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1.
FOS/DECAFE 91 (Fire of Savannas/Dynamique et Chimie Atmosphérique en Forêt Equatoriale) was the first multidisciplinary experiment organized in Africa to determine gas and aerosol emissions by prescribed savanna fires. The humid savanna of Lamto in Ivory Coast was chosen for its ecological characteristics representative of savannas with a high biomass density (900 g m–2 dry matter). Moreover the vegetation and the climate of Lamto have been studied for more than twenty years. The emission ratios (X/CO2) of the carbon compounds (CO2, CO, NMHC, CH4, PAH, organic acids and aerosols), nitrogen compounds (NOx, N2O, NH3 and soluble aerosols) and sulfur compounds (SO2, COS and aerosols) were experimentally determined by ground and aircraft measurements. To perform this experiment, 4 small plots (100×100 m) and 2 large areas (10×10 km) were prepared and burnt in January 1991 during the period of maximum occurrence of fires in this type of savanna. The detailed ecological study shows that the carbon content of the vegetation is constant within 1% (42 g C for 100 g of vegetal dry matter), the nitrogen content (0.29 g N for 100 g of dry matter) may vary by 10% and the sulfur content (0.05 g S/100 d.m.) by 20%. These variations of the biomass chemical content do not constitute an important factor in the variation of the gas and particle emission levels. With the emission ratios characteristic of humid savanna and flaming conditions (CO/CO2 of 6.1% at the ground and 8% for airborne measurements), we propose a set of new emission factors, taking into account the burning efficiency which is about 80%: 74.4% of the carbon content of the savanna biomass is released to the atmosphere in the form of CO2, 4.6% as CO, 0.2% as CH4, 0.5% as NMHC and 0.7% as aerosols. 17.2% of the nitrogen content of the biomass is released as NOx, 3.5% as N2O, 0.6% as NH3 and 0.5% as soluble aerosols.  相似文献   

2.
The stable carbon isotope ratios of nonmethane hydrocarbons (NMHC) and methyl chloride emitted from biomass burning were determined by analyzing seven whole air samples collected during different phases of the burning process as part of a laboratory study of wood burning. The average of the stable carbon isotope ratios of emitted alkanes, alkenes and aromatic compounds is identical to that of the burnt fuel; more than 50% of the values are within a range of ±1.5 of thecomposition of the burnt fuel wood. Thus for the majority of NMHC emitted from biomass burning stable carbon isotope ratio of the burnt fuel a good first order approximation for the isotopic composition of the emissions. Of the more than twenty compounds we studied, only methyl chloride and ethyne differed in stable carbon isotope ratios by more than a few per mil from the composition of the fuel. Ethyne is enriched in 13C by approximately 20–30, and most of the variability can beexplained by a dependence on flame temperature. The 13C values decreaseby 0.019 /K (±0.0053/K) with increasing temperature. Methyl chloride is highly depleted in 13C, on average by25. However the results cover a wide range of nearly 30. Specifically, in two measurements with wood from Eucalyptus (Eucalyptus delegatensis) as fuel we observed the emission of extremely light methyl chloride (–68.5and–65.5). This coincides with higher than average emission ratiosfor methyl chloride (15.5 × 10–5 and 18 ×10–5 mol CH3Cl/mol CO2). These high emission ratios are consistent with the highchlorine content of the burnt fuel, although, due to the limited number of measurements, it would be premature to generalize these findings. The limited number of observations also prevents any conclusion on a systematic dependence between chlorine content of the fuel, emission ratios and stable carbon isotope ratio of methyl chloride emissions. However, our results show that a detailed understanding of the emissions of methyl chloride from chloride rich fuels is important for understanding its global budget. It is also evident that the usefulness of stable carbon isotope ratios to constrain the global budget of methyl chloride will be complicated by the very large variability of the stable carbon isotope ratio of biomass burning emissions. Nevertheless, ultimately the large fractionation may provide additional constraints for the contribution of biomass burning emissions to the atmospheric budget of methyl chloride.  相似文献   

