An apparatus includes a sampling probe having a first portion and a second portion. The first portion is configured to penetrate inside a wall of a duct having an inner chamber that is configured to carry a gas stream containing particulate matter therethrough. The first portion is further configured to divert a sample of the gas stream from the inner chamber of the duet to the second portion that extends from the wall of the duct opposite the inner chamber. The second portion of the sampling probe is configured to direct the sample of the gas stream in a first direction with a second direction corresponding to a direction of the gravitational force of the earth. A first ray corresponding to the first direction forms an angle β with a second ray corresponding to the second direction. The angle β is less than 90 degrees.