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1.
A comparison of the atmospheric chemistry mechanisms EMEP (Co-operative Programme for Monitoring and Evaluation of the Long-Range Transmission of Air Pollutants in Europe), RADM2 (Regional Acid Deposition Model, version 2) and RACM (Regional Atmospheric Chemistry Mechanism) has been conducted. Each mechanism was used to simulate the PLUME case of Kuhn et al. (1998) and to simulate an additional 150 and 81 scenarios with and without emissions, respectively. These simulations covered scenarios that ranged from relatively clean, through rural and polluted urban conditions. Ozone isopleths and scatter plots were generated from the simulations. The mechanisms were compared primarily on the basis of calculated ozone and ozone precursor concentrations. For the gas-phase ozone precursors the differences between the mechanisms were rather small under clean conditions and more significant under polluted conditions. The differences were especially significant for the concentrations of NO2 and organic peroxy radicals. In general the EMEP mechanism yielded the most ozone and the RADM2 mechanism yielded the least. Furthermore the results suggest that a broad range simulation conditions should be used to compare mechanisms and not just a few selected scenarios.  相似文献   

2.
A new atmospheric micro-scale chemistry, transport and stream model, MITRAS, has been developed within the Tropospheric Research Program (TFS). MITRAS is an obstacle resolving model solving simultaneously the governing equations for chemistry, pollutant transport including soot as well as for the flow and temperature field. The chemical reaction module is based on a simplified RACM mechanism. MITRAS has been tested against quality ensured wind tunnel data. The model results on soot and ozone concentrations as well as on the spatial representativeness of measurement sites underline the necessity for high-resolution flow simulations for case studies on close-to-source chemistry and pollutant transport within the urban canopy layer.  相似文献   

3.
Using the “lumped mechanism” and “counting species” methods, we developed a condensed gas-phase chemical model based on a simplified one. The modified quasi-steady-state approximation (QSSA) scheme and the error redistribution mass conservation technique are adopted to solve the atmospheric chemistry ki-netic equations. Results show that the condensed model can well simulate concentration variations of gas species such as SO2, NOx, O3, H2O2 and conversion rates of SO2 and NOx, transformation to H2SO4 and HNO3. These results are in good agreement with those from the simplified model, The conversion rates of SO2 and NOx under different initial concentrations and meteorological conditions are computed, and the results can be directly applied to regional acid deposition model.  相似文献   

4.
Two recent gas-phase chemical kinetic mechanisms for tropospheric ozone formation, one based on the lumped-structure approach (CB05) and the other based on the lumped-molecule approach (RACM2), are compared for simulations of ozone over Europe. The host air quality model is POLAIR3D of the Polyphemus modeling platform. A one-month period (15 July to 15 August 2001) is simulated. Model performance is satisfactory with both mechanisms. Overall, the two mechanisms give similar results with a domain-averaged difference of 3 ppb and a mean fractional absolute difference of 5% (values averaged over the month for the daily 8-h average maximum ozone concentrations). This difference results from different treatments in the two mechanisms for both inorganic and organic chemistry. Differences in the treatment of the inorganic chemistry are due mainly to differences in the kinetics of two reactions: NO + O3 \(\longrightarrow\) NO2 + O2 and NO + HO2 \(\longrightarrow\) NO2 + OH. These differences lead to a domain-averaged difference in ozone concentration of 5%, with RACM2 kinetics being more conducive to ozone formation. Differences in the treatment of organic chemistry lead to a domain-averaged difference in ozone concentration of 3%, with CB05 chemistry being more conducive to ozone formation. This average difference results in part from compensating effects among various VOC classes and some significant differences are identified at specific locations (the coastline of northern Africa and eastern Europe: 9%) and for specific organic classes (aldehydes, biogenic alkenes and aromatics). Differences in the treatment of the organic chemistry result from various aspects. For some VOC classes, such as aldehydes and biogenic alkenes, the more detailed explicit treatments using more model species in RACM2 lead to either greater or lower reactivity depending on the assumptions made for the oxidation products. For other VOC species, such as aromatics, the assumptions made about the major chemical oxidation pathways (aromatic alcohol formation in CB05 vs. ring opening in RACM2) affect the ozone formation significantly. Reconciliation of different chemical kinetic mechanisms will require experimental data to reduce current uncertainties in the kinetic (e.g., NO oxidation) and mechanistic (e.g., aromatics oxidation) representations of major chemical pathways.  相似文献   

