Urban VOCs intensity calculation method and system

Abstract

The invention discloses an urban VOCs intensity calculation method and system, and belongs to the technical field of urban pollutant early warning. The method comprises the step of directly inverting the discharge of a target product according to the column concentration of the product by constructing a function relationship between the target pollutant and the product thereof. The HCHO is used as a photochemical product of the VOCs, and the HCHO and the photochemical product can establish a relation according to the yield and the atmospheric life, so that the emission of the VOCs can be directly calculated by utilizing the HCHO column concentration by improving a Gaussian fitting function and combining with a linear density distribution curve. According to the method, the emission load is effectively constrained, the VOCs diffusion plume released by the research area is effectively limited in the urban area, and the overestimation of a calculation result caused by the influence of a nearby interference source is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of urban pollutant early warning, and in particular to a method and system for calculating urban VOCs intensity. Background Art

[0002] Document 1: Science 333,1737(2011)Megacity Emissions and Lifetimes ofNitrogen Oxides Probed from space

[0003] This paper proposes for the first time to use the line density fitting method to simultaneously calculate the nitrogen oxide emissions and lifetime of large cities and other strong point sources. The specific method is as follows:

[0004] Step 1: Select the study area. The target area must meet the requirements of large population, large NO2 emissions, and high tropospheric NO2 column concentration. Secondly, the target area is an isolated point source (no other NOx emission sources exist within a 200km radius), and the contrast between the polluted urban center and the relatively low background is high.

[0005] Step 2: Divide the study area into 8 wind direction sectors and divide the NO 2 After determining the dominant wind direction, the column concentration data are allocated to eight wind direction sectors for source strength calculation.

[0006] Step 3: Using the linear density fitting method, 2 The linear density distribution curve is fitted with the simple model function M(x) to obtain the best fitting parameters, which include NO 2 Molecular emission E and mean lifetime τ.

[0007] M(x) is obtained by convolving the Gaussian function with the exponential function, where the Gaussian function represents the diffusion distribution pattern of pollutants after they are discharged from the emission source. The concentration of pollutants undergoes physical and chemical attenuation during the outward spreading process. The physical process is the diffusion dilution caused by the influence of wind, and the chemical process is the concentration attenuation due to the chemical reaction of pollutants in the atmosphere into other substances. The exponential function is used to convolve the downwind area of ​​the Gaussian function, thereby indicating the influence of physical and chemical attenuation on the concentration of pollutants in the downwind area.

[0008]

[0009] Detailed explanation of e(x):

[0010] It means that pollutants in the downwind area will not maintain a Gaussian diffusion distribution pattern. Due to the influence of wind and chemical transformation processes, the pollutant concentration will decay at an exponential rate of e. The distance from the highest value to the background value is called the folding distance x0.

[0011] Document 2: Pommier, M.; McLinden, CA; Deeter, M., Relative changes in COemissions over megacities based on observations from space. Geophysical Research Letters 2013, 40, (14), 3766-3771.

[0012] This paper analyzes the relative changes in CO emissions in large cities based on the vertical column concentration of CO and the MOPITT algorithm. The MOPPITT algorithm proposes to integrate all column concentration data in the vertical wind direction along the dominant wind direction to form a one-dimensional column concentration spatial distribution map of CO, thereby achieving dimensionality reduction of the spatial distribution of pollutants. Secondly, a downwind-upwind model is proposed, in which the integral value of the CO column concentration in the upwind direction is used as the background value, and the integral value of the CO column concentration in the downwind direction is used as the enhancement value. Assuming that the difference between the downwind and upwind column concentrations of the megacity is proportional to the change in the city's CO emissions, the integral difference between the downwind and upwind CO column concentrations can be used as an estimate of the relative change in emissions. Therefore, this paper selects the average of the 5 largest CO column concentration integral values ​​in the downwind area and the 5 smallest CO column concentration integral values ​​in the upwind area as an estimate of the relative change in CO emissions in the megacity. The formula is as follows:

[0013]

[0014] Previous literature has achieved the quantification of nitrogen oxide emissions using this method, but only for isolated large-scale pollution point sources, with no other interference sources within a radius of 200km. Secondly, the background technology cannot directly quantify the target pollutant, but first quantifies its precursor, and then multiplies it by a fixed conversion coefficient based on the conversion relationship between the two to obtain the target pollutant emissions. When considering designing a fitting function, a standard Gaussian diffusion function is usually selected or a new function is formed by convolving an exponential function with a Gaussian function (considering the downwind attenuation of pollutants). However, both of them did not consider the chemical transformation process of pollutants when fitting pollutant emissions. Although the fitted parameters have physical meaning, they cannot be explained in the process of atmospheric source-sink transformation.

[0015] The use of Gaussian diffusion function to estimate molecular emissions is a fixed estimate of the target pollutant emissions using the target pollutant column concentration, without establishing a connection between the pollutant and its product. If you want to further obtain the emissions of the target pollutant, further theoretical derivation is required, so it is more complicated and has too many application limitations. Secondly, the fitting area determined by the background technology method is much larger than the urban area, so it will be greatly interfered by the surrounding interference sources during the fitting process, resulting in large errors in the calculation results. Summary of the invention

[0016] The purpose of the present invention is to provide an efficient method and system for calculating urban VOCs intensity. According to the urban VOCs intensity inversion algorithm provided by the present invention, the VOCs emission intensity can be directly calculated using secondary HCHO, and the VOCs emission level information can be obtained quickly and accurately, providing a reference and basis for the prevention and control of regional atmospheric complex pollution.

[0017] In order to solve the above technical problems, the present invention provides a method for calculating urban VOCs intensity, comprising the following steps:

[0018] According to the HCHO to CO emission ratio of the combustion source and the ground concentration of CO, the primary HCHO ground concentration C is determined. HCHO_Pr ;

[0019] No 2 The ratio of the ground concentration to the satellite column concentration was used as the ratio of the primary HCHO ground concentration to the satellite column concentration. Based on the ideal gas state equation, NO 2 The conversion equation between satellite column concentration and ground concentration is used to calculate the satellite column concentration Ω of primary HCHO HCHO_pri ;

[0020] According to the satellite column concentration of primary HCHO Ω HCHO_pri , ground data and high-altitude data, construct a line density scatter plot, and obtain the VOCs line density;

[0021] Fit the linear VOCs density with the Gaussian formula to obtain the VOCs emission flux;

[0022] The VOCs emission flux is scaled according to the scaling factor λ to obtain the VOCs emission scaling result A HCHO_sec ;

[0023] Scaling results according to VOCs emissions A HCHO_sec , calculate the emission intensity E VOCs .

[0024] Preferably, the primary HCHO ground concentration C HCHO_Pr The calculation formula is:

[0025] C HCHO_pri =ER C1:CO ×C co

[0026] Where: ER C1:CO is the emission ratio of HCHO to CO in the flue gas / exhaust gas of the combustion source; C co is the ground concentration of CO.

