Characterisation of individual aerosol particles on moss surfaces: implications for source apportionment

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Geochemistry

Background:

• Moss (Hylocomium splendens) is a valuable bioindicator for atmospheric deposition.
• Previous studies on atmospheric input in Southern Norway may have overlooked temporal trends in particle composition.
• Source apportionment studies often rely on bulk chemical analysis, potentially misinterpreting particle origins.

Purpose of the Study:

• To investigate the size, morphology, and chemical composition of particles on moss surfaces.
• To analyze temporal changes in particle deposition between 1977 and 2005.
• To assess the impact of fly ash particles on source apportionment studies.

Main Methods:

• Scanning electron microscopy (SEM) for particle visualization.
• Energy-dispersive X-ray microanalysis (EDX) for chemical composition.
• Analysis of 8405 particles from 12 moss samples across three Norwegian locations and two sampling years.

Main Results:

• Particle deposition on moss surfaces decreased significantly over time at all locations.
• Fly ash particles (silicate, iron-rich silicate, iron oxide) showed a substantial relative decrease in abundance.
• Small fly ash particles (<1 micrometer) decreased from 30-60% to 10-18%; large particles (≥1 micrometer) decreased from 10-35% to 2-9%.

Conclusions:

• The decline in fly ash deposition between 1977 and 2005 was previously overlooked.
• Ignoring fly ash particles in source apportionment can lead to overestimation of the geogenic component.
• Complementing bulk chemical analysis with SEM is crucial for accurate identification of anthropogenic aerosols like fly ash.