5.
非线性大气化学动力学方程组数值解法的比较   总被引：2，自引：0，他引：2  
大气化学模式中描述化学反应动力学的是一组高度耦合、刚性、非线性的常微分方程组,高效精确的计算方法在空气质量模拟预测、气候化学相互作用研究中尤为重要。本文介绍了求解此类非线性常微分方程组(ODEs)的七种常见的数值计算方法,包括QSSA、MQSSA、HYBRID、MHYBRID、LSODE、GongCho以及TWOSTEP方法,并基于同一反应机理进行24 h的数值模拟,通过对模拟结果的讨论分析,比较了各种方法的优劣。研究结果表明,就计算效率而言,QSSA方法最为省时。就计算精度而言,LSODE方法最优。若综合考虑计算精度和效率,HYBRID、MHY-BRID是比较适中的数值解法。  相似文献   

6.
提出了一种求解非线性大气化学动力学方程组的新算法,即预测／校正拟稳定近似法（ＰＣＱＳＳＡ）该方案集中了传统的ＱＳＳＡ方案和Ｈｙｂｒｉｄ方案的优点,具有较高的计算效率和精度,对于复杂的大气化学模式和区域污染模式较适用。  相似文献   

7.
大气化学机理的发展及应用   总被引：3，自引：0，他引：3  
大气化学机理是研究大气化学过程的重要手段和方法之一,也是发展空气质量模式必不可少的重要组成部分。作者综述了几种应用广泛的简化机理——碳键机理（Carbon Bond Mechanism,CBM）、加州大气污染研究中心机理（Statewide Air Pollution Research Center mechanism,SAPRC）、区域酸沉降机理（Regional Acid Deposition Mechanism,RADM）、区域大气化学机理（Regional Atmospheric Chemical Mechanism,RACM）以及详细化学机理——主要大气化学机理（Master Chemical Mechanism,MCM）和共同代表性中间体机理（Common Representative Intermediates,CRI）的发展及应用。对上述大气化学机理的产生、发展、包含的物种类型、集总方式等方面进行了对比分析,总结了采用烟雾箱数据评价大气化学机理的研究成果以及大气化学机理在模式发展方面的应用,并对大气化学机理的进一步发展与完善提出了需求。  相似文献   

8.
A new approach is proposed to predict concentration fluctuations in the framework of one-particle Lagrangian stochastic models. The approach is innovative since it allows the computation of concentration fluctuations in dispersing plumes using a Lagrangian one-particle model with micromixing but with no need for the simulating of background particles. The extension of the model for the treatment of chemically reactive plumes is also accomplished and allows the computation of plume-related chemical reactions in a Lagrangian one-particle framework separately from the background chemical reactions, accounting for the effect of concentration fluctuations on chemical reactions in a general, albeit approximate, manner. These characteristics should make the proposed approach an ideal tool for plume-in-grid calculations in chemistry transport models. The results are compared to the wind-tunnel experiments of Fackrell and Robins (J Fluid Mech, 117:1–26, 1982) for plume dispersion in a neutral boundary layer and to the measurements of Legg et al. (Boundary-Layer Meteorol, 35:277–302, 1986) for line source dispersion in and above a model canopy. Preliminary reacting plume simulations are also shown comparing the model with the experimental results of Brown and Bilger (J Fluid Mech, 312:373–407, 1996; Atmos Environ, 32:611–628, 1998) to demonstrate the feasibility of computing chemical reactions in the proposed framework.  相似文献   

9.
正The atmospheric oxidation capacity(AOC) is the essential driving force of atmospheric chemistry in forming complex air pollution, which determines the removal rate of trace gases and the production rates of secondary pollutants. The processes and rates of species being oxidized in the atmosphere thus constitute the key factors to quantify the AOC. Currently,  相似文献   