[0027] Preferably, the NO 2 The conversion equation between satellite column concentration and ground concentration is:

[0028] Ω HCHO_pri ×R×T×10 10 =β×C HCHO_pri ×P×NA

[0029] Where: β is the ratio of the primary HCHO ground concentration to the satellite concentration.

[0030] Preferably, according to the satellite column concentration Ω of the primary HCHO HCHO_pri , ground data and high-altitude data, construct a line density scatter plot, and obtain the VOCs line density, which specifically includes the following steps:

[0031] According to the satellite column concentration of primary HCHO Ω HCHO_pri and background concentration Ω HCHO_B , stripping out the secondary formaldehyde column concentration Ω HCHO_sec ;

[0032] Determine the prevailing wind direction based on ground data and high-altitude data;

[0033] Determine the direction of the fitting wireframe according to the dominant wind direction;

[0034] Based on the land use type and population density data, the urban area scope is determined and the urban area grid is obtained;

[0035] According to the urban area grid, the emission area of ​​VOCs is obtained and the width of the fitting wireframe is determined;

[0036] According to the secondary formaldehyde column concentration Ω HCHO_sec , fit the direction and width of the wireframe, construct a line density scatter plot, and obtain the VOCs line density.

[0037] Preferably, the secondary formaldehyde column concentration Ω HCHO_sec The calculation formula is as follows:

[0038] Ω HCHO_sec =Ω HCHO -Ω HCHO_pri -Ω HCHO_B

[0039] Where: ΩHCHO_B is the background concentration; Ω HCHO_pri is the satellite column concentration.

[0040] Preferably, fitting the linear VOCs density with the Gaussian formula to obtain the VOCs emission flux specifically includes the following steps:

[0041]

[0042] In the formula: A represents the emission flux of VOCs; X represents the prior coordinates of the emission source; σ represents the standard deviation of the Gaussian formula, which actually means the diffusion attenuation rate of VOCs.

[0043] N(x)=τ·Y·E·G(x)+bx+c

[0044] Set τ·Y·E=A;

[0045]

[0046] Where: τ HCHO The unit is h; k HCHO:OH is the reaction rate constant of HCHO and OH free radicals; [OH] is the OH free radical concentration at noon; j HCHO is the photolysis rate constant of HCHO; N(x) is a new function based on Gaussian distribution, E is the emission flux of VOCs; G(x) is the diffusion distribution function satisfied by secondary HCHO, Y is the conversion yield of VOCs to secondary HCHO simulated based on the MCM model; bx+c is the linear baseline.

[0047] Preferably, the VOCs emission flux is scaled according to the scaling factor λ to obtain the VOCs emission scaling result A HCHO_sec , specifically including the following steps:

[0048] The Gaussian function is integrally scaled according to the width b of the fitting wireframe and the migration length I;

[0049] The smear distance is defined as the displacement length of VOCs from emission to the generation of the highest concentration of secondary HCHO column concentration. Considering the entire urban area as a point source, the maximum distance that VOCs can migrate after being emitted from position X is

[0050] The scaling method is: in the main part of the Gaussian function, the center of city X is taken as the reference and extended to both sides. The whole pollutant plume is captured by integrating with infinity as the upper and lower limits. The ratio of the two is used as a scaling factor to constrain the pollutant diffusion plume, and then the fitted molecular emission A is scaled by the scaling factor λ.

[0051] Preferably, the calculation formula of the migration length I is:

[0052]

[0053] Where: k voc is the total VOC loss rate constant, k HCHO is the loss rate constant of formaldehyde;

[0054] The calculation formula of the scaling factor λ is:

[0055]

[0056] The VOCs emission scaling result A HCHO_sec The calculation formula is:

[0057] A HCHO_sec =λ·A

[0058] Where: A HCHO_sec is the linear density of HCHO.

[0059] Preferably, the emission intensity E VOCs The calculation formula is:

[0060]

[0061] Where: NA is Avogadro's constant; S is the area of ​​the study area.

[0062] The present invention also provides a system for calculating urban VOCs intensity, comprising:

[0063] The ground concentration calculation module is used to determine the primary HCHO ground concentration C according to the HCHO to CO emission ratio of the combustion source and the ground concentration of CO. HCHO_Pr ;

[0064] Conversion module, used to convert NO 2 The ratio of the ground concentration to the satellite column concentration was used as the ratio of the primary HCHO ground concentration to the satellite column concentration. Based on the ideal gas state equation, NO 2 The conversion equation between satellite column concentration and ground concentration is used to calculate the satellite column concentration Ω of primary HCHO HCHO_pri ;

[0065] Line density scatter plot construction module for satellite column concentration Ω based on primary HCHO HCHO_pri , ground data and high-altitude data, construct a line density scatter plot, and obtain the VOCs line density;

[0066] The emission flux calculation module is used to fit the linear VOCs density with the Gaussian formula to obtain the VOCs emission flux;

[0067] The scaling module is used to scale the VOCs emission flux according to the scaling factor λ to obtain the VOCs emission scaling result A HCHO_sec ;

[0068] Emission intensity calculation module, used to scale the results according to VOCs emissions A HCHO_sec , calculate the emission intensity E VOCs .

[0069] Compared with the prior art, the present invention has the following beneficial effects:

[0070] 1. Accurate wind direction selection. When determining the wind direction, the present invention selects to use a timely meteorological station data set, which can provide wind direction and wind speed data for every hour of every day in the Beijing-Tianjin-Hebei urban area, and can be synchronized with the atmospheric remote sensing satellite transit time (12:00-14:00), accurately extracting the exact wind direction when the satellite passes at noon that day, and at the same time using the backward trajectory model to reverse the movement of high-altitude air masses at noon every day and compare with the meteorological station wind direction data, further verifying the accuracy of the meteorological station data, so the wind direction data determined by the present invention is more accurate.

[0071] Second: The existing technologies all study large spatial scales, usually treating isolated large cities as a whole emission source for research, and the fitting results are limited to the molar emission level. The present invention divides the functional areas of key cities by combining population density data with land use type data, and assigns clear regional areas. The calculated emission data can be accurate to the intensity level, that is, the emission per unit area per unit time, providing more timely and refined emission data.

[0072] 3: The present invention further divides the fitting wireframe into multiple unit fitting wireframes (bkm×7km) according to the satellite column concentration resolution, creates a unit fitting wireframe, improves the line density fitting method, and thus constructs a more accurate and reasonable line density distribution curve.

[0073] Fourth: By constructing the functional relationship between secondary HCHO and its precursor VOCs through yield and atmospheric lifetime, the emission of precursor VOCs can be directly inferred using the column concentration of the product secondary HCHO, thereby achieving the purpose of pollutant quantification. The present invention redefines the fitting parameter A so that it can directly characterize the VOCs emission flux without considering the source-sink conversion relationship between secondary HCHO and VOCs again, which can effectively avoid the influence of ozone on the experimental results.

