A baffle for use with an environmental sensor such as a particle counter. The environmental sensor includes a housing and an inlet. The inlet has an axis and defines a first cross-sectional area with respect to the axis. The baffle includes a bullet configured to be positioned adjacent to the inlet along the axis. The bullet has a second cross-sectional area with respect to the axis that is between about seventy-five percent smaller than the first cross-sectional area and about three-hundred percent larger than the first cross-sectional area. In some constructions, the baffle substantially reduces interference from external light sources without substantially inhibiting the transport of particles entrained in the fluid to be analyzed by the environmental sensor.