Investigating Ultrafine Aerosol Turbulent Fluxes during Atmospheric New Particle Formation Events

Area of Science:

• Atmospheric Chemistry
• Aerosol Science
• Planetary Boundary Layer Dynamics

Background:

• Accurate prediction of new particle formation (NPF) is hindered by uncertainty in the origin of observed particles, often misattributing aloft-formed particles to ground-level events.
• This ambiguity compromises atmospheric models reliant on local measurements for predicting NPF and its impact.

Purpose of the Study:

• To develop and validate an analytical framework for directly quantifying the vertical turbulent flux and transport direction of newly formed particles.
• To improve the attribution of NPF events to specific altitudes and enhance process-level understanding of atmospheric particle formation.

Main Methods:

• Utilized airborne eddy covariance and continuous wavelet transform to measure vertical turbulent flux of newly formed particles.
• Analyzed data from an airborne campaign over the Southern Great Plains, including spectral analysis of aerosol instrumentation data.

Main Results:

• Observed a consistent and strong downward turbulent flux of ultrafine aerosols during NPF events (-133.8 cm^-3 m s^-1 in the entrainment zone).
• Fluxes were negligible on non-NPF days, confirming the directional flux measurement's reliability with standard 1 Hz aerosol instrumentation.
• Identified entrainment from the residual/stable layer as a significant source of boundary layer aerosols during NPF events.

Conclusions:

• The proposed framework accurately quantifies vertical particle transport, enabling correct altitude attribution of NPF events.
• Entrainment-driven NPF events are a significant, potentially underestimated, source of boundary layer aerosols.
• This methodology enhances process-level understanding and predictive modeling of atmospheric particle formation.