Evaluation of correlation between PM2.5 and radon-progeny equilibrium factor in radon chamber

Evaluation of correlation between PM2.5 and radon-progeny equilibrium factor in radon chamber 1 first-author 1 1 corresp Corresponding author. E-mail address: smzhou@ecit.cn Corresponding author. E-mail address: smzhou@ecit.cn smzhou@ecit.cn 1 Engineering Research Center of Nuclear Technology Application, Ministry of Education, East China University of Technology, Nanchang 330013, China Engineering Research Center of Nuclear Technology Application, Ministry of Education, East China University of Technology, Nanchang 330013, China The dosage of environmental radon progeny is typically estimated according to the environmental radon exposure and the recommended radon-progeny equilibrium factor, F . To investigate the relationship between PM2.5 and the radon-progeny equilibrium factor, cigarettes are used to simulate the haze-fog in a multi-functional radon chamber to achieve a stable-radon concentration environment. A radon detector and a Portable Laser Aerosol Spectrometer are used to obtain the values for C mean PM2.5, C Rn , and C p . The results show that the mean values of F conform with the typical value recommended by the United Nations Scientific Committee on the Effects of Atomic Radiation and are within the reasonable range of 0.1–0.9. In this study, a positive correlation is observed between the F values and PM2.5 concentrations. PM2.5 Radon chamber Equilibrium factor Linear regression 1. Introduction 1 In recent years, the issue of haze-fog in the middle-eastern region of China has become increasingly serious. According to analysis of the relationship between the air visibility and the aerosol levels in China, this phenomenon is mainly due to the significant increase of anthropogenic atmospheric aerosols [ 1 1 - 3 3 1-3 ] . Haze-fog is a general expression for the excess amounts of various suspended particulates in the atmosphere. Among these, PM2.5 ( < 2.5 μm in diameter) is considered as the main factor of haze-fog. High concentrations of fine particles in the air can result in the accumulation of hazardous substances, such as heavy metals, acid, alkali, salt, amine, and phenol [ 4 4 , 5 5 ] . These substances affect the respiratory tract and cardiovascular system in humans, inducing or aggravating chronic asthma, heart disease, diabetes, etc. [ 6 6 - 8 8 6-8 ] . Moreover, when 222 Rn decays, the new progenies are all heavy-metal radioisotopes [ 9 9 , 10 10 ] . Most of the radon products, such as 218 Po, 214 Po, 214 Pb, and 214 Bi, rapidly attach to the surrounding PM2.5 [ 11 11 , 12 12 ] . The size of the attachment depends on the number of available particles in the air. In addition to the radioactive decay, the physical behavior of the attached part is the same as that of stabilizing atmospheric particles [ 13 13 - 15 15 13-15 ] . Therefore, the concentration and behavior of fine particulate matter in air can affect the fraction of radon progenies attached to aerosols and may affect the equilibrium factor ( F ). The dosage of environmental radon progeny is estimated according to the environmental radon exposure and the recommended radon-progeny equilibrium factor. F is defined as the ratio of the equilibrium equivalent radon concentration ( EEC Rn ) to the radionuclide concentration of radionuclides in the air. It is a very important parameter for estimating radon and its progenies exposure for humans. In 2000, the evaluation report of the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) suggested an indoor standard value of F [ 16 16 ] . At present, many studies focus on the aerosol conditions, gas exchange rate, humidity, and other factors or on theoretical research regarding the influence of these factors on indoor radon progeny. The effects of the aerosol, wind speed, temperature, and humidity on the radon, combined radon progeny, and equilibrium factor have not been studied in a stable-radon concentration environment (such as a radon chamber) [ 17 17 , 18 18 ] . To investigate the relationship between PM2.5 and the F value, we first focus on an experiment involving solid particles produced by burning cigarettes to examine the role of the radon progeny in the multi-functional ecological radon chamber. Then, a radon detector is used to monitor the radon and its progeny concentration in the chamber. Finally, the F value is calculated according to the radon and its progeny concentration. 