Hydrogen Peroxide, Organic Peroxides and Higher Carbonyl Compounds Determined during the BERLIOZ Campaign

Gas-phase H₂O₂, organic peroxides and carbonyl compoundswere determined at various sites from Mid-July to early August 1998 during the BERLIOZ campaign in Germany. The sites were located northwest of Berlin and were chosen to determine pollutants downwind of the city emissions during a summer smog episode. Hydrogen peroxide (H₂O₂),methyl hydroperoxide (MHP, CH₃OOH) and occasionally hydroxymethyl hydroperoxide (HMHP, HOCH₂OOH) were quantified in air samples by commercial fluorimetric methods and classical HPLC with post-column derivatisation by horseradish peroxidase/p-hydroxyphenyl acetic acid and fluorimetric detection. Carbonyl compounds were determined in ambient air by a novel method based onO-pentafluorobenzyl hydroxylamine as derivatisation agent.Mixing ratio profiles of the hydroperoxides and the carbonyl compounds are reported for the intensive phase of the campaign, 20–21 July, 1998. Peroxides showed pronounced diurnal variations with peak mixing ratios in the early afternoon. At times, a second maximum was observed in the late afternoon. The major part of the H₂O₂ was formed throughrecombination reactions of HO₂ radicals, but there is some evidencethat H₂O₂ is also formed from ozonolysis ofanthropogenic and/or biogenic alkenes. Diurnal variations of mixing ratios of various carbonyl compounds are reported: alkanals (C₂ to C₁₀,isobutanal), unsaturated carbonyl compounds (methacrolein, methylvinylketone, acrolein), hydroxycarbonyl (glycolaldehyde, hydroxyacetone) and dicarbonyl compounds (glyoxal, methylglyoxal, biacetyl), aromatic compounds (benzaldehyde, o- and m-tolylaldehyde) and pinonaldehyde.     

Formation and occurrence of organic hydroperoxides in the troposphere: Laboratory and field observations

The formation and occurrence of hydroperoxides in the troposphere have been studied by laboratory experiments and by preliminary field measurements. Nine alkenes were reacted individually with ozone in a reaction chamber in the presence of excess water, and the amounts of hydrogen peroxide and of nine organic hydroperoxides produced in the gas and aerosol phases and deposited on the chamber walls determined by HPLC. The reactions of ethene, propene, 1-butene and isoprene gave hydroxymethyl hydroperoxide as the major product with no hydrogen peroxide observed. In the case of - and -pinene, 2-carene and limonene the major product was hydrogen peroxide. Cis-2-butene produced hydrogen peroxide and methyl hydroperoxide. Preliminary measurements of hydrogen peroxide and five organic hydroperoxides in ambient air were made at Niwot Ridge, Colorado from 24 July–4 August 1989. The gas-phase species were preconcentrated by cryotrapping with subsequent HPLC separation. The gas-phase concentrations of H₂O₂ ranged from 0.5–2 ppbv with the lowest concentrations being measured at night and the highest under conditions of strong photochemical activity. The maximum concentrations of hydroxymethyl hydroperoxide approximated those of H₂O₂. Methyl hydroperoxide concentrations ranged from <50 to 800 pptv and three other organic hydroperoxides were detected at concentrations below 200 pptv. High volume aerosol samples yielded H₂O₂ and methyl hydroperoxide concentrations <10 ng m^-3 while H₂O₂ and six organic species were detected in rainwater at concentrations in the range <0.01–50 M.     

Behaviour of H2O2, NH3, and black carbon in mixed-phase clouds during CIME

We investigated the partitioning of trace substances during the phase transition from supercooled to mixed-phase cloud induced by artificial seeding. Simultaneous determination of the concentrations of H₂O₂, NH₃ and black carbon (BC) in both condensed and interstitial phases with high time resolution showed that the three species undergo different behaviour in the presence of a mixture of ice crystals and supercooled droplets. Both H₂O₂ and NH₃ are efficiently scavenged by growing ice crystals, whereas BC stayed predominantly in the interstitial phase. In addition, the scavenging of H₂O₂ is driven by co-condensation with water vapour onto ice crystals while NH₃ uptake into the ice phase is more efficient than co-condensation alone. The high solubility of NH₄⁺ in the ice could explain this result. Finally, it appears that the H₂O₂–SO₂ reaction is very slow in the ice phase with respect to the liquid phase. Our results are directly applicable for clouds undergoing limited riming.     

