Disentangling source, biogeochemical, and transport influences on marine aerosol properties via long-term observations in the north-east Atlantic

Background: Marine aerosol forcing remains one of the dominant uncertainties in Earth’s radiative balance, largely due to limited constraints on natural submicron aerosol composition, source contributions, and their coupling to ocean biological processes. This thesis uses the long-term observational record at the Mace Head Atmospheric Research Station to disentangle the chemical, physical, and biogeochemical drivers controlling marine aerosol in the North-East Atlantic. Methodology: High-resolution time-of-flight aerosol mass spectrometry, size-resolved particle measurements, positive matrix factorisation along with information theoretic metrics, trajectory-based source region analyses, and global phytoplankton functional type (PFT) models are combined to resolve the sources, dynamics, and ecosystem linkages of marine aerosol seasonal and synoptic scales. Results and Conclusions: Chapter 3.1 shows that summer organic aerosol at Mace Head carries unambiguous biological signatures, with primary marine organic aerosols and methane sulphonic organic aerosols responding to phytoplankton exposure on two distinct timescales: a near-instantaneous release of labile precursors and a slower response consistent with viral lysis or other heterotrophic processes To determine whether this behaviour persists year-round and varies with seasonal community structure or meteorology, a continuous annual record was required. For this reason, the analyses were next performed on up to a full year of measurements. Extending the analysis to a full year. In Chapter 3.2, a full year of high-resolution aerosol mass spectrometry measurements at Mace Head (West coast of Ireland) is combined with HYSPLIT air-masses exposure metrics and gap-free PFT fields to explore influences on primary marine organic aerosol (PMOA) and methane sulphonic acid organic aerosol (MSA-OA). During the spring-summer diatoms climax, PMOA correlates with dominant bloom taxa (R=0.65-0.70), with rapid 1-3 days responses and secondary maxima near ~25 days, consistent with early labile release and later lysis emissions. Comparable phytoplankton exposure in late summer (i.e. theoretical early depletion phase) does not reproduce these high correlation values, with time-scale analyses indicating weakened coupling under warmer, weaker-wind conditions. MSA-OA also exhibits a positive association with micronekton exposure derived from the spatial ecosystem and population dynamics model (SEAPODYM) during diatoms climax (R=0.75), hinting at dimethyl sulphide trophic amplification. Overall, these results indicate that structured ecosystem composition and physical forcing both contribute to cross-basin differences in marine organic aerosols formation. This motivates future research vessel campaigns and controlled mesocosm experiments to explicitly manipulate trophic interactions and air-sea physics. Chapter 3.3 presents heuristic SMPS-based source apportionment methods to retrieve size-resolved distributions of marine aerosol sources. Sulphate, MSA-OA, and PMOA contributions were resolved and interpreted using Wasserstein similarity to link size distributions with previous studies. In addition, nucleation and Aitken modes showed strongest sensitivity to diatoms and dinoflagellates linked processes, whereas accumulation-mode variability aligns more closely with prokaryotic groups, although these relationships require further investigation. Finally, Chapter 3.4 shows that the capture vaporizer (i.e. an enclose vaporizer geometry designed to enhance particle collection efficiency and reduce particle bounce relative to the standard open vaporiser) yields spectra that can remain interpretable despite systematic fragmentation shifts. To address this, a dual-constraint methodological framework was developed, combining Jensen-Shannon divergence of time series with entropy similarity of mass spectra in a manner that will allow for the continuity assessment of future source apportionment endeavours despite CV-induced fragmentation. Overall, this work sought to establish a unified framework linking marine aerosol composition, size distributions, and air masses exposure to surface ocean ecosystems while maintaining source apportionment continuity across instrumental changes.

Funder

University of Galway
Environmental Protection Agency, Ireland
Department of the Environment, Climate and Communications
Science Foundation Ireland

Publisher

University of Galway

Rights

CC BY-NC-ND

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Collections

University of Galway Theses (PhD Theses)