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

Abstract

Abstract. This study aims to report and characterise the frequent new particle formation (NPF) events observed at the Maïdo observatory, Réunion, a Southern Hemisphere site located at 2150 m (a.s.l.) and surrounded by the Indian Ocean. From May 2014 to December 2015, continuous aerosol measurements were made using both a differential mobility particle sizer (DMPS) and an air ion spectrometer (AIS) to characterise the NPF events down to the lowest particle-size scale. Carbon monoxide (CO) and black carbon (BC) 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 in the NPF frequency, with a maximum observed during transition periods (autumn and spring). A high yearly median particle growth rate (GR) of 15.16 nm h −1 is also measured showing a bimodal seasonal variation with maxima observed in July and November. Yearly medians of 2 and 12 nm particle formation rates (J 2 and J 12 ) are 0.858 and 0.508 cm −3 s −1 , respectively, with a seasonal variation showing a maximum during winter, that correspond to low temperature and RH typical of the dry season, but also to high BC concentrations. We show that the condensation sink exceeds a threshold value (1.04 × 10 −3 s −1 ) with a similar seasonal variation than the one of the NPF event frequency, suggesting that the occurrence of the NPF process might be determined by the availability of condensable vapours, which are likely to be transported together with pre-existing particles from lower altitudes.

New particle formation in the volcanic eruption plume of the Piton de la Fournaise: specific features from a long-term dataset

“…Indeed, measurements conducted in various environments suggest that NPF might be an important source of cloud condensation nuclei (CCN) (e.g. Kerminen et al, 2012;Rose et al, 2017), which is further supported by model investigations (Merikanto et al, 2009;Makkonen et al, 2012;Gordon et al, 2017). However, despite significant improvement of instrumental techniques for the characterization of the newly formed particles and their precursors (Junninen et al, 2010;Vanhanen et al, 2011;Jokinen et al, 2012), model predictions are still affected by our limited understanding of NPF.…”

“…Indeed, those might have dominated NPF and CCN formation in the pristine pre-industrial era, when anthropogenic emissions were much lower. Our incomplete knowledge of the pre-industrial conditions is responsible for a significant fraction of the uncertainty on the impact of aerosols on climate, since these conditions form the baseline to calculate the radiative forcing caused by anthropogenic emissions in climate model simulations (Carslaw et al, 2013;Gordon et al, 2016Gordon et al, , 2017. Specifically, substantial uncertainties in the pre-industrial baseline cloud radiative state related to the activity of continuously degassing volcanoes were reported by Schmidt et al (2012).…”

New particle formation in the active volcanic plume of the Piton de la Fournaise: specific features from a long-term dataset

“…The detection limit of the instrument was about 0.5 ppb, which is above the usual SO2 mixing ratios encountered at Maïdo outside of the eruptive periods of the Piton de la Fournaise (see Fig. A1 in Foucart et al 2018).…”

“…More detailed information about the facility can be found in Baray et al (2013) and Foucart et al (2018), including a description of the large and local scale atmospheric dynamics which affect the observations performed at the site. An overview of the monitoring of the volcanic plume performed at Maïdo during the eruptions of the Piton de la Fournaise observed in 2015 is in addition available in Tulet et al (2017).…”

“…The instrumental setup used in the present work was previously described in the companion study by Foucart et al (2018).…”