Comment on egusphere-2026-3660

Résumé fourni par la source

Abstract. Atmospheric aerosols in the free troposphere (FT) exert a disproportionate influence on climate forcing yet remain poorly constrained. Here, we present an 11-year (2011–2021) characterization of PM10 chemical composition at the High Altitude Research Station Jungfraujoch (3580 m above sea level), capturing both FT conditions and episodic planetary boundary layer intrusions (PBLi). We integrate long-term measurements of organic aerosol (OA), elemental carbon, sulfate, crustal elements, trace metals, and bulk and molecular-level organic composition with gas-phase observations and proxies for atmospheric transport and oxidative capacity to quantify the drivers of aerosol loading and composition. The concentrations of primary aerosol species, including metals and elemental carbon, are strongly controlled by episodic PBL-to-FT transport (2-3-fold seasonal amplitude, e.g. 0.15 to 0.3 ng m-3 for Pb). Secondary species, including sulfate and OA, also reflect PBLi impact, but their formation requires sustained oxidative processing, for which the atmospheric humidity ratio (ω) acts as a key control. OA exhibits the strongest seasonal amplitude (10-fold, 0.1 to 1 μg m-3), additionally reflecting enhanced biogenic emission intensities in the PBL. This is accompanied by a systematic shift in C9 and C10 compounds, likely related to seasonal maxima in monoterpene emissions. Together, these results demonstrate that FT aerosol is governed by a dynamic interplay between episodic PBL-FT transport, source emission intensities and oxidative processing. This dataset constrains their relative contributions, and provides decade-scale observational benchmarks for improving the representation of transport and aging in atmospheric models, with implications for reducing uncertainties in climate forcing.

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