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1.
This study demonstrates that oxalate has a strong inhibiting effect onFe-catalyzed S(IV) oxidation by oxygen in aqueous solution. While thepseudo-first order rate constant of S(IV) oxidation was determined to be1.6 × 103 M-1 s-1 in experimentswithout oxalate, the oxidation of S(IV) was totally inhibited at a molarconcentration ratio of iron:oxalate = 1:5 at an oxalate concentration of 4M. Under these conditions, the Fe(II)/Fe(III) ratio remained nearlyconstant during the observed reaction time. The determined rate constants wereindependent of the initial oxidation state of iron. However, with increasingconcentrations of oxalate, a longer induction period is observed forexperiments with iron initially in the Fe(II) oxidation state.  相似文献   

2.
During April 1986, as part of an international arctic air chemistry study (AGASP-2), ground level observations of aerosol trace elements, oxides of sulphur and nitrogen and particle number size distribution were made at Alert Canada (82.5N, 62.3W). Pollution haze was evident as indicated by daily aerosol number (size > 0.15 m diameter) and SO4 = concentrations in the range 125 – 260 cm–3 and 1.6 – 4.5 g m–3, respectively. Haze and associated acidic gases tended to increase throughout the period. SO2 and peroxyacetylnitrate (PAN) mixing ratios were in the range 140 – 480 and 370 – 590 ppt(v), respectively. About 88% of the total end-product nitrogen was in the form of PAN. In air dried to 2% relative humidity by warming to room temperature, the aerosol mass size distribution had a major mode at 0.3 m diameter and a minor one at 2.5 m. Aerosol mass below 1.5 m was well correlated with SO4 =, K+ and PAN. There was a steady increase in the oxidized fraction of total airborne sulphur and nitrogen oxide throughout April as the sun rose above the horizon and remained above. The mean oxidation rate of SO2 between Eurasia and Alert was estimated as 0.25 – 0.5% h–1. The molar ratio of total nitrogen oxide to total sulphur oxide in the arctic atmosphere (0.67±0.17) was comparable to that in European emissions. A remarkably strong inverse correlation of filterable Br and O3 led to the conclusion that O3 destruction and filterable Br production below the Arctic surface radiation inversion is associated with tropospheric photochemical reactions involving naturally occurring gaseous bromine compounds.  相似文献   

3.
Measurements at Barrow during the second Arctic Gas and Aerosol Sampling Program (AGASP-II), conducted in April 1986, showed no rapid long-range transport from lower-latitude source regions to Barrow, and only limited vertical transport from above the boundary layer to the surface. New aerosol size distribution measurements in the 0.005–0.1 m diameter size range using a Nuclepore-filter diffusion battery apparatus showed a median diameter of about 0.01 m during times of high condensation nucleus (CN) concentrations. Aerosol black carbon concentrations exceeding 400 ng m–3 were detected at the surface and were more strongly correlated with CN concentrations than with aerosol scattering extinction (sp), suggesting that aerosol carbon was generally associated with small particles rather than large particles. Measurements at Barrow during AGASP-I, conducted in March–April 1983, showed a series of aerosol events detected at the ground that were caused by rapid long-range transport paths to the vicinity of Barrow from Eurasia. These events were strongly correlated with aerosol loading in the vertical column (optical depth).  相似文献   

4.
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   

5.
Differences in total iron and manganese concentrations between large (d > 23 m) and small (4 < d < 23 m) cloud and fog drops were investigated at four locations in the United States. The study examined coastal stratus and stratocumulus clouds in southern California and northern Oregon, frontal and orographic clouds at Mt. Mitchell, North Carolina, and radiation fogs in California's San Joaquin Valley. The speciation of iron as a function of drop size was also examined in some fog samples from the San Joaquin Valley. Total iron and manganese concentrations were generally higher in large drops than in small drops in clouds sampled at Mt. Mitchell and along the southern California coast. These species were typically enriched in small drops at the Oregon coast and San Joaquin Valley sites. Ratios of dissolved Fe(III) to total dissolved Fe ranged from 0.88 to 0.93 in small fog drops. Non-uniform distributions of iron and manganese across the drop size spectrum can influence rates of metal catalyzed S(IV) autooxidation. Approximately 50% of the sampled clouds were calculated to experience autooxidation rate enhancements greater than 30% due to variations in drop acidity and catalyst concentrations with drop size.  相似文献   

