Method for analyzing micro-nano plastic in atmosphere and mixed state of micro-nano plastic based on biological aerosol single particle mass spectrometer

Abstract

The invention belongs to the technical field of environmental monitoring, and particularly relates to a method for analyzing micro-nano plastic in atmosphere and a mixed state of the micro-nano plastic based on a biological aerosol single-particle mass spectrometer. The invention discloses a method for analyzing micro-nano plastic in atmosphere and a mixed state of the micro-nano plastic based on a biological aerosol single-particle mass spectrometer. The micro-nano plastic and the mixed state of the micro-nano plastic and other components in the atmosphere can be accurately monitored on line from the angle of a single particle. It is determined that 91 [C7H7 +], 104 [C8H8 +] and 115 [C9H7 +] can serve as characteristic ions (tracer ions) of PS MNPs, meanwhile, the relative peak area of 104 [C8H8 +] is limited to be larger than or equal to 0.005, and particles with PS MNPs characteristics can be successfully distinguished from environmental aerosol.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental monitoring, and in particular relates to an analysis method for micro-nano plastics and their mixed states in the atmosphere based on a bioaerosol single particle mass spectrometer. Background Art

[0002] Micro- and nanoplastics (MNPs) are a prominent emerging global pollution problem. Atmospheric micro- and nanoplastics (AMNPs) can act as carriers of other pollutants in the atmosphere, such as acting as a reaction interface in aerosols, altering their physical and chemical properties and, consequently, influencing the environmental behavior of pollutants in the atmosphere. However, existing detection methods struggle to characterize MNPs and their mixing states (and thus, their interactions) in real time.

[0003] Current research on atmospheric micro- and nanoplastics primarily focuses on offline sampling and analysis, with virtually no research utilizing online sampling and analysis. The main analytical methods for identifying and quantifying MNPs include visual inspection, spectroscopy, and mass spectrometry (O'brien et al., 2023; Wang et al., 2021). Visual inspection, involving stereomicroscopes and fluorescence microscopes (Li et al., 2023), can determine the particle morphology, size, color, and number of microplastics and is widely used for large microplastics (1-5 mm) (Lin et al., 2020). This method is simple but primitive (Lin et al., 2020), highly subjective, and fails to provide any chemical information about the MNPs. This method can lead to overestimation or underestimation of microplastic abundance, depending on the quality of the microscope and the particle shape, color, and size of the microplastics. Among spectroscopic methods, Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy are currently the mainstream techniques for determining the number and concentration of MNPs, and can also provide information on the morphology, size, and chemical composition of microplastics (microplastic species). The smallest particle that can be detected by FTIR is 20 μm, and the smallest particle that can be detected by Raman spectroscopy is 10 μm (Lin et al., 2020). However, these techniques are time-consuming and labor-intensive in identifying micro- and nano-plastics (Mai et al., 2018; Primpke et al., 2020; Xuet al., 2020; Fan et al., 2022). In addition, the experimental results are easily affected by complex media. Lin et al., 2020 ).

[0004] Among mass spectrometry (MS), pyrolysis gas chromatography-mass spectrometry (Pyr-GC-MS) and TDS-GC-MS are two of the most popular analytical methods for measuring the mass concentration of MNPs (Chen et al., 2024). Studies have also utilized pyrolysis matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF MS) (Lin et al., 2020). These mass spectrometry methods can determine the type and mass concentration of MNPs of any size (Lykkemark et al., 2024). However, because they are all offline analyses, they require various pretreatments and experimental calibrations, which can introduce errors into the results and are complex and time-consuming. A literature search revealed only one study (Niu et al., 2024) that reported on the online identification and quantification of micro- and nanoplastics (PSMNPs) in the atmosphere using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). This is already a major advancement in the field of quantitative identification of atmospheric micro-nanoplastics. However, given that this method currently uses a full-sample analysis method, micro-nanoplastics account for a very small proportion in the atmosphere, and aerosols are relatively complex, when analyzed by a full sample, the amount of tracer ions of the target object may be overestimated, and the mixing state and particle size of individual particles cannot be observed. Summary of the Invention

[0005] In response to the above-mentioned problems existing in the prior art, the present invention provides an analysis method for micro-nano plastics and their mixed state in the atmosphere based on a bioaerosol single particle mass spectrometer, which can accurately monitor micro-nano plastics and their mixed state with other components in the atmosphere online.

