Measurements of size-resolved aerosol concentration and
fluxes were made in a forest in the Athabasca Oil Sands Region (AOSR) of
Alberta, Canada, in August 2021 with the aim of investigating (a) particle
size distributions from different sources, (b) size-resolved particle
deposition velocities, and (c) the rate of vertical mixing in the canopy.
Particle size distributions were attributed to different sources determined
by wind direction. Air mixed with smokestack plumes from oil sands
processing facilities had higher number concentrations with peak number at
diameters near 70 nm. Aerosols from the direction of open-pit mine faces
showed number concentration peaks near 150 nm and volume distribution peaks
near 250 nm (with secondary peaks near 600 nm). Size-resolved deposition
fluxes were calculated which show good agreement with previous measurements
and a recent parameterization. There is a minimum deposition velocity of
vd=0.02 cm s−1 for particles of 80 nm diameter; however, there is
a large amount of variation in the measurements, and this value is not
significantly different from zero in the 68 % confidence interval.
Finally, gradient measurements of aerosol particles (with diameters
<1 µm) demonstrated nighttime decoupling of air within and
above the forest canopy, with median lag times at night of up to 40 min and
lag times between 2 and 5 min during the day. Aerosol mass fluxes (diameters <1 µm) determined using flux–gradient methods (with
different diffusion parameterizations) underestimate the flux magnitude
relative to eddy covariance flux measurements when averaged over the nearly
1-month measurement period. However, there is significant uncertainty in the
averages determined using the flux–gradient method.</p
