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Southern Ocean latitudinal gradients of cloud condensation nuclei

Citation

Humphries, RS and Keywood, MD and Gribben, S and McRobert, IM and Ward, JP and Selleck, P and Taylor, S and Harnwell, J and Flynn, C and Kulkarni, GR and Mace, GG and Protat, A and Alexander, SP and McFarquhar, G, Southern Ocean latitudinal gradients of cloud condensation nuclei, Atmospheric Chemistry and Physics, 21, (16) pp. 12757-12782. ISSN 1680-7316 (2021) [Refereed Article]


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DOI: doi:10.5194/acp-21-12757-2021

Abstract

The Southern Ocean region is one of the most pristine in the world and serves as an important proxy for the pre-industrial atmosphere. Improving our understanding of the natural processes in this region is likely to result in the largest reductions in the uncertainty of climate and earth system models. While remoteness from anthropogenic and continental sources is responsible for its clean atmosphere, this also results in the dearth of atmospheric observations in the region. Here we present a statistical summary of the latitudinal gradient of aerosol (condensation nuclei larger than 10 nm, CN10) and cloud condensation nuclei (CCN at various supersaturations) concentrations obtained from five voyages spanning the Southern Ocean between Australia and Antarctica from late spring to early autumn (October to March) of the 2017/18 austral seasons. Three main regions of influence were identified: the northern sector (40-45 degrees S), where continental and anthropogenic sources coexisted with background marine aerosol populations; the mid-latitude sector (45-65 degrees S), where the aerosol populations reflected a mixture of biogenic and sea-salt aerosol; and the southern sector (65-70 degrees S), south of the atmospheric polar front, where sea-salt aerosol concentrations were greatly reduced and aerosol populations were primarily biologically derived sulfur species with a significant history in the Antarctic free troposphere. The northern sector showed the highest number concentrations with median (25th to 75th percentiles) CN10 and CCN0.5 concentrations of 681 (388-839) cm(-3) and 322 (105-443) cm(-3), respectively. Concentrations in the mid-latitudes were typically around 350 cm(-3) and 160 cm(-3) for CN10 and CCN0.5, respectively. In the southern sector, concentrations rose markedly, reaching 447 (298-446) cm(-3) and 232 (186-271) cm(-3) for CN10 and CCN0.5, respectively. The aerosol composition in this sector was marked by a distinct drop in sea salt and increase in both sulfate fraction and absolute concentrations, resulting in a substantially higher CCN0.5/CN10 activation ratio of 0.8 compared to around 0.4 for mid-latitudes. Long-term measurements at land-based research stations surrounding the Southern Ocean were found to be good representations at their respective latitudes; however this study highlighted the need for more long-term measurements in the region. CCN observations at Cape Grim (40 degrees 390 S) corresponded with CCN measurements from northern and mid-latitude sectors, while CN10 observations only corresponded with observations from the northern sector. Measurements from a simultaneous 2-year campaign at Macquarie Island (54 degrees 30' S) were found to represent all aerosol species well. The southernmost latitudes differed significantly from both of these stations, and previous work suggests that Antarctic stations on the East Antarctic coastline do not represent the East Antarctic sea-ice latitudes well. Further measurements are needed to capture the long-term, seasonal and longitudinal variability in aerosol processes across the Southern Ocean.

Item Details

Item Type:Refereed Article
Keywords:number-size distribution, aerosol-particles, dimethyl sulfide, boundary-layer, cape grim, ace 1, system, 1st, methanesulfonate, uncertainty
Research Division:Engineering
Research Group:Environmental engineering
Research Field:Environmental engineering not elsewhere classified
Objective Division:Environmental Management
Objective Group:Management of Antarctic and Southern Ocean environments
Objective Field:Management of Antarctic and Southern Ocean environments not elsewhere classified
UTAS Author:Keywood, MD (Dr Melita Keywood)
UTAS Author:Protat, A (Dr Alain Protat)
UTAS Author:Alexander, SP (Dr Simon Alexander)
ID Code:152371
Year Published:2021
Web of Science® Times Cited:6
Deposited By:Physics
Deposited On:2022-08-18
Last Modified:2022-08-18
Downloads:0

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