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1.
We report the first measurements of the mixing ratios of acetic (CH3COOH) and formic (HCOOH) acids in the air filling the pore spaces of the snowpacks (firn air) at Summit, Greenland and South Pole. Both monocarboxylic acids were present at levels well above 1 ppbv throughout the upper 35 cm of the snowpack at Summit. Maximum mixing ratios in Summit firn air reached nearly 8 ppbv CH3COOH and 6 ppbv HCOOH. At South Pole the mixing ratios of these acids in the top 35 cm of firn air were also generally >1 ppbv, though their maximums barely exceeded 2.5 ppbv of CH3COOH and 2.0 ppbv of HCOOH. Mixing ratios of the monocarboxylic acids in firn air did not consistently respond to diel and experimental (fast) variations in light intensity, unlike the case for N oxides in the same experiments. Air-to-snow fluxes of CH3COOH and HCOOH apparently support high mixing ratios (means of (CH3COOH/HCOOH) 445/460 and 310/159 pptv at Summit and South Pole, respectively) in air just above the snow during the summer sampling seasons at these sites. We hypothesize that oxidation of carbonyls and alkenes (that are produced by photo- and OH-oxidation of ubiquitous organic compounds) within the snowpack is the source of the monocarboxylic acids.  相似文献   

2.
Chemical actinometry was used to measure nitrate photolysis rate coefficients, JNO3, on and in snowpack at Summit, Greenland. Sealed glass tubes containing nitrate and a hydroxyl radical trapping system were buried in snow and exposed for between 2 and 24 h. Average JNO3 values for 2-h midday exposures in early June on surface snow were 10–14×10−7 s−1. Averages over 24 h were 3.5–4.5×10−7 s−1. These values reflect the integrated photon flux and also any variation of the nitrate photolysis rate with temperature. Attenuation of JNO3 within the firn was 0.03–0.04 cm−1 for 24-h exposures and 0.08 cm−1 for a 2-h exposure. Different attenuation coefficients may relate to differential light penetration due to changes in sun angle over the course of 24 h.  相似文献   

3.
The concentrations of C1–C8 carbonyl compounds were measured at two urban sites in Hong Kong from October 1997 to September 2000. The daily total carbonyl concentrations were found to range from 2.4 to 37 μg m−3. Formaldehyde was the most abundant species, which comprised from 36 to 43% of the total detected carbonyls, followed by acetaldehyde (18–21%) and acetone (8–20%). The highest 24-hour average concentrations measured were 10 and 7.7 μg m−3 for formaldehyde and acetaldehyde, respectively. Seasonal and temporal variations in the concentrations of formaldehyde and acetaldehyde were not obvious, but lowest concentrations often occurred from June to August. The mean formaldehyde/acetaldehyde molar ratios at the two sites in summer (2.8±1.1 and 2.5±1.2) were significantly higher (p⩽0.01) than those in winter periods (1.9±0.6 and 2.0±0.6). The phenomena were explained by influences of both photochemical reactions and local meteorological conditions. Better correlations between formaldehyde and acetaldehyde, and between NOx and each of the two major carbonyls were obtained in winter periods indicating direct vehicular emissions were the principal sources. The ambient formaldehyde and acetaldehyde concentrations in the urban atmosphere of Hong Kong were within the normal ranges reported in the literature for other urban sites world-wide.  相似文献   

