Types of regional and localised new aerosol particle formation and growth processes: Atmospheric Banana Atlas

The structure and variability of atmospheric new particle formation and particle diameter growth (NPF&G) processes provide valuable insights into the underlying chemical, physical and meteorological mechanisms including atmospheric mixing and transport-related effects. Therefore, we systematically categorised and characterised the NPF&G events observed over 13 years in an urban environment. Six regional-scale banana plot types with narrow onset, broad onset, arch shape, double onset, tandem growth and nocturnal occurrence were identified. Additionally, two localised types were defined: one exhibiting multiple, but underdeveloped banana shapes, and another with diverse angulate structures, both being limited in time. The localised processes typically occurred on 7% of days, and produced high (up to 60 × 10³ cm⁻³) ultrafine particle number concentrations. Regional and localised processes can also happen on the same day. Our findings highlight the need to extend current NPF&G identification and classification frameworks by incorporating an additional step to distinguish localised events from regional processes.