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1.
There are large uncertainties in identifying and quantifying the globally significant sources and sinks of methyl bromide (CH3Br) and methyl iodide (CH3I). Long-term, quasi-continuous observations can provide valuable information about their regional sources, which may be significant in the global context. We report 3 years of in situobservations of these trace gases from the AGAGE (Advanced Global Atmospheric Gas Experiment) program at Cape Grim, Tasmania (41 °S, 145 °E). The average background levels of CH3Br and CH3I during March 1998–March 2001 were 8.05 and 1.39 ppt (dry air mole fractions expressed in parts per 1012), respectively. The CH3Br background data showed little seasonal variability. Trajectory analyses reveal that air masses showing elevated CH3Br levels at Cape Grim have had significant contact with coastal-terrestrial and/or coastal-seawater and/or urban source regions. The CH3I background data showed a seasonal cycle with a 3-year average amplitude of 0.47 ppt and maximum concentrations in summer, suggesting that the Southern Ocean is a significant source.Trajectory analyses reveal that air masses showing highly elevated CH3I levels at Cape Grim have had significant contact with coastal-terrestrial and/or coastal-seawater regions and/or the open-ocean regions of Bass Strait and the Tasman Sea.  相似文献   

2.
There are large uncertainties in identifying and quantifying the natural and anthropogenic sources of chloromethanes – methyl chloride (CH3Cl), chloroform (CHCl3) and dichloromethane (CH2Cl2), which are responsible for about 15% of the total chlorine in the stratosphere. We report two years of in situ observations of these species from the AGAGE (Advanced Global Atmospheric Gas Experiment) program at Cape Grim, Tasmania (41° S, 145° E). The average background levels of CH3Cl, CHCl3 and CH2Cl2 during 1998–2000 were 551± 8, 6.3± 0.2 and 8.9± 0.2 ppt (dry air mole fractions expressed in parts per 1012) respectively, with a two-year average amplitude of the seasonal cycles in background air of 25, 1.1 and 1.5 ppt respectively. The CH3Cl and CHCl3 records at Cape Grim show clear episodes of elevated mixing ratios up to 1300 ppt and 55 ppt respectively, which are highly correlated, suggesting common source(s). Trajectory analyses show that the sources of CH3Cl and CHCl3 that are responsible for these elevated observations are located in coastal-terrestrial and/or coastal-seawater regions in Tasmania and the south-eastern Australian mainland. Elevated levels of CH2Cl2 (up to 70 ppt above background) are associated mainly with emissions from the Melbourne/Port Phillip region, a large urban/industrial complex (population 3.5 million) 300 km north of Cape Grim.Now at the Centre for Atmospheric ChemistryNow at School of Environmental Sciences  相似文献   

3.
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.  相似文献   

4.
Airborne measurements of volatile organic compounds (VOC) were performed overthe tropical rainforest in Surinam (0–12 km altitude,2°–7° N, 54°–58° W) using the proton transferreaction mass spectrometry (PTR-MS) technique, which allows online monitoringof compounds like isoprene, its oxidation products methyl vinyl ketone,methacrolein, tentatively identified hydroxy-isoprene-hydroperoxides, andseveral other organic compounds. Isoprene volume mixing ratios (VMR) variedfrom below the detection limit at the highest altitudes to about 7 nmol/molin the planetary boundary layer shortly before sunset. Correlations betweenisoprene and its product compounds were made for different times of day andaltitudes, with the isoprene-hydroperoxides showing the highest correlation.Model calculated mixing ratios of the isoprene oxidation products using adetailed hydrocarbon oxidation mechanism, as well as the intercomparisonmeasurement with air samples collected during the flights in canisters andlater analysed with a GC-FID, showed good agreement with the PTR-MSmeasurements, in particular at the higher mixing ratios.Low OH concentrations in the range of 1–3 × 105molecules cm-3 averaged over 24 hours were calculated due to lossof OH and HO2 in the isoprene oxidation chain, thereby stronglyenhancing the lifetime of gases in the forest boundary layer.  相似文献   

