Radon-based atmospheric stability classification in contrasting sub-Alpine and sub-Mediterranean environments

Area of Science:

• Environmental Science
• Atmospheric Science
• Geophysics

Background:

• Atmospheric stability and mixing are crucial for air quality.
• Topography significantly influences local atmospheric conditions.
• Radon (Rn) is a naturally occurring radioactive gas used as a tracer for atmospheric processes.

Purpose of the Study:

• To investigate relative changes in summertime atmospheric stability using a radon-based technique.
• To compare atmospheric mixing conditions at two sites in Slovenia with contrasting geographical settings.
• To assess the influence of local topography on atmospheric stability and pollutant dilution.

Main Methods:

• Utilized a recently developed radon-based technique to monitor atmospheric stability.
• Compared radon variability and diurnal amplitude at an urban sub-Alpine site (Ljubljana) and a near-coastal site (Ajdovščina).
• Analyzed wind speed, wind direction, and radon accumulation rates to understand local contributions to the radon signal.

Main Results:

• Contrasting topographic settings caused differences in mixing conditions despite similar synoptic conditions.
• Wind speeds under stable conditions were higher in Ljubljana (0.2-0.3 m/s) than Ajdovščina (0-0.2 m/s).
• Diurnal radon amplitude was significantly larger at Ajdovščina (∼47 Bq m⁻³) compared to Ljubljana (∼24 Bq m⁻³), indicating greater nocturnal accumulation.

Conclusions:

• Radon measurements effectively distinguish subtle changes in atmospheric mixing in complex terrain.
• Topography plays a key role in modulating atmospheric stability and the capacity for pollutant dilution.
• Urban basin environments, like Ljubljana, exhibit considerably less capability for diluting primary pollutants compared to foothills environments.