Development of a two stage virtual impactor for stationary source PM₁₀ and PM_2.5 sampling

China does not have a national standard method for stationary source PM₁₀ and PM_2.5 sampling. Current commercial PM₁₀/PM_2.5 samplers have some limitations when used in China. In this study, we developed a two stage virtual impactor for sampling PM₁₀/PM_2.5 from stationary source. Its performance was evaluated using laboratory generated aerosol. Its collection efficiency curve satisfies the requirement of ISO 7708:1995 for PM₁₀/PM_2.5 samplers. The diameter of this cylindrical virtual impactor is 74mm, smaller than the diameter of the sampling port in most stationary sources in China. Both filter papers and filter thimbles can be used with this impactor which makes it suitable for both low and high dust concentration sampling. The ratio of the minor flowrate to the total flowrate influences the cutoff size (D₅₀) of the virtual impactor. Reducing this ratio will lead to an increase in D₅₀. The distance from the bottom of the accelerating nozzle to the top of the collecting nozzle should be greater than 1.5- 2.0 times the diameter of the accelerating nozzle.