4.
Patterns of gaseous elemental mercury (GEM) were monitored at 20 and 150 cm above the snowpack near Resolute Bay, Cornwallis Island, Nunavut, Canada near the Upper Air Station of Environment Canada (74°42′N, 94°58′W) from 7 May (day 127) to 12 June (day 163) 2003. At this time of year there was 24 h daylight but still a strong diel change in solar radiation. Daily patterns of GEM-tracked solar radiation with a lag of about 2 h and the GEM gradient between these two heights showed the direction of flux. In addition to the previously established autocatalytic reactions involving halogens where reactive gaseous mercury and fine particulate mercury result in direct deposition to the snow, both diffusion to and volatilization from the snow occurred on a regular basis. Total mercury (THg) in the snowpack increased to near 30 ng L−1 following 8 d of atmospheric mercury depletion then decreased to values near 1 ng L−1. Losses from the snow could not be accounted for in melt water as stream runoff values were also low. In other words, most of the mercury associated with increased levels in snow was volatilized back to the atmosphere either directly from the snow or from the water surfaces. However, using accepted mass transport coefficients, the flux appeared low and other mechanisms are suggested. In contrast to THg, methyl mercury (MeHg) in the snow reached values near 140 pg L−1 but also declined to less than detection limit (10 pg L−1) with the onset of warmer temperatures. MeHg in stream runoff water was similar to maximal values seen in the snow. This observation is consistent with the view that MeHg came in the snowfall or was deposited to the snow pack rather than produced in the snow. In contrast, much of the THg associated with mercury depletion events was volatilized back to the atmosphere.  相似文献   

5.
Steppe ecosystems are regarded as an important sink of atmospheric methane (CH4) and grazing is hypothesized to reduce CH4 uptake. However, firm experimental evidence is required to prove this hypothesis. Using a fully automated, chamber-based measuring system, we conducted continuous high-frequency (at a 3-h interval) measurements of CH4 uptake in a Leymus chinensis steppe, which is a typical grassland ecosystem in Inner Mongolia, China. Two management regimes were investigated: ungrazed since 1999 (UG99) and winter-grazed since 2001 (WG01). Measurements were carried out continuously during the periods of June–September 2004, May–September 2005 and March–June 2006. During all of these periods, significantly lower mean CH4 uptake (±S.E.) at WG01 (28±0.7 μg C m−2 h−1) as compared to UG99 (56±1.0 μg C m−2 h−1) (p<0.01) was found. Total CH4 uptake during the growing seasons (May–September) 2004 and 2005 at WG01 and UG99 was quantified as 1.15 and 2.15 kg C ha−1, respectively. Annual rates of CH4 uptake were approximately 1.91 (WG01) and 3.58 kg C ha−1 (UG99), respectively. These results indicate that winter-grazing of steppe significantly reduced atmospheric CH4 uptake by ca. 47%. The winter-grazing practice may have inhibited CH4 uptake by (a) increasing the likelihood of physiological water stress for CH4-consuming bacteria during dry periods, (b) decreasing gas diffusion into the soil and, (c) reducing the populations of CH4 oxidizing bacteria. These three mechanisms could have collectively or independently facilitated the observed inhibitory effects. Our results suggest that grazing exerts a considerable negative impact on CH4 uptake in semi-arid steppes at regional scales. Notwithstanding, further studies involving year-round, intensive measurements of CH4 uptake are needed.  相似文献   

6.
We have recently completed a methane emissions inventory for the New England region. Methane emissions were calculated to be 0.91 Tg yr-1, with wetlands and landfills dominating all other sources. Wetlands are estimated to produce 0.33 Tg CH4 yr-1, of which 74% come from Maine. Active landfills emit an estimated 0.28 Tg CH4 yr-1, 60% of which are generated from twelve landfills. Although uncertainty in the estimate is greater, emissions from closed landfills are on the same order of magnitude as active landfills and wetlands; 0.25 Tg CH4 yr-1. Sources of moderate magnitude include ruminant animals (0.05 Tg CH4 yr-1) and residential wood combustion (0.03 Tg CH4 yr-1). Motor vehicles, natural gas, and wastewater treatment make only minor contributions. New England is heavily forested and the soil uptake of atmospheric methane in upland forests, 0.06 Tg CH4 yr-1, decreases emissions from soils by about 18%. Although uncertainties remain, our estimates indicate that even in a highly urbanized region such as New England, natural sources of methane make the single greatest contribution to total emissions, with state totals varying between 8% (Massachusetts) and 92% (Maine). Because emissions from only a few large landfills dominate anthropogenic sources, mitigation strategies focused on these discrete point sources should result in significant improvements in regional air quality. Current federal regulations mandate landfill gas collection at only the largest sites. Expanding recovery efforts to moderately sized landfills through either voluntary compliance or further regulations offers the best opportunity to substantially reduce atmospheric methane in New England. In the short term, however, the large contribution from closed, poorly regulated landfills may make the attribution of air quality improvements difficult. Mitigation efforts toward these landfills should also be a priority.  相似文献   