[0006] To achieve the above-mentioned purpose, the technical solution provided by the present invention is as follows: This application provides a method for analyzing micro-nanoplastics and their mixed states in the atmosphere based on a bioaerosol single particle mass spectrometer, including: Obtain standard mass spectra of micro-nanoplastics; A bioaerosol single particle mass spectrometer is used to sample and analyze the atmosphere at the test point to obtain the particle size and mass spectrum information of micro-nanoplastics in the atmosphere at the test point; According to the characteristic ion extraction method, the number concentration, relative number concentration information and characteristic ion mass spectrum of micro-nano plastics in the atmosphere of the test point are obtained from the particle size and mass spectrum information of micro-nano plastics in the atmosphere of the test point; By comparing the standard mass spectrum with the mass spectrum of characteristic ions of micro-nano plastics, the mixed state of micro-nano plastics in the atmosphere was obtained.

[0007] Optionally, obtaining the mixing state of micro-nano plastics in the atmosphere by comparing the standard mass spectrum with the mass spectrum of characteristic ions of micro-nano plastics includes: Observe whether there are new peaks in the mass spectrum of characteristic ions of micro-nano plastics compared with the standard mass spectrum; When a new peak appears, the type of ion can be judged by the position of the new peak, and it can be obtained that the type of ion interacts with the micro-nano plastic.

[0008] Optionally, the micro-nano plastic is polystyrene micro-nano plastic.

[0009] Optionally, the characteristic ions of the polystyrene micro-nano plastic include: 91 [C7H7 + ]、 104 [C8H8 + ]and 115 [C9H7 + ] one or more.

[0010] Optionally, the method of obtaining the number concentration, relative number concentration information and characteristic ion mass spectrum of the micro-nano plastics in the atmosphere at the test point based on the particle size and mass spectrum information of the micro-nano plastics in the atmosphere at the test point according to the characteristic ion extraction method includes: by 91 [C7H7 + ]、 104 [C8H8 + ]and 115 [C9H7 + ] as the characteristic ion, and 104 [C8H8 + ] The relative peak area is greater than or equal to 0.005, and the number concentration, relative number concentration information and micro-nano plastic characteristic ion mass spectrum of the micro-nano plastic in the atmosphere of the test point are obtained from the particle size and mass spectrum information of the micro-nano plastic in the atmosphere of the test point.

[0011] Optionally, obtaining a standard mass spectrum of micro-nano plastics includes: aerosolizing an aqueous solution of standard polystyrene, performing sampling and analysis using a bioaerosol single particle mass spectrometer, and obtaining a standard mass spectrum of micro-nano plastics.

[0012] Alternatively, a polystyrene standard aqueous solution is aerosolized to a particle size of 500 nm.

[0013] Optionally, the laser energy E used for ionization of the bioaerosol single particle mass spectrometer satisfies: 301.87 ± 6.12 μJ ≤ E ≤ 635.61 ± 33.11 μJ.

[0014] Optionally, the method further includes optimizing the particle size of the aerosolized aqueous solution of the standard polystyrene sample and the laser energy used for ionization of the bioaerosol single particle mass spectrometer, and then obtaining a standard mass spectrum of the micro-nano plastic at the optimal particle size and optimal laser energy; the optimization method includes: Aerosolized polystyrene was sampled and analyzed at different bioaerosol single-particle mass spectrometer ionization laser energies. The ionization laser energy corresponding to the case with high integrity and high hit rate was selected as the optimal laser energy. Under the optimal laser energy of the bioaerosol single-particle mass spectrometer, aqueous solution aerosols of standard polystyrene with different particle sizes were sampled and analyzed. The ratio of the total relative peak area of ​​the characteristic ion to the total relative peak area of ​​all fragment ions and the case with a high strike rate were obtained by screening, and the corresponding aerosol particle size was taken as the optimal particle size.

[0015] Compared with the prior art, this application has at least the following beneficial effects:

[0016] The present invention has developed an analytical method for micro-nano plastics and their mixed state in the atmosphere based on a bioaerosol single-particle mass spectrometer, which can accurately monitor micro-nano plastics and their mixed state with other components in the atmosphere online from the perspective of a single particle.

[0017] Confirmed 91 [C7H7 + ], 104 [C8H8 + ]and 115 [C9H7 + ] can be used as the characteristic ion (tracer ion) of PS MNPs, while limiting 104 [C8H8 + ] has a relative peak area greater than or equal to 0.005, which can successfully distinguish particles with PS MNPs characteristics from ambient aerosols. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the experimental process setup in this application; (a) schematic diagram of the aerosol generation and collection process in the laboratory; (b) schematic diagram of the outdoor aerosol collection setup with sprayed standard samples;

[0019] Figure 2 Mass spectra of PS MNPs micro-nanoplastics at different laser energies;

[0020] Figure 3 Mass spectra of PS MNPs micro-nanoplastics at different particle sizes;

[0021] Figure 4Figures (a) and (b) show the effects of different laser energies and particle sizes on the detection of PS MNPs by Bio-SPAMS.

