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ItemNo Preview AvailableSurface ozone exceedances in Melbourne, Australia are shown to be under NOx control, as demonstrated using formaldehyde:NO2 and glyoxal:formaldehyde ratios(ELSEVIER, 2020-12-20)Two and a half years of multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements of nitrogen dioxide (NO2), formaldehyde (HCHO) and glyoxal (CHOCHO) are presented alongside in-situ ozone (O3) measurements in Melbourne, Australia. Seasonal and diurnal cycles, vertical profiles and relationships with key meteorological variables are provided. NO2 and CHOCHO were found at highest concentration for low wind speeds implying that their sources were predominantly localised and anthropogenic. HCHO showed an exponential relationship with temperature and a strong wind direction dependence from the northern and eastern sectors, and therefore most likely originated from oxidation of biogenic volatile organic compounds (VOCs) from surrounding forested and rural areas. The glyoxal:formaldehyde ratio (Rgf), reported for the first time in Australia, was consistently high compared to values elsewhere in the world with a mean of 0.105 ± 0.0503 and tended to increase with increasing anthropogenic influence. The HCHO:NO2 ratio (Rfn) was used to characterise tropospheric ozone formation conditions. A strong relationship was found between high temperature, low Rgf, high Rfn and high ozone surface concentrations. Therefore, we propose that both Rgf and Rfn may be useful indicators of tropospheric ozone production regimes and concentrations. The Rfn showed that the vast majority of high ozone production episodes occurred under NOx-limited conditions, suggesting that surface ozone pollution events in Melbourne could be curtailed using NOx emission controls.
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ItemUse of portable air cleaners to reduce aerosol transmission on a hospital COVID-19 ward(Cambridge University Press, 2021-01-01)Objective To study the airflow, transmission and clearance of aerosols in the clinical spaces of a hospital ward that had been used to care for patients with COVID-19, and to examine the impact of portable air cleaners on aerosol clearance. Design: Observational study. Setting: A single ward of a tertiary public hospital in Melbourne Australia. Intervention: Glycerine-based aerosol was used as a surrogate for respiratory aerosols. The transmission of aerosols from a single patient room into corridors and a nurses’ station in the ward was measured. The rate of clearance of aerosols was measured over time from the patient room, nurses’ station and ward corridors with and without air cleaners (also called portable HEPA filters). Results: Aerosols rapidly travelled from the patient room into other parts of the ward. Air cleaners were effective in increasing the clearance of aerosols from the air in clinical spaces and reducing their spread to other areas. With two small domestic air cleaners in a single patient room of a hospital ward, 99% of aerosols could be cleared within 5.5 minutes. Conclusion: Air cleaners may be useful in clinical spaces to help reduce the risk of healthcare acquired acquisition of respiratory viruses that are transmitted via aerosols. They are easy to deploy and are likely to be cost effective in a variety of healthcare settings.
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ItemAtmospheric Trace Metal Deposition from Natural and Anthropogenic Sources in Western Australia(MDPI AG, 2020-05-07)Aerosols from Western Australia supply micronutrient trace elements including Fe into the western shelf of Australia and further afield into the Southern and Indian Oceans. However, regional observations of atmospheric trace metal deposition are limited. Here, we applied a series of leaching experiments followed by total analysis of bulk aerosol samples to a unique time-series of aerosol samples collected in Western Australia to determine atmospheric concentrations and solubilities of Fe and V, Mn, Co, Zn, and Pb. Positive matrix factorisation analysis indicated that mineral dust, biomass burning particulates, sea salt, and industrial emissions were the major types of aerosols. Overall, natural sources dominated Fe deposition. Higher atmospheric concentrations of mineral dust (sixfold) and biomass burning emissions were observed in warmer compared to cooler months. The fraction of labile Fe (0.6–6.0%) was lower than that reported for other regions of Australia. Bushfire emissions are a temporary source of labile Fe and may cause a peak in the delivery of its more easily available forms to the ocean. Increased labile Fe deposition may result in higher ocean productivity in regions where Fe is limiting, and the effect of aerosol deposition on ocean productivity in this region requires further study.
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ItemAtmospheric Trace Metal Deposition near the Great Barrier Reef, Australia(MDPI, 2020-04)Aerosols deposited into the Great Barrier Reef (GBR) contain iron (Fe) and other trace metals, which may act as micronutrients or as toxins to this sensitive marine ecosystem. In this paper, we quantified the atmospheric deposition of Fe and investigated aerosol sources in Mission Beach (Queensland) next to the GBR. Leaching experiments were applied to distinguish pools of Fe with regard to its solubility. The labile Fe concentration in aerosols was 2.3–10.6 ng m−3, which is equivalent to 4.9%–11.4% of total Fe and was linked to combustion and biomass burning processes, while total Fe was dominated by crustal sources. A one-day precipitation event provided more soluble iron than the average dry deposition flux, 0.165 and 0.143 μmol m−2 day−1, respectively. Scanning Electron Microscopy indicated that alumina-silicates were the main carriers of total Fe and samples affected by combustion emissions were accompanied by regular round-shaped carbonaceous particulates. Collected aerosols contained significant amounts of Cd, Co, Cu, Mo, Mn, Pb, V, and Zn, which were mostly (47.5%–96.7%) in the labile form. In this study, we provide the first field data on the atmospheric delivery of Fe and other trace metals to the GBR and propose that this is an important delivery mechanism to this region.