7.
To evaluate the tropical wetlands contribution to the methane (CH4) burden better, field campaigns were performed during 2004 and 2005 near the Miranda River, in five sites inside the Brazilian Pantanal region. The CH4 fluxes were determined using the static chamber technique. Environmental variables that may affect CH4 emissions, as the water depth, the water and air temperatures were also measured. The overall average of the 320 individual CH4 flux measurements made between March/2004 and March/2005 was 142±314 mg CH4 m−2 d−1, which is a value near the ones observed in other tropical flooded regions. About 47% of the fluxes measurements presented nonlinear increases in the chamber concentrations, which were assumed to be linked to CH4 losses through bubbles. The bubble flux represented about 90% of the total CH4 losses in the measurements and ranged from 1 to 2187 mg CH4 m−2 d−1 with an average of 292±410 mg CH4 m−2 d−1 (median: 153 mg CH4 m−2 d−1). The diffusive flux ranged from 1 to 124 mg CH4 m−2 d−1, with an average of 10±17 mg CH4 m−2 d−1 (median: 5 mg CH4 m−2 d−1). The fluxes from lakes were smaller than those observed in the floodplains, where the flooding was more dependent on the seasonal cycle. The diffusive flux showed a slight, but not statistically significant seasonal variation, following the seasonal variation of the flooding of the Pantanal region. A rough estimative of the total annual CH4 emission shows that the contribution of the Pantanal is about 3.3 Tg CH4 yr−1, which represents about 3.3% of the total CH4 emissions estimated to be originated in wetlands ecosystems. It may be a conservative estimate, which may present a large interannual variation, since it was obtained during one of the lowest flood of the Pantanal in recent years.  相似文献   

8.
Micrometeorological flux-gradient and nocturnal boundary layer methods were combined with Fourier transform infrared (FTIR) spectroscopy for high-precision trace gas analysis to measure fluxes of the trace gases CO2, CH4 and N2O between agricultural fields and the atmosphere. The FTIR measurements were fully automated and routinely obtained a precision of 0.1–0.2% for several weeks during a measurement campaign in October 1995. In flux-gradient measurements, vertical profiles of the trace gases were measured every 30 min from the ground to 22 m. When combined with independent micrometeorological measurements of water vapour fluxes, trace gas fluxes from the underlying surface could be determined. In the nocturnal boundary layer method the rate of change in mass storage in the 0–22 m layer was combined with fluxes measured at 22 m to estimate surface fluxes. Daytime fluxes for CO2 were −0.78±0.40 (1σ) mg CO2 m−2 s−1. Daytime fluxes of N2O and CH4 were very small and difficult to measure reliably using the flux-gradient technique, despite the high precision of the concentration measurements. Mean daytime flux for N2O was 17±48 ng N m−2 s−1, while the corresponding flux for CH4 was 47±410 ng CH4 m−2 s−1. The mean nighttime flux of CO2 estimated using the nocturnal boundary layer method was +0.15±0.05 mg CO2 m−2 s−1, in good agreement with chamber measurements of respiration rates. Nighttime fluxes of CH4 and N2O from the nocturnal boundary layer method were 109±69 ng CH4 m−2 s−1 and 2±3.2 ng N m−2 s−1, respectively, in good agreement with chamber measurements and inventory estimates based on the sheep and cattle stocking rates in the region. The suitability of FTIR-based methods for long term monitoring of spatially and temporally averaged flux measurements is discussed.  相似文献   