2. Experimental 1 The radon chamber is a metering device in a radon laboratory. It can be used to perform experiments at a certain radon concentration under a controlled temperature and humidity, as well as for radon instrument calibration. The multi-functional radon chamber is a medium-sized radon chamber developed by the East China University of Technology, whose structure is shown in Fig. 1 Fig. 1 . The volume of the radon cabinet is 4.13 m 3 . The glass cabinet around the chamber is equipped with eight sampling holes. A PM2.5 aerosol generator can be connected to two of these holes to ensure the full combustion of the cigarette after air circulation. The monitoring system for the PM2.5 concentration and the radon and its progeny comprises a Portable Laser Aerosol Spectrometer and a radon detector. These devices are placed on the working stage in the radon chamber before the experiment. Control software allows remote control of the radon detector instruments as well as the dynamic stabilization of the radon concentration in the radon chambers. In the experiment, the radon concentration is maintained at approximately 1,000 Bq/m 3 . For setting the temperature / humidity simulation value, the Nanchang area is used as an example. Over a recent 10-year period (2008–2017), the average temperature / humidity was 28.04 ℃ / 77.51% in summer and 7.91 ℃ / 83.04% in winter [ 19 19 ] . However, the winter temperature and humidity simulation value exceed the range of the multi-functional radon chamber. To obtain the simulation effect at a low temperature and contrast with the higher temperature, 15.50℃ / 50.00% is selected as an alternative value for the multi-functional radon chamber temperature and humidity stability experimental results. According to the PM2.5 detection network of new air-quality standards, a set of five levels of experiments are conducted at two different temperature/humidity settings: the excellent level (0–35 μg/m 3 ), good level (35–75 μg/m 3 ), mild pollution level (75–115 μg/m 3 ), moderate pollution level (115–150 μg/m 3 ), and heavy pollution level (150–250 μg/m 3 ). The experiment lasted for 24 h at each grade. 2.1. Generation of PM2.5 aerosol 2 The semi-automatic cigarette smoke emitter (PM2.5 generator) consists of a 1,000-mL heat-resistant glass sealed container, a pump, a fixed clip, a silicone tube, and two sampling holes with quick coupling, as shown in Fig. 2. Fig. 2. The pump connects the heat-resistant glass sealed container to the radon chamber cabinet through the silicone tube, and the cigarette to burn is affixed to the container using a clip. Thus, smoke generated in the container can be injected into the radon chamber cabinet. The cigarette can be lit or extinguished by opening the lid of the heat-resistant glass sealed container. 2.2. Measurement of PM2.5 concentration 2 The PM2.5 concentration is measured using a Portable Laser Aerosol Spectrometer (GRIMM GmbH, Germany). The device uses 31 size channels, allowing particles to be detected in a very broad size range of 0.25–32 µm. The value of the sampling flow is 1.2 L/min, whereas the minimum value of the mass concentration is 0.1 µg/m 3 . After the measurement begins, results are obtained continuously every 6 s. During the experiment, real-time data are depicted on a personal computer and can be controlled remotely via Bluetooth. 2.3. Measurement of radon and its progeny 2 The radon concentration ( C Rn ) and the potential alpha energy concentration ( C p ) are measured using a radon detector (SARAD GmbH, Germany) in the fast measurement mode. The sampling flow is 1.5 L/min, with a 10-min measurement cycle. The C Rn uncertainty is 5.7%, and the C p uncertainty is 5.0%. The fast measurement mode calibration constant is 0.0032 cpm/Bq/m 3 , which equals 312.5 Bq/(m 3 ·cpm). In this study, only the number of 218 Po atoms is recorded, and the response time is 15 min. In measuring the radon progeny, the response time is 120 min owing to the collection of radon-progeny particles in the steady state. 2.4. Calculation method for C p and F 2 The F value characterizes the nonequilibrium between the short-lived progeny mixture in the air and its mother nuclide, which is expressed according to the alpha potential: <math display="block" id="M1"><mrow><mi>F</mi><mo>=</mo><mn>1.81</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mn>8</mn></msup><msub><mi>C</mi><mtext>p</mtext></msub><mo>/</mo><msub><mi>C</mi><mrow><mtext>Rn</mtext></mrow></msub><mo>,</mo></mrow></math> where 1.81 × 10 8 is called the conversion factor; C p represents the radon progeny potential concentration, J/m 3 (1 MeV = 1.6 × 10 -13 J); and C Rn represents the radon concentration, Bq/m 3 . 