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ItemCharacterization of aerosols over the Great Barrier Reef: The influence of transported continental sources(ELSEVIER, 2019-11-10)The rapid environmental changes in Australia prompt a more thorough investigation of the influence of transportation, local emissions, and optical-chemical properties on aerosol production across the region. A month-long intensive measurement campaign was conducted during spring 2016 at Mission Beach, a remote coastal site west of the Great Barrier Reef (GBR) on the north-east coast of Australia. One aerosol pollution episode was investigated in early October. This event was governed by meteorological conditions and characterized by the increase in black carbon (BC) mass concentration (averaged value of 0.35 ± 0.20 μg m-3). Under the influence of the continental transportation, a new layer of nucleation-mode aerosols with an initial size diameter of 20 nm was observed and aerosol number concentrations reached the peak of 6733 cm-3 at a diameter of 29 nm. The averaged aerosol extinction coefficient at the height of 2 km was 150 Mm-1, with a small depolarized ratio (3.5-5%). Simultaneously, the boundary layer height presented a fall-rise trend in the presence of these enhanced aerosol concentrations and became stable in a later stage of the episode. We did not observe clear boundary layer height diurnal variations from the LiDAR observations or from the Weather Research and Forecasting (WRF) model outputs, except in an earlier stage of the aerosol episode for the former. Although the sea breeze may have been responsible for these particles, on the balance of available data, we suggest that the aerosol properties at the GBR surface during this period are more likely influenced by regional transportation of continental sources, including biomass-burning aerosols.
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ItemNo Preview AvailableEvaluating the Relationship between Interannual Variations in the Antarctic Ozone Hole and Southern Hemisphere Surface Climate in Chemistry-Climate Models(AMER METEOROLOGICAL SOC, 2019-06-01)Studies have recently reported statistically significant relationships between observed year-to-year spring Antarctic ozone variability and the Southern Hemisphere annular mode and surface temperatures in spring–summer. This study investigates whether current chemistry–climate models (CCMs) can capture these relationships, in particular, the connection between November total column ozone (TCO) and Australian summer surface temperatures, where years with anomalously high TCO over the Antarctic polar cap tend to be followed by warmer summers. The interannual ozone–temperature teleconnection is examined over the historical period in the observations and simulations from the Whole Atmosphere Community Climate Model (WACCM) and nine other models participating in the Chemistry–Climate Model Initiative (CCMI). There is a systematic difference between the WACCM experiments forced with prescribed observed sea surface temperatures (SSTs) and those with an interactive ocean. Strong correlations between TCO and Australian temperatures are only obtained for the uncoupled experiment, suggesting that the SSTs could be important for driving both variations in Australian temperatures and the ozone hole, with no causal link between the two. Other CCMI models also tend to capture this relationship with more fidelity when driven by observed SSTs, although additional research and targeted modeling experiments are required to determine causality and further explore the role of model biases and observational uncertainty. The results indicate that CCMs can reproduce the relationship between spring ozone and summer Australian climate reported in observational studies, suggesting that incorporating ozone variability could improve seasonal predictions; however, more work is required to understand the difference between the coupled and uncoupled simulations.
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ItemTropospheric ozone in CCMI models and Gaussian process emulation to understand biases in the SOCOLv3 chemistry-climate model(Copernicus Publications, 2018-11-13)Previous multi-model intercomparisons have shown that chemistry-climate models exhibit significant biases in tropospheric ozone compared with observations. We investigate annual-mean tropospheric column ozone in 15 models participating in the SPARC-IGAC (Stratosphere-troposphere Processes And their Role in Climate-International Global Atmospheric Chemistry) Chemistry-Climate Model Initiative (CCMI). These models exhibit a positive bias, on average, of up to 40 %-50 % in the Northern Hemisphere compared with observations derived from the Ozone Monitoring Instrument and Microwave Limb Sounder (OMI/MLS), and a negative bias of up to ∼ 30 % in the Southern Hemisphere. SOCOLv3.0 (version 3 of the Solar-Climate Ozone Links CCM), which participated in CCMI, simulates global-mean tropospheric ozone columns of 40.2 DU- A pproximately 33 % larger than the CCMI multi-model mean. Here we introduce an updated version of SOCOLv3.0, SOCOLv3.1, which includes an improved treatment of ozone sink processes, and results in a reduction in the tropospheric column ozone bias of up to 8 DU, mostly due to the inclusion of N2O5 hydrolysis on tropospheric aerosols. As a result of these developments, tropospheric column ozone amounts simulated by SOCOLv3.1 are comparable with several other CCMI models. We apply Gaussian process emulation and sensitivity analysis to understand the remaining ozone bias in SOCOLv3.1. This shows that ozone precursors (nitrogen oxides (NOx), carbon monoxide, methane and other volatile organic compounds, VOCs) are responsible for more than 90 % of the variance in tropospheric ozone. However, it may not be the emissions inventories themselves that result in the bias, but how the emissions are handled in SOCOLv3.1, and we discuss this in the wider context of the other CCMI models. Given that the emissions data set to be used for phase 6 of the Coupled Model Intercomparison Project includes approximately 20 % more NOx than the data set used for CCMI, further work is urgently needed to address the challenges of simulating sub-grid processes of importance to tropospheric ozone in the current generation of chemistry-climate models.
