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    Characterization of aerosols over the Great Barrier Reef: The influence of transported continental sources
    Chen, Z ; Schofield, R ; Rayner, P ; Zhang, T ; Liu, C ; Vincent, C ; Fiddes, S ; Ryan, RG ; Alroe, J ; Ristovski, ZD ; Humphries, RS ; Keywood, MD ; Ward, J ; Paton-Walsh, C ; Naylor, T ; Shu, X (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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    Cloud, precipitation and radiation responses to large perturbations in global dimethyl sulfide
    Fiddes, SL ; Woodhouse, MT ; Nicholls, Z ; Lane, TP ; Schofield, R (Copernicus Publications, 2018)
    Natural aerosol emission represents one of the largest uncertainties in our understanding of the radiation budget. Sulfur emitted by marine organisms, as dimethyl sulfide (DMS), constitutes one-fifth of the global sulfur budget and yet the distribution, fluxes and fate of DMS remain poorly constrained. This study evaluates the Australian Community Climate and Earth System Simulator (ACCESS) United Kingdom Chemistry and Aerosol (UKCA) model in terms of cloud fraction, radiation and precipitation, and then quantifies the role of DMS in the chemistry–climate system. We find that ACCESS-UKCA has similar cloud and radiation biases to other global climate models. By removing all DMS, or alternatively significantly enhancing marine DMS, we find a top of the atmosphere radiative effect of 1.7 and −1.4W m−2 respectively. The largest responses to these DMS perturbations (removal/enhancement) are in stratiform cloud decks in the Southern Hemisphere's eastern ocean basins. These regions show significant differences in low cloud (−9∕ + 6%), surface incoming shortwave radiation (+7∕ − 5W m−2) and large-scale rainfall (+15∕ − 10%). We demonstrate a precipitation suppression effect of DMS-derived aerosol in stratiform cloud deck regions due to DMS, coupled with an increase in low cloud fraction. The difference in low cloud fraction is an example of the aerosol lifetime effect. Globally, we find a sensitivity of temperature to annual DMS flux of 0.027 and 0.019K per Tg yr−1 of sulfur, respectively. Other areas of low cloud formation, such as the Southern Ocean and stratiform cloud decks in the Northern Hemisphere, have a relatively weak response to DMS perturbations. We highlight the need for greater understanding of the DMS–climate cycle within the context of uncertainties and biases of climate models as well as those of DMS–climate observations.