A method for calculating the cumulative concentration of NO2 by measuring the photolysis rate

Abstract

The present invention belongs to the technical field of environmental monitoring, and discloses a method for calculating the cumulative concentration of NO2 by measuring the photolysis rate. The technical solution includes: comparing and verifying the solar irradiance measured by a photolysis spectrometer with the ground solar irradiance observed by the TROPOMI satellite; continuously observing the NO2 photolysis rate and the NO2 concentration by using a photolysis spectrometer and a MAX-DOAS instrument respectively; analyzing the mutual relationship between the NO2 photolysis rate, the NO2 concentration and environmental factors to obtain the daily variation curves of the two; analyzing the relationship between the NO2 photolysis rate and the NO2 concentration, integrating the daily variation curves of the two to respectively obtain the change trends of the cumulative total amounts of the two; averaging and fitting the integral curves of the two, and finally the cumulative amount of NO2 concentration can be calculated. Through long-term continuous field observations, data analysis and formula derivation, the present invention obtains the relationship between concentration data and photolysis rate, expands the use of the photolysis spectrometer, and saves the measurement cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental monitoring, and particularly relates to a method for calculating the cumulative concentration of NO2 by measuring the photolysis rate. Background Art

[0002] The NO2 monitoring methods mainly include point source monitoring and remote sensing monitoring, both of which require the use of special measuring instruments, and most of them have the characteristics of complex systems, large volumes, and relatively high prices.

[0003] Under the radiation of the sun, trace gases in the atmosphere absorb the energy in solar photons, causing the breakage of their own chemical bonds, undergoing photolysis reactions, generating active atoms and free radicals, and these atoms and free radicals will combine with each other to form new substances to maintain the dynamic balance in the atmosphere. Therefore, the photolysis reaction of trace gases is often called the initiation reaction in the atmospheric chain reaction and plays an important role in the atmospheric photochemical reaction. In order to accurately describe the photolysis reaction process, scientists have introduced the photolysis rate of gases. This parameter is the first-order rate constant that quantifies the occurrence of the photolysis process, and is not only crucial for quantitatively understanding the rapid photochemical reactions in the troposphere, but also of great significance for understanding the formation mechanism of air pollutants in local areas. Scientists have discovered a variety of photolysis rate measurement techniques, such as the chemical actinometer measurement method, the filter radiometer measurement method, and the spectral radiometer measurement method. Especially in 1999, the spectral radiometer measurement method proposed by scientist Hofzumahaus calculates the photolysis rate by integrating the formula in combination with the absorption cross-section and quantum yield data of the molecule to be measured. With the advantages of simple structure, accurate measurement, and diversity of measurement types, this method has become the most commonly used technology in photolysis rate measurement.

[0004] The measurement of the photolysis rate of substances can provide observational data for on-site investigations of atmospheric photochemistry, help understand the chemical changes observed in the atmosphere, further verify the atmospheric chemical model, and at the same time, due to its correlation with the concentration of specific polluting gases, it can also evaluate and predict the pollution level.

[0005] The present invention has carried out long-term continuous observations on the NO2 photolysis rate using a self-developed photolysis spectrometer (a spectrometer device with the publication number of CN115728248A), analyzed the correlation between the NO2 photolysis rate and the concentration, and then obtained an empirical formula, thus obtaining a method for calculating the cumulative concentration of NO2 gas while measuring the photolysis rate. Summary of the Invention

[0006] The object of the present invention is to provide a method for calculating the cumulative concentration of NO2 by measuring the photolysis rate, which can find that the process and intensity of the photochemical reaction are closely related to the energy driving the photochemical reaction, and the photolysis rate value on sunny days is significantly higher than that on cloudy and rainy days. At the same time, it is found that there is an empirical formula between the integral curve of the NO2 photolysis rate and the concentration, with a correlation greater than 0.9, and the cumulative amount of NO2 concentration can be quickly calculated by measuring the NO2 photolysis rate.