3.
Carbonyl sulfide emissions from biomass burning have been studied during field experiments conducted both in an African savanna area (Ivory Coast) and rice fields, central highland pine forest and savanna areas in Viet-Nam. During these experiments CO2, CO and C2H2 or CH4 have also been also monitored. COS values range from 0.6 ppbv outside the fires to 73 ppbv in the plumes. Significant correlations have been observed between concentrations of COS and CO (R 2=0.92,n=25) and COS and C2H2 (R 2=0.79,n=26) indicating a COS production during the smoldering combustion. COS/CO2 emission factors (COS/CO2) during field experiments ranged from 1.2 to 61×10–6 (11.4×10–6 mean value). COS emission by biomass burning was estimated to be up to 0.05 Tg S/yr in tropics and up to 0.07 Tg S/yr on a global basis, contributing thus about 10% to the global COS flux. Based on the S/C ratio measured in the dry plant biomass and the COS/CO2 emission factor, COS can account for only about 7% of the sulfur emitted in the atmosphere by biomass burning.  相似文献   

4.
Ambient atmospheric aerosols and savanna fireparticulate emission samples from southern Africa werecharacterised in terms of particle classes and theirnumber abundance by electron probe X-ray microanalysis(EPXMA). About ten particle classes were identifiedfor each sample. The major classes werealuminosilicates and sea salts for ambient coarse(2–10 m equivalent aerodynamic diameter (EAD))samples, and K-S and S-only particles for ambient fine(<2 m EAD) samples. The K-S particles are oneof the major products of biomass burning. The EPXMAresults were found to be consistent with the resultsfrom bulk analyses on a sample by sample basis. Forsavanna fire fine samples, quantitative EPXMA revealedthat many particles had a composition of simple saltssuch as KCl. Some particles had a deviatingcomposition in the sense that more ionic species wereinvolved in sustaining the balance between cations andanions, and they were composite or mixed salts.Because of extensive processing during the atmospherictransport, the composition of the K-S particles in theambient samples was different from K2SO4,and such particles were enriched with S. The finepyrogenic KCl particles and the fine sea-saltparticles were much depleted in chlorine.  相似文献   

5.
Atmospheric samples from savanna burnings were collected in the Ivory Coast during two campaigns in January 1989 and January 1991. About 30 nonmethane hydrocarbons from C2 to C6, carbon monoxide, carbon dioxide and methane were measured from the background and also at various distances from the burning. Concentrations in the fire plume reached ppmv levels for C2-C4 hydrocarbons, and 5300, 500 and 93 ppmv for CO2, CO and CH4 respectively. The excess in the mixing ratios of these gases above their background level is used to derive emission factors relative to CO and CO2. For the samples collected immediately in the fire plume, a differentiation between high and low combustion efficiency conditions is made by considering the CO/CO2 ratio. Ethene (C2H4), acetylene (C2H2), ethane (C2H6) and propene (C3H6) are the major NMHC produced in the flaming stage, whereas a different pattern with an increasing contribution of alkanes is observed in samples typical of post flaming processes. A strong correlation between methane and carbon monoxide suggests that these compounds are produced during the same stage of the combustion. In samples collected at a distance from the fire and integrated over a period of 30 minutes, the composition is very similar to that of flaming. NMHC/CO2 is of the order of 0.7%, CH4/CO2 of the order of 0.4% and CO/CO2 of the order of 6.3%. From this study, a global production by African savanna fires is derived: 65 Tg of CO-C, 4.2 Tg of CH4-C and 6.7 Tg of NMHC-C. Whereas acetylene can be used as a conservative tracer of the fire plumes, only ethene, propene and butenes can be considered in terms of their direct photochemical impact.  相似文献   