[0022] Figure 5 Figure (c) shows the mass spectrum of the standard PS MNPs.

[0023] Figure 6 Figure (d) shows the mass spectrum of nitro-polycyclic aromatic hydrocarbons under a laser energy of 0.5 mJ.

[0024] Figure 7 Figure (e) shows the mass spectrum of polycyclic aromatic hydrocarbons under a laser energy of 0.5 mJ.

[0025] Figure 8 Figure (f) shows the mass spectra of the standard PS MNPs and incense particles.

[0026] Figure 9 Figure (g) shows the mass spectra and particle size distribution of the standard PS MNPs and their mixture with inorganic salts.

[0027] Figure 10 Figure (h) shows the results of on-site detection of PS MNPs in ambient aerosols in Guangzhou based on Bio-SPAMS. (a-c) Changes in the peak areas of 91 [C7H7 + ]、 104 [C8H8 + ] and 115 [C9H7 + ] and the amount of PS MNPs detected over time; (d) mass spectrum of the characteristic PS MNPs detected in the yellow shaded area; (e) particle size distribution of the characteristic PS MNPs detected in the yellow shaded area. DETAILED DESCRIPTION

[0028] The application will be further described in detail below with reference to the accompanying drawings:

[0029] The experimental methods used in the embodiments of the application are all conventional methods unless otherwise specified.

[0030] The reagent materials used in this example can be purchased conventionally. The quantitative experiments involved in the embodiments were all set up with at least three repeated experiments, and the results were averaged.

[0031] The present application provides an analysis method for micro-nano plastics and their mixed states in the atmosphere based on a biological aerosol single-particle mass spectrometer, comprising: obtaining a standard mass spectrum of micro-nano plastics; using a biological aerosol single-particle mass spectrometer to sample and analyze the atmosphere at the test site to obtain the particle size and mass spectrum information of micro-nano plastics in the atmosphere at the test site. According to the characteristic ion extraction method, the number concentration, relative number concentration information and characteristic ion mass spectrum of micro-nano plastics in the atmosphere of the test point are obtained from the particle size and mass spectrum information of micro-nano plastics in the atmosphere of the test point; By comparing the standard mass spectrum with the mass spectrum of characteristic ions of micro-nano plastics, the mixed state of micro-nano plastics in the atmosphere was obtained.

[0032] In certain embodiments of the present invention, the method of obtaining the mixed state of micro-nano plastics in the atmosphere by comparing the standard mass spectrum with the mass spectrum of characteristic ions of micro-nano plastics includes: Observe whether there are new peaks in the mass spectrum of characteristic ions of micro-nano plastics compared with the standard mass spectrum; When a new peak appears, the type of ion can be judged by the position of the new peak, and it can be obtained that the type of ion interacts with the micro-nano plastic.

[0033] In certain embodiments of the present invention, the micro-nano plastic is polystyrene micro-nano plastic.

[0034] In certain embodiments of the present invention, the characteristic ions of the polystyrene micro-nano plastics include: 91 [C7H7 + ]、 104 [C8H8 + ]and 115 [C9H7 + ] one or more.

[0035] In certain embodiments of the present invention, the method of obtaining the number concentration, relative number concentration information, and characteristic ion mass spectrum of micro-nano plastics in the atmosphere at the test point based on the particle size and mass spectrum information of micro-nano plastics in the atmosphere at the test point according to the characteristic ion extraction method includes:

[0036] by 91 [C7H7 + ]、 104 [C8H8 + ]and 115 [C9H7 + ] as the characteristic ion, and 104 [C8H8 + ] The relative peak area is greater than or equal to 0.005, and the number concentration, relative number concentration information and micro-nano plastic characteristic ion mass spectrum of the micro-nano plastic in the atmosphere of the test point are obtained from the particle size and mass spectrum information of the micro-nano plastic in the atmosphere of the test point.

[0037] In certain embodiments of the present invention, obtaining a standard mass spectrum of micro-nano plastics includes: aerosolizing a standard polystyrene aqueous solution, performing sampling and analysis using a bioaerosol single particle mass spectrometer, and obtaining a standard mass spectrum of micro-nano plastics.

[0038] In some embodiments of the present application, the standard polystyrene solution is aerosolized to a particle size of 500 nm.

[0039] In some embodiments of the present application, the laser energy E used for ionization by the bioaerosol single particle mass spectrometer satisfies: 301.87 ± 6.12 μJ ≤ E ≤ 635.61 ± 33.11 μJ.