3. Results and Discussion 1 The temperature / humidity value in the radon chamber is controlled before the experiment. After the temperature / humidity value is stable, we can start the experiment. The change of the temperature / humidity value in the radon chamber is shown in Fig. 3. Fig. 3. 3.1. C mean PM2.5, C Rn , C p (15.50 ℃/50.00%) 2 Figure 4 Figure 4 shows the measurement results for C mean PM2.5, C Rn , and C p when the temperature / humidity is stabilized at 15.50 ℃ / 50.00%. The average radon concentration for the whole experiment is 1,042.0 Bq/m 3 . As shown in Fig. 4 Fig. 4 , the result is close to the theoretical radon concentration of 1,000 Bq/m 3 . The average PM2.5 concentrations at the five levels are 20.4, 56.8, 94.1, 129.5, and 191.8 μg/m 3 . This shows that the PM2.5 concentrations comply with the new air-quality standard. To study the effect of the wind speed on the radon-progeny equilibrium factor F, the rotation frequency of the built-in fan in the HD-6 multi-functional radon chamber is increased from 30 to 35 Hz under PM2.5 with a mild pollution level (as shown in Fig. 4b Fig. 4b ). During this period, the average PM2.5 concentration is 94.1 ± 10.8 μg/m 3 . 3.2. C mean PM2.5, C Rn , C p (28.04 ℃/77.51%) 2 Fig. 5 Fig. 5 shows the time-dependent C mean PM2.5, C Rn , and C p when the temperature / humidity is stable at 28.04 ℃ / 77.51%. The average PM2.5 concentrations at the five levels are 19.0, 49.8, 91.6, 130.3, and 196.2 μg/m 3 . The average radon concentration for the whole experiment is 1,048.0 Bq/m 3 , which is within a reasonable range. The activity of the gas increases owing to the temperature rise. Therefore, the fluctuation of the radon concentration increases. In this study, approximately 2 min of data is not measured, because the PTFE filter is replaced during the experiment. Relative to the whole experiment, 2 min is an extremely short period, and the impact of this omission on the experimental results can be ignored. 3.3. Discussion regarding radon-progeny equilibrium factor 2 According to the equation F = 1.81 × 10 8 C p / C Rn , the F values are shown in Table 1 Table 1 . The average F value is 0.54 ± 0.15 ( n = 120) when the temperature / humidity is stable at 15.50 ℃ / 50.00%, calculated using values of 0.48 ± 0.12 (0–75 μg/m 3 , n = 48) and 0.58 ± 0.16 (75–250 μg/m 3 , n = 72), respectively. The results conform with the indoor F standard value recommended by UNSCEAR, which is related to the low temperature and low humidity. C mean for PM2.5 is 98.5 μg/m 3 during the entire monitoring period. 1 1 Temperature and humidity 1 1 PM2.5 level 1 1 C mean PM2.5 (μg/m 3 ) 1 1 C Rn (Bq/m 3 ) 1 1 C p (Bq/m 3 ) 1 1 n 1 1 F 1 1   1 1   1 1 X±SD 1 1 X±SD 1 1 X±SD 1 1   1 1 X±SD 1 1 15.50℃/50.00% 1 1 Excellent 1 1 20.4±7.6 1 1 1048.7±126.9 1 1 485.4±129.3 1 1 24 1 1 0.46±0.10 1 1   1 1 Good 1 1 56.8±8.9 1 1 994.5±101.5 1 1 505.1±154.0 1 1 24 1 1 0.50±0.13 1 1   1 1 Mild pollution 1 1 94.1±10.8 1 1 1057.8±127.0 1 1 574.4±125.3 1 1 24 1 1 0.54±0.10 1 1   1 1 Moderate pollution 1 1 129.5±9.4 1 1 1061.0±138.3 1 1 593.8±189.0 1 1 24 1 1 0.56±0.17 1 1   1 1 Heavy pollution 1 1 191.8±28.7 1 1 1048.0±138.2 1 1 655.5±179.9 1 1 24 1 1 0.63±0.17 1 1 28.04℃/77.51% 1 1 Excellent 1 1 19.0±5.9 1 1 1046.6±104.1 1 1 530.6±181.5 1 1 24 1 1 0.50±0.15 1 1   1 1 Good 1 1 49.8±8.7 1 1 1027.2±145.1 1 1 542.9±141.8 1 1 24 1 1 0.52±0.12 1 1   1 1 Mild pollution 1 1 91.6±10.0 1 1 1033.9±122.3 1 1 553.2±138.1 1 1 24 1 1 0.54±0.12 1 1   1 1 Moderate pollution 1 1 130.3±8.9 1 1 1061.0±141.9 1 1 608.4±142.2 1 1 24 1 1 0.57±0.10 1 1   1 1 Heavy pollution 1 1 196.2±24.7 1 1 1071.6±135.2 1 1 708.3±174.9 1 1 24 1 1 0.66±0.15 In Figs. 5(a) and (b) Figs. 5(a) and (b) , the average F value is 0.56 ± 0.14 ( n = 120) when the temperature / humidity is stable at 28.04 ℃ / 77.51%, calculated using values of 0.52 ± 0.14 (0–75 μg/m 3 , n = 48) and 0.59 ± 0.16 (75–250 μg/m 3 , n = 72), respectively. Notably, the F value is not only higher than the indoor standard value (UNSCEAR 2000) but also higher than the value at the same PM2.5 level (mild pollution) when the temperature / humidity is stable at 28.04 ℃ / 77.51%. This indicates that the environmental damage caused by fine-particle pollution is more serious at a high temperature. The rotation frequency of the built-in fan in the multi-functional radon chamber is increased from 30 to 35 Hz under mild pollution at a temperature / humidity of 15.50 ℃ / 50.00%. During this time, the average F value is 0.54 ± 0.10, whereas the temperature / humidity remains stable at 28.04 ℃ / 77.51%. It is proven that the enhanced wind speed has a reduced effect on F . 