5.
Surface ozone data from 25 Europeanlow-altitude sites and mountain sites located between79°N and 28°N were studied. The analysiscovered the time period March 1989–February 1993.Average summer and winter O3 concentrations inthe boundary layer over the continent gave rise togradients that were strongest in the north-west tosouth-east direction and west-east direction, respectively. WintertimeO3 ranged from 19 to 27 ppbover the continent, compared to about 32 ppb at thewestern border, while for summer the continentalO3 values ranged between 39 and 56 ppb and theoceanic mixing ratios were around 37 ppb. In the lowerfree troposphere average wintertime O3 mixingratios were around 38 ppb, with only an 8 ppbdifference between 28°N and 79°N. For summerthe average O3 levels decreased from about 55 ppbover Central Europe to 32 ppb at 79°N. Inaddition, O3 and Ox(= O3 + NO2)in polluted and clean air were compared. Theamplitudes of the seasonal ozone variations increasedin the north-west to south-east direction, while thetime of the annual maximum was shifted from spring (atthe northerly sites) to late summer (at sites inAustria and Hungary), which reflected the contributionof photochemical ozone production in the lower partsof the troposphere.  相似文献   

6.
Data on a variety of organic gases are presented, obtained with a protontransfer mass spectrometer (PTR-MS) operated during the March 1998 LBA/CLAIREairborne measurement campaign, between 60 and 12500 m over the rainforest inSurinam (2° N–5° N, 54° W–57° W). The instrumentcan detect molecules with a proton affinity greater than water, includingalkenes, dialkenes, carbonyls, alcohols, and nitriles. Many such molecules areemitted from the rainforest (e.g., isoprene) or formed from the oxidation ofprimary emissions (e.g., methylvinylketone (MVK) and methacrolein (MACR)).From a comparison with modelled data; the variation with altitude; previouslyreported biogenic emissions and the time and location of the measurement,possible and probable identities for the significant masses encountered in therange 33–140 amu have been deduced.The main observed protonated masses, postulated identities and observedaverage boundary layer mixing ratios over the rainforest were: 33 methanol(1.1 nmol/mol); 42 acetonitrile (190 pmol/mol); 43 multiple possibilities (5.9nmol/mol), 45 acetaldehyde (1.7 nmol/mol), 47 formic acid (not quantified);59 acetone (2.9 nmol/mol), 61 acetic acid (not quantified), 63 dimethylsulphide (DMS) (289 pmol/mol), 69 isoprene (1.7 nmol/mol), 71 MVK + MACR (1.3nmol/mol), 73 methyl ethyl ketone (1.8 nmol/mol), 75 hydroxyacetone (606pmol/mol), 83 C5 isoprene hydroxy carbonylsC5H8O2, methyl furan, and cis 3-hexen-1-ol(732 pmol/mol), 87 C5 carbonyls and methacrylic acid, 95 possibly2-vinyl furan (656 pmol/mol), 97 unknown (305 pmol/mol), 99 cis hexenal (512pmol/mol) and 101 isoprene C5 hydroperoxides (575 pmol/mol). Somespecies agreed well with those derived from an isoprene only photochemicalmodel (e.g., mass 71 MVK + MACR) while others did not and were observed athigher than previously reported mixing ratios (e.g., mass 59 acetone, mass 63DMS). Monoterpenes were not detected above the detection limit of 300pmol/mol. Several species postulated are potentially important sources ofHOx in the free troposphere, e.g., methanol, acetone, methyl ethylketone, methyl vinyl ketone and methacrolein.  相似文献   

7.
In summer, atmospheric ozone was measured from an aircraft platform simultaneously with nitric oxide (NO), oxides of nitrogen (NO y ), and water vapor over the Pacific Ocean in east Asia from 34° N to 19° N along the longitude of 138±3°E. NO y was measured with the aid of a ferrous sulfate converter. The altitude covered was from 0.5 to 5 km. A good correlation in the smoothed meridional distributions between ozone and NO y was seen. In particular, north of 25° N, ozone and NO y mixing ratios were considerably higher than those observed in tropical marine air south of 25° N. NO y and O3 reached a minimum of 50 pptv and 4 ppbv respectively in the boundary layer at a latitude of 20° N. The NO concentration between 2 and 5 km at the same latitude was 30 pptv. The profiles of ozone and water vapor mixing ratios were highly anti-correlated between 25° N and 20° N. In contrast, it was much poorer at the latitude of 33° N, suggesting a net photochemical production of ozone there.  相似文献   