Measurements of atmospheric hydroperoxides at a rural site in central Japan

Measurements of hydroperoxides (H₂O₂ and MHP) at ground level were made from 2012 to 2015 in Imizu City, Toyama Prefecture in central Japan. H₂O₂ and MHP concentrations ranged from 0.01 to 3.5 ppb and from below the level of detection (< 0.01 ppb) to 1.4 ppb, respectively. The concentrations of H₂O₂ and MHP were high in the summer and low in the winter. The H₂O₂ concentration was at its maximum in July and August, whereas the concentration of O₃ in the daytime was highest in May and June. The ratio of [H₂O₂]/[SO₂] presented clear seasonal variations. Many cases showed the condition of [H₂O₂] < [SO₂], called oxidant limitation especially in the cold months. Hydroperoxide concentrations in the rainwater were also high in the summer. The concentrations of MHP were much lower than those of H₂O₂ in the rain water. High concentrations of H₂O₂ (> 2.5 ppb) were detected in the summer during the inflow of air pollution. The concentrations of H₂O₂ were significantly high in July and August of 2013. The H₂O₂ was well correlated with the O₃ in July and August whereas there was no correlation between O₃ and H₂O₂ in May and June. There was a negative correlation between NO_X and H₂O₂.     

Distributions of O3, CO and NMHCs over the rural sites in central India

The surface level measurements of O₃, CO, CH₄ and light NMHCs were made at eight different rural sites in the central part of India during February, 2004. The online analyzer was used for in-situ measurement of O₃ while air samples were collected for the analyses of CO, CH₄ and NMHCs using the gas chromatography techniques. The average mixing ratios of O₃, which were in the range of 60–90 ppbv, are significantly higher compared to the typical values reported for urban sites of India. The increase rates of O₃ in the forenoon hours were estimated to be in the range of about 8.8–10 ppbv h⁻¹. The slopes of ∆O₃/∆CO, which is an indicator of the efficiency of photochemical production, were in the range of 0.24–0.33 ppbv ppbv⁻¹. However, levels of primary pollutants e.g., NMHCs, CO, etc. at these sites were much lower than urban sites, but higher compared to previously observed values surrounding marine region of India. The estimated ratios of NMHCs and CO indicate fossil fuel combustion process as the dominant source of primary pollutants in this corridor.     

Hydroperoxides in the marine troposphere over the Atlantic Ocean

Hydrogen peroxide (H₂O₂) and organic hydroperoxides (ROOH) were measured on board of theRV Polarstern during its cruise across the Atlantic Ocean from 20 October to 12 November 1990 (54° N to 51° S latitude) by the enzyme fluorometric method. The H₂O₂ mixing ratio varied from below the detection limit of about 0.12 ppbv up to 3.89 ppbv, showing a latitudinal dependence with generally higher values around the equator and decreasing values poleward. The shape of the latitudinal H₂O₂ distribution agrees well with an analytical steady state expression for H₂O₂ using the measured H₂O and O₃ distribution and a wind dependent H₂O₂ deposition rate. The ROOH mixing ratio varied from below the detection limit of about 0.08 ppbv up to 1.25 ppbv with qualitatively the same latitudinal dependence as H₂O₂. The observed ratio ROOH/(ROOH + H₂O₂) varied between 0.17 and 0.98 showing higher values at the lowest H₂O₂ mixing ratios at high latitudes. The measured H₂O₂ mixing ratio shows a significant diurnal variation with a maximum around 14:00 local time, explicable by a superposition of the photochemical H₂O₂ production with a constant H₂O₂ deposition rate. Four independent estimations of the average effective H₂O₂ deposition rate inferred from the H₂O₂ decrease in the night, from the midday H₂O₂ production deficit (as derived from comparison with a photochemical model and from the daily ozone loss), and from the offset in the latitudinal H₂O₂ distribution, were consistent. An episode of maximum H₂O₂ concentration suggests the possibility of its formation in clouds.     

