Aerosol flux measurements above a mixed forest at Borden, Ontario

Abstract

Abstract. Aerosol fluxes were measured above a mixed forest by Eddy Covariance (EC) with a Fast Mobility Particle Sizer (FMPS) at the Borden Forest Research Station in Ontario, Canada between 13 July and 12 August 2009. Chemically speciated flux measurements were made at a height of 29 m at the same location between 19 July and 2 August, 2006 using a Quadrupole Aerosol Mass Spectrometer (Q-AMS). The Q-AMS measured an average sulphate deposition velocity of 0.3 mm s −1 and an average nitrate deposition velocity of 4.8 mm s −1 . The FMPS, mounted at a height of 33 m (approximately 10 m above the canopy top) and housed in a temperature controlled enclosure, measured sizeresolved particle concentrations from 3 to 410 nm diameter at a rate of 1 Hz. For the size range 18 < D < 452 nm, 60 % of fluxes were upward. The exchange velocity was between −0.5 and 2.0 mm s −1 , with median values near 0.5 mm s −1 for all sizes between 22 and 310 nm. The size distribution of the apparent production rate of particles at 33 m peaked at a diameter of 75 nm. Results indicate a decoupling of the above and below canopy spaces, whereby particles are stored in the canopy space at night, and are then diluted with cleaner air above during the day.

A large‐eddy simulation of the phase transition of ammonium nitrate in a convective boundary layer

“…[], who pointed out that this downward flux can lead to overestimations of the dry‐deposition velocity of nitrate. Several other studies also measured large apparent deposition fluxes of aerosol nitrate and ammonium with an aerosol mass spectrometer eddy‐covariance flux system and by measuring concentration gradients [ Fowler et al ., ; Gordon et al ., ; Nemitz et al ., ; Wolff et al ., ; Wyers and Duyzer , ]. We have confirmed that flux measurements of total nitrate are more suitable for estimating deposition velocities.…”

“…Unfortunately, experimental confirmation needs fast measurements (more than 1 Hz) of the nitrate mixing ratio, which is technically challenging [ Crosier et al ., ]. Such fast measurements are normally only performed for specific flux studies at the surface [ Farmer et al ., ; Fowler et al ., ; Gordon et al ., ; Nemitz et al ., ]. Our simulations further predict that gas‐aerosol partitioning induces a downward flux of nitrate in the convective boundary layer.…”

Review and Integration of Biosphere-Atmosphere Modelling of Reactive Trace Gases and Volatile Aerosols

“…Besides, measurements show that during nucleation events particle concentrations are larger at higher heights than in the forest canopy, suggesting that the canopy is not a source region for nucleation (Gordon et al 2011;Pryor et al 2008aPryor et al , 2009). There is the general understanding that there is no effective primary source of submicron particles from vegetation, except for the release of some small PBAP.…”

“…However, these surfaces are usually considered unrepresentative of vegetation. Special fast data acquisition modes have been developed (Crosier et al 2007;Kimmel et al 2011) that allow its application for eddy-covariance flux measurements (Gordon et al 2011;Nemitz et al 2008;Thomas 2007;Zalakeviciute et al 2012). Duyzer 1994;Wyers and Duyzer 1997), and sulphate fluxes were measured by eddy-covariance with a fast chemiluminescence detector as early as the 1980s (Wesely et al 1985b).…”

An approach to investigate new particle formation in the vertical direction on the basis of high time-resolution measurements at ground level and sea level

“…A combination of fastresponse particle sizers and an eddy covariance system have been used to study vertical transport of atmospheric particles (Gordon et al, 2011). The calculated vertical exchange fluxes of atmospheric particles of different sizes are always positive; however, this is practically impossible in the atmosphere.…”