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ItemThe influence of mixing on the stratospheric age of air changes in the 21st century(COPERNICUS GESELLSCHAFT MBH, 2019-01-24)Climate models consistently predict an acceleration of the Brewer-Dobson circulation (BDC) due to climate change in the 21st century. However, the strength of this acceleration varies considerably among individual models, which constitutes a notable source of uncertainty for future climate projections. To shed more light upon the magnitude of this uncertainty and on its causes, we analyse the stratospheric mean age of air (AoA) of 10 climate projection simulations from the Chemistry-Climate Model Initiative phase 1 (CCMI-I), covering the period between 1960 and 2100. In agreement with previous multi-model studies, we find a large model spread in the magnitude of the AoA trend over the simulation period. Differences between future and past AoA are found to be predominantly due to differences in mixing (reduced aging by mixing and recirculation) rather than differences in residual mean transport. We furthermore analyse the mixing efficiency, a measure of the relative strength of mixing for given residual mean transport, which was previously hypothesised to be a model constant. Here, the mixing efficiency is found to vary not only across models, but also over time in all models. Changes in mixing efficiency are shown to be closely related to changes in AoA and quantified to roughly contribute 10 % to the long-term AoA decrease over the 21st century. Additionally, mixing efficiency variations are shown to considerably enhance model spread in AoA changes. To understand these mixing efficiency variations, we also present a consistent dynamical framework based on diffusive closure, which highlights the role of basic state potential vorticity gradients in controlling mixing efficiency and therefore aging by mixing.
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ItemNo Preview AvailableDaytime HONO, NO2 and aerosol distributions from MAX-DOAS observations in Melbourne(COPERNICUS GESELLSCHAFT MBH, 2018-10-02)Toxic nitrogen oxides produced by high temperature combustion are prevalent in urban environments, contributing to a significant health burden. Nitrogen oxides such as NO2 and HONO in pollution are important for hydroxyl radical (OH) production and overall oxidative capacity in urban environments; however, current mechanisms cannot explain high daytime levels of HONO observed in many urban and rural locations around the world. Here we present HONO, NO2 and aerosol extinction vertical distributions retrieved from multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements in suburban Melbourne, which are the first MAX-DOAS results from the Australian continent. Using the optimal estimation algorithm HEIPRO we show that vertical profiles for NO2 and HONO can be calculated with a low dependence on the retrieval forward model and a priori parameters, despite a lack of independent co-located aerosol or trace gas measurements. Between December 2016 and April 2017 average peak NO2 values of 8±2ppb indicated moderate traffic pollution levels, and high daytime peak values of HONO were frequently detected, averaging 220±30ppt in the middle of the day. HONO levels measured in Melbourne were typically lower than those recorded in the morning in other places around the world, indicating minimal overnight accumulation, but peaked in the middle of the day to be commensurate with midday concentrations in locations with much higher NO2 pollution. Regular midday peaks in the diurnal cycle of HONO surface concentrations have only previously been reported in rural locations. The HONO measured implies a daytime source term 1ppbh−1 above the predicted photostationary state (PSS) concentration and represents an OH radical source up to 4 times stronger than from ozone photolysis alone in the lowest 500m of the troposphere. The dependence of the high midday HONO levels on soil moisture, combined with the observed diurnal and vertical profiles, provides evidence for a strong photoactivated and ground-based daytime HONO source.
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ItemNo Preview AvailableThe Antarctic ozone hole during 2013(Australian Bureau of Meteorology, 2015-01-01)We review the 2013 Antarctic ozone hole, making use of various ground-based, in-situ and remotely-sensed ozone measurements, ground-based measurements of ultraviolet radiation and meteorological reanalyses. Based on analysis of 34 years of satellite records spanning 1979-2013 (which excludes 1995), we find that in terms of maximum area, minimum ozone level and total ozone deficit, the ozone hole in 2013 was typical of other years of moderate ozone loss. The estimated integrated ozone mass effectively depleted within the ozone hole of 2013 was approximately 1037 Mt, which was the 17th largest deficit on record and 41% of the peak deficit observed in 2006. Anomalously cold winter temper-atures in the lower stratosphere over Antarctica and concurrent strong and stable vortex conditions favoured the potential for strong ozone depletion in 2013. However, anomalous warming of the polar vortex that occurred from late Au-gust limited the overall severity of ozone depletion during spring, and resulted in the relatively early breakup of the ozone hole in mid-November.