6.
As global greenhouse warming continues to intensify, it is likely that demands to employ technologies of climate engineering will become increasingly insistent. This paper addresses the possibility of canceling the radiative effects of the increasing greenhouse gases through solar reflectors. Two promising approaches, according to COSEPUP (1992), are the employment of aerosols in the stratosphere, directly as reflectors, or in the troposphere, for the seeding of clouds to increase cloud amounts and brightness. Besides technological and economic feasibility, such schemes could be relatively reversible, and describing their impact may be within the reach of future scientific study.The climate system is not yet sufficiently understood for such actions to be warranted. However, there is considerable potential for an increased understanding of what such actions might do through the study of the role of similar aerosols already added to the climate system. In particular, the most intense volcanoes (e.g. Pinatubo) supply the stratosphere with enough aerosol over a period of a year or two to cancel out greenhouse warming from a resulting doubling of carbon dioxide. Furthermore, the addition of sulfate aerosols to the troposphere from the burning of fossil fuel may already be canceling out globally up to half of the greenhouse-gas warming. These comparisons suggest that at least 10 times as much sulfate aerosol would be needed in the troposphere as would be needed in the stratosphere for a comparable climatic effect. A better understanding of the role of the already-present aerosols is a prerequisite for further progress in the use of aerosols for climate engineering. The links between the horizontal and vertical distribution of radiative sources and sinks and various atmospheric feedback processes, especially those related to the hydrological cycle and the consequent global and regional responses, are also needed.  相似文献   

7.
The effects of deep convection on the potential for forming ozone (ozone production potential) in the free troposphere have been simulated for regions where the trace gas composition is influenced by biomass burning. Cloud dynamical and photochemical simulations based on observations in 1980 and 1985 Brazilian campaigns form the basis of a sensitivity study of the ozone production potential under differing conditions. The photochemical fate of pollutants actually entrained in a cumulus event of August 1985 during NASA/GTE/ABLE 2A (Case 1) is compared to photochemical ozone production that could have occurred if the same storm had been located closer to regions of savanna burning (Case 2) and forest burning (Case 3). In each case studied, the ozone production potential is calculated for a 24-hour period following convective redistribution of ozone precursors and compared to ozone production in the absence of convection. In all cases there is considerably more ozone formed in the middle and upper troposphere when convection has redistributed NOx, hydrocarbons and CO compared to the case of no convection.In the August 1985 ABLE 2A event, entrainment of a layer polluted with biomass burning into a convective squall line changes the free tropospheric cloud outflow column (5–13 km) ozone production potential from net destruction to net production. If it is assumed that the same cloud dynamics occur directly over regions of savanna burning, ozone production rates in the middle and upper troposphere are much greater. Diurnally averaged ozone production following convection may reach 7 ppbv/day averaged over the layer from 5–13 km-compared to typical free tropospheric concentrations of 25–30 ppbv O3 during nonpolluted conditions in ABLE 2A. Convection over a forested region where isoprene as well as hydrocarbons from combustion can be transported into the free troposphere leads to yet higher amounts of ozone production.  相似文献   

8.
Atmospheric oxidation of monoterpenes contributes to formation of tropospheric ozone and secondary organic aerosol, but their products are poorly characterized. In this work, we report a series of outdoor smog chamber experiments to investigate both gaseous and particulate products in the ozone oxidation of four monoterpenes: -pinene, -pinene, 3-carene, and sabinene. More than ten oxygenated products are detected and identified in each monoterpene/O3 reaction by coupling derivatization techniques and GC/MS detection. A denuder/filter pack sampling system is used to separate and simultaneously collect gas and aerosol samples. The identified products, consisting of compounds containing carbonyl, hydroxyl, and carboxyl functional groups, are estimated to account for about 34–50%, 57%, 29–67%, and 24% of the reacted carbon mass for -pinene, sabinene, -pinene, and 3-carene, respectively. The identified individual products account for >83%, 100%, >90%, and 61% of the aerosol mass produced in the ozone reaction of -pinene, sabinene, -pinene, and 3-carene. The uncertainty in the yield data is estimated to be ±50%. Many of the products partition between gas and aerosol phases, and their gas-aerosol partitioning coefficients are determined and reported here. Reaction schemes are suggested to account for the products observed.  相似文献   