[0074] 5. Effectively constrain the emission volume. By reasonably scaling the fitting result A (λ), the VOCs diffusion plume released in the study area is effectively limited to the urban area, avoiding the overestimation of the calculation results due to the influence of nearby interference sources. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] The specific implementation modes of the present invention are further described in detail below with reference to the accompanying drawings.

[0076] Figure 1 It is the line density definition diagram; where: a is the main wind direction fitting length, b is the integral width, and white represents the point source position;

[0077] Figure 2 is the Ω of Example 1 HCHO_sec Distribution map;

[0078] Figure 3 It is a schematic diagram of the Beijing-Tianjin-Hebei region grid of Example 1, Example 2, and Example 3;

[0079] Figure 4 is the Ω of Example 1 HCHO_sec Wireframe schematics;

[0080] Figure 5 is the HCHO_sec line density fitting diagram of Example 1;

[0081] Figure 6 is the Ω of Example 2 HCHO_sec Distribution map;

[0082] Figure 7 is the Ω of Example 2 HCHO_sec Wireframe schematics;

[0083] Figure 8 is the HCHO_sec line density fitting diagram of Example 2;

[0084] Fig. 9 is the Ω of Example 3 HCHO_sec Distribution map;

[0085] Fig.10 is the Ω of Example 3 HCHO_sec Satellite distribution map

[0086] Fig.11 This is the HCHO_sec line density fitting diagram of Example 3. DETAILED DESCRIPTION

[0087] Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar generalizations without violating the connotation of the present invention, so the present invention is not limited to the specific implementation disclosed below.

[0088] The terms used in one or more embodiments of this specification are only for the purpose of describing specific embodiments, and are not intended to limit one or more embodiments of this specification. The singular forms of "a", "said" and "the" used in one or more embodiments of this specification and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used in one or more embodiments of this specification refers to and includes any or all possible combinations of one or more associated listed items.

[0089] It should be understood that although the terms first, second, etc. may be used to describe various information in one or more embodiments of this specification, this information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of one or more embodiments of this specification, the first may also be referred to as the second, and similarly, the second may also be referred to as the first. Depending on the context, the word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining".

[0090] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0091] The present invention provides a method for calculating the intensity of VOCs in cities, investigates the emission factors of aldehydes and CO from the main combustion sources in cities, and calculates the emission ratio of primary HCHO to CO (ER C1:CO ), based on the CO ground concentration and the proportion of ER C1:CO The primary HCHO ground concentration is obtained. 2 The ratio of ground concentration to satellite column concentration β represents the ratio of primary HCHO ground concentration to satellite column concentration, and then the column concentration of primary HCHO is obtained. The secondary HCHO column concentration is extracted by combining HCHO satellite remote sensing data with HCHO background concentration. The urban fitting range is determined according to the soil utilization type and population density data, and the dominant wind direction of the day of the satellite data used is determined by the national meteorological station data. Figure 1 As shown in the figure, the secondary HCHO column concentration in the integral direction y is integrated along the dominant wind direction x (the integral width is b), and then the two-dimensional secondary HCHO column concentration distribution map is converted into a one-dimensional "line density" curve distribution map. The best pollutant diffusion function is selected to fit the secondary HCHO line density distribution to obtain parameters (the parameters include VOCs emissions E), thereby realizing the quantification of VOCs emissions.

[0092] The present invention needs to optimize the background technology. By constructing a functional relationship between the target pollutant and its product, the emission of the target product can be directly inverted according to the column concentration of the product. HCHO is a photochemical product of VOCs. The two can establish a connection based on the yield and the atmospheric lifetime. Therefore, the Gaussian fitting function is improved and combined with the line density distribution curve, and the VOCs emission can be directly inferred using the HCHO column concentration. Secondly, the fitting parameters are optimized. According to the determined fitting area range combined with the migration length, the main part of the Gaussian function is integrally scaled, and then the lower integral area of ​​the fitting curve is reasonably scaled. The purpose is to constrain the HCHO diffusion plume directly converted from VOCs from urban emission sources within the range of the migration length, so as to accurately capture the HCHO diffusion plume and prevent overfitting caused by the influence of interference sources, which makes the inferred emissions too large.

[0093] When considering designing fitting parameters, the present invention fully considers the conversion relationship between VOCs and secondary HCHO in the atmosphere, and constructs a reasonable fitting function based on the atmospheric lifetime and conversion rate. The function can reflect the spatial distribution relationship and conversion relationship between the secondary HCHO column concentration and VOCs emissions. The VOCs emissions can be directly inverted by the constructed new function.

[0094] The linear density fitting method is to take the emission source as the center, along the main wind direction x, on the basis of unit resolution length, by integrating and summing all column concentrations in the Y direction, so as to convert the two-dimensional concentration data into a one-dimensional distribution with a curve representing the concentration size distribution. The ordinate in the one-dimensional distribution graph represents the linear density of the pollutant distribution, and the unit is usually molecule / cm, which represents the number of pollutant molecules per unit length and per unit area of ​​the integral width b in the dominant wind direction. Figure 1 As shown, a is the main wind direction fitting length, b is the integration width, and white represents the "point source" position.

[0095] The specific scheme of the present invention comprises the following steps:

[0096] Step 1: Since the HCHO emission sources in urban areas are relatively stable and single, the primary HCHO directly generated by the emission sources has no significant difference in time and space, so when considering the primary HCHO, the overall average value of all urban areas is taken. The present invention investigates the emission factors of aldehydes and CO for the main combustion sources of diesel vehicles, gasoline vehicles, coal-fired boilers, and wood stoves, and calculates the HCHO to CO emission ratio (ERC1:CO) in the flue gas / exhaust gas of the combustion source, and then calculates the primary HCHO ground concentration C based on the ground concentration of CO Cco. HCHO_Pr The calculation formula is as follows:

[0097] C HCHO_pri=ER C1:CO ×C co

[0098] Step 2: NO 2 It has the same atmospheric lifetime as primary HCHO, so it can be used as NO 2 The ratio of the ground concentration to the satellite column concentration, β, is used as the ratio of the primary HCHO ground concentration to the satellite column concentration. Based on the ideal gas state equation, NO 2 The conversion equation between satellite column concentration and ground concentration is used to calculate the satellite column concentration Ω of primary HCHO. HCHO_pri The calculation formula is as follows:

[0099] Ω HCHO_pri ×R×T×10 10 =β×C HCHO_pri ×P×NA

[0100] Where, β is the ratio of primary HCHO ground concentration to satellite concentration, unit: km. Primary HCHO ground concentration CHCHO_pri, unit: ppb. Primary HCHO column concentration Ω HCHO_pri , unit: molecule / cm 2 R is the molar gas constant, which is usually 8.314. P is the local ground pressure, in pa. T is the local daily average temperature, in K.