[0040] In some embodiments of the present application, the particle size of the aerosolized water solution of the standard polystyrene and the laser energy used for ionization by the bioaerosol single particle mass spectrometer are optimized, and then under the optimal particle size and the optimal laser energy, a standard mass spectrum of the micro-nano plastic is obtained; the optimization method comprises:

[0041] Under different ionization laser energies of the bioaerosol single particle mass spectrometer, aerosolized polystyrene is sampled and analyzed, and through screening, a case with high completeness and strike rate in the mass spectrum is obtained, and the corresponding ionization laser energy under the case is taken as the optimal laser energy; Under the optimal ionization laser energy of the bioaerosol single particle mass spectrometer, aerosolized water solutions of standard polystyrene of different particle sizes are sampled and analyzed, and through screening, a case with high ratio of total relative peak area of characteristic ions to total relative peak area of all fragment ions and strike rate is obtained, and the corresponding aerosol particle size under the case is taken as the optimal particle size.

[0042] Since the mass spectrum with laser as ionization source cannot obtain a standard database at present, by optimizing the detection conditions of the bioaerosol single particle mass spectrometer, a complete standard PS MNP mass spectrum can be obtained.

[0043] Embodiment

[0044] The present application mainly uses a bioaerosol single particle mass spectrometer (Bio-SPAMS, Nanjing Fengshun Intelligent Technology Co., Ltd.) for laboratory experiments and environmental aerosol sampling. Bio-SPAMS is developed based on a single particle aerosol mass spectrometer (SPAMS) technology platform, mainly composed of control acquisition software, a sampling system, a particle size measurement system, an ionization system and a mass spectrometry system, which can realize real-time detection of particle size and chemical component information of aerosol single particles, and is widely used in the study of aerosol aging and mixing state.

[0045] This instrument's analytical system primarily uses an aerodynamic lens to focus aerosol particles into a particle beam, which is then introduced into a vacuum chamber. The focused particle beam first passes through two 532 nm (Nd:YAG) laser beams for real-time aerodynamic size measurement (based on light scattering principles). A timing control module then precisely calculates the particle's trajectory. When the target particle reaches the center of the ionization zone, a 266 nm ultraviolet pulsed Nd:YAG laser is emitted, simultaneously generating positive and negative ion fragments through a laser ablation ionization process. The ionized products are then detected by a dual-polarity time-of-flight mass spectrometer (dual TOF-MS), achieving high-resolution mass-to-charge ratio (m / z) characterization with microsecond temporal resolution, enabling measurement of the different chemical components within a single particle.

[0046] To ensure data quality, the Bio-SPAMS instrument was precalibrated for particle size and mass spectrometry before the experiment and sampling. The sampling flow rate was set to 0.35 L / min, and the ionization laser energy was adjusted under exploratory conditions. The chemical composition and size of single particles collected by SPAMS were analyzed using MATLAB and COCO V1.3 (Computational Continuation Core 1.3).

[0047] A high-resolution time-of-flight (HR-TOF)-AMS (Aerodyne Research Inc., USA) was used to simultaneously acquire standard samples with the Bio-SPAMS for comparison. The HR-TOF-AMS was operated in V mode with a sampling flow rate of 1.43 cm³·s⁻¹ and a vaporization temperature of approximately 600°C. The acquired HR-TOF-AMS data were analyzed using the Igor-based software packages ToolkitSOUIRREL v1.59D and PIKA v1.19D (https: / / cires1.colorado.edu / jimenez-group / wiki / index.php?title=ToF-AMS_Main).

[0048] In this application, a constant-output nebulizer (TSI, Model 9302) was used to aerosolize an aqueous solution of 500 nm monodisperse PS MNPs (Thermo Scientific, 8% mass fraction) and simultaneously collected and analyzed by Bio-SPAMS and HR-ToF-AMS. Sampling was stopped after Bio-SPAMS acquired 5000 mass spectra. Figure 1 As shown in a.

[0049] 1. Optimization of laser energy and particle size to obtain a standard mass spectrum

[0050] Six different energy levels (300 μJ – 1550 μJ) were tested under the condition that the particle size of the standard PS MNPs (polystyrene micro-nanoplastics, purchased from Thermo Fisher Scientific) was 500 nm. Effect of particle size: Based on the optimized laser energy (about 380 μJ), the particle size of the standard PS MNPs with 6 particle sizes ranging from 0.3 μm to 2 μm (ThermoScientific, 8 wt %) was tested. The specific experiment included: using a constant output nebulizer to aerosolize the aqueous solution containing the standard monodisperse PS MNPs particles, and then using Bio-SPAMS for collection and analysis ( Figure 1 a). To determine the possibility of Bio-SPAMS detection of PSMNPs, Bio-SPAMS and HR-ToF-AMS were used to collect and analyze the mass spectra. Figure 5 (Based on C8H8 + relative intensity calculated from the relative peak area or mass concentration).