[0007] To achieve the above object, the present invention proposes a method for calculating the cumulative concentration of NO2 by measuring the photolysis rate, including:

[0008] Continuously observing the NO2 photolysis rate and the NO2 concentration respectively by using a photolysis spectrometer and a MAX-DOAS instrument, and comparing and verifying the measured solar irradiance with the ground solar irradiance observed by the TROPOMI satellite;

[0009] Analyze the mutual relationships between the NO2 photolysis rate and the NO2 concentration and environmental factors respectively to obtain their daily variation curves;

[0010] Analyze the mutual relationship between the NO2 photolysis rate and the NO2 concentration, integrate the daily variation curves of the two, respectively obtain the change trends of the cumulative integral totals of each, and perform normalization processing;

[0011] Average the data of the NO2 concentration and the data of the NO2 photolysis rate at each moment and perform least squares polynomial fitting to obtain a curve equation.

[0012] Optionally, the photolysis spectrometer and the MAX-DOAS instrument are located adjacent to each other during observation.

[0013] Optionally, the environmental factors corresponding to the NO2 photolysis rate include solar radiation intensity and weather.

[0014] Optionally, the environmental factors corresponding to the NO2 concentration include weather and daily time intervals.

[0015] Optionally, the daily time intervals include morning, noon, and evening, where the NO2 concentration has the maximum value in the morning and evening, and the lowest value at noon.

[0016] Optionally, the time interval of the morning is 9:00 - 10:00, and the corresponding concentration value reaches the maximum value of the day. The time interval of noon is 12:00 - 16:30, and due to the increase in the photolysis reaction rate, the corresponding concentration value gradually reaches the minimum value of the day.

[0017] Optionally, the curve equation is a regression equation determined by minimizing the sum of squared errors.

[0018] Optionally, the regression equation is expressed as:

[0019] where E is the objective function, p is a polynomial fitting function of degree n, x j is the independent variable, y j is the dependent variable, Calculate and find a set of θ (θ0, θ1, θ2,..., θ n ) that minimizes E.

[0020] Optionally, integrate the data of the NO2 concentration and the data of the NO2 photolysis rate at each moment respectively, take the average of the two, fit the mean curve of the two, and the average of the mean curves of the two is approximately expressed by the formula: y = -4.0*10 -5 *x 3 +0.001*x 2 +0.015*x - 0.1365;

[0021] where x is the time and y is the mean of the two, and then the approximate value of the NO2 concentration integral can be obtained.

[0022] Optionally, the correlation between the average value of the integral and the value obtained by the approximate formula is greater than 0.90.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. The present invention provides a new measurement algorithm for the cumulative concentration of NO2 and expands the use of the photolysis spectrometer;

[0025] 2. The present invention uses the existing photolysis spectrometer, without additional equipment, has a relatively simple measurement structure, and has low cost and high accuracy;

[0026] 3. The data measured by the present invention is compared and verified with the TROPOMI satellite observation data, and has good consistency and accurate measurement results;

[0027] 4. The present invention can calculate the cumulative concentration of NO2 by using the original photolysis rate measurement data, without additional measurement, simplifies the measurement process, and improves the measurement efficiency;

[0028] In summary, the purpose of the present invention is to obtain the relationship between the concentration data and the photolysis rate through long-term continuous field observations, data analysis and formula derivation, expand the use of the photolysis spectrometer, and save the measurement cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1This is the correlation data graph between the photolysis spectrometer in the present invention and the TROPOMI satellite observation data;

[0030] Figure 2 This is the daily average monthly data graph of the measured NO2 photolysis rate in the present invention;

[0031] Figure 3 This is the NO2 photolysis rate graph divided by weather conditions measured in the present invention;

[0032] Figure 4 This is the change curve graph of NO2 concentration under different weather conditions (left) and the change curve graph of NO2 concentration and photolysis rate (right) in the present invention;

[0033] Figure 5 This is the integral curve graph of NO2 photolysis rate and concentration from August to September 2023 (left) and the integral curve graph of NO2 photolysis rate and concentration from September to October 2023 (right) in the present invention. Detailed implementation manners

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0035] Refer to Figure 1 , the present invention applies the developed trace gas photolysis rate measurement instrument, namely the photolysis spectrometer, and expands the use of the photolysis spectrometer. To verify the correctness of its calibration results, a comparison verification is made with the ground solar irradiance observed by the TROPOMI satellite. The results show that there is a high degree of consistency between the two, and the correlation reaches 0.982.