[0101] Step 3: Combine HCHO satellite column concentration with background concentration Ω HCHO_B , stripping out the secondary formaldehyde column concentration ΩΩ HCHO_sec , the calculation formula is as follows:

[0102] Ω HCHO_sec =Ω HCHO -Ω HCHO_pri -Ω HCHO_B

[0103] Where: Ω HCHO For remote sensing data;

[0104] Step 4: Based on the wind direction and speed data (ground data) of China's national monitoring stations and the air mass direction (upper-air data) of the backward trajectory model, the daily dominant wind direction in Tianjin is determined, and the fitting direction is determined according to the dominant wind direction.

[0105] The scope of the urban area is determined based on land use type and population density data. It is stipulated that in a unit grid of 7*7km, areas with a population density of 6,000 to 10,000 people per square kilometer and an artificial surface area of ​​no less than 70% of the unit grid belong to the urban area, and other areas belong to the rural area.

[0106] Step 5: Determine the emission area of ​​VOCs based on the urban area grid to determine the width of the fitting wireframe, such as the size of b in the figure above. It is stipulated that the width of the fitting wireframe cannot be less than the longest side of the regional area to prevent the omission of emission sources and the underestimation of emissions; it cannot be too large to include emissions from other areas and cause overestimation of emissions. Taking into account the smearing phenomenon caused by the movement of air masses after VOCs are emitted, the fitting length is extended outward as much as possible to maintain sufficient data volume and fully capture the entire emission plume. However, try to ensure that it does not cross provinces to prevent interference from other emission sources.

[0107] Step 6: Based on the daily average column concentration distribution map of secondary HCHO in major cities in Beijing, Tianjin and Hebei, after determining the direction and size of the fitting wireframe, construct the line density scatter plot of the day: Since the satellite grid resolution is 7*7km, the fitting wireframe is divided into a unit density wireframe every 7km along the dominant wind direction, with a length of 7km, a width of the fitting wireframe b, and the number of unit wireframes is the length of the fitting wireframe a / 7 (pieces). The column concentrations of all grids in each unit density wireframe are added up and multiplied by the wireframe width b to obtain the VOCs line density point with 7km as a unit, unit: molecule / cm. The VOCs line density curve is fitted with a Gaussian function with a baseline to obtain the fitting parameter A, that is, the molecular emission of VOCs in the fitting area, unit: molecule.

[0108] line density=∑Ω HCHO_sec ×b×10 10

[0109] Where: b is the width of the fitting wireframe; 1010 is the unit conversion, width km is converted to cm, length km is converted to cm;

[0110] Step 7: Since VOCs will be partially converted into HCHO_sec after emission, and the secondary HCHO still satisfies the Gaussian diffusion distribution in spatial distribution, the linear density distribution curve of the secondary HCHO can be constructed and fitted with the Gaussian formula, where the Gaussian formula characterizes the spatial distribution relationship between the linear density of the secondary HCHO and the VOCs emission flux. Through the above fitting operation, the emission flux of VOCs can be directly inverted through the secondary HCHO, realizing the quantification of VOCs emissions.

[0111]

[0112] In the formula: G(x) is a Gaussian function; A represents the molecular emission of VOCs in the fitting area (VOCs emission flux); X represents the prior coordinates of the emission source; σ represents the standard deviation of the Gaussian formula, which actually means the diffusion attenuation rate of VOCs.

[0113] N(x)=τ·Y·E·G(x)+bx+c

[0114] Where τ·Y·E=A;

[0115]

[0116] In the formula, τ HCHO is the atmospheric lifetime of formaldehyde gas, in h, k HCHO:OH is the reaction rate constant of HCHO and OH radical, in cm 3 ·molecules -1 ·s -1 ; [OH] is the OH radical concentration at noon, in molecules / cm 3 ;j HCHO is the photolysis rate constant of HCHO, in s -1 .

[0117] N(x) is a new function based on Gaussian distribution, E is the emission flux of VOCs, unit: molecule / h; G(x) is the diffusion distribution function satisfied by secondary HCHO, Y is the conversion yield of VOCs to secondary HCHO simulated based on the MCM model. In order to prevent nearby interference sources, a linear baseline bx+c is introduced at the tail of the Gaussian function, and the influence of interference sources on the overall spatial distribution is weakened by the tilt of the baseline.

[0118] Step 8: Constrain the emission. Since VOCs will diffuse to the outside of the urban area with the wind during the emission process, the Gaussian function needs to be scaled to completely constrain the diffusion plume. The Gaussian distribution functions of steps 6 and 7 are integrally scaled according to the set fitting width b and migration length I. The smear distance is defined as the displacement length of VOCs from emission to the generation of the highest concentration of secondary HCHO column concentration, in km. Considering the entire urban area as a point source, the maximum distance that VOCs can migrate after being emitted from position X is The scaling method is: in the main part of the Gaussian function, the center of city X is taken as the reference and extended to both sides. As the upper and lower limits, the whole pollutant plume is captured by integration. Then the whole Gaussian function is integrated with infinity as the upper and lower limits of integration. The ratio of the two is used as a scaling factor to reasonably and effectively constrain the pollutant diffusion plume, and then the fitted molecular emission A is scaled by the scaling factor λ. The method is as follows:

[0119] Migration length I calculation:

[0120]

[0121] Among them, k vocis the total VOC loss rate constant, k HCHO is the formaldehyde loss rate constant, unit is s-1.

[0122]

[0123] Where: A HCHO_sec Scale the results for VOCs emissions.

[0124] Step 9: Calculate emission intensity E from HCHO linear density VOCs (t / km 2 / h):

[0125]

[0126] Where NA is Avogadro's constant 6.02×10 23 , S is the area of ​​the study area, unit: km 2 . It is the weighted relative molecular mass of 99 VOCs, which is obtained by the product of the relative molecular mass and the molar proportion of each species.

[0127] The key points of the above steps of the present invention are:

[0128] Key point one: determination of wind direction. The present invention needs to design the fitting direction of the fitting wireframe according to the dominant wind direction, and then construct a line density curve. Therefore, it is necessary to determine the dominant wind direction of the day of the study. Therefore, in terms of obtaining wind direction data, the high-frequency wind direction of the meteorological station in the study area on that day is selected as the dominant wind direction. At the same time, the direction of the high-altitude air mass on that day is simulated based on the backward trajectory model (HYSPLIT). The height of the air mass in the backward trajectory is 100m, and four time nodes are set, namely 0 o'clock, 6 o'clock, 12 o'clock, and 18 o'clock. The running time is 6 hours, and the diffusion direction of the air mass within the day can be obtained. The air mass diffusion direction of 12-18 is compared and verified with the dominant wind direction of the meteorological station, and then the final dominant wind direction at noon on that day is determined.

