An FI having an in-situ particle detector and a method for particle detection therein are provided. In one aspect, the FI includes a fan, a substrate support, a particle detector, and an exhaust outlet. The fan, substrate support, and particle detector are arranged such that, in operation, the fan directs air towards the exhaust outlet and over a substrate on the substrate support to create laminar flow. The particle detector, positioned downstream from the substrate support and upstream from the exhaust outlet, analyzes the air and detects particle concentration before the particles are exhausted. The collected particle detection data may be combined with data from other sensors in the FI and used to identify the source of particle contamination. The particle detector may also be incorporated into other system components, including but not limited to, a load-lock or buffer chamber to detect particle concentration therein.