9.
A budget for the methane (CH4) cycle in the Xilin River basin of Inner Mongolia is presented. The annual CH4 budget in this region depends primarily on the sum of atmospheric CH4 uptake by upland soils, emission from small wetlands, and emission from grazing ruminants (sheep, goats, and cattle). Flux rates for these processes were averaged over multiple years with differing summer rainfall. Although uplands constitute the vast majority of land area, they consume much less CH4 per unit area than is emitted by wetlands and ruminants. Atmospheric CH4 uptake by upland soils was ?3.3 and ?4.8 kg CH4 ha?1 y?1 in grazed and ungrazed areas, respectively. Average CH4 emission was 791.0 kg CH4 ha?1 y?1 from wetlands and 8.6 kg CH4 ha?1 y?1 from ruminants. The basin area-weighted average of all three processes was 6.8 kg CH4 ha?1 y?1, indicating that ruminant production has converted this basin to a net source of atmospheric CH4. The total CH4 emission from the Xilin River basin was 7.29 Gg CH4 y?1. The current grazing intensity is about eightfold higher than that which would result in a net zero CH4 flux. Since grazing intensity has increased throughout western China, it is likely that ruminant production has converted China's grazed temperate grasslands to a net source of atmospheric CH4 overall.  相似文献   

10.
The emissions of VOC from freshly cut and shredded Grevillea robusta (Australian Silky Oak) leaves and wood have been measured. The VOC emissions from fresh leaf mulch and wood chips lasted typically for 30 and 20 h respectively, and consisted primarily of ethanol, (E)-2-hexenal, (Z)-3-hexen-1-ol and acetaldehyde. The integrated emissions of the VOCs were 0.38±0.04 g kg−1 from leaf mulch, and 0.022±0.003 g kg−1 from wood chips. These emissions represent a source of VOCs in urban and rural air that has previously been unquantified and is currently unaccounted for. These VOCs from leaf mulch and wood chips will contribute to both urban photochemistry and secondary organic aerosol formation. Any CH4 emissions from leaf mulch and wood chips were <1×10−11 g g dry mass−1 s−1.  相似文献   

11.
A water surface sampler (WSS) was employed in combination with greased knife-edge surface deposition plates (KSSs) to measure the vapor phase deposition rates of PCBs to the sampler at an urban site, Chicago, IL. This sampler employed a water circulation system that continuously removed deposited PCBs. Total (gas+particle) and particulate PCB fluxes were collected with the WSS and KSSs, respectively. Gas phase PCB fluxes were then calculated by subtracting the KSS fluxes (particulate) from the WSS fluxes (gas+particle). The calculated gas phase PCB fluxes averaged 830±910 ng m−2d−1. This flux value is, in general, higher than the fluxes determined using simultaneously measured air–water concentrations in natural waters and is in the absorption direction. This difference is primarily because the PCBs were continuously removed from the WSS water keeping the water PCB concentration near zero.Concurrently, ambient air samples were collected using a modified high volume air sampler. The gas phase PCB concentrations ranged between 1.10 and 4.46 ng m−3 (average±SD, 2.29±1.28 ng m−3). The gas phase fluxes were divided by the simultaneously measured gas phase ambient concentrations to determine the overall gas phase mass transfer coefficients (MTCs) for PCBs. The average gas phase overall MTCs (Kg) for each homolog group ranged between 0.22 and 1.32 cm s−1 (0.54±0.47 cm s−1). The average MTC was in good agreement with those determined using similar techniques.  相似文献   

