High occurrence of new particle formation events at the Maïdo high altitude observatory (2150 m), Reunion Island (Indian Ocean)

Abstract : This study aims to report and characterize the frequent new particle formation (NPF) events observed at the Maïdo observatory, Reunion Island, a Southern Hemisphere site located at 2150 m and surrounded by the Indian Ocean. In 2014 and 2015, continuous aerosol measurements were made using both a Differential Mobility 15 Particle Sizer (DMPS) and an Air Ion Spectrometer (AIS) to characterize the NPF events down to the lowest particle size scale. Carbon monoxide (CO) and sulfur dioxide (SO2) concentrations were monitored, as well as meteorological parameters, in order to identify the conditions that were favourable to the occurrence of nucleation in this specific environment. We point out that the annual NPF frequency average (65%) is one of the highest reported so far. Monthly averages show a bimodal variation of the NPF frequency, with a maximum observed 20 during off-season periods (March to May and September to December). A high yearly median particle Growth Rate (GR) of 15.16 nm.h-1 is also measured, occasionally peaking at values of the order of 100 nm.h-1 and showing a bimodal seasonal variation with maxima observed in July and November. Yearly medians of 2 and 12 nm particle formation rates (J2 and J12) are 0.858 and 0.508 cm-3 .s-1 respectively, with a seasonal variation similar to that of the GR. The seasonal variations of GR and J correspond to the seasonal variation of radiation, which may be 25 responsible for more efficient photochemistry and also for a higher influence of the boundary layer, as shown by the CO seasonal variation. Multiple sources can contribute to the NPF frequency and intensity, including marine, biogenic from vegetation, and anthropogenic sources.
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Brice Foucart, Karine Sellegri, Pierre Tulet, Clémence Rose, Jean-Marc Metzger, et al.. High occurrence of new particle formation events at the Maïdo high altitude observatory (2150 m), Reunion Island (Indian Ocean). Atmospheric Chemistry and Physics Discussions, European Geosciences Union, In press, 18 (13), pp.1 - 28. ⟨10.5194/acp-2017-825⟩. ⟨hal-01596673v2⟩

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