10.
For atmospheric photochemistry, clouds can significantly affect actinic flux distributions. In this paper, we examine the effects of convective clouds on the three-dimensional distribution of the spectral actinic flux and on photolysis frequencies for various chemical species. Three-dimensional solutions of the UV-VIS radiative transfer equation are produced using the Spherical Harmonic Discrete Ordinary Method solution technique. This solver uses as input the 3-D cloud characteristics simulated by a dynamical cloud model. The ultraviolet and visible spectra are divided into 5 intervals in order to explore the wavelength dependency of the cloud effect on the actinic flux. Results show that the distribution of the actinic flux over the cloud domain is far from homogeneous and depends primarily on the cloud extinction associated with the hydrometeors. Maximum actinic flux is found at the top edge of the cloud and is related to scattering by ice crystals. The actinic flux is enhanced by a factor of 2 to 5, compared to clear air values, above, at the top edge, and around the cloud. The 3-D actinic flux is used to calculate the photolysis rates for some chemical species (e.g. NO2, O3, and HCHO). Forcomputing photolysis rates, a discretized spectral representation of the absorption wavelengths is used in the model. The calculated photolysis rates are distributed inhomogeneously throughout the cloud, and maxima are found in regions where the actinic flux is enhancement is large. Temperature effects on absorption are found in the photolysis frequencies of some species. Finally, the potential importance of this photolysis enhancement on photochemistry is studied using box model simulations. Results show that enhanced OH concentrations are found in the upper troposphere (120–200%) overthe clouds and changes in ozone production rates (+15%) are obtained in quasi-steady state conditions.  相似文献   

11.
不同方案求解非线性化学动力学方程组的比较   总被引：1，自引：0，他引：1       下载免费PDF全文
在一个简化的气相化学模式的基础上，比较了Ｈｙｂｒｉｄ、ＱＳＳＡ、Ｓｋｌａｒｅｗ三种计算方案求解非线性化学动力学方程组的差异，并引入误差分配和线性组合两种质量守恒技术，分析它们对模拟结果的影响．研究结果表明：不同方案对有机烃类浓度的计算几乎没有影响，但对其它气态物浓度有一定的影响．用ＱＳＳＡ和Ｓｌａｒｅｗ方案预测的结果更为相近，而采用Ｈｙｂｒｉｄ方案得到的气态物浓度的平衡时间略为提前．从计算效率来看，ＱＳＳＡ方案优于其它两种方案，两种质量守恒技术均能改善模拟结果．  相似文献   

12.
A detailed set of reactions treating the gas and aqueous phase chemistry of the most important iodine species in the marine boundary layer (MBL) has been added to a box model which describes Br and Cl chemistry in the MBL. While Br and Cl originate from seasalt, the I compounds are largely derived photochemically from several biogenic alkyl iodides, in particular CH2I2, CH2ClI, C2H5I, C3H7I, or CH3I which are released from the sea. Their photodissociation produces some inorganic iodine gases which can rapidly react in the gas and aqueous phase with other halogen compounds. Scavenging of the iodine species HI, HOI, INO2, and IONO2 by aerosol particles is not a permanent sink as assumed in previous modeling studies. Aqueous-phase chemical reactions can produce the compounds IBr, ICl, and I2, which will be released back into the gas phase due to their low solubility. Our study, although highly theoretical, suggests that almost all particulate iodine is in the chemical form of IO-3. Other aqueous-phase species are only temporary reservoirs and can be re-activated to yield gas phase iodine. Assuming release rates of the organic iodine compounds which yield atmospheric concentrations similar to some measurements, we calculate significant concentrations of reactive halogen gases. The addition of iodine chemistry to our reaction scheme has the effect of accelerating photochemical Br and Cl release from the seasalt. This causes an enhancement in ozone destruction rates in the MBL over that arising from the well established reactions O(1D) + H2O 2OH, HO2 + O3 OH + 2O2, and OH + O3 HO2 + O2. The given reaction scheme accounts for the formation of particulate iodine which is preferably accumulated in the smaller sulfate aerosol particles.  相似文献   

13.
Particulate matter with diameters of 2.5 μm or smaller(PM_(2.5)) and ozone(O_3) are major pollutants in the urban atmosphere. PM_(2.5) can affect O_3 by altering the photolysis rate and heterogeneous reactions. However, these two processes and their relative importance remain uncertain. In this paper, with Nanjing in China as the target city, we investigate the characteristics and mechanism of interactions between particles and O_3 based on ground observations and numerical modeling.In 2008, the average concentrations of PM_(2.5) and O_3 at Caochangmen station are 64.6 ± 47.4 μg m~(-3) and 24.6 ± 22.8 ppb,respectively, while at Pukou station they are 94.1 ± 63.4 μg m~(-3) and 16.9 ± 14.9 ppb. The correlation coefficient between PM_(2.5) and O_3 is -0.46. In order to understand the reaction between PM_(2.5) and O_3, we construct a box model, in which an aerosol optical property model, ultraviolet radiation model, gas phase chemistry model, and heterogeneous chemistry model,are coupled. The model is employed to investigate the relative contribution of the aforementioned two processes, which vary under different particle concentrations, scattering capability and VOCs/NOxratios(VOCs: volatile organic compounds;NOx: nitric oxide and nitrogen dioxide). Generally, photolysis rate effect can cause a greater O_3 reduction when the particle concentrations are higher, while heterogeneous reactions dominate O_3 reduction with low-level particle concentrations.Moreover, in typical VOC-sensitive regions, O_3 can even be increased by heterogeneous reactions. In Nanjing, both processes lead to O_3 reduction, and photolysis rate effect is dominant. Our study underscores the importance of photolysis rate effect and heterogeneous reactions for O_3, and such interaction processes should be fully considered in future atmospheric chemistry modeling.  相似文献   