[0051] Laser energy optimization:

[0052] 500 nm PS MNPs were detected at six laser energy levels (300 μJ – 1550 μJ, see Table 1), and 5000 mass spectra were collected at each energy level. The average mass spectra corresponding to different laser energies are detailed in Figure 2 The effects of different laser energies on the detection of PS MNPs are shown in Figure 4 a.

[0053] Table 1 Six types of laser energy

[0054]

[0055] The results showed that the signal intensity of macromolecular fragment ions decreased with the increase of laser energy in positive ion mode, e.g. 91 [C7H7 + ]、 104 [C8H8 + ]and 115 [C9H7 + ]; In negative ion mode, the types of fragment ions increased, but the main ions (such as m / z 25 [C2H - ], 49 [C4H5 - ]) also significantly weakened ( Figure 4 a and Figure 2This phenomenon is consistent with the results reported by Silva and Prather (2000), which indicated that higher laser energy would promote the further fragmentation of large ions into small ion species. Therefore, lower laser energy is more conducive to the observation of large fragment ions, which is crucial for the identification of target compounds, and also indicates that the laser energy in the lower range is more likely to obtain a complete mass spectrum.

[0056] In addition, laser energy not only affects the mass spectral characteristics of particles, but also affects the hit rate of collecting particles. When the laser energy is in the range of 635.61 ± 33.11 μJ ~ 1166.92 ± 15.74 μJ, the hit rate reaches a peak of about 96.89% ~ 98.72% (Fig. 4b). Figure 4 a). However, when the laser energy exceeds 635.61 ± 33.11 μJ, the signals of main fragment ions such as C7H7⁺, C8H8⁺, C9H7⁺ almost disappear, as shown in Fig. 4a and Fig. 4b. Figure 4 aand Figure 2 Therefore, in order to ensure the existence of main large fragment ions (large relative mass) while the hit rate is high, the detection laser energy (E) is set to be greater than 301.87 ± 6.12 μJ and less than 635.61 ± 33.11 μJ. The laser energy in this range can ensure the hit rate during the collection process, while minimizing the excessive fragmentation of particle ions, thereby preserving the characteristic fingerprint of PS MNPs.

[0057] Particle size optimization:

[0058] Within the optimized laser energy range (301.87 ± 6.12 μJ to 635.61 ± 33.11 μJ), six different particle sizes of PS MNPs (300 nm, 500 nm, 700 nm, 1 μm, 1.4 μm and 2 μm) were detected using Bio-SPAMS. The results confirmed that Bio-SPAMS can effectively detect PS MNPs with a particle size range of 0.3 μm to 2 μm, and can detect main fragment ions (such as C2H⁻, C4H5⁻, C3H3⁺, C4H3⁺, C5H5⁺, C6H5⁺, C7H7⁺, C8H8⁺ and C9H7⁺), as shown in Fig. 5a and Fig. 5b. Figure 5 and Figure 4 a.

[0059] However, there are differences in the relative peak areas of main fragment ions under different particle sizes (see Fig. 5a and Fig. 5b, Figure 3 and Figure 4 b, Figure 4In b, MIA: main ion abundance, which represents the sum of the relative peak areas of the main ions. TIA: total ion abundance, which represents the sum of the relative peak areas of the total ions. MIA / TIA: the ratio of main ion abundance to total ion abundance. MIA / TIA can quantitatively evaluate the proportion of the main ion in the total ionization products). The relative peak areas of C2H⁻ of 500 nm PS MNPs and 700 nm PS MNPs are significantly larger, while the relative peak areas of C8H8⁺ of 300 nm PS MNPs and 500 nm PS MNPs are larger. In addition, we also calculated the ratio of the total relative peak area of ​​the main fragment ions to the total relative peak area of ​​all fragment ions (MIA / TIA) to comprehensively evaluate the detection efficiency of the target. The results showed that the MIA / TIA ratio of 500 nm PS MNPs was the highest (51.54%), indicating that its detection efficiency of the main fragment ions was the best. At the same time, 500 nm PS MNPs also showed the highest hit rate of 80.88% ( Figure 4 b). These results indicate that the particle size of PS MNPs with a diameter of 500 nm achieves a good balance between the detection efficiency and the hit rate of the main fragment ions, and is the optimal particle size for experimental detection.

[0060] Therefore, the optimized conditions for detecting PS MNPs using Bio-SPAMS are as follows: the laser energy is set between greater than 301.87 ± 6.12 μJ and less than 635.61 ± 33.11 μJ to ensure the presence of major fragment ions while maintaining a high hit rate; when the particle size ranges from 500 nm to 700 nm, the particles have a high hit rate while ensuring high detection efficiency of the complete mass spectrum and major fragment ions.