The ESCOMPTE program: an overview

In this paper, the “Expérience sur Site pour COntraindre les Modèles de Pollution atmosphérique et de Transport d'Emissions” (ESCOMPTE) program is presented. The ESCOMPTE program is used to produce a relevant set of data for testing and evaluating regional pollution models. It includes high-resolution (in space and time) atmospheric emission inventories and field experiments, and covers an area of 120×120 km, centered over the Marseilles-Berre area in the southeast of France during Summer 2001. This region presents a high occurrence of photochemical pollution events, which result from numerous industrial and urban sources of primary pollutants. From the dynamical characteristics of the area, sea-breeze circulation and channeling effects due to terrain features highly influence the location of the pollutant plumes. ESCOMPTE will provide a highly documented framework for dynamics and chemistry studies.Campaign strategies and experimental set up are described. During the planning phase, existing modeling results helped defining the experimental design. The campaign involved surface measurement networks, remote sensing, ship-borne, balloon-borne, and airplane measurements. Mean standard meteorological parameters and turbulent fluxes, ozone, ozone precursors, photochemically active trace gases, and aerosols were measured. Five intensive observation periods (IOPs) were documented using a wide spectrum of instruments, involving aircraft (7) (one of them equipped with a Doppler lidar, the others for in situ meteorological and chemical measurements), constant volume balloons (33), ozone lidars (5), wind profilers (15 sodars and radars), Doppler scanning lidar (1), radiosonde systems (at 4 locations), instrumented ships (2). In addition to the air quality networks from environmental agencies, 15 supplementary ground stations equipped for chemistry and/or meteorology and/or surface flux measurements, were operational. All instruments were calibrated and compared during a Quality Control/Quality Assurance (QC/QA) week, at the very beginning of the campaign.Fifteen days were intensively documented during five IOPs, referenced as 1, 2a, 2b, 3, and 4. High pollution levels were encountered during sea-breeze conditions observed during IOPs 2b and 3, whereas IOPs 2a and 4 corresponded to moderate wind, and channeled plume regimes. In addition, hourly emissions inventories for all IOPs were established to complete data sets and to finalize the ESCOMPTE database (EDB).Two other projects were associated to ESCOMPTE: urban boundary layer (UBL) and tropospheric water vapor content by GPS tomography (GPS/H₂O). They took advantage of the scientific environment provided by ESCOMPTE.     

Multiphase chemistry and acidity of clouds at Kleiner Feldberg

The chemistry of cloud multiphase systems was studied within the Kleiner Feldberg Cloud Experiment 1990. The clouds encountered during this experimental campaign could be divided into two categories according to the origin of air masses in which the clouds formed. From the chemical point of view, clouds passing the sampling site during the first period of the campaign (26 October-4 November) were characterized by lower pollutant loading and higher pH, as compared to clouds during the final period of the experimental campaign (10–13 November). The study of multiphase partitioning of the main chemical constituents of the cloud systems and of atmospheric acidity within the multiphase systems themselves (gas + interstitial aerosol + liquid droplets) are presented in this paper. A general lack of gaseous NH₃ was found in these cloud systems, which caused a lack of buffer capacity toward acid addition. Evidence supports the hypothesis that the higher acidity of the cloud systems during this final period of the campaign was due to input of HNO₃. Our measurements, however, could not determine whether the observed input was due to scavenging of gaseous HNO₃ from the air feeding into the cloud, or to heterogeneous HNO₃ formation via NO₂ oxidation by O₃ to NO₃ and N₂O₅. Sulfate in cloud droplets mainly originated from aerosol SO ₄ ^2– scavenging, since S(IV) to S(VI) liquid phase conversion was inhibited due to both lack of H₂O₂ and low pH of cloud droplets, which made O₃ and metal catalyzed S(IV) oxidation inefficient.     

A comparison of the enzyme fluorometric and the peroxyoxalate chemiluminescence methods for measuring H2O2

During September 25 to October 28, 1985, the enzyme fluorometric (Lazrus et al., 1985) and the peroxyoxalate chemiluminescence (Klockow and Jacob, 1986; Jaeschke, 1986) techniques for analyzing H₂O₂ were compared in laboratory studies at the National Center for Atmospheric Research in Boulder, Colorado, U.S.A. and under field conditions at the Whiteface Mt. field station of the Atmospheric Sciences Research Center, Albany, New York, U.S.A. Both methods showed excellent agreement, with a maximum deviation of ±5%. Only at unusually high concentrations of some potential atmospheric species could slight interferences be observed. During the experiments the detection limits were 1.3×10^-8 mol/l (0.44 ppbm) of H₂O₂ for the fluorometric instrument and 4×10^-8 mol/l (1.36 ppbm) of H₂O₂ for the chemiluminescence instrument. For the chemiluminescence technique, the response to methylhydroperoxide was approximately 80-fold less than that to an equivalent concentration of H₂O₂.     

