Abstract：The working principle of ELPI diluter was analysed, and PM_2.5 test method for negative pressure gas environment was proposed, which was diluter same pressure treatment and improving dilution air pressure, explored the rationality of the test method through the field test. Both of the methods can meet the requirements in the smaller negative pressure environment. When sampling gas pressure reaches around-7 000 Pa. there will be more apparent dilution ratio to the variation of environmental change of 200 kPa diluter, 300 kPa diluter will be no longer applicable with-17 000 Pa; For a bigger negative pressure environment, it is suggested that develops bigger pressure diluter.The research aims to explore a scientific and reasonable low concentration testing techniques and methods, expand the ELPI scope further.

Keywords: PM_2.5; negative pressure; smoke