[0061] When Bio-SPAMS uses 384.24 ± 5.68 μJ laser energy and a particle size of 500 nm, the mass spectrum of PS MNPs obtained ( Figure 5 ) presents a hydrocarbon ion (n[C x H y ± ]) is the main fragmentation spectrum, the main ion fragments include: m / z25[C2H - ]、49[C4H5 - ]、39[C3H3 + ]、51[C4H3 + ]、63[C5H5 + ]、77[C6H5 + ]、91[C7H7 + ]、104[C8H8 + ] and 115[C9H7 +], which is highly consistent with the aromatic-aliphatic main chain structure of polystyrene.

[0062] Compared with the detection results of HR-ToF-AMS ( Figure 5 ), the positive ions of PS MNPs detected by Bio-SPAMS are not only different from the same type of ions detected by HR-ToF-AMS (m / z 39[C3H3 + ]、51[C4H3 + ]、63[C5H5 + ]、77[C6H5 + ]、91[C7H7 + ]、104[C8H8 + ]、115[C9H7 + ] and 193[C 15 H 13 + ]) and is consistent with the previous research results of Niu et al. (2024) The mass spectral characteristics of PS-MNPs are consistent with those of styrene in the NIST database, confirming that both platforms can identify the characteristic spectral fingerprints of PS-MNPs.

[0063] However, Bio-SPAMS in negative ion mode captured aliphatic fragments (m / z 25 [C2H - ]、49[C4H5 - ]), this difference highlights the advantage of Bio-SPAMS bipolar detection in capturing complex components. Both methods stably detected m / z 104 (104[C8H8 + ]), but the relative intensity of this peak was higher in Bio-SPAMS. These results indicate that Bio-SPAMS can retrieve PS-MNPs by characteristic ions. Figure 5 The mass spectrum obtained by Bio-SPAMS was obtained under optimized conditions and can be used as the standard mass spectrum (fingerprint) of PS MNPs.

[0064] 2. Determine the characteristic ions

[0065] Due to the complexity of environmental samples, it is impossible to detect all substances that interfere with the detection of PS MNPs using standard samples. Therefore, it is necessary to use literature research to statistically analyze the main fragments of various substances in aerosols and laboratory standards using single particle mass spectrometry. The results are compared with the results of standard PS MNPs to determine more optimized tracer ions for PS MNPs. The statistical results are shown in Table 2.

[0066] Table 2 Main ions of various substances based on single particle mass spectrometry (laboratory and environmental samples)

[0067]

[0068] Among them, the references are as follows: (3)Li, J. et al. Atmospheric deposition of microplastics in a ruralregion of North China Plain. Science of The Total Environment 2023, 877 , 162947. (4)Lin, Y. et al. Thermal fragmentation enhanced identification and quantification of polystyrene micro / nanoplastics in complex media. Talanta2020, 208, 120478. (5)Mai, L. et al. A review of methods for measuring microplastics inaquatic environments. (1614-7499 (Electronic)). (6)Mai, L. et al. A review of methods for measuring microplastics inaquatic environments. 2018, (1614-7499 (Electronic)). (7)Primpke, S. et al. Critical Assessment of Analytical Methods for the Harmonized and Cost-Efficient Analysis of Microplastics. 2020, 74 , 1012 -1047.

[0069] As shown in Table 2, compared with the main ion fragments of the standard PS MNPs, the ions that may interfere with the detection of PS MNPs mainly appear in OC, BB and PAH. 25 [C2H - ], 49 [C4H5 - ], 39 [K + ],51 [C4H3 + ], 63 [C5H5 + ]and 77 [C6H5 + ]. Studies have shown that due to organic carbon (OC) , Biomass Burning (BB) and polycyclic aromatic hydrocarbons (PAHs) The structures of organic components such as PEG and PEG are similar to those of PS MNPs, both of which contain benzene rings and thus produce similar ions. This proves that substances interfering with the detection of PS MNPs mainly come from substances with similar chemical structures.

[0070] Therefore, the above interfering ions and fragment ions are excluded. 91 [C7H7 + ], 104 [C8H8 + ]and 115 [C9H7 + ] may have the characteristics of the marker ions of PSMNPs. Under optimized conditions, laboratory experiments were conducted to detect 8 PAHs (see Table 3) and incense burning experiments to verify 91 [C7H7 + ], 104 [C8H8 + ]and 115 [C9H7 + ] can be used as a labeling ion for PS MNPs. The results showed that (e.g. Figure 6 , Figure 7 and Figure 8 shown), 91 [C7H7 + ], 104 [C8H8 + ]and 115 [C9H7 + ] do not appear simultaneously in the mass spectra of standard PAHs and burning incense ( Figure 6 , Figure 7 and Figure 8 ).therefore 91 [C7H7 + ], 104 [C8H8 + ]and 115 [C9H7 + ] can be used as a tracer ion to identify PS MNPs.