6.
We present the first application of a multi-stage impactor to study volcanic particle emissions to the troposphere from Masaya volcano, Nicaragua. Concentrations of soluble SO4 2–,Cl–, F–, NO3 –, K+, Na+,NH4 +, Ca2+ and Mg2+ were determined in 11 size bins from 0.07 m to >25.5 m. The near-source size distributions showed major modes at 0.5m (SO4 2–, H+,NH4 +); 0.2 m and 5.0 m (Cl–) and 2.0–5.0 m(F–). K+ and Na+ mirrored the SO4 2– size-resolvedconcentrations closely, suggesting that these were transported primarily asK2SO4 and Na2SO4 in acidic solution, while Mg2+ andCa2+ presented modes in both <1 m and >1 m particles. Changes in relative humidity were studied by comparing daytime (transparent plume) and night-time (condensed plume) results. Enhanced particle growth rates were observed in the night-time plume as well as preferential scavenging of soluble gases, such as HCl, by condensed water. Neutralisation of the acidic aerosol by background ammonia was observed at the crater rim and to a greater extent approximately 15 km downwind of the active crater. We report measurements of re-suspended near-source volcanic dust, which may form a component of the plume downwind. Elevated levels ofSO4 2–, Cl–, F–,H+, Na+, K+ and Mg2+ were observed around the 10 m particle diameter in this dust. The volcanic SO4 2– flux leaving the craterwas 0.07 kg s–1.  相似文献   

7.
The reactivity of dissolved iron compounds towards different pollutants and photooxidants in atmospheric liquid water depends upon the oxidation state and speciation of iron. Our measurements of the oxidation state of dissolved iron eluted from aerosol particles (Dae: 0.4–1.6 m) collected in the urban atmosphere of Ljubljana showed that a large fraction of the iron content is present as Fe(II). The concentration ratio [Fe(II)]/[Fe(III)] varied between 0.9 and 3.1. The kinetics of S(IV) autoxidation catalyzed by Fe(II) under the conditions representative for acidified atmospheric liquid water and the influence of oxalate on this reaction under dark conditions was investigated. The reaction rate is the same if Fe(II) or Fe(III) is used as a catalyst under the condition that Fe(II) can be oxidized in Fe(III), which is the catalytically active species. Oxalate has a strong inhibiting effect on the S(IV) autoxidation in the presence of Fe(II). The reaction is autocatalytic with an induction period, that increases with higher concentrations of oxalate. The inhibiting effect of oxalate differs according to whether iron is initially in the Fe(II) or Fe(III) state. However, in both cases the inhibition by oxalate is a result of the formation of complexes with the catalyst.  相似文献   

8.
A liquid jet of 90 m diameter and variable length has been utilized to determine absorption rates and, hence, mass accommodation coefficients , of atmospheric trace gases. The compounds investigated are HCl (0.01), HNO3 (0.01), N2O5 (0.005), peroxyacetyl nitrate (>0.001), and HONO (0.005). It is concluded that the absorption of these trace gases by liquid atmospheric water is not significantly retarded by interfacial mass transport. The strengths and limitations of the liquid jet technique for measuring mass accommodation coefficients are explored.  相似文献   

9.
The carbon isotopic ratio of atmospheric carbon dioxide at Tsukuba,Japan   总被引：1，自引：0，他引：1  
To find out the secular and seasonal trends of the 13C value and CO2 concentration in the surface air and the determination of the 13C in the atmospheric CO2 collected at Tsukuba Science City was carried out during the period from July 1981 to October 1983. The monthly average of the 13C value of CO2 in the surface air collected at 1400 LMT ranged from -7.52 to \s-8.45 with an average of -7.96±0.25 and the CO2 concentration in the air varied from 334.5 l 1-1 to 359 l 1-1 with an average of 347.2±6.3 l 1-1. The 13C value is high in summer and low in winter and is negatively correlated with the CO2 concentration. In general, the relationship between the 13C and the CO2 concentration is explainable by a simple mixing model of two different constant carbon isotopic species but the relationship does not always follow the model. The correlation between the 13C value and the CO2 concentration is low during the plant growth season and high at other times. The observed negative deviation of the 13C value from the simple mixing model in the plant growth season is partly due to the isotopic fractionation process which takes place in the land biota.  相似文献   

