Volatility-resolved chemical characterization of airborne particles

Patent metadata

Field	Value
Publication number	US-11733148-B2
Application number	US-202016775033-A
Country	US
Kind code	B2
Filing date	Jan 28, 2020
Priority date	Jan 29, 2019
Publication date	Aug 22, 2023
Grant date	Aug 22, 2023

Abstract

A method and apparatus for evaluating the chemical composition of airborne particles by sequentially collecting and analyzing airborne particles in-situ. The method includes: collecting particles; enlarging the particles through water condensation; accelerating the enlarged particles onto a surface to collect enlarged particles; and analyzing the enlarged particles by: isolating the surface; passing a carrier gas over the surface; heating the surface to thermally desorb collected particles into the carrier gas; transporting this evolved vapor into detectors; and assaying the evolved vapor as a function of a desorption temperature. The apparatus includes: a sample flow inlet; a condensational growth tube; a collection and thermal desorption (CTD) cell; a carrier gas source; a heater coupled to the CTD; one or more gas detectors; and a controller configured to operate valves, the heater, the growth tube, and the CTD cell in at least an in-situ sequential collection mode and analysis mode.

First claim

We claim:

1. A method for evaluating the chemical composition of airborne particles, comprising:
sequentially collecting and analyzing airborne particles in-situ, including collecting the particles by:
introducing airborne particles in a gas flow through an inlet into a growth tube;
enlarging the airborne particles through water condensation at least partially within a region of water vapor saturation in the growth tube; and
accelerating the gas flow containing enlarged particles from the growth tube onto a surface to collect enlarged particles in a focused area on the surface by passing the flow through an orifice; and

analyzing the enlarged particles by:
isolating the surface from the inlet;
passing a carrier gas over the surface;

heating the surface to thermally desorb collected particles on the surface into the carrier gas, thereby forming an evolved vapor including the chemical constituents and decomposition products of the collected particles;
transporting the evolved vapor through a heated interface into one or more detectors; and
assaying the evolved vapor as a function of a desorption temperature.

2. The method of claim 1 further including repeating the collecting and analyzing automatically using a controller including switching between the sequentially collecting and analyzing by controlling one or more valves, gas flows and heaters.

3. The method of claim 1 wherein the heating of the surface comprises heating the surface in a stepwise manner, such that the surface temperature held steady for a prescribed period of time prior to a next temperature increase.

4. The method of claim 1 wherein the assaying is performed using a flame ionization detector connected to a detector for carbon dioxide.

5. The method of claim 4 wherein the assaying includes removing water vapor in the flow exiting the flame ionization detector.

6. The method of claim 4 wherein an oxygen to carbon ratio in evolved vapors in the flow exiting the flame ionization detector is determined from a ratio in detectable carbon mass from the flame ionization detector to a mass of carbon detected as carbon dioxide.

7. The method of claim 6 wherein the mass of carbon and the oxygen to carbon ratio in the evolved vapors is determined as a function of the desorption temperature.

8. The method of claim 1 further including partially replacing the inert carrier gas with an oxygen-bearing carrier gas to evolve a refractory carbonaceous material.

9. The method of claim 1 further including calibrating the one or more detectors by introducing gas standards into one or more detectors.

10. The method of claim 1 further including calibrating the one or more detectors introducing liquid standards into a collection cell.

11. The method of claim 1 wherein passing an inert carrier gas over the collected particles includes introducing the carrier gas through the orifice and through a side port of a collection cell and constraining the flow to exit through a second side port of the collection cell.

12. The method of claim 1 wherein the surface is in a collection cell and the isolating comprises closing a valve placed between the collection cell and the inlet.

13. The method of claim 1 wherein the surface is in a collection cell, and wherein the isolating comprises redirecting the flow containing the condensationally enlarged particles to an exhaust to bypass the collection cell, and simultaneously introducing an excess of carrier gas above the orifice.

14. The method of claim 1 wherein said introducing includes introducing at the inlet having at an ambient pressure, and wherein a pressure at the surface is within a few percent of the ambient pressure.

15. An apparatus, comprising:
a sample flow inlet;
one or more condensational growth tubes coupled to the sample flow inlet, at least a portion of the one or more condensational growth tubes including a region of water vaper supersaturation;
at least one vacuum valve;
a collection and thermal desorption (CTD) cell adapted to receive an output of the one or more condensational growth tubes onto a surface of the CTD cell through an acceleration nozzle;
a carrier gas source and an interface including a carrier gas valve configured to provide carrier gas into the CTD cell;
a heater coupled to the CTD cell configured to selectively heat the CTD cell;
a heated transport interface coupled between the CTD cell and one or more gas detectors or detector trains; and
a controller coupled to the carrier gas and vacuum valves, the heater, the heated transport interface, the one or more condensational growth tubes, and the CTD cell, the controller configured to operate the valves, the controlled heater, the heated transport lines, the one or more condensational growth tubes, and the CTD cell in at least an in-situ sequential collection mode and analysis mode.

16. The apparatus of claim 15 wherein the one or more detectors comprises a flame ionization detector (FID).

17. The apparatus of claim 16 further including a non-dispersive infrared detector (NDIR) coupled to the FID detector.

18. The apparatus of claim 15 wherein the one or more detectors comprises a flame ionization detector (FID) and a nondispersive infrared detector (NDIR), and further including an interface configured to remove water vapor produced by a hydrogen flame of the flame ionization detector prior to introduction into the nondispersive infrared detector.

19. The apparatus of claim 15 further including an interface configured to introduce either gas or liquid standards from a gas or liquid standards source to the CTD cell.

20. The apparatus of claim 15 wherein the CTD cell is fabricated from fused quartz.

21. The apparatus of claim 15 wherein the CTD cell is fabricated from stainless steel and has surfaces which are chemically passivated.

22. The apparatus of claim 15 wherein the CTD cell has an internal volume of less than 1 cm 3 .

Assignees

• Aerosol Dynamics Inc
• Virginia Tech Intellectual Properties Inc

Inventors

• Isaacman-Vanwertz Gabriel
• Kreisberg Nathan M
• Hering Susanne V

Classifications

• G01N2015/1022

  Measurement of deformation of individual particles by non-optical means · CPC title

• G01N15/1404 Primary

  Handling flow, e.g. hydrodynamic focusing · CPC title

• G01N2015/105

  Physics · mapped topic

• G01N15/0606 Primary

  by collecting particles on a support · CPC title

• G01N1/2208

  with impactors · CPC title