Interpretation of aerosol particle fluxes over a pine forest: Dry deposition and random errors

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Abstract
Aerosol particle fluxes were measured above a Scots pine forest in southern Finland by the eddy covariance (EC) technique. Condensational particle counter (CPC) was used in the EC system to detect the total particle number concentration in the size interval from about 10 nm to 500 nm. Turbulent records of velocity components and concentrations as well as fluxes were analysed for non‐stationary behaviour by using quality tests. Aerosol particle concentration revealed often non‐stationary behaviour, more frequently than other scalars like temperature, water vapour and carbon dioxide. During stationary episodes most of the flux estimates indicated deposition of particles into forest. Size‐dependent deposition velocities were estimated by using auxiliary measurements of particle size distribution. A semi‐empirical deposition model explained most of the variance observed in particle fluxes when size spectrum was dominated by below 100 nm particles. However, deposition velocity estimates for above 100 nm particles remained very uncertain.