10.
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   

11.
Fourteen samples of fresh falling snow were collected at Antarctic coastal base Dumont d'Urville in 1984. The samples have been analysed for major ions (including MSA) by ion chromatography and acid titration. The results are relevant to the chemical composition of background precipitation in polar marine conditions. The seasalt aerosol contribution is dominant. All samples are found to be acidic in the range 3–16 eq/l. The calculated non-seasalt sulfate (nssSO4 2-) concentration is significantly negative for 3 of the 14 samples. NssSO4 2- is found to be relatively high in summer and fall. MSA also exhibits the same pattern probably linked to local marine biogenic activity and/or atmospheric photochemical processes. The MSA to nssSO4 2- ratio is in good agreement with values reported for coastal Antarctic ice cores and subantarctic acrosol. The background mean value for nitrate concentration is 1.1 eq/l but two very strong spikes (up to 16 eq/l) are observed. The first seems to be linked with long range transport of continental air masses while the second (in winter) is clearly due to a sudden input of nitric acid, possibly from the stratosphere.This paper represents a preliminary approach to a larger air and snow monitoring to be developped at this site.  相似文献   

12.
Summary The discrepancy between measured (or estimated) visual range (V g) and the one calculated from the drop size distribution (V b), stated byTrappenberg on the basis of the measurements ofRittberger, is discussed. It is assumed that in the measurement of the drop size distribution the small droplets are discriminated. If the distributions are extrapolated to drop diameters of 2 or 1 ,V b turns out to be in agreement withV g.
Diskussionsbeitrag zur Frage der Sicht in Wolken
Zusammenfassung Die vonTrappenberg auf Grund der Messungen vonRittberger festgestellte Diskrepanz zwischen gemessener (oder geschätzter) SichtweiteV g und der aus der Tropfengrößenverteilung berechnetenV b wird diskutiert. Es wird angenommen, daß bei der Messung der Tropfengrößenverteilung die kleinen Tropfen nicht genügend zur Geltung kommen. Extrapoliert man die Verteilungen in zwangloser Weise bis zu Tropfendurchmessern von 2 oder 1 , so ergibt sich eine gute Übereinstimmung vonV b mitV g.
Résumé L'auteur discute la discrépance existant entre la visibilité mesurée (ou estimée)Vg et la visibilité calculéeV b au moyen de la répartition de la grosseur des gouttes, discrépance établie parTrappenberg en partant des mesures deRittberger. On admet alors que, lors de la mesure de la répartition de la grosseur des gouttes, les plus petites d'entre elles n'ont pas suffisament de poids. Si l'on extrapole cette répartition jusqu'à un diamètre des gouttes de 2 ou 1 , on constate alors une bonne concordance entreV b etV g.

Mit 1 Textabbildung  相似文献   

13.
Two types of neutral planetary boundary layer (PBL) are distinguished:truly neutral – developed against a neutrally stratified free flow, and conventionally neutral – developed against a background stable stratification. Atmospheric PBLs treated asneutral are almost always conventionally neutral. Theoretical reasoning and results from large-eddy simulation (LES) show that A and B coefficients of the Rossby-number similarity theory are not constants. The same is true for thecoefficient Ch in the Rossby–Montgomery formula for the neutral boundary-layer depth h = Chu*/|f|, where u* is the friction velocity. Contrary to classical ideas, A, B and Ch depend on the ratio N N/|f| of the free-flow Brunt–V*auml;isäl ä frequency N to the absolute value of the Coriolis parameter |f|. This new development can explain why atmospheric and LES estimates of A, B and Ch appear inconsistent. It results from neglecting the fact that atmospheric data for N 102 were compared with LES data for N = 0, violating an obvious requirement of similarity with respect to N.  相似文献   

