Dataset Information

Summertime Primary and Secondary Contributions to Southern Ocean Cloud Condensation Nuclei.

ABSTRACT: Atmospheric aerosols in clean remote oceanic regions contribute significantly to the global albedo through the formation of haze and cloud layers; however, the relative importance of 'primary' wind-produced sea-spray over secondary (gas-to-particle conversion) sulphate in forming marine clouds remains unclear. Here we report on marine aerosols (PM₁) over the Southern Ocean around Antarctica, in terms of their physical, chemical, and cloud droplet activation properties. Two predominant pristine air masses and aerosol populations were encountered: modified continental Antarctic (cAA) comprising predominantly sulphate with minimal sea-salt contribution and maritime Polar (mP) comprising sulphate plus sea-salt. We estimate that in cAA air, 75% of the CCN are activated into cloud droplets while in mP air, 37% are activated into droplets, for corresponding peak supersaturation ranges of 0.37-0.45% and 0.19-0.31%, respectively. When realistic marine boundary layer cloud supersaturations are considered (e.g. ~0.2-0.3%), sea-salt CCN contributed 2-13% of the activated nuclei in the cAA air and 8-51% for the marine air for surface-level wind speed?-1. At higher wind speeds, primary marine aerosol can even contribute up to 100% of the activated CCN, for corresponding peak supersaturations as high as 0.32%.

SUBMITTER: Fossum KN

PROVIDER: S-EPMC6138724 | biostudies-literature | 2018 Sep

REPOSITORIES: biostudies-literature

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Publications

Summertime Primary and Secondary Contributions to Southern Ocean Cloud Condensation Nuclei.

Fossum Kirsten N KN Ovadnevaite Jurgita J Ceburnis Darius D Dall'Osto Manuel M Marullo Salvatore S Bellacicco Marco M Simó Rafel R Liu Dantong D Flynn Michael M Zuend Andreas A O'Dowd Colin C

Scientific reports 20180914 1

Atmospheric aerosols in clean remote oceanic regions contribute significantly to the global albedo through the formation of haze and cloud layers; however, the relative importance of 'primary' wind-produced sea-spray over secondary (gas-to-particle conversion) sulphate in forming marine clouds remains unclear. Here we report on marine aerosols (PM<sub>1</sub>) over the Southern Ocean around Antarctica, in terms of their physical, chemical, and cloud droplet activation properties. Two predominant ...[more]

PMID: 30218089

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Project description:Coastal southeast Florida experiences a wide range of aerosol conditions, including African dust, biomass burning (BB) aerosols, as well as sea salt and other locally-emitted aerosols. These aerosols are important sources of cloud condensation nuclei (CCN), which play an essential role in governing cloud radiative properties. As marine environments dominate the surface of Earth, CCN characteristics in coastal southeast Florida have broad implications for other regions with the added feature that this site is perturbed by both natural and anthropogenic emissions. This study investigates the influence of different air mass types on CCN concentrations at 0.2% (CCN0.2%) and 1.0% (CCN1.0%) supersaturation (SS) based on ground site measurements during selected months in 2013, 2017, and 2018. Average CCN0.2% and CCN1.0% concentrations were 373 ± 200 cm-3 and 584 ± 323 cm-3, respectively, for four selected days with minimal presence of African dust and BB (i.e., background days). CCN concentrations were not elevated on the four days with highest influence of African dust (289 ± 104 cm-3 [0.2% SS] and 591 ± 302 cm-3 [1.0% SS]), consistent with high dust mass concentrations comprised of coarse particles that are few in number. In contrast, CCN concentrations were substantially enhanced on the five days with the greatest impact from BB (1408 ± 976 cm-3 [0.2% SS] and 3337 ± 1252 cm-3 [1.0% SS]). Ratios of CCN0.2%:CCN1.0% were used to compare the hygroscopicity of the aerosols associated with African dust, BB, and background days. Average ratios were similar for days impacted by African dust and BB (0.54 ± 0.17 and 0.55 ± 0.17, respectively). A 29% higher average ratio was observed on background days (0.71 ± 0.14), owing in part to a strong presence of sea salt and reduced presence of more hydrophobic species such as those of a carbonaceous or mineral-dust nature. Finally, periods of heavy rainfall were shown to effectively decrease both CCN0.2% and CCN1.0% concentrations. However, the rate varied at which such concentrations increased after the rain. This work contributes knowledge on the nucleating ability of African dust and BB in a marine environment after varying periods of atmospheric transport (days to weeks). The results can be used to understand the hygroscopicity of these air mass types, predict how they may influence cloud properties, and provide a valuable model constraint when predicting CCN concentrations in comparable situations.

Dataset Information

Summertime Primary and Secondary Contributions to Southern Ocean Cloud Condensation Nuclei.

Publications

Summertime Primary and Secondary Contributions to Southern Ocean Cloud Condensation Nuclei.

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