Disclosed are apparatus and methods for sampling air-borne particles. According to one embodiment a nozzle is used to generate a jet of fog that includes a gas and liquid droplets of different sizes. The jet of fog is formed by the nozzle in a way to cause particles in the air surrounding the jet of fog to be drawn into the jet of fog and to further cause the particles to aggregate with the liquid droplets inside the jet of fog. A sample collecting surface is located opposite and spaced apart from an outlet of the nozzle. The sample collecting surface is preferably sloped so that the liquid sample can be forced by gravity off the collecting surface and into a vial or other liquid sample container. Inside the jet of fog and on the sample collection surface the liquid droplets merge with one another to form larger sized droplets that are collectable in the liquid sample container.