System and method for analyzing size distribution and chemical composition of neutral clusters below 3 nm

1 . A system for analyzing the size distribution and chemical composition of neutral clusters below 3 nm, comprising a sampling device, a unipolar charging device, a first coupling transport device, a nanoparticle electrical mobility size classification device, a second coupling transport device, a mass spectrometer, an aerosol number concentration measuring device, and a system control device,

wherein the sampling device, the unipolar charging device, the first coupling transport device, the nanoparticle electrical mobility size classification device, the second coupling transport device, and the mass spectrometer are sequentially connected along a particle inlet direction,

the second coupling transport device is connected with the aerosol number concentration measuring device, and

the system control device is in signal communication with the sampling device, the unipolar charging device, the nanoparticle electrical mobility size classification device, the mass spectrometer, and the aerosol number concentration measuring device,

wherein the first coupling transport device is configured to establish a stable and uniform reverse electric field so as to suppress interference caused by a local high-intensity electric field at an inlet of the nanoparticle electrical mobility size classification device on charged particles; and

wherein the second coupling transport device is configured to provide a particle transfer passage having an inner diameter the same as that of an outlet of the nanoparticle electrical mobility size classification device, so as to reduce particle loss caused by a mismatch in tube dimensions and/or flow field disturbances.

2 . The system according to claim 1 , wherein the sampling device comprises a main sampling tube and a core sampling tube which are sequentially connected along the particle inlet direction,

a reducing tee is provided between the main sampling tube and the core sampling tube, the reducing tee is also connected with a first particulate filter, and the first particulate filter is externally connected with a bypass blower.

3 . The system according to claim 1 , wherein the unipolar charging device comprises a tube body, and two ends of the tube body are provided with a sealing fitting, respectively;

an inlet tube is provided at an input end of the tube body as a particle inlet, and the inlet tube passes through the sealing fitting and then extends into the tube body;

an outlet tube is provided at an output end of the tube body as a particle outlet, and the outlet tube passes through the sealing fitting and then extends into the tube body;

the tube body is communicated with the sampling device through the inlet tube, and the tube body is communicated with the first coupling transport device through the outlet tube;

an inner tube is provided in the tube body, the inner tube is sleeved over the inlet tube that extends into the tube body, and the inner tube is spaced apart from the end of the outlet tube that extends into the tube body;

a discharge gas inlet and dielectric barrier discharge electrodes are sequentially arranged on an outer wall of the tube body along the particle inlet direction, the dielectric barrier discharge electrodes are annularly sleeved along a circumferential direction of the outer wall of the tube body, and the discharge gas inlet is communicated with the inside of the tube body; and

ion trapping electrodes are annularly disposed along a circumferential direction of an inner wall of the tube body.

4 . The system according to claim 1 , wherein the first coupling transport device comprises a stacked region, the stacked region comprises a first stacked section and a second stacked section, and the first stacked section and the second stacked section are spaced apart to form a passage;

the first stacked section and the second stacked section comprise multiple metal electrodes, wherein any two adjacent metal electrodes in the first stacked section and the second stacked section are provided with an insulating connection module therebetween, and the metal electrodes in the first stacked section and the second stacked section are externally connected with an integrated circuit experiment board;

a first transport inlet tube and a first transport outlet tube are respectively arranged at two ends of the stacked region, wherein an input end of the first transport inlet tube is communicated with an outlet port of the unipolar charging device, and an output end of the first transport outlet tube is communicated with an inlet port of the nanoparticle electrical mobility size classification device.

5 . The system according to claim 1 , wherein the nanoparticle electrical mobility size classification device comprises a fixed electric field and a fixed flow field,

the fixed electric field is provided through an upper electrode plate and a lower electrode plate sequentially arranged along the particle inlet direction, the upper electrode plate is parallel to the lower electrode plate, and the upper electrode plate and the lower electrode plate are spaced apart to form a sheath gas channel which acts as an electrostatic classification region;

the upper electrode plate and the lower electrode plate are respectively provided with a slit, the slit of the upper electrode plate is externally communicated with an aerosol inlet, the slit of the lower electrode plate serves as an aerosol outlet, and the upper electrode plate is externally connected with a third power supply;

the fixed flow field comprises a sheath gas flow closed loop containing the sheath gas channel, an inlet of the sheath gas channel is provided with a sheath gas inlet, and along the sheath gas flow closed loop excluding the sheath gas channel, and in a direction away from the sheath gas inlet, a second particle filter, a temperature and humidity sensor, a sheath gas cooling device and a circulating blower are sequentially arranged.

