Reply on RC1

Abstract

Understanding chemical processes leading to the formation of atmospheric aerosol particles is crucial to improve our capabilities in predicting the future climate. However, those mechanisms are still inadequately characterized, especially in polar regions, which are typically representative of the pre-industrial era in climate models. In this study, we report observations of neutral and charged aerosol precursor molecules and chemical clusters composition (qualitatively and quantitatively), as well as air ions and aerosol particle number concentrations and size distributions from the Marambio research station (64°15'S–56°38'W), located North of the Antarctic Peninsula. We conducted measurements during the austral summer, between 15 January and 25 February 2018. The scope of this study is to characterize New Particle Formation (NPF) event parameters and connect our observations of gas phase compounds with the formation of secondary aerosols to resolve the nucleation mechanisms at the molecular scale. NPF occurred on 40% of measurement days (i.e., 13 NPF events were recorded during 35 days). All NPF events were observed during sunny days (i.e., sufficient radiation), mostly with above freezing temperatures and low relative humidity (RH < 80 %). The averaged formation rate for 3 nm particles (J3) was 0.686 cm−3 s−1 and the average particle growth rate (GR 3.8–12 nm) was 4.2 nm h−1. Analysis of neutral aerosol precursor molecules showed measurable concentrations of iodic acid (IA), sulfuric acid (SA) and methane sulfonic acid (MSA) throughout the entire measurement period with average concentrations of 5.17 × 105, 1.18 × 106, 2.06 × 105 molecules cm−3, respectively. MSA and SA concentrations significantly increased during NPF events. We highlight SA as a key contributor to NPF processes, while IA and MSA would likely only contribute to particle growth. Mechanistically, anion clusters of dimethylamine (DMA)-bisulfate (2SA) as well as numerous ammonium-(bi)sulfate clusters were identified, with the latter at mass-to-charge ratios (m/z) larger than 1000 Th. All of which suggests elevated concentration of both ammonia and amines in the atmosphere. Those species are likely contributing to NPF events since SA alone is not sufficient to explain observed nucleation rates. Here, we provide evidence of the marine origin of the measured chemical precursors and discuss their potential contribution to the aerosol phase. Our observations highlight the importance of the Antarctic Ocean, water, and ice ecosystems interacting with the land-fauna – the plausible sources of the principal precursor molecules hereby investigated – for secondary aerosol formation.