14.
A three-dimensional Lagrangian tropospheric chemistry modelis used toinvestigate the impact of human activities on the tropospheric distributionofozone and hydroxyl radicals. The model describes the behaviour of 50 speciesincluding methane, carbon monoxide, oxides of nitrogen, sulphur dioxide andnineorganic compounds emitted from human activities and a range of other sources.Thechemical mechanism involves about 100 chemical reactions of which 16 arephotochemical reactions whose diurnal dependence is treated in full. The modelutilises a five minute chemistry time step and a three hour advection timestepfor the 50,000 air parcels. Meteorological data for the winds, temperatures,clouds and so on are taken from the UK Meteorological Office global model for1994 onwards. The impacts of a 50% reduction in European NOXemissions onglobal ozone concentrations are assessed. Surface ozoneconcentrations decrease in summertime and rise in wintertime, but to differentextents.  相似文献   

15.
G. I. Pearman 《Climatic change》1991,18(2-3):131-146
In the past decades there has been an explosive increase in studies of the chemistry of the atmosphere. These studies have shown that the chemical composition of the global atmosphere is far from constant. There is a clearly discernible chemical weather and climate and the latter is changing.Global atmospheric chemistry is at a relatively embryonic stage and much of the effort thus far has been directed towards the establishment of an observational basis upon which a sound theoretical understanding of chemical weather and climate can be built. Without this framework we will remain unable to rationally assess the consequences of, or even distinguish between, natural and man-made perturbations to the chemistry of the atmosphere or to understand the instabilities that already exist.Parallel with this development is the major upsurge of interest in the warming of the planet now expected with high probability as a result of the increase of the atmospheric levels of the so-called greenhouse gases. Such changes; although not the only environmental changes expected, are likely to have far-reaching effects on society and the natural environment. Serious decisions are ahead as we strive to adapt to and avoid climatically induced change.  相似文献   

16.
A calibrated spectroradiometer was used for the measurement of spectra of the absolute actinic flux F during the POPCORN field campaign in Pennewitt (53.8° N, 11.7° E, sea level) in August 1994. The obtained set of actinic flux spectra was used to determine the photolysis frequencies J(O1D), J(NO2), J(HCHO), J(H2O2), J(HONO), and J(CH3CHO), using molecular photodissociation data from literature. The accuracy of the actinic flux measurement was about ±5%. The accuracy of the photolysis frequency determination is limited by the uncertainties of the molecular absorption cross section and quantum yield data. A good agreement within the experimental uncertainties was found in comparison with measurements of J(O1D) and J(NO2) by filterradiometer which were calibrated absolutely against chemical actinometer. A comparison of this work's photolysis frequency measurements at 40° solar zenith angle with respective measured and modeled data from the literature also shows good agreement for most of the processes considered in this work. However, in the case of J(NO2) data reported in the literature as a function of solar zenith angle differences up to a factor of 1.6 with respect to this work's J(NO2) data are observed. Since this is far beyond the estimated experimental uncertainties, other atmospheric variables, such as aerosols, seem to affect J(NO2) to an extent that is underestimated by now and make indirect comparisons of J(NO2) measurements difficult.  相似文献   

