IntroductionThe airborne particle counters APC-03-2 and APC-03-2A and liquidborne particle counter LQB-1-200 developed in the Research Institute for Solid State Physics together with Technoorg-Linda Ltd. for monitoring particle size distribution and concentration in air and in liquids are described elsewhere. The sizing and counting of particles in the air meet the requirements of the US Federal Standard 209 B relating to clean room monitoring, in the liquids - the requirements of the purity testing if ingredients in pharmacology, hematology, chemical industry, health care, etc. The computer controlled fast data evaluation and storage in these instruments provides efficient presentation of the measured data in a variety of table- and histogram-forms (full data table, differential concentration distribution table, size distribution-histogram, time-histograms, differential concentration distribution histogram etc.).Aerodynamic focusing and acceleration of the air stream to be tested (up to 200 m/s), the small testing volume together with the specific illumination and detection system and appropriate data evaluation in airborne particle counters, provide measurements in a wide range of concentrations (from 10 particles/liter up to 5 10 6 particles/liter) with a high resolution. These features make it possible to utilize the device not only for clean room monitoring and laminar box testing, but also for measuring contamination in health care facilities, in workshops using hazardous airborne compounds (e. g. in pharmacology) and in toxicology (e. g. in inhalation experiments) where the concentration of the contamination may be very high.Fields of application and some experimental resultsSeveral examples of practical applications of APC-03-2 and APC-03-2A airborne particle counters are:- monitoring of clean rooms in KFKI MSZKI, DSX-department, in Hungarian VISCOSA Works (Nyergesujfalu), in packaging workshop of CHINOIN Works for Pharmaceutical and Chemical Products, Budapest, Hungary, in FORTE Works for Photochemical Products;- monitoring of air quality in operating theaters of St. Imre Hospital, St. Janos Hospital, in the University for Postgraduate Medical Education (OTE), Budapest, Hungary;- testing of laminar boxes in the Works for Laminar Box Production -DEFI, Debrecen;- determination of the size distribution and concentration of the evaporated particles in Toxicological Center of the Research Institute for Heavy Chemical Industry (NEVIKI) Veszprem-Szabadsagpuszta, Hungary; Hungarian Hygiene Institute, Budapest;- testing of air filters in PARAPLAN Ltd., Budapest, testing of TEMAFORG filters;- monitoring of air contamination within the city of Budapest;- Measuring of size distribution and concentration of the aerosol released from heated LWR fuel rods in Reactor accident simulation in the Research Institute for Atomic Energy.Examples of practical applications of LQB-1-200 liquidborne particle counters are:- testing of purity of tap water in different places in Budapest;- measurement of particulate contamination of the water in lake Balaton;- measurement of purity of different hydraulic oils;- testing of pharmacological products.An example of the measurement performed by LQB-1-200 particle counter in the high concentration conditions (up to 10 particles/ml) is shown on fig. 1. On this figure we can see the particle size distribution in suspended electron emission mixture having concentration above 20.000 particles/ml where most of the particles are multiplets consisting of 8-10 2μm sized singlets. As we can see the maximum of these particles is in the range of 10-30 μm. This size distribution which can be change in time due to sedimentation and coagulation is important in the technology of cathode activation.