9.
Eighteen soil samples from central Sudan were fractionated by dry sieving ina size fraction from <45 m to >300 m while aerosols generatedfrom these soils were fractionated in the particle size range from 0.25 mto >16 m. The elemental concentrations of soil samples were determinedby energy-dispersive X-ray fluorescence, while the elemental concentrationsof generated aerosols were analysed by particle-induced X-ray emission. Theelements Al, K and Rb show a slight positive fractionation with decreasingparticle size throughout the particle size range studied. The concentrationsof Ca, Mn, Fe, Sr and Y are maximum in the small soil size fraction (<45m) and decrease for the coarse soil size fractions, while in the mineralaerosol particle sizes (0.25– > 16 m) the concentrations remainmore or less constant. The size distributions for Cr, Ti and Zr show a maximumin the particle size range 45–100 m and the concentrations of theseelements decrease sharply in the aerosol fraction down to 16 m to remainconstant in the smaller aerosol fractions.Enrichment factors for the elements were calculated relative to five referencematerials: average crustal rock, average soil, the investigated Sahara bulksoil, the finest fraction of this soil and the aerosol generated from thissoil, and using four reference elements: Al, Si, Ti and Fe. The enrichmentfactors were found to vary significantly depending on the choice of thereference material or the reference element. The enrichment factors for theSudan mineral aerosol were almost identical to those for Khartoum atmosphericaerosol but different from those for Namib mineral aerosol and Israelatmospheric aerosol following dust storms. Multivariate display methods(cluster analysis, principal component analysis and linear discriminantanalysis) were applied to the element ratios in the mineral aerosol from theSahara and Namib and this showed that these mineral aerosol can bedifferentiated into different groups. An attempt was also made to relate themineral aerosol to its parent soil through the use of these multivariatetechniques and the elemental ratios in both the mineral aerosols and the bulksoils (Namib and Sahara). It was also possible using the elemental ratios andthe multivariate display methods to associate the crustal component to themineral aerosol generated from the Sahara.  相似文献   

10.
Cloud water and interstitial aerosol samples collected at Mt. Sonnblick (SBO) were analyzed for sulfate and aerosol carbon to calculate in-cloud scavenging efficiencies. Scavenging efficiencies for sulfate (SO) ranged from 0.52 to 0.99 with an average of 0.80. Aerosol carbon was scavenged less efficiently with an average value (AC) of 0.45 and minimum and maximum values of 0.14 and 0.81, respectively. Both SO and AC showed a marked, but slightly different, dependence on the liquid water content (LWC) of the cloud. At low LWC, SO increased with rising LWC until it reached a relatively constant value of 0.83 above an LWC of 0.3 g/m3. In the case of aerosol carbon, we obtained a more gradual increase of AC up to an LWC of 0.5 g/m3. At higher LWCs, _ remained relatively constant at 0.60. As the differences between SO and A varied across the LWC range observed at SBO, we assume that part of the aerosol carbon was incorporated into the cloud droplets independently from sulfate. This hypothesis is supported by size classified aerosol measurements. The differences in the size distributions of sulfate and total carbon point to a partially external mixture. Thus, the different chemical nature and the differences in the size and mixing state of the aerosol particles are the most likely candidates for the differences in the scavenging behavior.  相似文献   

11.
The photooxidation of -humulene in the presence of NOx, natural sunlight, and rural background air was investigated using a combination of gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC). Identification and quantification of gas and particulate reaction products were reported over the course of the reaction. The daytime photooxidation was carried out in a large outdoor smog chamber (190 m3). A wide range of ring retaining and ring opening products in the gas and particle phase are reported. On average, measured gas and particle phase products accounted for 44% of the reacted -humulene carbon. Measurements show that a number of reaction products with low vapor pressures (e.g. 3-seco--humulone aldehyde, 7-seco--humulone aldehyde, -humulal aldehyde, -humulene 3-oxide or -humulene 7-oxide, -humulaic/alic acid isomers, and 3-seco--14-hydroxyhumulone aldehyde) were found in the early stage of the reaction and may play an important role in the early formation of secondary organic aerosol. A detailed mechanism is proposed to account for most products observed in this investigation.  相似文献   