NUMERICAL SIMULATION OF THE INFLUENCE OFO3,CO2 AND SPECTRUM VARIATION ON THE PHOTOSYNTHESIS OF CROP CANOPY*

Coupled the photosynthesis with transpiration and adjustment of stoma,a dynamic ecological model for simulating the canopy photosynthesis of winter wheat was established by scaling up from the biochemical scale to canopy scale,in which the effects of O₃,CO₂ and solar spectrum on crop photosynthesis were fully considered.Validation of the model against the data measured with CI-301PS portable photosynthesis analyzer showed that the leaf photosynthesis model passed the correlation significance test and had a fairly high accuracy.Numerical analysis showed that the canopy photosynthesis rate would be reduced by 29% if the O₃ concentration increases from 0 ppbv to 200 ppbv,whereas the canopy photosynthesis rate would increase by about 37% while the CO₂ concentration increases from 330 ppmv to 660 ppmv,and the canopy photosynthesis rate would be reduced by 27%0 or so under the condition that the spectrum coefficient changed from 0.5 to 0.4.If the O₃ concentration reached 200 ppbv at noon on the typical sunny day with higher radiation,the canopy photosynthesis will be reduced slightly in the suburb area where the pollution is serious and the photochemical fog is easy to be formed,contrast with that in the clear region and regardless of the climate change,due to the fact that the positive effect of CO₂ on crop photosynthesis can not compensate the negative effect of O₃ on crop photosynthesis.The canopy photosynthesis will be reduced by 35% or so than the BASE value at present,when the spectrum of photosynthetic active radiation(PAR) reduces to 0.4 or so.     

Measurements of Trace Substances in the Arctic Troposphere as Potential Precursors and Constituents of Arctic Haze

During two measuring campaigns in early spring 1994 and 1995 (March/April) and one campaign in summer 1994, measurements of ozone, PAN, sulfur dioxide, nitric acid, and particulate nitrate, sulfate, and ammonium (only 1995) were recorded in the Arctic. Observations were made by aircraft at various sites in the eastern and western Arctic. Ozone concentrations showed a steady increase with altitude both in spring and summer. During five flights in springtime, low ozone events (LOEs) could be observed near the surface and up to altitudes of 2000 m. SO₂ background concentrations, ranging from detection limit (0.5 nmol/m³) to 5 nmol/m³, were observed during both spring and summer. Distinct maxima up to 55 nmol/m³ in lower altitudes were only obtained in springtime. Concentrations of the organic nitrate PAN were within a similar range as those of the inorganic nitrate HNO₃ during spring campaigns. In contrast, concentrations of particulate nitrate were one half an order of magnitude lower. HNO₃ concentrations increased significantly with altitude. Evidently, HNO₃ was intruded from the stratosphere into the troposphere. Sulfate concentrations ranged between 5 and 30 nmol/m³; ammonium concentrations were obtained within a range from 10 to 50 nmol/m³.     

Comparison of flux measurements with open- and closed-path gas analyzers above an agricultural field and a forest floor

Comparison was made of the flux measurements of a closed-path CO₂/H₂O analyzer and an open-path H₂O analyzer above a clover field and the forest floor of a Douglas-fir stand. The attenuation of the gas concentration fluctuations caused by the sampling tube of the closed-path analyzer resulted in underestimation of the H20 flux above both surfaces. The degree of underestimation above the clover field depended on wind speed, but was smaller than that calculated from the transfer function for laminar flow in a circular tube and the scalar cospectrum in the neutral and unstable surface layer. Above the forest floor CO₂ fluctuations led those of H₂O by 0.7s. The implications of this are discussed regarding the determination of the time delay caused by the sampling tube of the closedpath analyzer. The day-time CO₂ efflux from the forest floor, averaged over three days, was 0.043 mg/(m²s).     

Multi-Phase Chemistry of C<Subscript>2</Subscript> and C<Subscript>3</Subscript> Organic Compounds in the Marine Atmosphere

