This article explains the principle and operation of a particulate matter meter using beta-ray absorption, how it can accurately measure the concentration of particulate matter in the air and why it is important. It also highlights the impact of measuring particulate matter on environmental management and public health.
Since fine dust, which is 10 micrometers in diameter or less, can cause various respiratory diseases, it is necessary to know the concentration of fine dust in the air for prevention purposes. The effects of fine particulate matter on the human body are not limited to respiratory illnesses; long-term exposure can lead to a variety of health problems, including cardiovascular disease, asthma, and reduced lung function. For this reason, international organizations such as the World Health Organization (WHO) have identified fine dust as a major public health threat and are constantly tightening standards for monitoring and controlling it.
To this end, fine dust instruments have been developed, most of which use beta-ray absorption. Beta-ray absorption instruments automatically measure the concentration of particulate matter over a set period of time, regardless of the composition of the particles. The instrument consists of a separation device, filter paper, a beta-ray light source and detector, and a computing device.
In order to accurately measure the concentration of fine dust, it is necessary to collect the sample, the material to be analyzed. The sample air is drawn into the sample inlet by a suction pump, which is set to draw in a certain amount of air for a certain period of time. The separator accelerates the airborne particulate matter through an internal nozzle. It then collides with a collision plate to capture particles larger than 10 micrometers, while allowing smaller ones to pass through.
Eventually, dust larger than 10 micrometers in diameter stays on the impact plate, while the smaller particles fall down and collect on the filter paper. The filter paper is in the form of a long tape and traps the fine dust for a period of time. This capture process is crucial for determining the concentration of fine dust in the atmosphere, providing essential data for environmental management and air pollution research, especially in urban areas. The fine dust captured on the filter paper is measured by a beta-ray light source and a beta-ray detector, and then discharged by an automatic conveying drive.
The reason for using beta rays as a light source is that when beta rays pass through a substance, their intensity decreases as the mass of the substance increases. In addition, beta rays are safe because they penetrate quickly through paper but not through thin metal or plastic. For these reasons, beta rays are chosen as a light source that can provide both reliability and precision in measuring fine dust concentrations. The beta rays from the beta ray source pass through the fine dust captured on the filter paper and reach the beta ray detector. The intensity of the detected beta rays is necessarily less than the intensity of the beta rays passing through the filter paper without fine dust, because when the beta rays pass through the fine dust captured on the filter paper, some of them are absorbed or annihilated by the fine dust particles. Therefore, there is a difference between the intensity of the beta rays passing through the filter paper without fine dust and the intensity of the beta rays passing through the filter paper with fine dust.
The beta ray detector converts these two beta ray intensities into data signals and sends them to a computing device. The computing unit converts these data signals into a number and calculates the mass of fine dust captured by the filter paper by taking into account the amount of beta rays absorbed by the fine dust. The resulting mass of particulate matter is then expressed as the concentration of particulate matter in the air in parts per billion (ppb), taking into account the volume of air inhaled during sample collection, as measured by the flow meter. This number is essential information for air quality assessment and pollution control, and is utilized to assess the severity of air pollution and develop appropriate countermeasures.
