A method for measuring wall adsorption constants and skin mass transfer parameters in actual environments

Abstract

This invention belongs to the field of indoor environmental testing technology and can determine the wall adsorption constant and mass transfer mechanism parameters of volatile organic compounds (VOCs) in real environments and the skin lipid layer. The method includes establishing a physical model of the VOCs release process and wall adsorption process in the skin; conducting tests in a real environment in three stages; collecting real-world air samples using perfluoro-heptaalkyl PFA sampling tubes; and performing quantitative analysis using proton transfer reaction-time-of-flight mass spectrometry (PTR-ToF-MS); and calculating the hourly concentration C of VOCs in the three stages. a By combining a physical model and using a genetic algorithm for nonlinear fitting, the wall adsorption constant k of VOCs is obtained. a and k d The obtained hourly concentrations C of VOCs in stage one will be... a By combining the physical model and the wall adsorption constant, and using a particle swarm optimization algorithm coupled with ant colony optimization for nonlinear fitting, the mass transfer mechanism parameters of VOCs in the skin's lipid layer can be obtained, including the initial concentration C0 and the diffusion coefficient D. m And the allocation coefficient K. This method has simple experimental equipment and operation, low cost, simple solution process and higher accuracy. It overcomes the limitation of existing experimental methods that can only measure two mass transfer mechanism parameters at the same time, and can be used for laboratory testing and engineering applications.

Description

Technical Field

[0001] This invention belongs to the field of indoor environmental testing technology and can realize the determination of the wall adsorption constant of volatile organic compounds and the mass transfer mechanism parameters of the skin lipid layer in actual environment. Background Technology

[0002] Volatile organic compounds (VOCs) are widely present in indoor environments and have a significant impact on indoor air quality. Among them, cyclomethylsiloxanes (cVMS) are mainly related to human behavior. cVMS are colorless, odorless, inert, have low surface tension, and a smooth texture, making them widely used in cosmetics and household products. During cosmetic use, cVMS are gradually released from their source into the indoor environment due to their high Henry's constant. Common cVMS include octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecylcyclohexasiloxane (D6). D4 is considered to have "persistence, bioaccumulation, and toxicity," while D5 has "very persistent and very bioaccumulative" properties. Both D4 and D5 are classified as endocrine and reproductive disruptors. The mass transfer characteristics of cVMS release from the skin's lipid layer into the indoor environment are determined by the initial concentration C0 of cVMS in the skin lipid layer and the diffusion coefficient D. m Three mass transfer mechanism parameters: the partition coefficient K at the interface between the skin's lipid layer and air, and the adsorption rate coefficient k at the wall surface. a and desorption rate coefficient k d Characterization. Accurately determining the mass transfer mechanism parameters and wall adsorption constants of these cVMSs is fundamental for studying the mass transfer behavior of cVMSs in vitro and for assessing human health risks. Currently, methods for determining the mass transfer mechanism parameters of cVMSs are very limited, and can only measure C0 and D. m The two parameters, K and K, are estimated based on the physicochemical properties of cVMS, without considering the adsorption characteristics of cVMS on the wall surface in the actual environment. Existing methods for determining the mass transfer mechanism parameters of cVMS suffer from drawbacks such as large measurement errors, long measurement cycles, and complex systems. Furthermore, there is no effective method for determining the wall adsorption constant, which greatly limits the widespread application of these methods. Summary of the Invention

[0003] The purpose of this invention is to overcome the limitations of existing methods in determining VOCs mass transfer mechanism parameters in real-world environments, and to propose a new method for rapidly and accurately determining VOCs, especially cVMS mass transfer mechanism parameters and wall adsorption constants. This method has the advantages of ease of operation and high measurement accuracy, making it suitable for practical environmental monitoring and engineering applications.

[0004] To achieve the above objectives, this invention proposes a method for rapidly determining VOCs, especially cVMS mass transfer mechanism parameters CO and D, based on the mass transfer mechanism of VOCs in the skin's lipid layer and the wall adsorption equilibrium in real-world environments.m K and the wall adsorption rate coefficient k a and desorption rate coefficient k d The new method includes the following steps:

[0005] 1) Establish a physical model of the release process and wall adsorption process of volatile organic compounds (VOCs) in the skin in a real environment. The model can be described as follows:

[0006]

[0007]

[0008]

[0009] Cm(x,t)=Co,t=0,0≤x≤δ(4)

[0010]

[0011] M(t)=0,t=0(6)

[0012]

[0013] C(t)=0,t=0(8)

[0014]

