School of Geography, Earth and Atmospheric Sciences - Research Publications
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ItemNo Preview AvailableAerosol generation related to respiratory interventions and the effectiveness of a personal ventilation hood.(College of Intensive Care Medicine of Australia and New Zealand, 2020-09)OBJECTIVE: To quantify aerosol generation from respiratory interventions and the effectiveness of their removal by a personal ventilation hood. DESIGN AND SETTING: Determination of the aerosol particle generation (in a single, healthy volunteer in a clean room) associated with breathing, speaking, wet coughing, oxygen (O2) 15 L/min via face mask, O2 60 L/min via nasal prongs, bilevel non-invasive positive-pressure ventilation (BiPAP) and nebulisation with O2 10 L/min. INTERVENTIONS: Aerosol generation was measured with two particle sizer and counter devices, focusing on aerosols 0.5-5 μm (human-generated aerosols), with and without the hood. An increase from baseline of less than 0.3 particles per mL was considered a low level of generation. MAIN OUTCOME MEASURES: Comparisons of aerosol generation between different respiratory interventions. Effectiveness of aerosol reduction by a personal ventilation hood. RESULTS: Results for the 0.5-5 μm aerosol range. Quiet breathing and talking demonstrated very low increase in aerosols (< 0.1 particles/mL). Aerosol generation was low for wet coughing (0.1 particles/mL), O2 15 L/min via face mask (0.18 particles/mL), and high flow nasal O2 60 L/min (0.24 particles/mL). Non-invasive ventilation generated moderate aerosols (29.7 particles/mL) and nebulisation very high aerosols (1086 particles/mL); the personal ventilation hood reduced the aerosol counts by 98% to 0.5 particles/mL and 8.9 particles/mL respectively. CONCLUSIONS: In this human volunteer study, the administration of O2 15 L/min by face mask and 60 L/min nasal therapy did not increase aerosol generation beyond low levels. Non-invasive ventilation caused moderate aerosol generation and nebulisation therapy very high aerosol generation. The personal ventilation hood reduced the aerosol counts by at least 98%.
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ItemFuture changes in stratospheric quasi-stationary wave-1 in the extratropical southern hemisphere spring and summer as simulated by ACCESS-CCM(CSIRO PUBLISHING, 2021)Seasonally dependent quasi-stationary planetary wave activity in the southern hemisphere influences the distribution of ozone within and near the equatorward edge of the stratospheric polar vortex. Accurate representation of this zonal asymmetry in ozone is important in the characterisation of stratospheric circulation and climate and their associated effects at the surface. In this study, we used the Australian Community and Climate Earth System Simulator-Chemistry Climate Model to investigate the influence of greenhouse gases (GHGs) and ozone depleting substances (ODSs) on the zonal asymmetry of total column ozone (TCO) and 10 hPa zonal wind between 50 and 70°S. Sensitivity simulations were used from 1960 to 2100 with fixed ODSs and GHGs at 1960 levels and a regression model that uses equivalent effective stratospheric chlorine and carbon dioxide equivalent radiative forcing as the regressors. The model simulates the spring and summer zonal wave-1 reasonably well, albeit with a slight bias in the phase and amplitude compared to observations. An eastward shift in the TCO and 10 hPa zonal wave-1 is associated with both decreasing ozone and increasing GHGs. Amplitude increases are associated with ozone decline and amplitude decreases with GHG increases. The influence of ODSs typically outweigh those by GHGs, partly due to the GHG influence on TCO phase at 50°S likely being hampered by the Andes. Therefore, over the 21st century, influence from ozone recovery causes a westward shift and a decrease in amplitude. An exception is at 70°S during spring, where the GHG influence is larger than that of ozone recovery, causing a continued eastward trend throughout the 21st century. Also, GHGs have the largest influence on the 10 hPa zonal wave-1 phase, but still only induce a small change in the wave-1 amplitude. Different local longitudes also experience different rates of ozone recovery due to the changes in phase of the zonal wave-1. The results from this study have important implications for understanding future ozone layer distribution in the Southern Hemisphere under changing GHG and ODS concentrations. Important future work would involve conducting a similar study using a large ensemble of models to gain more statistically significant results.
