Method for measuring wall adsorption constant and skin mass transfer parameter in actual environment

Abstract

The invention belongs to the technical field of indoor environment inspection, and can measure the wall adsorption constant of volatile organic compounds (VOCs) and the mass transfer mechanism parameters of a skin oil layer in an actual environment. The implementation method comprises the following steps: establishing a physical model of a release process of VOCs in skin and a wall adsorption process; the method comprises the following steps: testing in three stages in an actual environment, collecting an air sample in the actual environment by using a perfluoro-heptaalkyl PFA sampling tube, and carrying out quantitative analysis by using a proton transfer reaction-time-of-flight-mass spectrometer PTR-ToF-MS (Proton Transfer Reaction-Time of Flight-Mass Spectrometer); carrying out nonlinear fitting on the obtained stage-three VOCs hourly concentration Ca in combination with a physical model by applying a genetic algorithm to obtain wall adsorption constants ka and kd of the VOCs; and combining the obtained stage-one VOCs hourly concentration Ca with a physical model and a wall adsorption constant, and performing nonlinear fitting by applying a particle swarm coupling ant colony optimization algorithm to obtain mass transfer mechanism parameters of the VOCs in the skin grease layer, including an initial concentration C0, a diffusion coefficient Dm and a distribution coefficient K. The method is simple in experimental equipment and operation, low in cost, simple in solving process and higher in precision, overcomes the limitation that an existing experimental method can only measure two mass transfer mechanism parameters at the same time, and can be used for laboratory detection and engineering application.

Description

Technical Field

[0001] The invention belongs to the technical field of indoor environment inspection and can realize the measurement of the wall adsorption constant of volatile organic matter and the mass transfer mechanism parameters of the skin oil layer in the actual environment. Background Art

[0002] Volatile organic compounds (VOCs) are widely present in indoor environments and have a significant impact on indoor air quality. Among them, cyclomethylsiloxane (cVMS) is the main one related to human behavior. cVMS has the characteristics of being colorless, odorless, inert, having low surface tension, and having a lubricated texture, and is widely used in cosmetics and household items. During the use of cosmetics, cVMS will gradually be released from the source into the indoor environment due to its high Henry constant. Common cVMS include octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6), of which D4 is considered to be "persistent, bioaccumulative, and toxic", and D5 is "very persistent and very bioaccumulative". Both D4 and D5 are listed as endocrine and reproductive disruptors. The mass transfer characteristics of cVMS released from the skin oil layer to the indoor environment are determined by the initial concentration of cVMS in the skin oil, C0, the diffusion coefficient D m , the distribution coefficient K at the interface between the skin oil layer and the air, and the adsorption rate coefficient k at the wall a and the desorption rate coefficient k d How to accurately measure the mass transfer mechanism parameters and wall adsorption constants of these cVMS is the basis for studying the mass transfer laws of cVMS in indoor environments and conducting human health risk assessments. Currently, the methods for measuring the mass transfer mechanism parameters of cVMS are very limited, and can only measure C0 and D m Of the two parameters, K is an estimated value based on the physical and chemical properties of cVMS, without considering the adsorption characteristics of cVMS on the wall surface of the actual environment. The existing methods for determining the mass transfer mechanism parameters of cVMS have the defects of large measurement errors, long measurement cycles, and complex systems. In addition, there is no effective method for determining the wall adsorption constant, which greatly limits the promotion and application of these methods. Summary of the invention

[0003] The purpose of the present invention is to overcome the limitations of existing methods for measuring VOCs mass transfer mechanism parameters in actual environments, and to propose a new method for quickly and accurately measuring VOCs, especially cVMS mass transfer mechanism parameters and wall adsorption constants. The method has the advantages of easy operation and high measurement accuracy, and is convenient for actual environmental detection and engineering applications.