[0129] Key point two: dividing functional areas. The fitting emission intensity of the present invention is defined as the emission per unit area per unit time in the urban area. Therefore, it is necessary to divide the study area into regions, vegetation zones, and mixed zones. And accurately define the regional division standards to determine the regional area. According to the regional division standards: areas with a population density of 6,000 to 10,000 people per square kilometer and a residential building area accounting for more than 70% are divided into regions. Therefore, based on China's population density data and land use type data, unit grids (7*7km) with a population density of more than 6,000 people / km2 and an artificial surface area accounting for more than 70% are classified as regional grids; unit grids with a vegetation coverage rate of more than 60% are classified as vegetation zones; other areas are classified as mixed zones.

[0130] Key point 3: Design the fitting wireframe and move the width of the fitting wireframe along the dominant wind direction to ensure that the entire area can be covered. The length of the fitting wireframe extends outward along the dominant wind direction with the city center as the midpoint, but cannot cross the city.

[0131] Key point 4: Parameter design. In the process of fitting using the line density method, the set parameters are given relevant practical meanings and can reflect the state of the pollutant diffusion process. For example, parameter A in step 4 means the lower integral area in mathematics, which actually represents the molecular mass of pollutant emissions, unit: molecule. The mathematical meaning of parameter X is the x-coordinate of the peak point of the Gaussian function, which actually represents the prior coordinates of the pollution source. The mathematical meaning of σ is the standard deviation of the Gaussian function, which actually represents the rate at which pollutants diffuse from the source point to the dominant wind direction. bx+c reflects the influence of surrounding interference sources. All parameters characterize all spatial distribution information of VOCs.

[0132] Key point five: Line density curve construction. The key to this link is to achieve dimensionality reduction processing of the spatial diffusion of pollutants. Pollutants are discharged and diffused from the pollution source, forming a "two-dimensional" plane diffusion plume with high concentration in the center and decreasing concentrations in the surrounding areas. By accumulating all column concentrations per unit length in a specific area to form a "one-dimensional" data point, the two-dimensional diffusion plume is transformed into a "one-dimensional" diffusion curve. Since the satellite column concentration data used in the present invention is a grid data with a resolution of 0.07°×0.07°, the line density is defined as one line density unit per 7km, forming multiple 7*b (fitting cumulative width) unit fitting wireframes, and adding the column concentrations in the unit fitting wireframes to form a unit line density point. The specific meaning is: molecular column density per unit length, unit: molecule / cm.

[0133] Key point 6: By constructing the functional relationship between secondary HCHO and its precursor VOCs through yield and atmospheric lifetime, the precursor emission can be directly inferred using the product column concentration. It is necessary to design the integral area A under the fitting curve. The definition of A includes the conversion relationship between the secondary VOCs emission flux and the secondary HCHO emission: E HCHO =Y·τ HCHO_sec ·E HRVOCs Therefore, the Gaussian formula of secondary HCHO can be improved, in which A representing the emission of secondary HCHO molecules is converted into a linear expression representing the VOCs emission flux, that is, A = Y·τ HCHO ·E HRVOCs Then, the Gaussian function relationship between the secondary HCHO column concentration and VOCs emission was constructed: N(x)=τ·Y·E·G(x)+bx+c.

[0134] Key point seven: Constrained emissions. Since the length of the fitting wireframe is extended as much as possible to ensure sufficient line density point data, the line density points contain data other than the emission area, and the lower integral area A obtained by fitting the line density curve contains other interference areas. Therefore, based on the fitting width b, the key part of the Gaussian function is integrated and scaled to obtain the scaling factor λ, and then the integral area A under the line density fitting is multiplied by the scaling factor λ to obtain the molecular emissions of the emission area with the city center as the geometric center and a side length of b.

[0135] In order to better illustrate the technical effect of the present invention, the present invention provides the following specific embodiments to illustrate the above technical process:

[0136] Example 1: Taking the effective day of June 30, 2021 in Tianjin as an example:

[0137] Step 1: Based on the daily average ground CO concentration data from national monitoring stations, combined with the calculated ER C1:CO , the initial formaldehyde ground concentration data of Tianjin on that day was obtained, and the calculation is as follows:

[0138] C HCHO_pri =ER C1:CO ×C co =2.83ppb

[0139] ER C1:CO 0.004, C co It is 696.83, unit: ppb;

[0140] Step 2: Based on the NO data from national monitoring stations at noon every day in June 2021 2 The ground concentration and the daily average column concentration data in June 2021 provided by the TROPOMI satellite were used to construct the NO 2 The ratio of column concentration to ground concentration β is used to calculate the primary formaldehyde satellite column concentration:

[0141]

[0142] Among them, β = 0.78, unit: km. P is the local atmospheric pressure, which is 101325 Pa. Avogadro's constant is 6.02×1023, and temperature is the average temperature of the day, unit: K.

[0143] Step 3: Based on the HCHO satellite column concentration data of Tianjin on June 13, 2021 and the background column concentration of Tianjin, the secondary formaldehyde column concentration Ω of Tianjin on that day was obtained. HCHO_sec , calculated as follows:

[0144] Ω HCHO_sec =Ω HCHO -Ω HCHO_pri -Ω HCHO_B

[0145] Where Ω HCHO is the TROPOMI satellite remote sensing data with a resolution of 7*7km, Ω HCHO_B The average background concentration in Tianjin is 450×1013molecule / cm2. The satellite distribution map of secondary HCHO in Tianjin on June 30, 2021 is obtained as follows: Figure 2 As shown;

[0146] Step 4: Based on the data from China's meteorological stations, the daily wind direction and speed data for Tianjin in June 2021 were extracted and compared with the backward trajectory to determine that the dominant wind direction on June 30, 2021 was southeast wind, with a wind direction angle of 128.9° and a wind speed of 1.6 m / s.

[0147] Step 5: Based on the population density data and land use type data, the urban area of ​​Tianjin is determined (black grid). It is finally determined that the urban area of ​​Tianjin is based on the longitude and latitude of the center of Tianjin, and expands outward by 5 unit grids (245km2), as shown in the red area in the figure below. It expands horizontally by 3 grids (21km) and vertically by 3 grids (21km). Therefore, the fitting width of Tianjin is determined to be 21km. Figure 3 As shown;

[0148] Step 6: Based on the secondary HCHO column concentration ΩHCHO_sec in Tianjin on June 30, 2021, the spatial distribution of the secondary HCHO column concentration on that day was obtained, and a fitting wireframe was constructed, such as Figure 4 As shown:

[0149] Step 7: Based on the line density method, the secondary HCHO line density distribution map on June 30, 2021 was obtained, and the improved new function N(x)=τ·Y·E·G(x)+bx+c with Gaussian form was used for fitting. The fitting results are shown in Figure 5 As shown, the ordinate is the secondary HCHO linear density, unit: 1026molecule / cm.