17.
Difunctional organic nitrates are important products of the atmospheric reaction of NO3 radicals with unsaturated hydrocarbons about which relatively little is known. In a continuation of the investigation of the atmospheric chemistry of such compounds, the UV absorption spectra of the following organic dinitrates and keto nitrates have been quantitively measured in the gas phase at 298±2 K and atmospheric pressure: 1,2-propandiol dinitrate, CH3CH(ONO2)CH2(ONO2); 1,2-butandiol dinitrate, CH3CH2CH(ONO2)CH2(ONO2); 2,3-butandiol dinitrate, CH3CH(ONO2)CH(ONO2)CH3;cis 1,4-dinitrooxy-2-butene, CH2(ONO2)CH=CHCH2(ONO2); 3,4-dinitrooxy-1-butene, CH2(ONO2CH(ONO2)CH=CH2; -nitrooxy acetone, CH3COCH2(ONO2); 1-nitrooxy-2-butanone, CH3CH2COCH2(ONO2); 3-nitrooxy-2-butanone, CH3CH(ONO2)COCH3.Although the UV spectra of the nitrates are all very similar in shape those of the keto nitrates are red-shifted compared to the dinitrates and in the spectral range of atmospheric interest (>290 nm) their absorption cross-sections are approximately a factor of 5 higher. The cross-sections of the dinitrates are a factor of 2 higher than those reported in the literature for the corresponding alkyl mononitrates.The UV absorption cross-sections of the difunctional nitrates were used in combination with solar actinic flux data to estimate photolysis frequencies and consequently atmospheric lifetimes for these compounds. The results indicate that for the saturated difunctional nitrates studied in this work photolysis will generally be somewhat some important than reaction with OH radicals as an atmospheric removal process. However, for unsaturated nitrates loss due to reaction with OH will dominate over photolysis as an atmospheric sink.Preliminary FT-IR analyses of the photolysis products of -nitrooxy acetone, 3-nitrooxy-2-butanone and 2,3-butandiol dinitrate using both mercury and fluorescent lamps indicate that NO2 is released in the primary step. The further reactions of the radicals thus produced result in the formation of CO, aldehydes and PAN. The possible significance of the results for difunctional organic nitrate as reservoirs for reactive odd nitrogen NO y in the atmosphere, especially during the night, is briefly discussed.  相似文献   

18.
The laser flash photolysis/UV absorption spectrometry technique has been used to investigate the kinetics of the peroxy radical permutation reactions (i.e. self and cross reactions) arising from the OH-initiated oxidation of isoprene (2-methyl-1,3-butadiene), and of the simpler, but related conjugated dienes, 1,3-butadiene and 2,3-dimethyl-1,3-butadiene. The results of the two simpler systems are analysed to provide values of the rate coefficients for the 6 peroxy radical permutation reactions of the three types of isomeric peroxy radical produced in each system (T = 298 K, P = 760 Torr). The rate coefficients are all significantly larger than values estimated previously by extrapolation of structure-reactivity relationships based on the kinetics of a limited dataset of simpler radicals containing similar structural features. The results are discussed in terms of trends in self and cross reaction reactivity of primary, secondary and tertiary peroxy radicals containing combinations of allyl, -hydroxy and -hydroxy functionalities. Since the peroxy radicals formed in these systems are structurally very similar to those formed in the isoprene system, the kinetic parameters derived from the results of the simpler systems are used to assist the assignment of kinetic parameters to the 21 permutation reactions of the six types of isomeric peroxy radical generated in the isoprene system. Kinetic models describing the OH-initiated degradation of all three conjugated dienes to first generation products in the absence of NOx are recommended, which are also consistent with available end product studies. The model for isoprene is considered to be a further improvement on that suggested previously for its OH-initiated oxidation in the absence of NOx. The mechanism is further extended to include chemistry applicable to NOx-present conditions, and calculated product yields are compared with those reported in the literature.  相似文献   

19.
    
Using the “lumped mechanism” and “counting species” methods, we developed a condensed gas-phase chemical model based on a simplified one. The modified quasi-steady-state approximation (QSSA) scheme and the error redistribution mass conservation technique are adopted to solve the atmospheric chemistry kinetic equations. Results show that the condensed model can well simulate concentration variations of gas species such as SO2, NOX, O3, H2O2 and conversion rates of SO2 and NOX transformation to H2SO4 and HNO3. These results are in good agreement with those from the simplified model. The conversion rates of SO2 and NOX under different initial concentrations and meteorological conditions are computed, and the results can be directly applied to regional acid deposition model.  相似文献   

20.
A global 3-D Lagrangian chemistry-transport model STOCHEM is used to describe the tropospheric distributions of four components of the secondary atmospheric aerosol: nitrate, sulphate, ammonium and organic compounds. The model describes the detailed chemistry of the formation of the acid precursors from the oxidation of SO2, DMS, NOx, NH3 and terpenes and their uptake into the aerosol. Model results are compared in some detail with the available surface observations. Comparisons are made between the global budgets and burdens found in other modelling studies. The global distributions of the total mass of secondary aerosols have been estimated for the pre-industrial, present day and 2030 emissions and large changes have been estimated in the mass fractions of the different secondary aerosol components.  相似文献   

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