[0004] To achieve the above objectives, the present invention proposes a method for rapidly determining the mass transfer mechanism parameters C0, D1 and C2 of VOCs, especially cVMS, based on the mass transfer mechanism of VOCs in the skin oil layer and the wall adsorption equilibrium in the actual environment.m , K and wall adsorption rate coefficient k a and the desorption rate coefficient k d The new method comprises the following steps:

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

[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 oil layer, ppb; t is the emission time, s; Dm is the diffusion coefficient of VOCs in the skin oil layer, m 2 / s;h m is the convection mass transfer coefficient at the surface of the skin oil layer, m / s; K is the distribution coefficient of VOCs at the skin oil layer / air interface, dimensionless; Ca is the gas phase VOCs concentration in the actual environment, ppb; δ is the thickness of the skin oil layer, m; C0 is the initial concentration of VOCs in the skin oil layer, ppb; M is the concentration of VOCs in the wall, ppb / m 2 ; ka is the wall adsorption rate coefficient, m / h; kd is the wall desorption rate coefficient, h- 1 ; A is the area of ​​the skin oil layer of the human body including the face and hands in the actual environment, m 2 ; V is the actual environment space volume, m 3 ; Q is the actual ambient air exchange rate, h- 1 ; S / V is the ratio of the actual environmental adsorption surface area to the spatial volume; Ca,pre(t j ) is t j Gas phase VOCs concentration calculated at time, ppb; Ca,exp(t j ) is t jThe gas phase VOCs concentration measured at the time, ppb; k is the number of data points measured in the experiment; P j is the weighting factor, P j =ln(Ca,exp(t j )); FIT is the residual between the predicted value and the measured value of the gas phase VOCs concentration calculated using the mass transfer characteristic parameters;

[0016] 2) The test is conducted in three stages in the actual environment: Stage 1, normal ventilation, recording the number of people in the environment and the ventilation rate of the environment during the experiment; Stage 2, the people leave the actual environment and keep the environment closed; Stage 3, the people remain away, normal ventilation, and the ventilation rate is recorded;

[0017] 3) During the test, actual ambient air samples were collected using a perfluoro-heptyl PFA sampling tube, and then quantitatively analyzed using a proton transfer reaction-time of flight-mass spectrometer (PTR-ToF-MS) to obtain the hourly concentrations of VOCs in the actual environment at different times;

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

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

[0020] Features and effects of the present invention:

[0021] The determination method of the present invention studies the mass transfer characteristics of VOCs in the actual environment, combines the particle swarm coupled ant colony algorithm, performs nonlinear fitting on the hourly concentration of VOCs, and directly, quickly and accurately determines the initial concentration C0 and diffusion coefficient D0 of VOCs in the oil layer of the skin. m , distribution coefficient K and wall adsorption constant k a , k dThe method has simple experimental equipment and operation, low cost, simple solution process and higher accuracy, and can be used for laboratory testing and engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a diagram of the experimental system for the mass transfer process of VOCs in the skin oil layer considering wall adsorption in the actual environment of the present invention.

[0023] Figure 2 Fitting results of the concentration data of decamethylcyclopentasiloxane (D5) released from the skin oil layer considering wall adsorption in actual environment DETAILED DESCRIPTION

[0024] The method proposed by the present invention for quickly and accurately measuring the wall adsorption constant of volatile organic compounds and the mass transfer mechanism parameters of the skin oil layer in the actual environment is described in detail with reference to the accompanying drawings and examples as follows:

[0025] The experimental system diagram of the mass transfer process of cVMS (an important VOCs released by the human body) in the skin oil layer adsorbed on the wall in the actual environment of the present invention is as follows Figure 1 As shown, the actual environment 4 refers to an indoor environment, whose wall surface will adsorb cVMS, and cVMS is released by the skin oil layer of the person 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 the first test phase, the ventilation device 6 of the actual environment 4 is turned on, and the person 5 enters the actual environment 4; in the second test phase, the person 5 leaves, and the ventilation device 6 remains closed; in the third test phase, the ventilation device 6 is reopened; in each test phase, the air in the actual environment 4 is sampled by the perfluoro-heptyl 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 the wall adsorption constant of the present embodiment comprises the following steps:

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

[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 oil layer, ppb; t is the diffusion time, s; Dm is the diffusion coefficient of cVMS in the skin oil layer, m 2 / s;h m is the convective mass transfer coefficient at the surface of the skin oil layer, m / s; K is the distribution coefficient of cVMS at the skin oil layer / air interface, dimensionless; Ca is the cVMS concentration in the actual environment, ppb; δ is the thickness of the skin oil layer, m; C0 is the initial concentration of cVMS in the skin oil layer, ppb; M is the concentration of cVMS in the wall, ppb / m 2 ;k a is the wall adsorption rate coefficient, m / h; k d is the wall desorption rate coefficient, h- 1 ; A is the area of ​​the skin oil layer of the human body including the face and hands in the actual environment, which is 0.095m 2 / person; V is the actual environmental space volume, m 3 ; Q is the actual ambient air exchange rate, h- 1 ; S / V is the ratio of the actual environmental adsorption surface area to the spatial volume; Ca,pre(t j ) is t j Gas phase cVMS concentration calculated at time, ppb; Ca,exp(t j ) is t j The gas phase cVMS concentration measured at the time, ppb; k is the number of data points measured in the experiment; P j is the weighting factor, P j =ln(Ca,exp(t j )); FIT is the residual between the predicted value and the measured value of the gas phase cVMS concentration calculated using the mass transfer characteristic parameters;

