FALCON

Fluxes of AerosoL Continuous Observing Network

1 February 2023 - 1 February 2024

Lead Scientist: Delphine Farmer

Observatory: AMF (ARM Mobile Facility 1) - EPC

Aerosol particles impact climate through both direct and indirect effects. However, the contribution of aerosols remains the most uncertain component of radiative forcing predicted by global models, and the removal of particles by deposition remains particularly difficult to constrain. This removal rate determines the lifetime of aerosol in the atmosphere – and thus its potential to impact the planet’s radiative balance. Aerosol dry deposition is parameterized in both regional- and global-scale models, but these parameterizations rarely reflect observations of size-resolved aerosol deposition accurately. We recently proposed a revision to the parameterizations that included an enhanced role for interception and a diminished role for Brownian diffusion as mechanisms for particle dry deposition. Our work used measurements over a coniferous forest, and then tested the revised parameterization against both our and literature data from a variety of land surfaces. However, size-resolved particle flux data sets are limited in availability over the complex array of biomes present in the United States. The lack of observational constraints is a key limitation to reducing uncertainty of model parameterizations, and thus uncertainty in modeled aerosol concentration and impacts.

Surface properties play a substantial role in determining the relative importance of interception, impaction, and Brownian diffusion. Some surfaces, such as water and the cryosphere, are particularly poorly constrained by measurements. Other land-use types such as broadleaf forests and grasslands undergo substantial seasonal shifts in surface properties – but the role of seasonality on particle fluxes is poorly understood due to the lack of long-term measurements. Inherent challenges in making particle flux measurements have hindered observational constraints, but developments in online optical particle measurements coupled to sonic anemometers have enabled eddy covariance measurements of size-resolved particle flux over select sites. Now, newer (and lower-cost) instrument designs provide us an opportunity to deploy optical particle flux measurements across multiple surfaces. This project creates the Fluxes of AerosoL Continuous Observing Network (FALCON), a particle flux network over multiple surface types designed to investigate more deeply size-resolved aerosol deposition processes with the aim of improving the accuracy of modeled aerosol removal rates and thus life cycle predictions. We will deploy size-resolved particle flux measurements over five sites across the U.S. to investigate the reproducibility of particle flux measurements, the measurement uncertainties in those measurements, the extent to which current and revised parameterizations capture dry deposition across different surfaces of the planet, and the extent to which different surfaces act as particle sources, and the drivers of those upward fluxes.