12.
The gas and particle phase reaction products of a mixture of the atmospherically important terpenes -pinene and -pinene with the atmospheric oxidants O3 and OH/NOx were investigated using both gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC) for identification and quantification of reaction products. The nighttime oxidation of a mixture of -pinene and -pinene in the presence of O3/air, and the daytime oxidation of a mixture of -pinene + -pinene with NOx air in the presence of natural sunlight were carried out in the University of North Carolina's large outdoor smog chamber (190 m3) located in Chatham County, North Carolina. Mass balances for gaseous and aerosol reaction products are reported over the course of the reaction. More than twenty-nine products were identified and/or quantified in this study. On average, measured gas and particle phase products accounted for 74 to 80% of the reacted -pinen/-pinene mixture carbon. Measurements show that a number of reaction products were found in both O3 and NOx system [pinonaldehyde, pinic acid, pinonic acid, pinalic-3-acid, 4-hydroxypinalic-3-acid, 4-oxonopinone, 1-hydroxy-nopinone, 3-hydroxy-nopinone, and nopinone]. Pinonic acid, pinic acid, pinalic-3-acid, 4-hydroxypinalic-3-acid, and 10-hydroxypinonic acid were observed in the early stage in the aerosol phase and may play an important role in the early formation of secondary aerosols.  相似文献   

13.
Three-dimensional excitation–emission matrix (EEM) fluorescence spectra of water-soluble organic compounds (WSOC) from aerosol samples were measured and compared with those reported in the literature for natural dissolved organic matter. The EEM profiles of the WSOC presented three characteristic excitation/emission (Exc/Em) peaks: 240/405 nm, 310/405 nm and 280/340 nm. The fluorescence intensities at Exc/Em240/405 nm and Exc/Em310/405 nm are located at wavelengths shorter than those reported for aquatic humic substances, indicating a smaller content of both aromatic structures and condensed unsaturated bond systems in the WSOC fraction. The EEM profiles of fractions obtained by the isolation procedure of the WSOC by the XAD resins showed that a fractionation has occurred and the XAD-8 eluate is highly representative of the total WSOC of collected aerosol. Synchronous scan spectra were more detailed than conventional fluorescence emission spectra, appearing more suitable for studying multicomponent samples such as the WSOC from atmospheric aerosols.  相似文献   

14.
Measurements of Hg (total gas-phase, precipitation-phase andparticulate-phase), aerosol mass, particulate 210Pb and7Be and precipitation 210Pb were made at an atmosphericcollection station located in a near remote area of northcentral Wisconsin,U.S.A. (46°10N, 89°50W) during the summers of 1993, 1994and 1995. Total Hg and 210Pb were observed to correlate strongly(slope = 0.06 ± 0.03 ng mBq-1; r 2 =0.72) in rainwater. Mercury to 210Pb ratios in particulate matter(0.03 ± 0.02 ng mBq-1; r 2 = 0.06) wereconsistent with the ratio in rain. Enrichment of the Hg/mass ratio (approx.5–50×) relative to soil and primary pollutant aerosols indicatedthat gas-to-particle conversion had taken place during transport. Comparisonof these results with models for the incorporation of Hg into precipitationindicates that atmospheric particles deliver more Hg to precipitation than canbe explained by the presence of soot. A lack of correlation between totalgas-phase Hg (TGM) and a 7Be/210Pb function suggests novertical concentration gradient within the troposphere, and allows an estimateof TGM residence time of 1.5 ± 0.6 yr be made based on surface airsamples.  相似文献   