A box model is used to explore the detailed chemistry of C₂ and C₃ organic compounds in the marine troposphere by tracing the individual reaction paths resulting from the oxidation of ethane, ethene, acetylene, propane, propene and acetic acid. The mechanisms include chemical reactions in the gas phase and in the aqueous phase of clouds and aerosol particles at cloud level under conditions resembling those in the northern hemisphere. Organic hydroperoxides are found to be important intermediate products, with subsequent reactions leading partly to the formation of mixed hydroxy or carbonyl hydroperoxides that are readily absorbed into cloud water, where they contribute significantly to the formation of multifunctional organic compounds and organic acids. Organic hydroperoxides add little to the oxidation of sulfur dioxide dissolved in the aqueous phase, which is dominated by H₂O₂. Next to acetaldehyde and acetone, glycol aldehyde, glyoxal, methyl glyoxal and hydroxy propanone are prominent oxidation products in the gas and the aqueous phase. Acetaldehyde is not efficiently converted to acetic acid in clouds; the major local sources of acetic acid are gas-phase reactions. Other acids produced include hydroperoxy acetic, glycolic, glyoxylic, oxalic, pyruvic, and lactic acid. The mechanism of Schuchmann et al. (1985), which derives glycolic and glyoxylic acid from the oxidation of acetate, is found unimportant in the marine atmosphere. The principal precursors of glyoxylic acid are glyoxal and glycolic acid. The former derives mainly from acetylene and ethene, the latter from glycolaldehyde, also an oxidation product of ethene. The oxidation of glyoxylic acid leads to oxalic acid, which accumulates and is predicted to reach steady state concentrations in the range 30–90 ng m⁻³. This is greater, yet of the same magnitude, than the concentrations observed over the remote Pacific Ocean.     

Influence of dissolved organic carbon on photochemically mediated cycling of hydrogen peroxide in rainwater

The influence of sunlight and dissolved organic carbon (DOC) on the photochemically mediated cycling of hydrogen peroxide (H₂O₂) was investigated in rainwater samples collected in Wilmington, North Carolina USA. Upon exposure to simulated sunlight 14 of 19 authentic rainwater samples exhibited significant decreases in H₂O₂. The concentration of hydrogen peroxide did not change significantly in organic-free synthetic rainwater spiked with H₂O₂ in the light or in dark controls suggesting that the loss was not due to direct photolysis or dark mediated reactions. There was a significant correlation between pseudo-first order rate constants of H₂O₂ decay and initial H₂O₂ concentrations. There was also a significant correlation between the rate constant and the abundance of DOC suggesting that rainwater organic carbon plays an important role during photolytic decay either via direct reaction or indirectly through production of peroxide reactive species or scavenging of peroxide generating radicals. Several rain samples exhibited an initial increase in H₂O₂ during the first 2 h of irradiation. These increases were generally small and most likely do not represent a significant input of peroxide in precipitation. The photo-induced destruction of H₂O₂ is important because it may partly explain the late afternoon decrease of peroxide concentrations observed in earlier field studies and the substantial under saturation (<10%) of this oxidant in rainwater compared with gas phase concentrations.     

A summer and winter apportionment of particulate matter at urban and rural areas in northern France

The apportionment of atmospheric aerosols undertaken in Northern France during two sampling campaigns allowed to determine the influence of the atmospheric contribution of a heavy industrialized urban center on the particulate matter composition at a nearby rural site. The concentrations of major components and trace elements sampled by bulk filtration have been determined on June–July 2000 and January–February 2001, and the comparison of these two campaigns shows very well the importance of wind directions. The sources of 10 trace elements (Al, Ba, Cu, Fe, K, Mn, Pb, Sr, Ti and Zn) and 7 major components (Cl⁻, NO₃⁻, SO₄²⁻, NH₄⁺, Na, Mg and Ca) are better identified by studying their elemental contribution at each sampling site according to wind sectors. This kind of study shows that the concentrations recorded at the urban sampling site are always higher than those observed at the rural site as well during the summer campaign (about + 35%) as during the winter campaign (+ 90%), because of the predominance of the W–NW wind sector, corresponding to the influence of the urban and industrialized areas.     

Diurnal Variations of Atmospheric Hydrogen Peroxide Concentrations in Saxony (Germany)

During a 3-year study, gaseous hydrogenperoxide (H₂O₂) concentrations were measuredas part of the SANA project at the Melpitz FieldResearch Station and in the city of Leipzig. Typicaldaily mean H₂O₂ mixing ratios on sunny dayswere 0.15 to 0.25 ppbv with maximum values of 0.3 to0.5 ppbv at Melpitz, and 0.3 to 0.6 ppbv with maximumvalues of 0.4 to 1.0 ppbv in Leipzig. Over the entireperiod of the project the maximum hourly mean valueswere 2.1 ppbv and 5.3 ppbv in Melpitz and Leipzig,respectively. The data were not complete enough to show a trend.Linear regression analysis shows, that ozone(O₃), temperature and solar radiation arepositively correlated with H₂O₂, whereasnitrogen oxides (NO_x), carbon monoxide (CO) andrelative humidity are negatively correlated. Negativecorrelation between H₂O₂ and CO is caused byjoint occurrence of CO with NO_x in exhaust gases.Negative correlation between H₂O₂ andrelative humidity is not necessarily in contradictionto the accelerating effect of water vapour onH₂O₂ formation. The strong positivecorrelation of H₂O₂ with the dew pointdifference however seems to better reflect theinfluence of water vapour. Multiple linear regression analysis (MLRA) of thecomponents measured, indicates the great influence of CO on the formation of H₂O₂ in the gasphase.     