[0071] Table 3 Polycyclic aromatic hydrocarbons (PAH) and nitro PAH

[0072] Serial number category Serial number category 1 2-nitrofluorene 5 anthracene 2 9-nitroanthracene 6 pyrene 3 3-nitrofluoranthene 7 benz[a]anthracene 4 2,7-dinitrofluorene 8 benzo[a]pyrene

[0073] 3. Determination of the Mixed State of Micro-Nano Plastics

[0074] The mixed solution was aerosolized using a nebulizer and acquired using Bio-SPA-MS under optimized laser energy conditions to obtain particle size and mass spectral information. The mixed solution was prepared by mixing 500 nm PS MNPs with equal volumes of ammonium sulfate (AS, 8% by mass, 4 µl) and sodium nitrate (SN, 8% by mass, 4 µl) in ultrapure water.

[0075] The results are as follows Figure 9 (According to C8H8 + The relative peak areas and relative intensities obtained are shown in the mass spectrum of pure PS MNPs ( Figure 9 Compared with a), the nitrate and sulfate ion signals in the mass spectrum of the mixture are significantly enhanced ( Figure 9 b), indicating that these inorganic substances may be adsorbed on the surface of PS MNPs particles. In addition, the particle size distribution of the mixture ( Figure 9 b) shows a wider range, with most particles larger than 500 nm. The increase in particle size suggests that PS MNPs may be in a state of surface adsorption or mutual encapsulation with sulfate and nitrate. These phenomena demonstrate that Bio-SPAMS is capable of detecting the mixed state of PS MNPs.

[0076] 4. Atmospheric detection test

[0077] The sampling site was located in Huangpu District, Guangzhou, a megacity with a large permanent population and intensive plastic consumption. Atmospheric aerosol samples were collected over a three-day period. During the sampling period, 500 nm PS MNPs were injected into the air three times, each lasting 5 minutes. The injection port was 10 cm away from the sampling port (see Figure 1 b) The sampling port is about 9 meters from the ground.

[0078] In this study, within the optimized laser energy range, Bio-SPAMS was used to collect sample data from April 15 to 18, 2024. During the sampling period, standard 500 nm PS MNPs were sprayed into the atmosphere at irregular intervals, and a total of 122,348 mass spectra were collected. 91 [C7H7 + ], 104 [C8H8 + ]and 115 [C9H7 + ] as a qualitative fragment ion, limiting 104 [C8H8 + ]The relative peak area is greater than or equal to 0.005 , 3198 particles with PS MNPs characteristics were successfully identified, accounting for 2.614% of the total number of particles. Figure 10 As shown in a-10c (the purple shaded area is the 5-minute period when the standard PS MNPs are sprayed into the atmosphere, and the yellow shaded area is the period when the ambient aerosol is collected), the highest peak in the number of particles with PS MNP characteristics is detected during the period when the standard sample is sprayed into the air, and there is a significant correlation ( Figure 10 a-10c), while all the atmospheric 91 [C7H7 + ], 104 [C8H8 + ]and 115 [C9H7 + The change in the peak area of ​​] is consistent with the change in the number of particles with PS MNP characteristics, where 104 [C8H8 + ] is most consistent with the change in the peak area of ​​the standard sample spraying period and the change in the number of particles with PS MNPs characteristics, verifying that these tracer ions can extract particles with PS MNPs characteristics in complex environmental matrices.

[0079] like Figure 10 a-10c The yellow shaded area shows a total of 51,045 unlabeled PS MNPs ambient aerosol samples collected (27.5 hours, Figure 10 a-10c yellow area), the results showed that PS MNPs accounted for approximately 1.04% of the total detected particles ( Figure 10 d-10e), the particle size is mainly concentrated in the range of 0.3-0.8 μm ( Figure 10 e). 76.42% of all PS MNPs showed significant nitrate and sulfate signals ( 97 [HSO4 1- ], 96 [SO4 2- ], 81 [HSO3 1- ], 80 [SO3 2- ] and m / z 62 [NO3 - ], 46 [NO2 - ], 30 [NO - ]), of which the relative peak areas of nitrate and sulfate were 14.30% and 4.06%, respectively ( Figure 10 d), which indicates that there is a certain interaction between PS MNPs and atmospheric pollutants.