[0038] 2) In a volume of 350m 3 The test was conducted in three stages in the actual environment: Stage 1, normal ventilation, with 2 people in the environment and a ventilation rate of 0.35h- 1 ; Stage 2: People leave the actual environment and keep the environment closed; Stage 3: People remain away and ventilation is normal, with a ventilation rate of 0.25h- 1 ;

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

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

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

[0042] The principle of the invention is to obtain the hourly concentration of typical VOCs in the actual environment at different times by sampling during the release process of the skin lipid layer and after the person leaves the environment, combine the experimental data with the physical model, and use the particle swarm coupled ant colony algorithm for nonlinear fitting to obtain the mass transfer mechanism parameters C0 and D0 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 constants and skin mass transfer parameters in a real environment, characterized in that: The steps include: 1) Establish a physical model of the release process of volatile organic compounds (VOCs) in the skin and the wall adsorption process in the actual environment. The model can be described as: 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 is the concentration of VOCs in the skin oil layer, ppb; t is the emission time, s; D m is the diffusion coefficient of VOCs in the skin oil layer, m 2 / s;h m is the convection mass transfer coefficient at the surface of the skin oil layer, m / s; K is the distribution coefficient of VOCs at the skin oil layer / air interface, dimensionless; C a is the gas phase VOCs concentration in the actual environment, ppb; δ is the thickness of the skin oil layer, m; C0 is the initial concentration of VOCs in the skin oil layer, ppb; M is the concentration of VOCs in the wall, ppb / m 2 ;k a is the wall adsorption rate coefficient, m / h; k d is the wall desorption rate coefficient, h -1 ; A is the area of ​​the skin oil layer of the human body including the face and hands in the actual environment, m 2 ; V is the actual environment space volume, m 3 ; Q is the actual ambient air exchange rate, h -1 ; S / V is the ratio of the actual environmental adsorption surface area to the spatial volume; C a,pre (t j ) is t j Gas phase VOCs concentration calculated at the moment, ppb; C a,exp (t j ) is t j The gas phase VOCs concentration measured at the time, ppb; k is the number of data points measured in the experiment; P j is the weighting factor, P j =ln(C a,exp (t j )); FIT is the residual between the predicted value and the measured value of the gas phase VOCs concentration calculated using the mass transfer mechanism parameters; 2) The test is conducted in three stages in the actual environment: Stage 1, normal ventilation, recording the number of people in the environment and the ventilation rate of the environment during the experiment; Stage 2, the people leave the actual environment and keep the environment closed; Stage 3, the people remain away, normal ventilation, and the ventilation rate is recorded; 3) During the test, actual ambient air samples were collected using a perfluoro-heptyl PFA sampling tube, and then quantitatively analyzed using a proton transfer reaction-time of flight-mass spectrometer (PTR-ToF-MS) to obtain the hourly concentrations of VOCs in the actual environment at different times; 4) Using the VOCs hourly concentration C obtained in the third test phase a Combined with the ventilation rate, equations (5) and (7), the wall adsorption rate coefficient k a and the wall desorption rate coefficient k d As the unknown variable, the coefficient of determination R 2 As the evaluation criteria, the nonlinear fitting using genetic algorithm can obtain the wall adsorption constants of VOCs including k a and k d ; 5) The hourly concentration of VOCs obtained in the first test phase C a The ventilation rate and wall adsorption rate coefficient k in this stage a and the wall desorption rate coefficient k d , combined with equations (1) to (8), the skin oil layer mass transfer mechanism parameters C0, D m and K as unknown variables, and taking the minimum residual FIT of equation (9) as the evaluation target, the particle swarm coupled ant colony optimization algorithm is used for nonlinear fitting to obtain the mass transfer mechanism parameters C0, D0 of VOCs in the skin oil layer. m and K.

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