14.
A previously published technique for using tethered spherical balloons as anemometers for measuring light low-level winds has been further developed. Earlier data on the relationship between the aerodynamic drag coefficient and the Reynolds number of spherical rubber balloons were combined with a large number of new data and re-analysed; and the errors in the relationship were estimated. The results allowed a more accurate calculation of wind speed from the deflection of a tethered balloon from the vertical. When combined with a new technique for calculating the effects of the tether, this enabled light to moderate low-level winds at fixed heights up to 600 m or more to be measured with simple, cheap, and readily mobile equipment; and a slight modification of the technique allowed measurement of winds in and above fog. Wind speeds measured by the ballon technique showed reasonably good agreement with measurements by an anemometer carried beneath the balloon.Glossary of Symbols a, b, c Coefficients in the relationship between lnC d and lnR - A Quantity under square root in solution for lnV whena0 - C d Wind drag coefficient for balloon - C dc Value ofC d given by calibration curve of Table I - D Dynamic wind pressure force on balloon - F Buoyant free lift of balloon with load - Re Reynold's number of balloon (sphere) - R = Re/105 - r Radius of sphere - T Tension in tether - V Wind speed - 83() =(lnC dc -lnC d ) when 83° , or 0 for other - Error in lnC d - Elevation of tether where attached to balloon - Elevation of balloon from ground tether point - Molecular viscosity of air - Ratio of circumference to diameter of circle - Density of air  相似文献   

15.
Telecommunication laser diodes emitting near 1.39 m and 1.65 m in combination with direct-differential absorption spectroscopy are efficient tools to monitor in situ stratospheric H2O andCH4 with a good precision error (a few percents), a high temporal resolution (ranging from 10 ms to 1 s), a large dynamic range in the concentration measurements (four orders of magnitude) and a high selectivity in the analyte species. To illustrate the capability of laser probing technique, we report balloonborne H2Oand CH4 simultaneous measurements obtained on October 2001 atmidlatitudes (43° N). The H2O vertical profile achieved with the lasersensor in the lower stratosphere is compared with the H2O data yielded by a balloonborne frost-point hygrometer. The total hydrogen mixing ratio in the lower stratosphere, 2[CH4] + [H2O], appears to beconstant at 7.5 ± 0.1 ppmv. Nevertheless, an unexpected largedehydration of 0.5 ppmv was detected by both the laser sensor and thehygrometer between 16 km and 23 km. We suspect the occurrence of a tropicalair intrusion into mid-latitudes. We support this interpretation using a high-resolution advection model for potential vorticity.  相似文献   

16.
The total suspended particulate (TSP) levels at Delhi (north India) were measured on 116 days between February and October 1980. The observations were stratified according to season and the values of cross-correlation of the TSP and its components were evaluated. High TSP (209 g m-3) levels were found during the summer period associated with hot and dry weather in the region and low TSP (109 g m-3) were found during the monsoon period. Most of the TSP mass was associated with natural soil elements, such as Fe, Al, Mn, Ca, and K. Only a fraction of the mass of the TSP was comprised of elements from anthropogenic sources, e.g., Pb, Ni, Cd, Sb, Cu, and Zn. The aerosols at Delhi were potentially basic in nature, unlike those in European countries which are acidic in nature and cause acid rainfall.  相似文献   

17.
Airborne measurements made during August 1985 over Greenland and its environs show that both accumulation-mode (0.1 m D2.0 m) and giant (D2 m) particles were present in relatively high concentrations in arctic haze layers and that the accumulation-mode particles dominated light scattering. Particles with diameters (D) between 1 and 4 m consisted predominately of mixed materials, small and dense inclusions, and probably organic compounds containing sulfur. Many of the particles from 0.1 to 1 m in diameter were also of mixed composition, with sulfuric acid, ammonium sulfate and organics probably the dominant constituents.  相似文献   

18.
Aerosol chemical composition and trace gas measurements were made at twolocations on the northeastern peninsula of Tenerife during the ACE-2HILLCLOUD experiment, between 28 June and 23 July 1997. Measurementswere made of coarse (#gt;2.5 m aerodynamic diameter) and fine (#lt; 2.5m) aerosol Cl–, NO3 –,SO4 2–, non-sea saltSO4 2– (NSSS),CH3SO3 – (MSA) andNH4 +, and gas phase dimethylsulphide (DMS), HCl,HNO3, SO2, CH3COOH, HCOOH andNH3. Size distributions were measured using a cascadeimpactor. Results show that in marine air masses NSSS and MSA wereformed via DMS oxidation, with additional NSSS present in air massescontaining a continental component. Using a Eulerian box model approachfor aerosols transported between upwind and downwind sites, a mean NSSSproduction rate of 4.36 × 10–4 gm–3 s–1 was calculated for daytimeclear sky periods (highest insolation), with values for cloudy periodsduring daytime and nighttime of 3.55 × 10–4 and2.40 × 10–4 g m–3s–1, respectively. The corresponding rates for MSA were6.23 × 10–6, 8.49 × 10–6and 6.95 × 10–6 g m–3s–1, respectively. Molar concentration ratios forMSA/NSSS were 8.7% (1.8–18.2%) and 1.9%(1.3–3.5%) in clean and polluted air masses, respectively.Reactions occurring within clouds appeared to have a greater influenceon rates of MSA production, than of NSSS, while conversely daytime gasphase reactions were more important for NSSS. For MSA, nighttimein-cloud oxidation rates exceeded rates of daytime gas phase productionvia OH oxidation of DMS. NSSS, MSA and ammonium had trimodal sizedistributions, with modes at 0.3, 4.0 and >10.0 m (NSSS andNH4 +), and 0.3, 1.5 and 4.0 m (MSA). Nosignificant production of other aerosol species was observed, with theexception of ammonium, which was formed at variable rates dependent onneutralisation of the aerosol with ammonia released from spatiallynon-uniform surface sources. Seasalt components were mainly present incoarse particles, although sub-micrometre chloride was also measured.Losses by deposition exceeded calculated expectations for all species,and were highest for the seasalt fraction and nitrate.  相似文献   