12.
Measurements of ammonia (NH3), nitrous oxide (N2O) and methane (CH4) were made from 11 outdoor concrete yards used by livestock. Measurements of NH3 emission were made using the equilibrium concentration technique while closed chambers were used to measure N2O and CH4 emissions. Outdoor yards used by livestock proved to be an important source of NH3 emission. Greatest emission rates were measured from dairy cow feeding yards, with a mean of 690 mg NH3-N m−2 h−1. Smaller emission rates were measured from sheep handling areas, dairy cow collecting yards, beef feeding yards and a pig loading area, with respective mean emission rates of 440, 280, 220 and 140 mg NH3-N m−2 h−1. Emission rates of N2O and CH4 were much smaller and for CH4, in particular, emission rates were influenced greatly by the presence or absence of dung on the measurement area.  相似文献   

13.
Biomass consumption and CO2, CO and hydrocarbon gas emissions in an Amazonian forest clearing fire are presented and discussed. The experiment was conducted in the arc of deforestation, near the city of Alta Floresta, state of Mato Grosso, Brazil. The average carbon content of dry biomass was 48% and the estimated average moisture content of fresh biomass was 42% on wet weight basis. The fresh biomass and the amount of carbon on the ground before burning were estimated as 528 t ha?1 and 147 t ha?1, respectively. The overall biomass consumption for the experiment was estimated as 23.9%. A series of experiment in the same region resulted in average efficiency of 40% for areas of same size and 50% for larger areas. The lower efficiency obtained in the burn reported here occurred possibly due to rain before the experiment. Excess mixing ratios were measured for CO2, CO, CH4, C2–C3 aliphatic hydrocarbons, and PM2.5. Excess mixing ratios of CH4 and C2–C3 hydrocarbons were linearly correlated with those of CO. The average emission factors of CO2, CO, CH4, NMHC, and PM2.5 were 1,599, 111.3, 9.2, 5.6, and 4.8 g kg?1 of burned dry biomass, respectively. One hectare of burned forest released about 117,000 kg of CO2, 8100 kg of CO, 675 kg of CH4, 407 kg of NMHC and 354 kg of PM2.5.  相似文献   

14.
In April 2000 atmospheric trace gas measurements were performed on the western Indian Ocean on a cruise of the Dutch research vessel Pelagia from the Seychelles (5°S, 55°E) to Djibouti (12°N, 43°E). The measurements included analysis of dimethyl sulfide (DMS), acetone and acetonitrile every 40 s using PTR-MS (proton-transfer-reaction mass spectrometry) and gas chromatographic analyses of C2–C7 hydrocarbons in air samples taken during the cruise. The measurements took place at the end of the winter monsoon season and the sampled air masses came predominantly from the Southern Hemisphere, resulting in low concentrations of some long-lived hydrocarbons, halocarbons, acetone (350 pptv) and acetonitrile (120 pptv). On three consecutive days a diurnal cycle in DMS concentration was observed, which was used to estimate the emission of DMS (1.5±0.7×1013 molecules m−2 s−1) and the 24 h averaged concentration of hydroxyl (OH) radicals (1.4±0.7×106 molecules cm−3). A strongly increased DMS concentration was found at a location where upwelling of deeper ocean waters took place, coinciding with a marked decrease in acetone and acetonitrile. In the northwestern Indian Ocean a slight increase of some trace gases was noticed showing a small influence of pollution from Asia and from northeast Africa as indicated with back trajectory calculations. The air masses from Asia had elevated acetonitrile concentrations showing some influence of biomass burning as was also found during the 1999 Indian Ocean Experiment, whereas the air masses from northeast Africa seemed to have other sources of pollution.  相似文献   

15.
In April 1996 snowpack samples were collected from the surroundings of the ore roasting and dressing plant at Zapoljarnij and the nickel smelters at Nikel and Monchegorsk, Kola Peninsula, NW Russia. In the laboratory, filter residues of snowpack samples (fraction>0.45 μm) from 15 localities (close to the nickel processing centres) were chemically for precious metals (Rh, Pt, Pd, Au) and Te by graphite furnace atomic absorption spectrometry (GFAAS) analysis, and for Cu and Ni by ICP-MS. Values up to 2770 ng/l Pd, 650 ng/l Pt and 186 ng/l Au were found in the filter residues. Additionally, platinum-group elements (PGE) and Au contents in ore samples from Noril’sk1, as well as in technogenic products (“Cu–Ni-feinstein” and copper concentrate) processed at the Monchegorsk smelter complex, were analysed using flameless atomic absorption spectroscopy (FAAS) for comparison with results obtained from snow. Rh, Pt, Pd and Au distribution data show the presence of two ore components (Noril’sk and Pechenga). Concentrations of these metals decrease with distance from the industrial sources and with the prevailing wind direction (generally north–south). Microscopic investigations and electron microprobe analysis of polished sections of snow filter residues (>0.45 μm) also reveal differences between particles from the two sources.  相似文献   

