GB/T 35099-2018 in English

1. Overview and significance of the standard

GB/T 35099-2018 standard specifies the method of using scanning electron microscope (SEM) and energy spectrometer (EDS) to observe the single particle morphology of fine particles in ambient air, qualitatively analyze elements, and classify ambient air particulate matter.

This technology combines the high-resolution imaging capability of SEM and the elemental analysis capability of EDS to intuitively identify and distinguish the types of particulate matter and make intuitive and clear judgments on their source types. Through the analysis of a large amount of single particle data, the number percentage of each type of particulate matter in different particle size ranges can be obtained, providing a scientific basis for the analysis of atmospheric pollution sources.

2. Analysis principles and technical features

SEM working principle: High-voltage accelerated electron beam bombards the sample surface to generate secondary electron signals. The sample surface morphology information is obtained by detecting the secondary electron signal.

EDS working principle: The focused electron beam excites the characteristic X-rays of the sample elements, and the element type is determined based on the ray energy, and the intensity is used for qualitative analysis.

Technical advantages:

• Rapid analysis of single particles, suitable for short-term component change research
• No need for a large amount of sample, suitable for precious sample analysis
• Intuitively distinguish the source type of particles

3. Instrument configuration and sample preparation requirements

- Electron source: tungsten filament or field emission source

- Accelerating voltage: 15 kV to 20 kV

- Image resolution: better than 30 nm

- Magnification range: 500 times to 30,000 times

- Energy spectrometer resolution: better than 137 eV

- Detection element range: B To U

Key steps of sample preparation

1. Sample collection: Use a nucleopore membrane (0.2 μm or 0.4 μm pore size) to capture particles and ensure sparse distribution.
2. Sample fixation: Use carbon double-sided tape to fix the filter membrane on the SEM sample stage.
3. Conductive layer sputtering: Use uncommon elements such as Au or Pd to reduce spectral interference.

4. Sample Analysis and Data Processing

Single Particle Analysis Process:

• Morphology observation: 1000x to 20,000x magnification, obtain secondary electron image
• Elemental analysis: point analysis mode to collect characteristic X-ray energy spectrum
• Particle size measurement: automatic length measurement tool with different fields of view

Data processing and result calculation:

• Particle classification: combined with morphology and element information, refer to the typical spectrum library for classification
• Number percentage calculation: use formula (1) to obtain the contribution rate of each type of particle in each particle size range$$ \omega_{ij}=\frac{c_{ij}}{\sum_{i=1}^{n} c_{ij}} \times 100\% $$