[0036] A one-month continuous observation was selected from July to August 2023 near Dongpu Reservoir in Hefei City, Anhui Province.

[0037] Specifically, the photolysis spectrometer and the MAX-DOAS instrument were used to continuously observe the NO2 photolysis rate and the NO2 concentration respectively, analyze the mutual relationship between the NO2 photolysis rate and environmental factors, and analyze its change law in detail.

[0038] Furthermore, the analysis results were averaged to obtain the daily change curve of the NO2 photolysis rate j(NO2), as shown in Figure 2As shown. The results show that the diurnal variation curve of the NO2 photolysis rate has a certain pattern, which is consistent with the diurnal variation pattern of solar radiation intensity, reaching a maximum value at noon and decreasing in the morning and evening, reflecting that the process and intensity of the photochemical reaction are closely related to the energy driving the photochemical reaction. For further analysis, the measurement results are divided into sunny, cloudy, and rainy days according to the weather conditions, and the results are as Figure 3 . It is found that the NO2 photolysis rate is very sensitive to weather changes. The photolysis rate is large and the curve is smooth on sunny days, while the photolysis rate is significantly smaller on rainy days. This further shows that the photochemical reaction is closely related to the energy (solar radiation) driving the photochemical reaction.

[0039] The photolysis reaction plays an important role in atmospheric chemical reactions and has an important impact on the transformation of chemical substances in the atmosphere. Among them, NO2 is a key chemical component in atmospheric chemistry. The rapid photolysis of NO2 in the troposphere largely controls the formation of tropospheric O3 and OH radicals. To study the mutual influence between the NO2 photolysis rate and the NO2 concentration, a photolysis spectrometer and a MAX-DOAS instrument were used to continuously observe the NO2 photolysis rate and the NO2 concentration for two months. During the measurement, the two instruments need to be placed at adjacent observation positions to ensure the consistency of the observations. The measurement data of the NO2 concentration and the NO2 photolysis rate are also averaged by time, and the obtained diurnal variation curve is as Figure 4 shown, and the NO2 concentration is also divided according to the weather conditions.

[0040] The results show that the NO2 concentration information is less affected by weather changes. It is worth noting that the difference between the maximum and minimum values of the NO2 concentration is the largest on sunny days. Analyzing the diurnal variation curves of the two, considering only the main influencing factors, it is found that the numerical value of the photolysis rate in the morning is small, and the NO2 concentration is mainly affected by the morning rush hour and vehicle emissions and will gradually increase, reaching the maximum value of the day around 9:45. At noon, the solar radiation increases, and the photolysis reaction rate is large. At this time, the photolysis reaction is the main factor affecting the NO2 concentration, and the photolysis reaction of NO2 causes its concentration to start to decrease, reaching the lowest value during the day at around 16:00. In the afternoon, the photolysis rate decreases, and at this time, there is an evening rush hour, and the NO2 concentration will increase accordingly.

[0041] To further analyze the mutual relationship between the NO2 concentration and the NO2 photolysis rate, the diurnal variation curves of each are integrated to obtain the change trend of the total accumulation of each in a day. After normalization, the concentration data and photolysis rate data at each moment are averaged, and the least squares polynomial fitting is performed to obtain the curve equation. The principle of the least squares method is as follows in formula (1), and the coefficients of the regression equation are determined by minimizing the sum of the squares of the errors.

[0042]

[0043] where \(E\) is the objective function, \(p\) is a polynomial fitting function of degree \(n\), \(x\) j is the independent variable, and \(y\) j is the dependent variable (here it is the observed value or calculated from the observed value), calculate and find a set of \(\theta (\theta_0,\theta_1,\theta_2,...,\theta\) n ) such that \(E\) is minimized.

