Detection system for determining filtering effectiveness of airborne molecular contamination
A novel filter effectiveness detection method for AMCs (Airborne Molecular Contaminations) is provided herein, which is on-line, economical and applicable for diverse AMCs, using gas-to-particle conversion with soft X-ray irradiation radiation. In one embodiment, this method was conducted through AMC filter evaluations comparing two granular activated carbons (GACs), which are widely used AMC filter media, challenged with sulfur dioxide (SO 2 ), which is one of the major known AMCs in cleanrooms. Using this method, the concentration of gaseous SO 2 was assessed in terms of particle volume concentrations after the gas-to-particle conversion assisted by the soft X-ray irradiation. The results of this detection method showed high sensitivity to SO 2 , down to parts per trillion-levels, which are levels that are too low to be detectable by currently available commercial gas sensors.
1. A system for assessing airborne molecular contamination (AMC) filter effectiveness of an AMC filter device, the system comprising:
at least one granular activated carbon filter device adapted to receive an AMC gas/humid air gas mixture, the activated carbon filter having an output sample gas flow after receiving the AMC air gas mixture;
an AMC gas monitor that receives a portion of the AMC gas/humid air gas mixture;
a treatment chamber with a soft X-ray ionizing source that receives a portion of the output sample gas flow from the activated carbon filter;
a diluter assembly that dilutes particles formed in an ionized gas sample received from the treatment chamber; and
a particle measurement system adapted to measure particle characteristics of particles in the ionized gas sample received from at least one of the treatment chamber or the diluter assembly, wherein an output of the AMC gas monitor is compared with an output of the particle measurement system to determine qualitatively the filter effectiveness of the activated carbon filter device.
2. The detecting system of claim 1 wherein the particle measurement system includes a scanning mobility particle sizer that receives the ionized gas sample with particles directly from the treatment chamber.
3. The detecting system of claim 1 , wherein the activated carbon filter is varied in a height and a carbon particle size to change the breakthrough time of the activated carbon filter to certain AMCs.
4. The detecting system of claim 1 , wherein a humidity of the AMC/humid air mixture is varied to improve AMC detection capability of the system as a function of the concentration of AMCs in the AMC/humid air mixture.
5. The detecting system of claim 1 wherein the particle measurement system is selected from the group consisting of a condensation particle counter, an ultrafine condensation particle counter (UCPC) and an electrical aerosol detector.
6. The detecting system of claim 5 wherein the diluter assembly includes a rotating disc diluter.
7. The detecting system of claim 5 further comprising a the diluter assembly coupled to the UCPC.
8. A method for detecting airborne molecular contamination (AMC) in a gas having AMCs at levels as low as in parts per trillion (PPT) through gas to particle conversion using soft X-ray irradiation, the method comprising:
providing a sample gas flow including AMCs;
mixing humidified air with the sample gas flow including the AMCs to form an AMC/humid air mixture;
directing a first portion of the AMC/humid air mixture into an AMC gas monitor and directing a second portion of the AMC/humid air mixture to a treatment chamber having a soft X-ray irradiation device as an ionizing radiation source, wherein gas to particle conversion occurs as the sample gas mixture is exposed to the ionizing radiation and particles are formed;
measuring particle size distributions of the particles in an output sample of gas flow received from the treatment chamber using a scanning mobility particle sizer;
comparing an output from the AMC gas monitor and an output from the scanning mobility particle sizer; and
generating at least one correlation equation at a level of parts per billion (PPB) of AMCs measured by the AMC monitor which are correlated to particle volume concentrations, and extrapolating the correlation equation for PPT detection of AMCs in the AMC/humid air mixture.
9. The method of claim 8 further comprising the step of using particle mass concentrations to generate the at least one correlation equation where a density of the measured particles in the AMC/humid air mixture is known.
10. The method of claim 8 further comprising the step of using known levels of AMCs in the AMC/humid air mixture detectable by the AMC monitor to generate the at least one correlation equation.
11. The method of claim 8 further comprising the step of operatively coupling an activated carbon filter prior to the treatment chamber after generating the correlation equation and evaluating qualitatively a filter effectiveness of the activated carbon filter of filtering out AMCs by comparing outputs of the AMC monitor and the scanning mobility particle sizer.
12. The method of claim 8 , further comprising the step of bifurcating the output sample gas flowing from the treatment chamber such that a portion of the sample gas with formed particles is directed to a diluter assembly operatively coupled to a condensation particle counter assembly.
13. The method of claim 12 , wherein the diluter assembly is selected from the group consisting of a rotating disc diluter and a rotating disc thermo-diluter.
14. The method of claim 12 wherein the condensation particle counter assembly is an ultrafine condensation particle counter assembly.
15. A system for assessing airborne molecular contamination (AMC) filter effectiveness of an AMC filter device, the system comprising:
at least one granular activated carbon filter device adapted to receive an AMC gas/humid air gas mixture, the activated carbon filter having an output sample gas flow after receiving the AMC air gas mixture;
an AMC gas monitor that receives a portion of the AMC gas/humid air gas mixture;
a treatment chamber with a soft X-ray ionizing source that receives a portion of the output sample gas flow from the activated carbon filter;
a diluter assembly that dilutes particles formed in an ionized gas sample received from the treatment chamber and directs the particles in the ionized gas sample to a condensation particle counter assembly; and
a particle measurement system adapted to measure particle characteristics of the particles in the ionized gas sample received from the treatment chamber, wherein an output of the AMC gas monitor is compared with an output of the condensation particle counter assembly and with an output of the particle measurement system to determine qualitatively the AMC filter effectiveness of the activated carbon filter device.
16. The system of claim 15 , wherein the diluter assembly is selected from the group consisting of a rotating disc diluter and a rotating disc thermo-diluter.
17. The system of claim 15 , wherein the activated carbon filter is varied in a height and a carbon particle size to change the breakthrough time of the activated carbon filter to certain AMCs.
18. The system of claim 15 , wherein a humidity of the AMC/humid air mixture is varied to improve AMC detection capability of the system as a function of the concentration of AMCs in the AMC/humid air mixture.
19. The system of claim 15 wherein at least one correlation equation is generated for detecting AMCs at a level of parts per billion (PPB) of AMCs measured by the AMC monitor which are correlated to particle volume concentrations, and the correlation equation is extrapolated for a parts per trillion (PPT) detection of AMCs in the AMC/humid air mixture.
20. The system of claim 19 wherein the at least one correlation equation is generated using net particle volume concentrations of AMCs in the AMC/humid air mixture.