[0150] Fitting equation:

[0151] Fitting parameter values: A = 40.2395, σ = 16.1033, X = -0.0385, a = 0.001, c = 36.4925

[0152] Fitting results (R2 = 0.94)

[0153] The fitting parameter A here is not the actual molecular weight A, but Therefore, it is necessary to convert it into the true molecular weight A, A = τ HCHO_sec ·Y·E

[0154]

[0155] Subsequent processing: The fitting result A is subjected to subsequent mathematical calculations to obtain the emission intensity on June 30, 2021:

[0156] 1. Migration length I:

[0157] Among them, k voc The value is 0.98s -1 , k HCHO The value is 0.32s -1 .

[0158] Scaling factor λ:

[0159]

[0160] 2. Secondary HCHO atmospheric lifetime:

[0161] In the formula, k HCHO:OH With j HCHO Derived from the SAPRC-99 list of gas-phase atmospheric chemistry mechanisms, k HCHO:OH =8.47×10 -12 , unit: cm 3 ·molecule -1 ·s -1 .j HCHO =7.24×10 -7 , unit: s -1 [OH] The midday value observed at Xianghe station in Beijing-Tianjin-Hebei was 1.13×10 7 , unit: molecules / cm 3 .

[0162] 3. VOCs emission scaling: A HCHO_sec =λ·A=0.84×1.6240×10 29 =1.3641×10 29 molecule

[0163] 4. Based on A HCHO_sec =τ HCHO_sec ·Y·E, the VOCs molecular emission flux is obtained:

[0164] In the formula, the yield Y is simulated by the MCM box model to obtain the concentration change trend in the Beijing-Tianjin-Hebei region in 2021, and the relationship between VOCs and secondary HCHO production and consumption is obtained. The result is a linear change relationship with a slope of 0.189, that is, the secondary HCHO yield Y generated by VOCs.

[0165] 5. Calculate emission intensity E from HCHO linear density VOCs (t / km 2 / h):

[0166] Example 2: Take the effective day of June 13, 2021 in Tianjin as an example;

[0167] Step 1: Based on the daily average ground concentration data of CO at the national monitoring station and the calculated ERC1:CO, the ground concentration data of primary formaldehyde in Tianjin on that day was obtained as follows:

[0168] C HCHO_pri =ER C1:CO ×C co =4.32ppb

[0169] Among them, ERC1:CO is 0.004, Cco is 1080.24, unit: ppb

[0170] Step 2: Based on the NO data from national monitoring stations at noon every day in June 2021 2 The ground concentration and the daily average column concentration data in June 2021 provided by the TROPOMI satellite were used to construct the NO 2 The ratio of column concentration to ground concentration β is used to calculate the primary formaldehyde satellite column concentration:

[0171]

[0172] Among them, β = 0.78, unit: km. P is the local atmospheric pressure, which is 101325 Pa. Avogadro's constant is 6.02×1023, and temperature is the average temperature of the day, unit: K.

[0173] Step 3: Based on the HCHO satellite column concentration data of Tianjin on June 13, 2021 and the background column concentration of Tianjin, the secondary formaldehyde column concentration Ω of Tianjin on that day was obtained. HCHO_sec , calculated as follows:

[0174] Ω HCHO_sec =Ω HCHO -Ω HCHO_pri -Ω HCHO_B

[0175] ΩHCHO is the remote sensing data of TROPOMI satellite with a resolution of 7*7km, and ΩHCHO_B is the average background concentration of Tianjin, 450×1013molecule / cm 2 The satellite distribution map of secondary HCHO in Tianjin on June 13, 2021 is obtained:

[0176] Step 4: Based on the data from China Meteorological Station, extract the daily wind direction and speed data of Tianjin in June 2021 and compare them with the backward trajectory to determine that the dominant wind direction on June 13, 2021 is south wind, with a wind direction angle of 196° and a wind speed of 2.4m / s; Figure 6 As shown;

[0177] Step 5: Based on the population density data and land use type data, the urban area of ​​Tianjin is determined (black grid). It is finally determined that the urban area of ​​Tianjin is based on the longitude and latitude of the center of Tianjin, and expands outward by 5 unit grids (245km2), as shown in the red area in the figure below. It expands horizontally by 3 grids (21km) and vertically by 3 grids (21km). Therefore, the fitting width of Tianjin is determined to be 21km. Figure 3 As shown;

[0178] Step 6: Based on the secondary HCHO column concentration ΩHCHO_sec in Tianjin on June 13, 2021, the spatial distribution of the secondary HCHO column concentration on that day was obtained, and a fitting wireframe was constructed, such as Figure 7 As shown:

[0179] Step 7: Based on the line density method, the secondary HCHO line density distribution map on June 13, 2021 was obtained, and the improved new function N(x)=τ·Y·E·G(x)+bx+c with Gaussian form was used for fitting. The fitting results are shown below. The ordinate is the secondary HCHO line density, unit: 1026molecule / cm; Figure 8 As shown:

[0180] Fitting equation:

[0181] Fitting parameter values: A = 76.6, σ = 9.7843, X = -7.6186, b = 1.1898, c = 55.7199

[0182] Fitting results (R2=0.78)

[0183] The fitting parameter A here is not the actual molecular weight A, but Therefore, it is necessary to convert it into the true molecular weight A, A = τ HCHO_sec ·Y·E

[0184]

[0185] Subsequent processing: The fitting result A is subjected to subsequent mathematical calculations to obtain the emission intensity on June 30, 2021:

[0186] 1. Migration length I:

[0187] Among them, the kvoc value is 0.98s-1 , kHCHO value is 0.32s -1 .

[0188] Scaling factor λ:

[0189] 2. Secondary HCHO atmospheric lifetime:

[0190] In the formula, k HCHO:OH With j HCHO Derived from the SAPRC-99 list of gas-phase atmospheric chemistry mechanisms, k HCHO:OH =8.47×10-12, unit: cm 3 ·molecule -1 ·s -1 .j HCHO =7.24×10 -7 , unit: s -1 [OH] The midday value observed at Xianghe station in Beijing-Tianjin-Hebei was 1.13×10 7 , unit: molecules / cm 3 .

[0191] 3. VOCs emission scaling: A HCHO_sec =λ·A=0.97×1.8786×10 29 =1.8223×10 29 molecule

[0192] 4. Based on A HCHO_sec =τ HCHO_sec ·Y·E, the VOCs molecular emission flux is obtained:

[0193] In the formula, the yield Y is simulated by the MCM box model to obtain the concentration change trend in the Beijing-Tianjin-Hebei region in 2021, and the relationship between VOCs and secondary HCHO production and consumption is obtained. The result is a linear change relationship with a slope of 0.189, that is, the secondary HCHO yield Y generated by VOCs.