6 . The system according to claim 1 , wherein the second coupling transport device comprises an ion flight chamber, an insulating coupler, and a stainless-steel coupler sequentially arranged from inside to outside;

the ion flight chamber and the insulating coupler are fastened to a lower electrode plate of the nanoparticle electrical mobility size classification device, and an inlet port of the ion flight chamber is coaxial with an outlet port of the nanoparticle electrical mobility size classification device;

the stainless-steel coupler is connected with an inlet port of the mass spectrometer;

an outlet port of the ion flight chamber is coaxial with the inlet port of the mass spectrometer, and the ion flight chamber is further provided with a number concentration sampling port which is communicated with the aerosol number concentration measuring device.

7 . The system according to claim 1 , wherein the system control device comprises a first data acquisition card, a second data acquisition card, and a controller module,

the first data acquisition card is configured to collect chemical composition data measured by the mass spectrometer,

the second data acquisition card is configured to collect particle size information and number concentration data of the nanoparticles measured by the aerosol number concentration measuring device, and

the controller module obtains the number concentration and the chemical composition information of the nanoparticles with different particle sizes through a time-matching technique.

8 . The system according to claim 2 , further comprising one or more of the following:

A11) in the unipolar charging device, an inlet tube is communicated with the core sampling tube;

A12) in the unipolar charging device, an axial length of an inner tube is greater than an axial length of the inlet tube extending into the tube body;

A13) in the unipolar charging device, an axial spacing distance between the end of the inner tube adjacent to an outlet tube and the end of the outlet tube extending into the tube body is 9-11 mm;

A14) in the unipolar charging device, a vertical distance between the end of the inner tube adjacent to the outlet tube and dielectric barrier discharge electrodes is in a range of 9-11 mm;

A15) in the unipolar charging device, a vertical distance between ion trapping electrodes and the end of the outlet tube extending into the tube body is in a range of 9-11 mm;

A16) in the unipolar charging device, an inert gas is introduced through a discharge gas inlet, and the inert gas is helium;

A17) in the unipolar charging device, the dielectric barrier discharge electrodes are externally connected with a first power supply;

A18) in the unipolar charging device, the ion trapping electrodes are externally connected with a second power supply;

A21) in the first coupling transport device, an input end of a first transport inlet tube is in communication with an outlet port of the unipolar charging device, and an output end of the first transport outlet tube is in communication with an aerosol inlet of the nanoparticle electrical mobility size classification device;

A22) in the first coupling transport device, an integrated circuit experiment board comprises multiple resistors connected in serial, wherein the number of the resistors is the same as that of metal electrodes, and each of the resistors is connected with a corresponding metal electrode; one end of an integrated circuit experiment board is connected with the nanoparticle electrical mobility size classification device, and the other end of the integrated circuit experiment board is connected with the unipolar charging device and grounded;

A31) in the nanoparticle electrical mobility size classification device, an aerosol inlet is communicated with the first coupling transport device, and an aerosol outlet is communicated with the second coupling transport device;

A32) in the nanoparticle electrical mobility size classification device, a thickness of an upper electrode plate and a lower electrode plate is in a range of 0.1-1 cm;

A33) in the nanoparticle electrical mobility size classification device, a length of the upper electrode plate and the lower electrode plate that form a sheath gas channel is in a range of 20-30 cm, and a width of the upper electrode plate and the lower electrode plate that form the sheath gas channel is in a range of 3-5 cm;

A34) in the nanoparticle electrical mobility size classification device, a horizontal distance between a slit of the upper electrode plate and a slit of the lower electrode plate is in a range of 3-5 cm;

A35) in the nanoparticle electrical mobility size classification device, a width of the slit of the upper electrode plate for allowing aerosol to enter is in a range of 0.5-0.7 mm, and a width of the slit of the lower electrode plate for allowing aerosol to exit is in a range of 0.1-0.2 mm;

A36) in the nanoparticle electrical mobility size classification device, an inlet of the sheath gas channel which enables the sheath gas to enter an electrostatic classification region between the upper electrode plate and the lower electrode plate is a converging frustum, and the angle between the wall of the inlet of the sheath gas channel and the central axis of the sheath gas channel is in a range of 25-35°; an outlet of the sheath gas channel which enables the sheath gas to exit the electrostatic classification region between the upper electrode plate and the lower electrode plate is a diverging frustum, and the angle between the wall of the outlet of the sheath gas channel and the central axis of the sheath gas channel is in a range of 25-35°;