[0015] In this model: Cm is the concentration of VOCs in the skin's lipid layer, ppb; t is the dissipation time, s; Dm is the diffusion coefficient of VOCs in the skin's lipid layer, m. 2 / s;h m δ is the convective mass transfer coefficient at the surface of the skin lipid layer, m / s; K is the VOCs partition coefficient at the skin lipid layer / air interface, dimensionless; Ca is the gas phase VOCs concentration in the actual environment, ppb; δ is the thickness of the skin lipid layer, m; C0 is the initial concentration of VOCs in the skin lipid layer, ppb; M is the concentration of VOCs in the wall surface, ppb / m. 2 ; ka is the wall adsorption rate coefficient, m / h; kd is the wall desorption rate coefficient, h- 1 A represents the area of ​​the skin's lipid layer on the human body, including the face and hands, in actual environments, in meters. 2 V represents the actual environmental space volume, in meters. 3 Q represents the actual ambient ventilation rate, in h- 1 S / V is the ratio of the actual adsorption surface area to the spatial volume; Ca,pre(t) j ) for t j The concentration of gaseous VOCs calculated at time t, ppb; Ca,exp(t j ) for t jThe gas phase VOCs concentration measured at time t, ppb; k is the number of data points measured in the experiment; P j As a weighting factor, P j =ln(Ca,exp(t) j FIT is the residual between the predicted and measured values ​​of gas-phase VOCs concentration calculated using mass transfer characteristic parameters.

[0016] 2) The test was conducted in three stages in a real environment: Stage 1, normal ventilation, and the number of people in the environment and the air exchange rate were recorded during the experiment; Stage 2, the people left the real environment and the environment was kept closed; Stage 3, the people remained in the closed state, normal ventilation was maintained, and the air exchange rate was recorded.

[0017] 3) During the test, actual ambient air samples were collected using perfluoro-heptaalkyl PFA sampling tubes, and then quantitative analysis was performed using a proton transfer reaction-time-of-flight mass spectrometer (PTR-ToF-MS) to obtain the hourly concentration of VOCs in the actual environment at different times.

[0018] 4) Using the hourly VOCs concentration Ca and air exchange rate obtained in test phase three, combined with equations (5) and (7), the wall adsorption rate coefficient k a and wall desorption rate coefficient k d As an unknown variable, the coefficient of determination R 2 As an evaluation criterion, nonlinear fitting using a genetic algorithm can yield the wall adsorption constants of VOCs, including k. a and k d ;

[0019] 5) The hourly concentration C of cVMS obtained in test phase one a Related to the air exchange rate and wall adsorption rate coefficient k at this stage a Combined with the wall desorption rate coefficient kd and equations (1) to (8), the mass transfer mechanism parameters C0, Dm, and K of the skin lipid layer are taken as unknown variables. The minimum residual FIT of equation (9) is used as the evaluation objective. The particle swarm optimization algorithm coupled with ant colony optimization is used for nonlinear fitting to obtain the mass transfer mechanism parameters C0, Dm, and K of VOCs in the skin lipid layer. m And K.

[0020] Features and effects of the present invention:

[0021] The measurement method of this invention studies the mass transfer characteristics of VOCs in real environments and combines particle swarm optimization with ant colony optimization to perform nonlinear fitting on the hourly concentration of VOCs, thereby directly, rapidly, and accurately measuring the initial concentration C0 and diffusion coefficient D of VOCs in the skin's lipid layer. m Distribution coefficient K and wall adsorption constant k a k dThis method features simple experimental equipment and operation, low cost, a simple solution process, and higher accuracy, making it suitable for both laboratory testing and engineering applications. Attached Figure Description

[0022] Figure 1 A schematic diagram of the experimental system for the mass transfer process of VOCs in the skin's lipid layer, considering wall adsorption, in a real-world environment, according to the present invention.

[0023] Figure 2 Fitting results for the concentration data of decamethylcyclopentasiloxane (D5) released from the skin's lipid layer due to wall adsorption in a real-world environment. Detailed Implementation

[0024] The method proposed in this invention for rapidly and accurately determining the wall adsorption constant of volatile organic compounds and the mass transfer mechanism parameters of the skin's lipid layer in real-world environments is described in detail below with reference to the accompanying drawings and examples:

[0025] The experimental system diagram of the cVMS (an important VOCs related to human release) mass transfer process of the skin lipid layer considering wall adsorption in the actual environment of this invention is shown below. Figure 1 As shown, the actual environment 4 refers to the indoor environment, where cVMS is adsorbed on the walls and released by the skin oil layer of the personnel 5 in this space; the tracer gas from the gas cylinder 1 flows into the actual environment after passing through the pressure reducing valve 2 and the mass flow controller 3; in test phase one, the ventilation device 6 of the actual environment 4 is turned on and the personnel 5 enters the actual environment 4; in test phase two, the personnel 5 leaves and the ventilation device 6 remains closed; in test phase three, the ventilation device 6 is turned on again; in each test phase, the air in the actual environment 4 is sampled by the perfluoro-heptaalkyl PFA sampling tube 7, and then the cVMS gas and tracer gas are quantitatively analyzed by the proton transfer reaction-time-of-flight mass spectrometer (PTR-ToF-MS) gas analyzer 8.