Claims

1. A method for analyzing micro-nano plastics and their mixed states in the atmosphere based on a bioaerosol single particle mass spectrometer, characterized in that: include: Obtain standard mass spectra of micro-nanoplastics; A bioaerosol single particle mass spectrometer is used to sample and analyze the atmosphere at the test point to obtain the particle size and mass spectrum information of micro-nanoplastics in the atmosphere at the test point; According to the characteristic ion extraction method, the number concentration, relative number concentration information and characteristic ion mass spectrum of micro-nano plastics in the atmosphere of the test point are obtained from the particle size and mass spectrum information of micro-nano plastics in the atmosphere of the test point; By comparing the standard mass spectrum with the mass spectrum of characteristic ions of micro-nano plastics, the mixed state of micro-nano plastics in the atmosphere was obtained.

2. The method for analyzing micro-nano plastics and their mixed states in the atmosphere based on a bioaerosol single particle mass spectrometer according to claim 1, characterized in that: The method of obtaining the mixed state of micro-nano plastics in the atmosphere by comparing the standard mass spectrum with the mass spectrum of characteristic ions of micro-nano plastics includes: Observe whether there are new peaks in the mass spectrum of characteristic ions of micro-nano plastics compared with the standard mass spectrum; When a new peak appears, the type of ion can be judged by the position of the new peak, and it can be obtained that the type of ion interacts with the micro-nano plastic.

3. The method for analyzing micro-nano plastics and their mixed states in the atmosphere based on a bioaerosol single particle mass spectrometer according to claim 1, characterized in that: The micro-nano plastic is polystyrene micro-nano plastic.

4. The method for analyzing micro-nano plastics and their mixed states in the atmosphere based on a bioaerosol single particle mass spectrometer according to claim 3, characterized in that: The characteristic ions of the polystyrene micro-nano plastics include: 91 [C7H7 + ]、 104 [C8H8 + ]and 115 [C9H7 + ] one or more.

5. The method for analyzing micro-nano plastics and their mixed states in the atmosphere based on a bioaerosol single particle mass spectrometer according to claim 1, characterized in that: The method of extracting characteristic ions, obtaining the number concentration, relative number concentration information and characteristic ion mass spectrum of micro-nano plastics in the atmosphere at the measured point from the particle size and mass spectrum information of the micro-nano plastics in the atmosphere at the measured point, includes: by 91 [C7H7 + ]、 104 [C8H8 + ]and 115 [C9H7 + ] as the characteristic ion, and 104 [C8H8 + ] The relative peak area is greater than or equal to 0.005, and the number concentration, relative number concentration information and micro-nano plastic characteristic ion mass spectrum of the micro-nano plastic in the atmosphere of the test point are obtained from the particle size and mass spectrum information of the micro-nano plastic in the atmosphere of the test point.

6. The method for analyzing micro-nano plastics and their mixed states in the atmosphere based on a bioaerosol single particle mass spectrometer according to claim 3, characterized in that: The method of obtaining a standard mass spectrum of micro-nano plastics includes: aerosolizing a standard polystyrene aqueous solution, performing sampling and analysis using a bioaerosol single particle mass spectrometer, and obtaining a standard mass spectrum of micro-nano plastics.

7. The method for analyzing micro-nano plastics and their mixed states in the atmosphere based on a bioaerosol single particle mass spectrometer according to claim 6, characterized in that: The polystyrene standard aqueous solution was aerosolized to a particle size of 500 nm.

8. The method for analyzing micro-nano plastics and their mixed states in the atmosphere based on a bioaerosol single particle mass spectrometer according to claim 6, characterized in that: The laser energy E used for ionization of the bioaerosol single particle mass spectrometer satisfies: 301.87 ± 6.12 μJ≤E≤635.61 ± 33.11 μJ.

9. The method for analyzing micro-nano plastics and their mixed states in the atmosphere based on a bioaerosol single particle mass spectrometer according to claim 6, characterized in that: The method also includes optimizing the particle size of an aerosolized aqueous solution of a standard polystyrene sample and the laser energy used for ionization of a bioaerosol single particle mass spectrometer, and then obtaining a standard mass spectrum of micro-nano plastics at the optimal particle size and optimal laser energy; the optimization method includes: Aerosolized polystyrene was sampled and analyzed at different bioaerosol single-particle mass spectrometer ionization laser energies. The ionization laser energy corresponding to the case with high integrity and high hit rate was selected as the optimal laser energy. Under the optimal laser energy of the bioaerosol single-particle mass spectrometer, aqueous solution aerosols of standard polystyrene with different particle sizes were sampled and analyzed. The ratio of the total relative peak area of ​​the characteristic ion to the total relative peak area of ​​all fragment ions and the case with a high strike rate were obtained by screening, and the corresponding aerosol particle size was taken as the optimal particle size.

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