[0194] 5. Calculate E from HCHO linear density VOCs (t / km 2 / h):

[0195] Example 3: Take the effective day of July 5, 2021 in Tianjin as an example;

[0196] Step 1: Based on the daily average ground concentration data of CO at the national monitoring station and the calculated ERC1:CO, the ground concentration data of primary formaldehyde in Tianjin on that day was obtained as follows:

[0197] C HCHO_pri =ER C1:CO ×C co =3.75ppb

[0198] Among them, ERC1:CO is 0.004, Cco is 937.5, unit: ppb

[0199] Step 2: According to the national monitoring stations, the NO at noon every day in July 2021 2 The ground concentration and the daily average column concentration data in July 2021 provided by the TROPOMI satellite were used to construct the NO 2 The ratio of column concentration to ground concentration β is used to calculate the primary formaldehyde satellite column concentration:

[0200]

[0201] Where, β = 0.75, unit: km. P is the local atmospheric pressure, which is 101325 pa. Avogadro's constant is 6.02×10 23 ,Temperature is the average temperature of the day, unit: K.

[0202] Step 3: Based on the HCHO satellite column concentration data of Tianjin on July 5, 2021 and the background column concentration of Tianjin, the secondary formaldehyde column concentration Ω of Tianjin on that day was obtained. HCHO_sec , calculated as follows:

[0203] Ω HCHO_sec =Ω HCHO -Ω HCHO_pri -Ω HCHO_B

[0204] ΩHCHO is the remote sensing data of TROPOMI satellite with a resolution of 7*7km, and ΩHCHO_B is the average background concentration of Tianjin, 450×1013molecule / cm 2 The satellite distribution map of secondary HCHO in Tianjin on July 5, 2021 is obtained:

[0205] Step 4: Based on the data from China Meteorological Station, extract the daily wind direction and speed data of Tianjin in July 2021 and compare them with the backward trajectory to determine that the dominant wind direction on July 5, 2021 is northeast wind, with a wind direction angle of 34° and a wind speed of 2.7m / s; Fig. 9 As shown;

[0206] Step 5: Based on the population density data and land use type data, the urban area of ​​Tianjin is determined (black grid). It is finally determined that the urban area of ​​Tianjin is based on the longitude and latitude of the center of Tianjin, and expands outward by 5 unit grids (245km2), as shown in the red area in the figure below. It expands horizontally by 3 grids (21km) and vertically by 3 grids (21km). Therefore, the fitting width of Tianjin is determined to be 21km. Figure 3 As shown;

[0207] Step 6: Based on the secondary HCHO column concentration ΩHCHO_sec in Tianjin on July 5, 2021, the spatial distribution of the secondary HCHO column concentration on that day was obtained, and a fitting wireframe was constructed, such as Fig.10 As shown:

[0208] Step 7: Based on the line density method, the secondary HCHO line density distribution diagram on July 5, 2021 was obtained, and the improved new function N(x)=τ·Y·E·G(x)+bx+c with Gaussian form was used for fitting. The fitting results are shown below. The ordinate is the secondary HCHO line density, unit: 1026molecule / cm. Fig.11 As shown:

[0209] Fitting equation:

[0210] Fitting parameter values: A = 76.42, σ = 7.43, X = 16.8906, b = -0.3349, c = 47.4662

[0211] Fitting results (R2=0.87)

[0212] The fitting parameter A here is not the actual molecular weight A, but Therefore, it is necessary to convert it into the true molecular weight A, A = τ HCHO_sec ·Y·E

[0213]

[0214] Subsequent processing: The fitting result A is subjected to subsequent mathematical calculations to obtain the emission intensity on July 5, 2021:

[0215] 1. Migration length I:

[0216] Among them, the kvoc value is 0.98s -1 , kHCHO value is 0.32s -1 .

[0217] Scaling factor λ:

[0218]

[0219] 2. Secondary HCHO atmospheric lifetime:

[0220] In the formula, k HCHO:OH With j HCHO Derived from the SAPRC-99 list of gas-phase atmospheric chemistry mechanisms, k HCHO:OH =8.47×10-12, unit: cm 3 ·molecule -1 ·s -1 .j HCHO =7.24×10 -7 , unit: s -1 [OH] The midday value observed at Xianghe station in Beijing-Tianjin-Hebei was 1.13×10 7 , unit: molecules / cm 3 .

[0221] 3. VOCs emission scaling: A HCHO_sec =λ·A=0.84×1.4233×10 29 =1.1955×10 29 molecule

[0222] 4. Based on A HCHO_sec =τ HCHO_sec ·Y·E, the VOCs molecular emission flux is obtained:

[0223] In the formula, the yield Y is simulated by the MCM box model to obtain the concentration change trend in the Beijing-Tianjin-Hebei region in 2021, and the relationship between VOCs and secondary HCHO production and consumption is obtained. The result is a linear change relationship with a slope of 0.189, that is, the secondary HCHO yield Y generated by VOCs.

[0224] 5. Calculate emission intensity E from HCHO linear density VOCs (t / km 2 / h):

[0225] In the several embodiments provided by the present invention, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic, for example, the division of the modules, modules or units is only a logical function division, and there may be other division methods in actual implementation, for example, multiple units, modules or components can be combined or integrated into another device, or some features can be ignored or not executed.

[0226] The units may or may not be physically separated, and the components displayed as units may be one physical unit or multiple physical units, that is, they may be located in one place or distributed in multiple different places. Some or all of the units may be selected according to actual needs to achieve the purpose of the present embodiment.

[0227] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0228] In particular, according to the embodiments disclosed in the present invention, the process described above with reference to the flowchart can be implemented as a computer software program. For example, the embodiments disclosed in the present invention include a computer program product, which includes a computer program carried on a computer-readable medium, and the computer program includes a program code for executing the method shown in the flowchart. In such an embodiment, the computer program can be downloaded and installed from the network through the communication part, and / or installed from a removable medium. When the computer program is executed by the central processing unit (CPU), the above-mentioned functions defined in the method of the present invention are executed. It should be noted that the above-mentioned computer-readable medium of the present invention can be a computer-readable signal medium or a computer-readable storage medium or any combination of the above two. The computer-readable storage medium can be, for example, but not limited to, a system, device or device of an electrical, magnetic, optical, electromagnetic, infrared segment, or semiconductor, or any combination of the above.

[0229] The flow chart and block diagram in the accompanying drawings illustrate the possible architecture, function and operation of the system, method and computer program product according to various embodiments of the present invention. In this regard, each square box in the flow chart or block diagram can represent a module, a program segment or a part of a code, and the module, the program segment or a part of the code contains one or more executable instructions for realizing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the square box can also occur in a sequence different from that marked in the accompanying drawings. For example, two square boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each square box in the block diagram and / or flow chart, and the combination of the square boxes in the block diagram and / or flow chart can be implemented with a dedicated hardware-based system that performs the specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions.