19.
Levels of formate and acetate in dew were measured at Dayalbagh, India, usingsurrogate surfaces. The dew formed per night ranged between 0.06 lm–2 and 1.38 l m–2, with an average of 0.59l m–2. pH ranged between 6.7 and 7.4. Mean concentrations offormate and acetate in dew were 10.2 ± 10.2 eql–1 and 7.5 ± 4.5 eq l–1,respectively. The correlation coefficient between the two ions was 0.80 (p =0.001), which suggested that concentrations of these species in dew are linkedtogether. They have either common or different sources with fairly constantstrengths or products of same reaction. Good correlation of formate andacetate with Ca (r = 0.82 and r = 0.70, respectively) and Mg (r = 0.74 and r= 0.71, respectively) suggested that these ions may be associated with Ca andMg after the neutralization process. Deposition rates for formate and acetatein dew per night were 10.2 ± 7.22 mol m–2 pernight and 4.6 ± 2.2 mol m–2 per night,respectively. The theoretical Henry's law constant (K* H)and the field-observed Henry's law coefficient (K* H) ascalculated from concurrent measurements of gas phase and dew for both acidsshowed large discrepancies of three orders of magnitude.  相似文献   

20.
We have devised a partial differential equation for the prediction of dust concentration in a thin layer near the ground. In this equation, erosion (detachment), transport, deposition and source are parameterised in terms of known quantities. The interaction between a wind prediction model in the boundary layer and this equation affects the evolution of the dust concentration at the top of the surface layer. Numerical integrations are carried out for various values of source strength, ambient wind and particle size. Comparison with available data shows that the results appear very reasonable and that the model should be subjected to further development and testing.Notation (x, y, z, t) space co-ordinates and time (cm,t) - u, v components of horizontal wind speed (cm s–1) - u g, vg components of the geostrophic wind (cm s–1) - V=(u2+v2)1/2 (cm s–1) - (û v)= 1/(h – k) k h(u, v)dz(cm s–1) - V * friction velocity (cm s–1) - z 0 roughness length (cm) - k 1 von Karman constant =0.4 - V d deposition velocity (cm s–1) - V g gravitational settling velocity (cm s–1) - h height of inversion (cm) - k height of surface layer (cm) - potential temperature (°K) - gr potential temperature at ground (°K) - K potential temperature at top of surface layer (°K) - P pressure (mb) - P 0 sfc pressure (mb) - C p/Cv - (t)= /z lapse rate of potential temperature (°K cm–1) - A(z) variation of wind with height in transition layer - B(z) variation of wind with height in transition layer - Cd drag coefficient - C HO transfer coefficient for sensible heat - C dust concentration (g m–3) - C K dust concentration at top of surface layer (g m–3) - D(z) variation with height of dust concentration - u, v, w turbulent fluctuations of the three velocity components (cm s–1) - A 1 constant coefficient of proportionality for heat flux =0.2 - Ri Richardson number - g gravitational acceleration =980 cm s–2 - Re Reynolds number = - D s thickness of laminar sub-layer (cm) - v molecular kinematic viscosity of air - coefficient of proportionality in source term - dummy variable - t time step (sec) - n time index in numerical equations On sabbatical leave at University of Aberdeen, Department of Engineering, September 1989–February 1990.  相似文献   

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