[0044] The fitting results are as Figure 5 shown. The results show that the integral curves of the NO2 photolysis rate and the NO2 concentration are both monotonically increasing and interactively rising. The red line represents the integral curve of the monthly average NO2 photolysis rate, the green line represents the integral curve of the monthly average NO2 concentration, and the black line is the average curve of the NO2 photolysis rate and the NO2 concentration integral curve at each moment. The fitting curve equations of the average curves of the two have strong similarity. For further experiments, the data of two months are divided into 8 weeks, and the integral curves are also fitted. It is found that the average values of the photolysis rate and the concentration integral curve can be approximated by the following formula (2), and their correlation is above 0.90:

[0045] \(y = -4.0\times10\) -5 \(\times x\) 3 \(+ 0.001\times x\) 2 \(+ 0.015\times x - 0.1365\) (2)

[0046] where \(x\) is the time and \(y\) is the average of the two, and then the approximate value of the NO2 concentration integral can be obtained.

[0047] Using this approximate formula, the NO2 concentration weekly or monthly accumulation can be estimated by measuring the NO2 photolysis rate. Analyzing the concentration status of NO2 in the atmosphere has reference significance for the early warning and intelligent supervision of photochemical pollution in the atmosphere.

[0048] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for estimating the cumulative concentration of NO2 by measuring the photolysis rate, characterized in that: include: The photolysis spectrometer and MAX-DOAS instrument were used to continuously observe the NO2 photolysis rate and NO2 concentration, and the measured solar radiance was compared and verified with the ground solar radiance observed by the TROPOMI satellite. Analyze the relationship between the NO2 photolysis rate and the NO2 concentration and environmental factors, and obtain daily variation curves of the two; Analyze the relationship between the NO2 photolysis rate and the NO2 concentration, integrate the daily variation curves of the two, obtain the variation trends of the respective total integral accumulations, and perform normalization processing; Conduct continuous observation for a period of multiple days, average the data of NO2 concentration and the data of NO2 photolysis rate at each moment of the multiple days, perform least squares polynomial fitting respectively, and obtain curve equations respectively; The data of NO2 concentration and the data of NO2 photolysis rate at each moment are integrated respectively, and the average value of the two is taken, and the average value curve of the two is fitted. The average value of the average value curve of the two is expressed by the approximate formula: y = -4.0*10 -5 *x 3 +0.001*x 2 +0.015*x-0.1365, Where x is time, y is the mean of the two, and the approximate value of the integral of NO2 concentration is obtained while measuring the photolysis rate.

2. The method for estimating the cumulative concentration of NO2 by measuring the photolysis rate according to claim 1, characterized in that: The photolysis spectrometer and the MAX-DOAS instrument were located adjacent to each other during observation.

3. The method for estimating the cumulative concentration of NO2 by measuring the photolysis rate according to claim 1, characterized in that: The environmental factors corresponding to the NO2 photolysis rate include solar radiation intensity and weather.

4. The method for estimating the cumulative concentration of NO2 by measuring the photolysis rate according to claim 1, characterized in that: The environmental factors corresponding to the NO2 concentration include weather and daily time intervals.

5. The method for estimating the cumulative concentration of NO2 by measuring the photolysis rate according to claim 4, characterized in that: The daily time period includes morning, noon and evening, wherein the NO2 concentration is the highest in the morning and evening, and the lowest in the noon.

6. The method for estimating the cumulative concentration of NO2 by measuring the photolysis rate according to claim 5, characterized in that: The morning time interval is 9:00-10:00, and the corresponding concentration value reaches the maximum value of the day. The afternoon time interval is 12:00-16:30, and the photolysis reaction rate increases, and the corresponding concentration value gradually reaches the minimum value of the day.

7. The method for estimating the cumulative concentration of NO2 by measuring the photolysis rate according to claim 1, characterized in that: The curve equation is a regression equation determined by minimizing the sum of squared errors.

8. The method for estimating the cumulative concentration of NO2 by measuring the photolysis rate according to claim 7, characterized in that: The regression equation is expressed as: In the formula, E is the objective function, p is the n-order polynomial fitting function, and x j is the independent variable, y j is the dependent variable, Calculate and find a set of θ(θ0,θ1,θ2,...,θ n ), so that E is minimized.

9. The method for estimating the cumulative concentration of NO2 by measuring the photolysis rate according to claim 1, characterized in that: The correlation between the mean value of the integral and the value obtained by the approximate formula is greater than 0.90.

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