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ItemComparison of formaldehyde tropospheric columns in Australia and New Zealand using MAX-DOAS, FTIR and TROPOMI( 2020-07-03)Abstract. South-eastern Australia has been identified by modelling studies as a hotspot of biogenic volatile organic compound (VOC) emissions, however long term observational VOC studies are lacking in this region. Here, two and a half years of MAX-DOAS formaldehyde (HCHO) measurements in Australasia are presented, from Broadmeadows in northern Melbourne, Australia and from Lauder, a rural site in the South Island of New Zealand. Across the measurement period from December 2016 to November 2019, the mean formaldehyde column measured by the MAX-DOAS at Lauder was 2.50 ± 0.61 × 1014 molec cm−2 and at Broadmeadows was 5.40 ± 1.59 × 1015 molec cm−2. In both locations the seasonal cycle showed a pronounced peak in Austral summer (DJF) consistent with temperature-dependent formaldehyde production from biogenic precursor gases. The amplitude of the seasonal cycle at Lauder was 0.7 × 1015 molec cm−2 while it was 2.0 × 1015 molec cm−2 at Broadmeadows. The Lauder MAX-DOAS HCHO measurements are compared with 27 months of co-located fourier-transform infrared (FTIR) observations. The seasonal variation of Lauder MAX-DOAS HCHO, smoothed by the FTIR averaging kernels, correlated strongly with the FTIR measurements, with linear regression slope of 0.91 and R2 of 0.81 for monthly averaged formaldehyde partial columns. In addition to ground-based observations, a clear way to address the VOC measurement gap in areas such as Australasia is with satellite measurements. Here we demonstrate that the Tropospheric Monitoring Instrument (TROPOMI) can be used to distinguish formaldehyde hotspots in forested and agricultural regions of south-eastern Australia. The MAX-DOAS measurements are also compared to TROPOMI HCHO vertical columns at Lauder and Melbourne; very strong monthly average agreement is found for Melbourne (regression slope of 0.61, R2 of 0.95) and a strong agreement is found at Lauder (regression slope of 0.73, R2 of 0.61) for MAX-DOAS vs. TROPOMI between May 2018 and November 2019. This study, the first long term satellite comparison study using MAX-DOAS in the southern hemisphere, highlights the improvement offered by TROPOMI's high resolution over previous satellite products and provides the groundwork for future studies using ground based and satellite DOAS for studying VOCs in Australasia.
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ItemCoral reef-derived dimethyl sulfide and the climatic impact of the loss of coral reefs( 2020-10-27)Abstract. Dimethyl sulfide (DMS) is a naturally occurring aerosol precursor gas which plays an important role in the global sulfur budget, aerosol formation and climate. While DMS is produced predominantly by phytoplankton, recent observational literature has suggested that corals and their symbionts produce a comparable amount of DMS, which is unaccounted for in models. It has further been hypothesised that the coral reef source of DMS may modulate regional climate. This hypothesis presents a particular concern given the current threat to coral reefs under anthropogenic climate change. In this paper, a global climate model with online chemistry and aerosol is used to explore the influence of coral reef-derived DMS on atmospheric composition and climate. A simple representation of coral reef-derived DMS is developed and added to a common DMS surface water climatology, resulting in an additional DMS flux of 0.3 Tg year−1 S, or 1.7 % of the global flux. By comparing the differences between both nudged and free running ensemble simulations with and without coral reef-derived DMS, the influence of coral reef-derived DMS on regional climate is quantified. In the Maritime Continent-Australian region, where the highest density of coral reefs exist, a small decrease in nucleation and Aitken mode aerosol number concentration and mass is found when coral reef DMS emissions are removed from the system. However, these small responses are found to have no robust effect on regional climate via direct and indirect aerosol effects. This work emphasises the complexities of the aerosol-climate system and the limitations of current modelling capabilities are highlighted, in particular surrounding convective responses to changes in aerosol. In conclusion we find no robust evidence that coral reef-derived DMS influences global and regional climate.