16.
A new application of the quasi-simultaneous gas/particle phase sampling and analysis principle first proposed by Simon and Dasgupta (Anal. Chem. 34 (1995) 71) is described. For the first time, a gradient chromatograph is used in connection with such a sampling system to allow the simultaneous determination of major organic (formic, acetic, propionic, oxalic, malonic and succinic) and inorganic (SO2, HNO2, HNO3, HCl and H2F2) acidic gases and related particles. Another addition to the previous systems is the analysis of cations other than ammonium from the particulate phase. The time resolution of the instrument still remains high, 1 h, during which gaseous water-soluble acidic compounds, ammonia, as well as related anionic particles and inorganic major cations are analysed. Sampling is based on diffusion in a wetted parallel plate denuder for gases and on growth in supersaturated water vapour for particles. The determination limits range from 2 ppt (acetate) to 0.4 ppb (ammonia) in the gas phase and 0.01 μg m−3 (citric acid) to 0.79 μg m−3 (calcium) for particulate matter. Collection efficiencies for gas and aerosol sampling were quantified and the supersaturation in the aerosol sampling apparatus investigated. The system has been used for field measurements at a background station; selected results of these measurements are presented.  相似文献   

17.
Carbonyl compounds in urban ambient air and street canyons were measured from December 2008 to August 2009 in a mountainous city in southwest China (Guiyang). The formaldehyde yield from the photo-oxidation of isoprene emitted by vegetation was estimated to be in the range of 0.63–3.62 μg m?3 from May to August, which accounted for 28.8–33.4% of ambient formaldehyde. Based on the calculation of photolysis rates and rates of reaction with the OH radical, it was found that photolysis was the predominant sink for formaldehyde and acetone in both summer and winter. For acetaldehyde, photo-oxidation by OH radicals and photolysis were the major sinks in summer while photo-oxidation by OH radicals was the dominant sink in winter. Wet precipitation was found to be an important removal process for the atmospheric carbonyls. In the urban ambient air, the average concentrations of formaldehyde, acetaldehyde, acetone and all carbonyls were 4.8 ± 2.1, 5.7 ± 3.3, 5.1 ± 2.5, and 25.1 ± 9.2 μg m?3 (n = 139), respectively. The average concentrations of these species in street canyons were 18.8 ± 6.5, 9.4 ± 3.2, 10.9 ± 2.1, and 64.1 ± 16.3 μg m?3 (n = 62), respectively. The significantly higher carbonyl levels on weekdays (compared to weekends) highlight the contribution of vehicle emissions to carbonyls in the street canyons.  相似文献   