3.4. Correlation analysis of data 2 In the air, the radon progeny combined with the condensation of nuclei is called the combined radon progeny. The radon progeny existing in the form of individual particles (ion or atom) is called the cluster radon progeny [ 20 20 , 21 21 ] . f p is defined as the ratio of the cluster radon progeny potential value (C p, u ) to the total potential value (C p, total ): <math display="block" id="M2"><mrow><msub><mi>f</mi><mtext>p</mtext></msub><mo>=</mo><msub><mi>C</mi><mrow><mtext>p,u</mtext></mrow></msub><mo>/</mo><msub><mi>C</mi><mrow><mtext>p,total</mtext></mrow></msub><mo>.</mo></mrow></math> The concentration of PM2.5 is gradually increased in the experiment, and f p is affected by changes in the cluster radon progeny. There is a relationship between C p and C mean PM2.5, as well as between F and C mean PM2.5. Linear regression is a statistical analysis method that employs regression analysis together with mathematical statistics to determine the quantitative relationship between two or more interdependent variables. Thus, the relationship between C p and C mean PM2.5 or between F and C mean PM2.5 can be calculated using linear regression. As shown in Table 1 Table 1 , five levels of PM2.5 average data ( n = 10) under two different temperature/humidity values are analyzed using linear regression. In Fig. 6(a) Fig. 6(a) , the results indicate that there is a positive correlation between F and C mean PM2.5 ( R 2 = 0.91805). Even if a set of data is discarded because of the impact of the enhanced wind speed ( n = 9), a positive correlation between F and C mean PM2.5 ( R 2 = 0.9173) is observed, as shown in Fig. 6(b) Fig. 6(b) . Even though based on classification method shown in Fig. 4 Fig. 4 or Fig. 5 Fig. 5 are analyzed by using linear regression. It is also not difficult to show that the correlation between F and C mean PM2.5 is stronger than that between C p and C mean PM2.5. The resulting R 2 values for C p – C mean PM2.5 and F – C mean PM2.5 are shown in Table 2 Table 2 . 1 1 Temperature and humidity 1 1 PM2.5 level 3 1 R 2 1 1   1 1   1 1 n 1 1 C p – C mean PM2.5 1 1 F – C mean PM2.5 1 1 15.50 ℃/50.00 % 1 1 Excellent and good 1 1 48 1 1 -0.01996 1 1 0.02997 1 1   1 1 pollution 1 1 72 1 1 0.04313 1 1 0.06239 1 1 28.04 ℃/77.51 % 1 1 Excellent and good 1 1 48 1 1 -0.00959 1 1 0.00176 1 1   1 1 pollution 1 1 72 1 1 0.11885 1 1 0.10757 The correlation factor R 2 for F – C mean PM2.5 ranges from 0.00176 to 0.10757. However, only one group of C p – C mean PM2.5 values has a correlation factor R 2 of > 0.1. When the PM2.5 level is excellent or good, the correlation factor R 2 of C p – C mean PM2.5 is negative. 4. Conclusion 1 In this study, the radon-progeny equilibrium factor F is 0.56 ± 0.14 (28.04 ℃/77.51%, n = 120) and 0.54 ± 0.15 (15.50 ℃/50.00%, n = 120). The F value conforms with the indoor standard value recommended by UNSCEAR. 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Dos . 145 , 316 - 319 ( 2011 ). doi: 10.1093/rpd/ncr081 http://doi.org/10.1093/rpd/ncr081 Evaluation and comparison of measurements of unattached and attached radon daughter in the radon chamber of PTB Braunschweig (Germany) with NRPI 10.1007/s41365-018-0481-2 The work was supported by the National Natural Science Foundation of China (No. 11565002), the Jiang Xi Young Science Foundation Project (No. GJJ150558), and Open Funds of Engineering Research Center of Nuclear Technology Application of Ministry of Education (No. HJSJYB2017-2). 2018-02-08 2018-03-20 2018-05-07 2018-09-11 2018-10-01 2021-04-11 © China Science Publishing & Media Ltd. (Science Press), Shanghai Institute of Applied Physics, the Chinese Academy of Sciences, ChineseNuclear Society and Springer Nature Singapore Pte Ltd. 2018 This is a post-peer-review, pre-copyedit version of an article published in Nuclear Science and Techniques. The final authenticated version is available online at: http://dx.doi.org/10.1007/s41365-018-0481-2 http://dx.doi.org/10.1007/s41365-018-0481-2 . 2018 Nuclear Science and Techniques 10 29