The present invention relates to a method, system and apparatus for continuously monitoring variations in the size of particles present in a fluid on a real time basis. The method comprises of passing one or more optical signal through the fluid such as engine oil. The variation (attenuation or enhancement) in the intensity of the optical signal is continuously measured with respect to time. In an embodiment, the method, system and apparatus of the present invention enable monitoring of the amount, size and onset of particle agglomeration using single or multiple wavelengths as interrogating optical signal(s). An exemplary embodiment is provided for monitoring of the amount, size and onset of soot particle agglomeration in engine oil using single or multiple wavelengths as interrogating optical signal(s).