15.
Although extensive areas of forests and grasslands are burned in the tropics, relatively little scientific attention has been focused on this phenomenon. In order to determine the land area burned and estimate the charcoal (elemental or graphitic carbon) produced, I monitored agricultural burning in a 1145 km2 area in central Panama during the 1981 dry season. Over 10% of the land surface was burned in that year. Charcoal concentrations in the aerosol were also measured and reached values of 3.1 gC/m3 during the peak in burning. Off-peak values of aerosol charcoal are less than 1 gC/m3. The high charcoal concentration reflects the massive amounts of vegetational burning occurring in the area.The charcoal advected by the air mass flowing over the area has been estimated using a box model. Assuming an average aerosol concentration of charcoal of 1 gC/m3 for a three-month burning period, a 2 km atmospheric mixed layer, a 14 km/h wind velocity to the south, and a 150 km wide zone across the western Gulf of Panama watershed, I estimate that, during the dry season, 9×109 g charcoal are mobilized by the troposphere. If 4.1×1012 g phytomass are annually burned in this region, then the charcoal emission factor to the troposphere is 2.2×10–3.  相似文献   

16.
Henry's law constants KH (mol kg-1 atm-1) have been measured between 278.15 K and 308.15 K for the following organic acids: CH2FCOOH (ln(KH[298.15 K]) = 11.3 ± 0.2), CH2ClCOOH (11.59 ± 0.14), CH2BrCOOH (11.94 ± 0.21), CHF2COOH (10.32 ± 0.10), CHCl2COOH (11.69 ± 0.11), CHBr2COOH (12.33 ± 0.29), CBr3COOH (12.61 ± 0.21), and CClF2COOH (10.11 ± 0.12). The variation of KH with temperature was determined for all acids except CH2FCOOH and CBr3COOH, with r H° for the dissolution reaction ranging from –85.2 ± 2.6 to –57.1 ± 2.5 kJ mol-1, meaning that their solubility is generally more sensitive to temperature than is the case for the simple carboxylic acids. The Henry's law constants show consistent trends with halogen substitution and, together with their high solubility compared to the parent (acetic) acid (ln(KH[298.15 K]) = 8.61), present a severe test of current predictive models based upon molecular structure. The solubility of haloacetic acids and strong dissociation at normal pH mean that they will partition almost entirely into cloud and fog in the atmosphere (0.05–1.0 g H2O m-3), but can reside in both phases for the liquid water contents typical of aerosols (10-5-10-4 g H2O m-3).  相似文献   

17.
The gas and particle phase products from the reaction of -pinene with the atmospheric oxidants O3 and OH radicals in the presence of NOx were investigated using both gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC) for identification and quantification of reaction products. The nighttime oxidation of -pinene in the presence of O3/air and the daytime oxidation of -pinene in the presence of NOx/air and natural sunlight were carried out in the University of North Carolina large outdoor smog chamber (190 m3) located in Chatham County, North Carolina. A Scanning Mobility Particle Sizer system (3936, TSI) and a Condensation Particle Counter (3025A, TSI) were used to study the secondary organic aerosol (SOA) formation, and a filter pack/denuder sampling system was used for simultaneously collecting gas and particle phase products for analysis. A gas chromatograph coupled to a mass spectrometer (GC-EIMS or GC-CIMS) was used for the identification and quantification of gas and aerosol products. A HPLC method was used for the measurement of small carbonyl compounds (aldehydes and ketones) as their 2,4-dinitrophenylhydrazones (DNPH) derivatives. Mass balances for gaseous and aerosol reaction products were reported over the course of the reaction. More than sixteen products were identified and/or quantified in this study. On average, measured gas and particle phase products accounted for 57 to 71% of the reacted -pinene carbon. Measurements showed that a number of reaction products were found in both O3 and NOx systems (pinic acid, pinalic-3-acid, 4-hydroxypinalic-3-acid, 4-oxonopinone, 1-hydroxynopinone, 3-hydroxynopinone, and nopinone). Pinic acid, pinalic-3-acid, and 4-hydroxypinalic-3-acid were observed in the early stage in the aerosol phase and may play an important role in the early formation of secondary aerosols. Detailed reaction schemes are presented to account for most of the observed reaction products.  相似文献   

