AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Seasonal Cycles in Particle Number Fluxes over a Pine Forest
HOLLY DEBOLT, Ryan Fulgham, John Ortega, Delphine Farmer, Colorado State University
Abstract Number: 414 Working Group: Remote and Regional Atmospheric Aerosols
Abstract The ability of global climate models to accurately reflect global warming and cooling processes is limited by our understanding of the physical mechanisms underlying these predictions and our ability to directly observe and accurately quantify the relevant measurements. The area of greatest uncertainty in predictive models is the magnitude of radiative forcing due to aerosol effects which may potentially mask a significant amount of warming due to anthropogenic greenhouse gas emissions. Underlying this uncertainty is a lack of observational study of the factors governing aerosol emission and removal mechanisms in various types of terrain. Measurements of relatively simple, smooth terrain such as grasslands have been shown to agree with predictive modeling of exchange velocities, However, predictions over rough surfaces, such as forests, have failed to match observed measurements. To improve these parameterizations, accurate quantification of particle flux and deposition velocity is needed.
The Manitou Experimental Forest Observatory (MEFO) in Colorado provides the surface-to-atmosphere interface for our study during a year-long deployment covering all four seasons. We have obtained fast (10 Hz), size-resolved (80-100nm) measurements of particle number concentrations with an Ultra High Sensitivity Aerosol Spectrometer (UHSAS) and calculated particle fluxes using the Eddy Covariance micrometeorological method. Deposition fluxes were observed through the daylight hours in each season with occasional upward fluxes occurring in the morning, corresponding to the breakup of the nocturnal boundary layer. An inter-seasonal comparison of particle fluxes shows differentiation of flux magnitude among the seasons with summer having the highest magnitude deposition flux, winter having the lowest, and with spring and fall fluxes falling in between. This observed trend is correlated with the observed particle number concentrations recorded in each respective season. These initial results provide a basis for further investigating the seasonal parameters that influence aerosol dry deposition processes over the forested surface-to-atmosphere interface.