as shown in this study is useful to understand the pollutant transport due to bushfires and its impact on regional air quality.     

Evaluation of the SAPRC-07 mechanism against CSIRO smog chamber data

The updated SAPRC-07 mechanism was evaluated against data from experiments performed in the CSIRO smog chamber. The mechanism predictions have been compared to experimental results as well as predictions by SAPRC-99.Experiments were performed using either toluene or m-xylene in the presence of NO_x at sub-0.1 ppmv concentrations. For the majority of m-xylene experiments, the modelled Δ(O₃–NO) concentration was within 20% of observed values for both SAPRC mechanisms. However during the oxidation of toluene the production of radicals was poorly predicted, with final Δ(O₃–NO) concentration under-predicted by up to 60%. The predictions of major oxidants from isoprene oxidation were in good agreement with observed values. For the NO_x-limited conditions however, the ozone concentration predicted by both mechanisms were under-predicted by approximately 20% in the five experiments tested.The performance of the SAPRC-07 mechanism was also evaluated against twelve evaporated fuel experiments. Two types of evaporative mode experiments were performed: headspace evaporated fuel and wholly evaporated fuel. The major difference was a significantly higher concentration of aromatic hydrocarbons and larger alkane products in wholly evaporated fuels. For headspace evaporated fuel experiments both SAPRC mechanisms were in good agreement with experimental results. For wholly evaporated experiments the average Δ(O₃–NO) model error was ?25% with SAPRC-07 compared to less than ?5% for SAPRC-99. Updates to the photolysis data for dicarbonyls, the light source used and the experimental conditions under which these experiments were performed are possible causes for the discrepancy between SAPRC-99 and -07 predictions for wholly evaporated experiments.     

Characterization of a new smog chamber for evaluating SAPRC gas-phase chemical mechanism

A new state-of-the-art indoor smog chamber facility (CAPS-ZJU) has been constructed and characterized at Zhejiang University, which is designed for chemical mechanism evaluation under well-controlled conditions. A series of characterization experiments were performed to validate the well-established experimental protocols, including temperature variation pattern, light spectrum and equivalent intensity (J_NO2), injection and mixing performance, as well as gases and particle wall loss. In addition, based on some characterization experiments, the auxiliary wall mechanism has been setup and examined. Fifty chamber experiments were performed across a broad range of experimental scenarios, and we demonstrated the ability to utilize these chamber data for evaluating SAPRC chemical mechanism. It was found that the SAPRC-11 can well predict the O₃ formation and NO oxidation for almost all propene runs, with 6 hr Δ(O₃ – NO) model error of –3% ± 7%, while the final O₃ was underestimated by ~20% for isoprene experiments. As for toluene and p-xylene experiments, it was confirmed that SAPRC-11 has significant improvement on aromatic chemistry than earlier version of SAPRC-07, although the aromatic decay rate was still underestimated to some extent. The model sensitivity test has been carried out, and the most sensitive parameters identified are the initial concentrations of reactants and the light intensity as well as HONO offgasing rate and O₃ wall loss rate. All of which demonstrated that CAPS-ZJU smog chamber could derive high quality experimental data, and could provide insights on chamber studies and chemical mechanism development.     

Modelling the photooxidation of ULP,E5 and E10 in the CSIRO smog chamber

The photooxidation of fuel vapour was investigated in a smog chamber and simulated using three chemical mechanisms, the Master Chemical Mechanism (MCMv3.1), SAPRC-99 and the Carbon Bond chemical mechanism (CB05). Three varieties of fuel were used, unleaded petrol (ULP) and two ULP-ethanol blends which contained 5% and 10% ethanol (E5, E10). The fuel vapours were introduced into the chamber using two methods, by injecting the vapours from wholly evaporated fuel directly, and by injecting the headspace vapour from fuel equilibrated at 38 °C. The chamber experiments were simulated using the selected mechanisms and comparisons made with collected experimental data.The SAPRC-99 mechanism reproduced Δ(O₃–NO) more accurately for almost all fuel types and injection modes, with negligible model error for both injection modes. The average model error for MCM simulations was ?16% and for CB05 the average model error was ?34%. The predictions for the CB05 mechanism varied depending on injection mode, the Δ(O₃–NO) model error for wholly evaporated experiments was ?44%, compared to ?24% for headspace vapour experiments. The difference in aromatic content between experiments of different injection modes was likely to be the cause of the difference in model error for CB05. The model error for all headspace experiments was dependent upon the initial carbon monoxide concentrations.The results for Δ(O₃–NO) were matched by the prediction of other key products, with formaldehyde predicted to within 20% by both SAPRC and the MCM. The addition of ethanol to the base SAPRC mechanism altered the predictions of Δ(O₃–NO) by less than 2%. Changes observed in the concentrations of formaldehyde and acetaldehyde were consistent with the expected yields from ethanol oxidation.     

Thermal behaviour of chrome shavings and of sludges recovered after digestion of tanned solid wastes with calcium hydroxide

The thermal behaviour of chrome shavings and of sludges recovered after digestion of tanned wastes with Ca(OH)2 was studied. Ashes obtained after incineration of wastes at various temperatures were analysed by X-ray diffraction and EDX method. The main crystallized phases present in the ash obtained at 600 degrees C are Cr2O3 and NaCl. The diffractograms revealed an increase in the intensities of the chromium oxide peaks and a very notable decrease of the amount of sodium chloride at 1100 degrees C. EDX analysis revealed a total disappearance of the chlorine peak at this temperature. Scanning electron micrographs show that the waste lost its fibrous aspect when the temperature increases. Formation of aggregates was noted after 550 degrees C. Combustion of organic matters and decarbonation phenomenon are the main stages observed on GTA and DTA curves of sludges. These phenomena are, respectively, exothermic and endothermic. The diffractogram of sludges recorded at 550 degrees C, in the presence of a constant oxygen surplus, revealed the presence of CaCrO4 and CaCO3.