A system and method is provided for monitoring and controlling the contaminant particle count contained in an aerosol during a photoresist coating and/or development process of a semiconductor. The monitoring system monitors the contaminate particle count present in the environment of the photoresist coating and/or development process, such as in a process chamber or a cup, enclosing the wafer during the process. The present invention employs in situ laser scattering or laser doppler anemometry techniques to detect the particle count level in the chamber or cup. A plurality of lasers and detectors can be positioned at different heights in or outside of a chamber or cup to facilitate detecting particles at different height levels. A laser could be used in conjunction with mirrors to provide a similar measurement. The particle count level can be used to compare with the defect level, so that it can be determined if a cleaner environment and/or process should be implemented.