Aerosol Processes at the Pristine High-Altitude Iza&#241;a Atmospheric Observatory (2367 m a.s.l.), Canary Islands
Authors: Huang Wei , Shen Jiali , Okuljar Magdalena , Agrò Myriam , Aliaga Diego , Barretov África , Rodríguez Sergio , González Yenny , López-Darias Jessica , Casquero-Vera Juan A. , Casans Andrea , Titos Gloria , Duplissy Jonathan , Petäjä Tuukka , Kulmala Markku , Bianchi Federico 
Published: March 2024

A significant fraction (>50%) of current cloud condensation nuclei (CCN) is estimated to stem from the formation of new particles. But the mechanisms governing new particle formation (NPF) process are still poorly understood, especially regarding preindustrial NPF.
In order to investigate preindustrial NPF process and its contribution to CCN budget, intensive ambient observations were carried out between March 28 and June 27, 2022 at the pristine high-altitude Iza&#241;a Atmospheric Observatory (IZO; 2367 m a.s.l., 28&#176;18'32.3"N 16&#176;29'58.1"W), which is located on the island of Tenerife, Canary Islands. This site is characterized by clean air and pristine skies with minimal local anthropogenic influence. Among with other instrumentations, a Multi-scheme chemical IONization (MION) inlet coupled to an atmospheric pressure interface time-of-flight mass spectrometer (APi-ToF-MS) was used to measure the molecular composition of neutral vapours including the less oxygenated organic compounds, sulphuric acid (SA), methane sulfonic acid (MSA), and highly oxygenated organic molecules (HOM) via the fast switching of two reagent ion schemes (Br- and NO3-). A Vocus proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF) was deployed to measure the potential precursor volatile organic compounds (VOC), dimethylsulphide (DMS) and their oxidation products. Filter samples were collected and analyzed in the laboratory with a filter inlet for gases and aerosols coupled to a high-resolution time-of-flight chemical ionization mass spectrometer (FIGAERO-HR-TOF-CIMS), yielding the molecular composition of particulate organics.
During the measurement period, clustering events were frequently observed, particularly in May and June. NPF precursors, e.g., SA and HOM, were also substantially higher in May and June, indicating their potential role in the NPF process. This is also consistent with the time series of their precursors such as DMS, SO2, and terpenes. NPF events in the presence of Sahara dust events were also observed, exhibiting lower levels of organics in the particle phase compared to clear NPF events. In addition, higher levels of marine MSA and SA were observed on some nights, potentially resulting from the updraft and transport from the Atlantic Ocean to the marine free troposphere.
The measurements at IZO station provide us with a valuable dataset regarding NPF at this pristine high-altitude location with marine and Sahara dust influences. Chemical characterization of the freshly formed clusters will increase our understanding of the nucleation mechanism responsible for preindustrial NPF, as well as free tropospheric chemistry. Our study will also provide new insights on a molecular basis to better understand present and future aerosols, and their effects on air quality and climate.