18.
During the continuous monitoring of atmospheric parameters at the station Cape Point (34°S, 18°E), a smoke plume originating from a controlled fire of 30-yr-old fynbos was observed on 6 May 1997. For this episode, which was associated with a nocturnal inversion and offshore airflow, atmospheric parameters (solar radiation and meteorological data) were considered and the levels of various trace gases compared with those measured at Cape Point in maritime air. Concentration maxima in the morning of 6 May for CO2, CO, CH4 and O3 amounted to 370.3 ppm, 491 ppb, 1730 ppb and 47 ppb, respectively, whilst the mixing ratios of several halocarbons (F-11, F-12, F-113, CCl4 and CH3CCl3) remained at background levels. In the case of CO, the maritime background level for this period was exceeded by a factor of 9.8. Differences in ozone levels of up to 5 ppb between air intakes at 4 and 30 m above the station (located at 230 m above sea level) indicated stratification of the air advected to Cape Point during the plume event. Aerosols within the smoke plume caused the signal of global solar radiation and UV–A to be attenuated from 52.4 to 13.0 mW cm−2 and from 2.3 to 1.3 mW cm−2, respectively, 5 h after the trace gases had reached their maxima. Emission ratios (ERs) calculated for CO and CH4 relative to CO2 mixing ratios amounted to 0.042 and 0.0040, respectively, representing one of the first results for fires involving fynbos. The CO ER is somewhat lower than those given in the literature for African savanna fires (average ER=0.048), whilst for CH4 the ER falls within the range of ERs reported for the flaming (0.0030) and smouldering phases (0.0055) of savanna fires. Non-methane hydrocarbon (NMHC) data obtained from a grab sample collected during the plume event were compared to background levels. The highest ERs (ΔNMHC/ΔCH4) have been obtained for the C2–C3 hydrocarbons (e.g. ethene at 229.3 ppt ppb−1), whilst the C4–C7 hydrocarbons were characterised by the lowest ERs (e.g. n-hexane at 1.0 and n-pentane at 0.8 ppt ppb−1).  相似文献   

19.
Chemical surveys of snow were carried out in the upper reaches of the Kunnes River, a tributary of the Yili River in East Tienshan Mountains, China. Some surprisingly high values of sodium and potassium (K++Na+) ranging from 4.44 to 8.99 mg/l compared with other data from neighboring areas are detected. Moreover, some relative high values of SO42− with mean concentration 15.8 mg/l for new snow and 14.40 mg/l for deposited snow, ranging from 10.43 to 23.71 mg/l are also found. Therefore, it is inferred that the sodium and potassium (K++Na+) are in the forms of sulfate and that the sources of the sulfate are deserts and some dried lakes in Central Asia. It is also found that there is obviously spatial variation of ions such as K++Na+, Ca2+, SO42− and HCO3. The concentrations of K++Na+ and SO42−, and that of Ca2+ and HCO3 have similar spatial pattern. The temporal pattern of ion concentration of new snow is considered to be mainly controlled by the depth and area of snow cover in the study area and in the areas to the west.  相似文献   

20.
The radiative properties of aerosols that are transparent to light in the near-UV and visible, such as sulfate aerosols, can be dramatically modified when mixed with absorbing material such as soot. In a previous work we had shown that the aldol condensation of carbonyl compounds produces light-absorbing compounds in sulfuric acid solutions. In this work we report the spectroscopic and kinetic parameters necessary to estimate the effects of these reactions on the absorption index of sulfuric acid aerosols in the atmosphere. The absorption spectra obtained from the reactions of six different carbonyl compounds (acetaldehyde, acetone, propanal, butanal, 2-butanone, and trifluoroacetone) and their mixtures were compared over 190–1100 nm. The results indicated that most carbonyl compounds should be able to undergo aldol condensation. The products are oligomers absorbing light in the 300–500 nm region where few other compounds absorb, making them important for the radiative properties of aerosols. Kinetic experiments in 96–75 wt% H2SO4 solutions and between 273 and 314 K gave an activation energy for the rate constant of formation of the aldol products of acetaldehyde of −(70±15) kJ mol−1 in 96 wt% solution and showed that the effect of acid concentration was exponential. A complete expression for this rate constant is proposed where the absolute value in 96 wt% H2SO4 and at 298 K is scaled to the Henry's law coefficient for acetaldehyde and the absorption cross-section for the aldol products assumed in this work. The absorption index of stratospheric sulfuric acid aerosols after a 2-year residence time was estimated to 2×10−4, optically equivalent to a content of 0.5% of soot and potentially significant for the radiative forcing of these aerosols and for satellite observations in channels where the aldol products absorb.  相似文献   

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