Browsing by Autor "Ilona Riipinen"

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Aerosols in the Andes: Microphysical Properties and Long-Term Variability
(2026) Diego Aliaga; Fernando Velarde; Marcos Antônio Ribeiro Andrade; Paolo Laj; Gaëlle Uzu; Kay Weinhold; Alfred Wiedensohler; Ilona Riipinen; Radovan Krejci
Aerosol properties, loading, trends, and variability in the upper troposphere are key to understanding the evolving state of the atmosphere and the role of aerosols in climate and cloud processes. However, long-term in-situ aerosol observations at high altitudes remain scarce worldwide, particularly in the Global South. This observational gap limits our ability to develop a global perspective on aerosol sources, processes, and impacts within the climate system.Here we present 13 years (2012–2024) of continuous aerosol-related measurements conducted at the world’s highest Global Atmosphere Watch (GAW) station, located on Mount Chacaltaya (CHC) in the central Andes of Bolivia at an elevation of 5.2 km a.s.l. This dataset is one of the longest in existence on the South American continent and therefore provides a unique opportunity to evaluate trends in aerosol concentrations and properties. These trends and properties are influenced by, for example, biomass burning in the Amazon, the transport of pollution from the conurbation of La Paz and El Alto, located 18 km to the south, and the subsidence of air masses from the upper troposphere.We focus on particle number size distributions (PNSD), equivalent black carbon (eBC), and related meteorological and chemical tracers, including water vapor mixing ratio (WVMR) and carbon monoxide (CO). We characterize aerosol properties and loading by combining traditional time-series analysis (e.g., separation by hour of day, season, and year) with an unsupervised k-means clustering approach that disentangles the dominant atmospheric regimes influencing aerosol properties at CHC. The clustering uses PNSD, eBC, and WVMR as input variables and identifies seven distinct categories of days, hereafter referred to as atmospheric regimes, which represent significantly different source regions and aerosol processing pathways (e.g., cloud processing, wet deposition, and new particle formation). The performance of the clustering is evaluated using independent tracers, namely CO concentrations and HYSPLIT back trajectories. For each regime, the individual days grouped within it exhibit internally consistent CO levels and air-mass provenance that are clearly distinct from those of other regimes. This result is particularly encouraging given that neither CO nor back trajectories were included as inputs to the clustering algorithm.One regime is particularly noteworthy, representing a persistent free-tropospheric state characterized by extremely low WVMR, CO, and eBC, along with signatures of early-morning new particle formation. We find that the concentration of particles in this regime has significantly decreased over the 13-year period which indicates a declining upper-tropospheric particle concentration. A second notable regime is associated with biomass burning. We find that its occurrence has increased over time, from ~10% of days during the biomass-burning season (August–November) in the first years to ~50% in the last years. This suggests an increment on the number of biomass burning episodes measured at the station. Additional categories capture aerosol–cloud processing during Amazonian boundary-layer uplift, local eBC influence from the La Paz–El Alto metropolitan area, and strong nucleation under dry, coastal/Altiplano air masses. Overall, these results emphasize a region in rapid change and the importance and utility of long-term measurements in under sampled areas.
Direct high-altitude observations of 2-methyltetrols in the gas- and particle phase in air masses from Amazonia
(Royal Society of Chemistry, 2025) Claudia Mohr; Joel A. Thornton; Manish Shrivastava; Anouck Chassaing; Ilona Riipinen; Federico Bianchi; Marcos Andrade; Cheng Wu
We present direct observations of 2-methyltetrol (C5H12O4) in the gas- and particle phase from the deployment of a Filter Inlet for Gases and Aerosols coupled to a Time-of-Flight Chemical Ionization Mass Spectrometer (FIGAERO-CIMS) during the Southern Hemisphere High Altitude Experiment on Particle Nucleation and Growth (SALTENA), which took place between December 2017 and June 2018 at the high-altitude Global Atmosphere Watch station Chacaltaya (CHC) located at 5240 m a s l in the Bolivian Andes. 2-Methyltetrol signals were dominant in a factor resulting from Positive Matrix Factorization (PMF) identified as influenced by Amazon emissions. We combine these observations with investigations of isoprene oxidation chemistry and uptake in an isolated deep convective cloud in the Amazon using a photochemical box model with coupled cloud microphysics and show that, likely, 2-methyltetrol is taken up by hydrometeors or formed in situ in the convective cloud, and then transported in the particle phase in the cold environment of the Amazon outflow and to the station, where it partially evaporates.