Atmospheric particulate matter (PM) is an important component of air pollution, directly affecting human health, environmental quality, and climate change. In order to scientifically monitor and evaluate the pollution status of atmospheric particulate matter, an atmospheric particulate matter composition network has been established to track and monitor the composition, concentration, and variation patterns of atmospheric particulate matter for a long time. Sampling and analysis frequency is one of the key factors in ensuring data quality and accuracy. Reasonable setting of sampling and analysis frequency can not only reflect the spatiotemporal characteristics of atmospheric particulate matter, but also provide reliable basis for policy formulation and pollution control.
This article will explore in detail the principles, methods, and practical experience of setting sampling and analysis frequencies for atmospheric particulate matter composition networks, and propose scientifically reasonable sampling frequency suggestions.
1、 Monitoring objectives
1. Monitoring of particulate matter concentration: By real-time monitoring of the mass concentration of particulate matter such as PM2.5 and PM10, data support is provided for air quality warning and pollution source identification.
2. Analysis of particulate matter components: By analyzing the chemical composition of particulate matter, the types and contributions of pollution sources can be understood, providing data support for source apportionment and pollution control.
3. Research on the impact of climate change: The influence of atmospheric particulate matter on climate change is increasingly being studied, especially its impact on the reflectivity of greenhouse gases and aerosols. Therefore, the chemical composition data of particulate matter is helpful for studying the feedback effect of atmospheric aerosols on climate.
2、 Principle of Sampling Frequency Setting
During the monitoring process, the sampling frequency should be set according to the following principles:
1. Monitoring requirements: Different research objectives and usage requirements determine the setting of sampling frequency. For example, if studying the seasonal variation of particulate matter, low-frequency sampling may be required; If studying short-term pollution fluctuations, a higher sampling frequency is required.
2. Changes in pollution levels: The concentration and composition of atmospheric particulate matter vary greatly with factors such as time, location, and meteorological conditions. The sampling frequency needs to be flexibly adjusted according to the changing patterns of pollutants in order to capture the spatiotemporal distribution characteristics of particulate matter concentration and components.
3. Equipment and technical limitations: Monitoring equipment typically collects particulate matter samples from the air and conducts component analysis through chemical analysis methods such as ion chromatography, mass spectrometry, etc. The detection capability, response time, and analysis speed of the equipment are one of the factors that affect the sampling frequency.
3、 Method for setting sampling frequency
1. Continuous monitoring method and periodic sampling method
The sampling methods for atmospheric particulate matter mainly include continuous monitoring and periodic sampling. Continuous monitoring method can obtain real-time and continuous particulate matter concentration data, but it is usually suitable for monitoring larger particles or conventional pollutants. The regular sampling method is suitable for situations where precise analysis of particulate matter components is required, usually by collecting samples at regular intervals and conducting laboratory analysis.
2. 24-hour sampling
At present, 24-hour sampling is a common sampling method. 24-hour sampling can accurately reflect changes in daily air quality and provide samples for regular analysis of particulate matter components. This type of sampling is suitable for monitoring daily air quality, especially in areas without real-time online monitoring equipment.
3. Short time interval sampling
For certain research needs, such as monitoring sudden pollution events, the sampling frequency may need to be increased to once every hour or every half hour. This high-frequency sampling is suitable for areas with large fluctuations in pollutant concentrations in the short term, especially in high pollution areas or urban areas with industrial emissions.
4. Seasonal or long-term monitoring
Due to the influence of seasonal and climatic factors on the composition and concentration of atmospheric particulate matter, seasonal variations need to be taken into account when setting the sampling frequency. For long-term monitoring networks, the sampling frequency can be set to once a month or once a quarter, especially when the monitoring area is relatively wide.
4、 Principles for Setting Analysis Frequency
In addition to sampling frequency, analysis frequency also has a significant impact on the data quality of atmospheric particulate matter composition networks. Analysis frequency refers to the frequency of chemical analysis of collected particulate matter samples. Reasonable analysis frequency can ensure the representativeness and accuracy of data.
1. Monitoring requirements and data accuracy requirements
When setting the analysis frequency, it is necessary to combine the monitoring objectives and data accuracy requirements. For example, for daily air quality assessment, it may be sufficient to analyze samples once a month or quarter; For studies that require high precision such as pollution source analysis, higher frequency analysis may be necessary.
2. Laboratory analysis time
Different chemical analysis methods require different amounts of time. For complex chemical analysis methods such as ion chromatography and gas chromatography-mass spectrometry, the analysis time is relatively long, and laboratory analysis capabilities and time arrangements need to be considered in advance. If the analysis frequency is too high, it may lead to excessive burden on the laboratory, thereby affecting the timeliness and accuracy of the analysis results.
3. Data integration and correction
The composition data of atmospheric particulate matter usually requires data quality control and correction. Low analysis frequency may result in significant spatiotemporal differences between data, making it difficult to reflect the dynamic changes of particulate matter pollution. Therefore, the analysis frequency needs to match the sampling frequency to ensure the timeliness and representativeness of the data.
The sampling and analysis frequency setting of atmospheric particulate matter composition network should be comprehensively considered based on monitoring objectives, data requirements, equipment capabilities, and laboratory analysis capabilities. Reasonably setting the sampling frequency can not only ensure the representativeness and accuracy of data, but also provide reliable basis for pollution source analysis, air quality assessment, and climate change research.