A41) in the second coupling transport device, an inlet of an ion flight chamber is coaxial with the aerosol outlet of the nanoparticle electrical mobility size classification device, and the inlet of the ion flight chamber is communicated with the aerosol outlet of the nanoparticle electrical mobility size classification device with the same inner diameter;

A42) in the second coupling transport device, the ion flight chamber is a particle transport tube, and the inner diameter of the ion flight chamber is in a range of 0.5-2 mm;

A43) in the second coupling transport device, a distance between the outlet of the ion flight chamber and an inlet of the mass spectrometer is in a range of 0.5-1.0 cm;

A44) in the second coupling transport device, a number concentration sampling port is located at a radial position of the ion flight chamber.

9 . A method for analyzing the size distribution and chemical composition of neutral clusters below 3 nm, using the system according to claim 1 , comprising:

1) setting a total flow rate and a core sampling flow rate in the sampling device, introducing nanoparticles into a main sampling tube of the sampling device, keeping the nanoparticles in a laminar flow state in a core sampling tube, and then transporting the nanoparticles to the unipolar charging device through a core sampling flow;

2) setting a discharge gas flow rate, a first power voltage, and a second power voltage in the unipolar charging device, forming a bipolar ion stream through the excitation of discharge gas molecules in a discharge gas under the action of the first power voltage, removing ions of one polarity from the bipolar ion stream to obtain a unipolar ion stream under the action of the second power voltage, enabling the unipolar ion stream to mix and collide with nanoparticles carried by the core sampling flow to obtain charged nanoparticles, and transporting the charged nanoparticles to the first coupling transport device;

3) reducing electrostatic loss of the charged nanoparticles by the first coupling transport device, and then transporting the charged nanoparticles to the nanoparticle electrical mobility size classification device;

4) setting a sheath gas flow rate and a third power voltage in the nanoparticle electrical mobility size classification device, performing classification of the charged nanoparticles in an electrostatic classification region between an upper electrode plate and a lower electrode plate under the action of a fixed flow field and an electric field formed by the third power voltage, and transporting the nanoparticles with a desired target electrical mobility size to the second coupling transport device;

5) transporting selected nanoparticles in the second coupling transport device respectively to the mass spectrometer and the aerosol number concentration measuring device for simultaneous measurement, determining the chemical compositions of the nanoparticles under a fixed mass spectrometry sampling flow rate in the mass spectrometer, and determining the number concentration of the nanoparticles in the aerosol number concentration measuring device under a fixed sampling flow rate;

6) performing matching among the particle size, number concentration, and chemical composition information of the nanoparticles by the system control device to obtain the number concentration and chemical composition information of the nanoparticles with different particle sizes.

10 . The method according to claim 9 , comprising one or more of the following:

B1) in step 1), a ratio of the total flow rate to the core sampling flow rate is no less than 5;

B2) in step 1), the core sampling flow rate is in a range of 5-10 L/min;

B3) in step 2), the discharge gas flow rate is in a range of 0.5-1.0 L/min;

B4) in step 2), the first power voltage is in a range of 2.0-3.5 kV;

B5) in step 2), the second power voltage is in a range of 1.0-1.3 kV;

B6) in step 2), a frequency of the unipolar charging device is in a range of 9-13 kHz;

B7) in step 2), when the charged nanoparticles are transported to the first coupling transport device, the bypass flow rate at an outlet of the unipolar charging device is in a range of 3-5 L/min;

B8) in step 3), in the first coupling transport device, a flow rate of the input charged nanoparticles is in a range of 3.0-5.0 L/min

B9) in step 4), the sheath gas flow rate is in a range of 300-1500 L/min;

B10) in step 4), the third power voltage is in a range of −10-10 kV;

B11) in step 4), a particle size resolution of 1.47-nm particles is greater than 80;

B12) in step 5), the mass spectrometry sampling flow rate is 0.8 L/min;

B13) in step 5), the aerosol sampling flow rate is in a range of 1-2.2 L/min.

11 . The system according to claim 8 , wherein in A31) the aerosol inlet is in communication with the first transport outlet tube.