18.
Precipitation Chemistry in the Sahelian Savanna of Niger, Africa   总被引：1，自引：0，他引：1  
Within the framework of the IDAF (IGAC DEBITS AFRICA) network, we present in this paper data on precipitation and aerosol chemistry in the semiarid savanna of the Sahelian region of Niger. An automatic wet-only precipitation collector was operated at the Banizoumbou station during the entire 1996 rainy season (June to September 1996). Inorganic (Na+, NH 4 + , K+, Mg2+, Ca2+, Cl-, NO 3 - , SO 4 2- ) and organic contents of the precipitation (HCOOH, CH3COOH, C2H5COOH) were determined by Ion Chromatography (IC) in 29 rainfall events. Once per week, bulk particle samples were collected on the same site, and soluble water material was determined by IC. We examined the influence of atmospheric gas and particle sources on the precipitation and aerosol chemical contents. We established the influence of marine, terrigenous, and biogenic sources in the Sahelian region. The terrigenous signature is dominant and related to Sahelian soil erosion, with a high calcium content in precipitation (31.2 eq L-1) and in aerosols (1.8 g m-3). Two other signatures of atmospheric sources are highlighted by the relatively high nitrogenous (ammonium and nitrate) and organic contents (formate, acetate) in the precipitation. Ammonium (12.9 eq L-1) and nitrate (12.3 eq L-1) contents confirm respectively the biogenic source of ammonia released by domestic animal excreta in Niger and the natural emissions from semiarid savannas soils, perturbed by wild or domestic animal grazing. In spite of a high potential acidity given by nitrate, formate and acetate; a weak acidity (H+ (2.1 eq L-1) is calculated from the mean pH of 5.67 measured. A statistical analysis of the aerosol chemical composition clearly indicates that nitrates are strongly correlated at the 1% level with terrigenous ions, i.e., Ca2+ and Mg2+ (0.95 < r < 1). We observed a similar relationship between all the terrigenous ions and nitrate in the precipitation. In the Sahelian region, alkaline soil dust representative of the terrigenous contribution interact, with gaseous nitrogenous and carbonaceous compounds, leading to the neutralization of acid gases and subsequent weak acidity in precipitation. Finally, taking into account the main chemical characteristics of Banizoumbou precipitations and aerosols, which demonstrate the importance of heterogeneous and multiphase chemical processes, we propose a conceptual model of the atmospheric chemistry in the Sahelian region.  相似文献   

19.
The physical properties and the chemical composition of atmospheric aerosols have been studied in an equatorial region in the southern Congo (Africa). Field experiments were conducted between 1978 and 1983 in the equatorial forest of the Mayombe during periods where the influence of biomass burning was minimum. The results indicate that the forest is a net source of both fine particles resulting primarily from gas-to-particle conversion and coarse particles produced by mechanical processes. Carbonaceous matter is the major component of these biogenic particles but the forest is also a significant source of sulfate, nitrate, ammonium and potassium. Half of this carbon is attached to submicron particles and likely derives from organic gaseous precursors naturally emitted by the local biosphere.Presented at the international Symposium Influence of marine and terrestrial biosphere on the chemical composition of the atmosphere, held in Mainz, F.R.G., on 16–22 March 1986.  相似文献   

20.
Gaseous nitrogen compounds (NO x , NO y , NH3, N2O) were measured at ground level in smoke plumes of prescribed savanna fires in Lamto, in the southern Ivory Coast, during the FOS/DECAFE experiment in January 1991. During the flaming phase, the linear regression between [NO x ] and [CO2] (differences in concentration between smoke plumes and atmosheric background) results volumic emission ratio [NO x ]/[CO2]=1.37×10–3 with only slight differences between heading and backing fires. Nearly 90% of the nitrogen oxides are emitted as NO. Average emission ratios of other compounds are: 1.91, 0.047, and 0.145×10–3 for NO y , NH3 and N2O, respectively. The emission ratios obtained during this field experiment are compred with corresponding values measured during former experiments with the same plant species in combustion chambers. An accurate determination of both the biomass actually burned and of the plant nitrogen content, allows an assessment of emission fluxes of N-compounds from Guinean savanna burns. Preliminary results dealing with the influence of fire on biogenic emissions from soils are also reported.  相似文献   

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