[0026] The method for determining the release characteristic parameters and wall adsorption constant in this embodiment includes the following steps:

[0027] 1) Establish a physical model of the release process and wall adsorption process of cVMS in the skin in a real environment. The model can be described as follows:

[0028]

[0029]

[0030]

[0031] C(x,t)=Co,t=0,0≤x≤δ(4)

[0032]

[0033] M(t)=0,t=0(6)

[0034]

[0035] Ca(t)=0, t=0(8)

[0036]

[0037] In this model: Cm is the concentration of cVMS in the skin's lipid layer, ppb; t is the dissipation time, s; Dm is the diffusion coefficient of cVMS in the skin's lipid layer, m. 2 / s;h m δ is the convective mass transfer coefficient at the surface of the skin lipid layer, m / s; K is the partition coefficient of cVMS at the skin lipid layer / air interface, dimensionless; Ca is the concentration of cVMS in the actual environment, ppb; δ is the thickness of the skin lipid layer, m; C0 is the initial concentration of cVMS in the skin lipid layer, ppb; M is the concentration of cVMS in the wall, ppb / m. 2 ;k a K is the wall adsorption rate coefficient, m / h; d h- is the wall desorption rate coefficient. 1 A represents the area of ​​the skin's lipid layer on the human body, including the face and hands, in a real-world environment, taken as 0.095m². 2 / person; V is the actual environmental space volume, in meters. 3 Q represents the actual ambient ventilation rate, in h- 1 S / V is the ratio of the actual adsorption surface area to the spatial volume; Ca,pre(t) j ) for t j Gas phase cVMS concentration calculated at time t, ppb; Ca,exp(t j ) for t j The gas phase cVMS concentration measured at time t, ppb; k is the number of data points measured in the experiment; P j As a weighting factor, P j =ln(Ca,exp(t) j FIT is the residual between the predicted and measured values ​​of the gas phase cVMS concentration calculated using mass transfer characteristic parameters.

[0038] 2) In a volume of 350m³ 3 The test was conducted in three phases in a real-world environment: Phase 1, with normal ventilation, two people in the environment, and an air exchange rate of 0.35 h⁻¹. 1 Phase Two: Personnel leave the actual environment, keeping it sealed. Phase Three: Personnel remain in the vacated state; normal ventilation continues, with an air exchange rate of 0.25 h⁻¹. 1 ;

[0039] 3) During the test, actual ambient air samples were collected using perfluoro-heptaalkyl PFA sampling tubes, and then quantitatively analyzed using a proton transfer reaction-time-of-flight mass spectrometer (PTR-ToF-MS) to obtain the real-time concentration of the target cVMS in the actual environment at different times. In this example, the target cVMS selected was decamethylcyclopentasiloxane (D5). The experimentally measured concentrations of D5 in the actual environment at 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, and 5h in stage one were 4.49229ppb, 11.07871ppb, 9.04729ppb, 6.90829ppb, and 5.53ppb, respectively. 500 ppb, 4.81543 ppb, 4.05543 ppb, 3.61414 ppb, 3.06257 ppb, 2.61143 ppb; the actual environmental D5 concentrations at 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, and 5h in Phase 3 were 0.02435 ppb, 0.03713 ppb, 0.04448 ppb, 0.05311 ppb, 0.05926 ppb, 0.06261 ppb, 0.06861 ppb, 0.06985 ppb, 0.07402 ppb, and 0.08007 ppb, respectively.