[0230] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for calculating urban VOCs intensity, characterized in that: The following steps are involved: According to the HCHO to CO emission ratio of the combustion source and the ground concentration of CO, the primary HCHO ground concentration C is determined. HCHO_Pr ; The ratio of NO2 ground concentration to satellite column concentration is taken as the ratio of primary HCHO ground concentration to satellite column concentration. Based on the ideal gas state equation, the conversion equation between NO2 satellite column concentration and ground concentration is established to calculate the satellite column concentration Ω of primary HCHO. HCHO_pri ; According to the satellite column concentration of primary HCHO Ω HCHO_pri , ground data and high-altitude data, construct a line density scatter plot, and obtain the VOCs line density; Fit the linear VOCs density with the Gaussian formula to obtain the VOCs emission flux; The VOCs emission flux is scaled according to the scaling factor λ to obtain the VOCs emission scaling result A HCHO_sec ; Scaling results according to VOCs emissions A HCHO_sec , calculate the emission intensity E VOCs .

2. The method for calculating urban VOCs intensity according to claim 1, characterized in that: The primary HCHO ground concentration C HCHO_Pr The calculation formula is: C HCHO_pri =IS C1:CO ×C co Where: ER C1:CO is the emission ratio of HCHO to CO in the flue gas / exhaust gas of the combustion source; C co is the ground concentration of CO.

3. The method for calculating urban VOCs intensity according to claim 2, characterized in that: The conversion equation between the NO2 satellite column concentration and the ground concentration is: Oh HCHO_pri ×R×T×10 10 =β×C HCHO_pri ×P×NA Where: β is the ratio of the primary HCHO ground concentration to the satellite concentration; R is the molar gas constant; P is the local ground pressure; T is the local daily average temperature.

4. The method for calculating urban VOCs intensity according to claim 3, characterized in that: According to the satellite column concentration of primary HCHO Ω HCHO_pri , ground data and high-altitude data, construct a line density scatter plot, and obtain the VOCs line density, which specifically includes the following steps: According to the satellite column concentration of primary HCHO Ω HCHO_pri and background concentration Ω HCHO_B , stripping out the secondary formaldehyde column concentration Ω HCHO_sec ; Determine the prevailing wind direction based on ground data and high-altitude data; Determine the direction of the fitting wireframe according to the dominant wind direction; Based on the land use type and population density data, the urban area scope is determined and the urban area grid is obtained; According to the urban area grid, the emission area of ​​VOCs is obtained and the width of the fitting wireframe is determined; According to the secondary formaldehyde column concentration Ω HCHO_sec , fit the direction and width of the wireframe, construct a line density scatter plot, and obtain the VOCs line density.

5. The method for calculating urban VOCs intensity according to claim 4, characterized in that: The secondary formaldehyde column concentration Ω HCHO_sec The calculation formula is as follows: Oh HCHO_sec =Oh HCHO -Oh HCHO_pri -Oh HCHO_B Where: Ω HCHO_B is the background concentration; Ω HCHO_pri is the satellite column concentration.

6. The method for calculating urban VOCs intensity according to claim 5, characterized in that: Fitting the linear VOCs density with the Gaussian formula to obtain the VOCs emission flux specifically includes the following steps: Where: A represents the emission flux of VOCs; X represents the a priori coordinates of the emission source; σ represents the standard deviation of the Gaussian formula, which actually means the diffusion attenuation rate of VOCs; N(x)=τ·Y·E·G(x)+bx+c Set τ·Y·E=A; Where: τ HCHO is the atmospheric lifetime of formaldehyde gas; k HCHO+OH is the reaction rate constant of HCHO and OH free radicals; [OH] is the OH free radical concentration at noon; j HCHO is the photolysis rate constant of HCHO; N(x) is a new function based on Gaussian distribution; E is the emission flux of VOCs; G(x) is the diffusion distribution function satisfied by secondary HCHO, Y is the conversion yield of VOCs to secondary HCHO simulated based on the MCM model; bx+c is the linear baseline.

7. The method for calculating urban VOCs intensity according to claim 6, characterized in that: The VOCs emission flux is scaled according to the scaling factor λ to obtain the VOCs emission scaling result A HCHO_sec , specifically including the following steps: The Gaussian function is integrally scaled according to the width b of the fitting wireframe and the migration length I; The smear distance is defined as the displacement length of VOCs from emission to the generation of the highest concentration of secondary HCHO column concentration. Considering the entire urban area as a point source, the maximum distance that VOCs can migrate after being emitted from position X is The scaling method is: in the main part of the Gaussian function, the center of city X is taken as the reference and extended to both sides. The whole pollutant plume is captured by integrating with infinity as the upper and lower limits. The ratio of the two is used as a scaling factor to constrain the pollutant diffusion plume, and then the fitted molecular emission A is scaled by the scaling factor λ.

8. The method for calculating urban VOCs intensity according to claim 7, characterized in that: The calculation formula of the migration length I is: Where: k voc is the total VOC loss rate constant, k HCHO is the loss rate constant of formaldehyde; The calculation formula of the scaling factor λ is: The VOCs emission scaling result A HCHO_sec The calculation formula is: A HCHO_sec =λ·A Where: A HCHO_sec Scale the results for VOCs emissions.

9. The method for calculating urban VOCs intensity according to claim 8, characterized in that: The emission intensity E VOCs The calculation formula is: Where: NA is Avogadro's constant; S is the area of ​​the study area; is the weighted relative molecular mass of VOCs.

10. A system for calculating urban VOCs intensity, used to implement the method for calculating urban VOCs intensity as described in any one of claims 1 to 9, characterized in that: include: The ground concentration calculation module is used to determine the primary HCHO ground concentration C according to the HCHO to CO emission ratio of the combustion source and the ground concentration of CO. HCHO_Pr ; The conversion module is used to use the ratio of NO2 ground concentration to satellite column concentration as the ratio of primary HCHO ground concentration to satellite column concentration, establish the conversion equation of NO2 satellite column concentration to ground concentration based on the ideal gas state equation, and calculate the satellite column concentration Ω of primary HCHO HCHO_pri ; Line density scatter plot construction module for satellite column concentration Ω based on primary HCHO HCHO_pri , ground data and high-altitude data, construct a line density scatter plot, and obtain the VOCs line density; The emission flux calculation module is used to fit the linear VOCs density with the Gaussian formula to obtain the VOCs emission flux; The scaling module is used to scale the VOCs emission flux according to the scaling factor λ to obtain the VOCs emission scaling result A HCHO_sec ; Emission intensity calculation module, used to scale the results according to VOCs emissions A HCHO_sec , calculate the emission intensity E VOCs .

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