Abstract
The function of the inlet of a particulate sampler is to capture particles in the air and duct them to a collection filter or a dynamic sensor. For a given inlet the aerosol concentration and size distribution registered by the sampler may be strongly modified by the orientation of the inlet, θ, relative to the ambient wind direction, and by the velocity ratio, R, defined as the ratio of wind velocity to inlet velocity. We have studied such dependence with a thin-walled inlet tube at wind velocities of 250 to 1000 cm/s, inlet velocities of 125 to 1000 cm/s, and angles of 0° to ±90°. For all the tested velocity-combinations differences in sampling efficiency were found for particles above 10 µm in diameter when the aerosol was sampled 15° upward vs. 15° downward from the horizontal. For θ=30 to 90° the sampling efficiency was found to be approximately a function of Stokes number with R as a parameter. At θ=90° the sampling efficiency was approximately a function of Stk . About half or more of the particle deposition in the inlet occurred within the first 1 cm of the 20 cm long inlet tube.