[0040] 4) Using the hourly concentration Ca and air exchange rate of D5 obtained in test phase three, combined with equations (5) and (7), the wall adsorption rate coefficient k a and wall desorption rate coefficient k d As an unknown variable, the coefficient of determination R 2 As an evaluation criterion, the wall adsorption constant k of D5 can be obtained by using a genetic algorithm for nonlinear fitting. a It is 0.0356 m / h, k d 0.0205h- 1 ;

[0041] 5) The hourly concentration C of D5 obtained in test phase one a Based on the actual environmental conditions of this stage, including the air exchange rate, wall adsorption rate coefficient ka, and wall desorption rate coefficient kd, and combined with equations (1) to (8), the mass transfer mechanism parameters of the skin lipid layer are taken as unknown variables. The minimum residual FIT of equation (9) is used as the evaluation objective. The particle swarm optimization algorithm coupled with ant colony optimization is used for nonlinear fitting, and the mass transfer mechanism parameter C0 of the skin lipid layer D5 is obtained as 2.78 × 10⁻⁶. 10 ppb, D m 2.48×10 -16 m 2 / s, K is 6.7×10 3 ;

[0042] The principle of this invention is as follows: During the release of VOCs from the skin lipid layer and after the person leaves the environment, the hourly concentrations of typical VOCs in the actual environment at different times are obtained through sampling. The experimental data are combined with a physical model, and a particle swarm optimization (PSO) coupled with an ant colony algorithm is used for nonlinear fitting to obtain the mass transfer mechanism parameters C0 and D of VOCs in the skin lipid layer. m K and wall adsorption constant k a k d .

Claims

1. A method for measuring wall adsorption constant and skin mass transfer parameters in a real environment, characterized in that, The steps include the following: 1) Establish a physical model of the release process and wall adsorption process of volatile organic compounds (VOCs) in the skin in a real environment. The model can be described as follows: C m (x,t)=C0,t=0,0≤x≤δ (4) M(t)=0,t=0 (6) C a (t)=0,t=0 (8) In this model: C m The concentration of VOCs in the skin's lipid layer is ppb; t is the dissipation time, s; D m m is the diffusion coefficient of VOCs in the skin's lipid layer. 2 / s;h m is the convective mass transfer coefficient at the surface of the skin's lipid layer, in m / s; K is the distribution coefficient of VOCs at the skin's lipid layer / air interface, dimensionless; C a This represents the concentration of gaseous VOCs in the actual environment, in ppb. δ represents the thickness of the skin's lipid layer, in meters; C0 represents the initial concentration of VOCs in the skin's lipid layer, in ppb; and M represents the concentration of VOCs in the cell wall, in ppb / m³. 2 ;k a K is the wall adsorption rate coefficient, m / h; d h is the wall desorption rate coefficient. -1 A represents the area of ​​the skin's lipid layer on the human body, including the face and hands, in actual environments, in meters. 2 V represents the actual environmental volume, in meters. 3 Q represents the actual ambient ventilation rate, in hours (h). -1 S / V is the ratio of the actual adsorption surface area to the spatial volume; C a,pre (t j ) for t j The concentration of gaseous VOCs calculated at time t, in ppb; C a,exp (t j ) for t j The gas phase VOCs concentration measured at time t, ppb; k is the number of data points measured in the experiment; P j As a weighting factor, P j =ln(C a,exp (t j FIT is the residual between the predicted and measured values ​​of gas-phase VOCs concentration calculated using mass transfer mechanism parameters. 2) The test was conducted in three stages in a real environment: Stage 1, normal ventilation, and the number of people in the environment and the air exchange rate were recorded during the experiment; Stage 2, the people left the real environment and the environment was kept closed; Stage 3, the people remained in the closed state, normal ventilation was maintained, and the air exchange rate was recorded. 3) During the test, actual ambient air samples were collected using perfluoro-heptaalkyl PFA sampling tubes, and then quantitative analysis was performed using a proton transfer reaction-time-of-flight mass spectrometer (PTR-ToF-MS) to obtain the hourly concentration of VOCs in the actual environment at different times. 4) Utilizing the hourly VOCs concentration C obtained in test phase three a Combined with the air exchange rate and equations (5) and (7), the wall adsorption rate coefficient k is determined. a and wall desorption rate coefficient k d As an unknown variable, the coefficient of determination R 2 As an evaluation criterion, a genetic algorithm is used for nonlinear fitting to obtain the wall adsorption constants of VOCs, including k. a and k d ; 5) The hourly concentration C of VOCs obtained in the first testing phase will be calculated. a Related to the air exchange rate and wall adsorption rate coefficient k at this stage a and wall desorption rate coefficient k d Combining equations (1) to (8), the mass transfer mechanism parameters C0 and D of the skin lipid layer are determined. m With K as unknown variables, and taking the minimum residual FIT of equation (9) as the evaluation objective, the nonlinear fitting was performed using the particle swarm optimization algorithm coupled with ant colony optimization to obtain the mass transfer mechanism parameters C0 and D of VOCs in the skin lipid layer. m And K.

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