Ground Based Gas Phase Measurements in Surinam during the LBA-Claire 98 Experiment

As part of the LBA-CLAIRE-98 experiment, ground level atmosphericconcentrations of O₃, CO, hydroperoxides and organic acids weremeasured in the rainforest region in Surinam. Measurements of CO andO₃ were also made at a coastal site.The results suggest that a significant consumption of `boundary layer' ozoneoccurs over the forested region of Surinam, with an estimated net ozoneconsumption of about 5% hr^–1 during daytime. Thiswould be mainly explained by a low photochemical production and high drydeposition to the forest vegetation. Compared to other tropical sites, lowerlevels of H₂O₂ were observed at the rainforest site,with an average boundary layer concentration of 0.55± 0.2 nmolmol^–1. Also acetic and formic acids showed relatively lowaverage boundary layer mixing ratios; 1.1± 0.4 nmolmol^–1 and 1.4± 0.5 nmol mol^–1,respectively. Significant correlations were found between both acids andbetween the acids and hydrogen peroxide, suggesting an atmospheric source forthe acids.From the available observations we discuss possible implications of ourmeasurements for the O₃, HO₂, and NO_x budgetsand concentrations in the boundary layer. We conclude that, despite the highsolar irradiation, relatively low levels of O₃,H₂O₂, HCOOH and CH₃COOH are observed in theboundary layer of the rainforest of Surinam, probably due to low levels ofNO_x and high levels of VOCs, which leads to loss of OH andHO₂ radicals. Additionally, high deposition rates of these gasesoccur to the forest vegetation.     

Biogenic emissions from Pinus halepensis: a typical species of the Mediterranean area

Volatile organic compounds (VOCs) emissions by vegetation present in the Mediterranean area are not well known. They may contribute with anthropogenic VOC emissions to the tropospheric ozone formation that reaches important level in the European Mediterranean region. The present work, carried out as part of the European ESCOMPTE project «fiEld experimentS to COnstrain Models of atmospheric Pollution and Transport of Emissions», adds a new contribution to the inventory of the main natural hydrocarbons sources likely to participate in the ozone production. The corresponding measurement campaign was conducted in La Barben, a site close to Marseilles (France), with the aim to quantify the terpenic emission pattern and the behaviour of Pinus halepensis, an important Mediterranean species slightly studied.The determination of biogenic emissions from P. halepensis was done by the enclosure of an intact branch in a Teflon cuvette. Main emitted monoterpenes were β trans-ocimene and linalool. The total monoterpenic emission rates thus recorded were found to reach maximum values around 30 μg g_{dry weight}⁻¹ h⁻¹. The normalized emission rates calculated at 30 °C and 1000 μmol m⁻² s⁻¹ with Guenther's algorithm was 14.76, 8.65 and 4.05 μg g_{dry weight}⁻¹ h⁻¹, respectively, for the total monoterpenes, β trans-ocimene and linalool.     

H2释放扰动电离层的数值模拟

由于电离层中分子性离子与电子的复合要比氧离子与电子的复合快得多,因此H₂在电离层高度释放可有效地引起电子的消耗。本文基于一个包括中性气体扩散方程和离子化学反应方程的二维动力学模型,对H₂在电离层高度释放过程进行了数值模拟研究,并分析了不同释放条件下的电子扰动特性。结果表明:1)500 mol H₂释放后,迅速向周围空间扩散,释放中心处的电子密度30 s内下降了近4%,F₂层临界频率下降了1%左右;2)在不同高度处释放H₂时,最大的电子密度相对变化率并不是在峰值高度附近处释放时出现的;3)释放化学物质的量越多,电子密度的扰动幅度也越大,但两者之间并不存在线性关系;4)相同量的H₂在电离层峰值高度处释放,白天的电子密度扰动幅度要大于夜间的扰动幅度。