8.
A series of 149 measurements of the HCHO mixing ratio were made between 0 and 10 km altitude and 70° N to 60° S latitude during TROPOZ II. The data show a vertical decrease of the HCHO mixing ratio with altitude at all latitudes and a broad latitudinal maximum in the HCHO mixing ratio between 30° N and 30° S at all altitudes. The measured mixing ratios of HCHO are considerably higher than those expected from CH4 oxidation alone, but agree broadly with the average latitude by altitude distribution of HCHO derived by a 2D model including emissions of C1–C7 hydrocarbons. A number of the regional scale deviations of the measured HCHO distribution from the average modelled one can be explained in terms of the local wind field.  相似文献   

9.
Organic and elemental carbon (OC and EC) content in PM10 was studied at two sites in Prague, which were located in a suburb and in the downtown. Similar overall average levels were found for both species and also for the PM10 mass at the two sites (i.e., 5.5 and 4.8 μg/m3 for OC, 0.74 and 0.80 μg/m3 for EC, and 33 μg/m3 and 37 μg/m3 for the PM10 mass at the suburb and downtown site, respectively), but substantial differences were observed between the two sites in some seasons and/or meteorological situations. Approximately three times higher values were found for OC in winter compared to summer, with a higher winter/summer ratio for the suburban site. The differences for EC were smaller, but still, compared to summer, more than two times higher EC levels were observed during autumn at the suburban site and 1.5 higher EC levels in winter and autumn at the downtown site. The lowest OC to EC ratios at the suburban site were 3.4, while they were around 1.3 for the downtown site. It was found that the origin of the air masses had a major impact on the observed PM10 mass and OC levels, with largest concentrations noted for air masses recirculating over central Europe and arriving from southeastern Europe in winter. Trajectories coming from the west and northwest originating above the Atlantic Ocean and the Artic brought the cleanest air masses to the sites. For EC the largest difference between the two sites was observed for northwesterly winds during the non-heating season when the suburban site was upwind of Prague.  相似文献   

10.
Formic and acetic acids were measured in a scrub-grass savanna and in a nearby semideciduous forest. Gaseous HCOOH and CH3COOH were collected using the mist-scrubber technique, and were determined using ion chromatography. A strong diurnal cycle was observed at both sites, with higher mixing ratios during daytime. Concentrations in the savanna were always higher than in the forest. Most of the time HCOOH/CH3COOH ratios greater than one were recorded at the savanna site, and ratios less than one at the forest site. Boundary-layer mixing ratios in the savanna region, derived from measurements during midday, are 1.3±0.4 ppbv and 0.7±0.3 ppbv for HCOOH and CH3COOH. Dry depositions velocities between 0.5 and 1 cm s-1 were estimated for the savanna region. Atmospheric residence times of <3 days and >5 days were estimated for the rainy and dry season, respectively.  相似文献   

11.
Since 1978, a measuring station has been operated at Cape Point (34°21 S, 18°29 E). In this article, results of measurements of CO, CFCl3, CCl4, O3, N2O and CH4 are presented as monthly means and analyzed with respect to long-term trends and seasonal variations. For CO and CH4, very similar seasonal variations have been observed, indicating strong interrelations between these two gases. For CO and O3, no significant changes of the mean annual concentrations can be established for the observation periods of 10 and 5 years, respectively. The measurements yield a growth rate of 9.1 pptv yr-1 for CFCl3 (1980–1987) and 0.6 ppbv yr-1 for N2O (1983–1987). The concentration increases of CH4 (10.3 ppbv yr-1 for 1983–1987) and of CCl4 (2.1 pptv yr-1 for 1980–1988) are analyzed for temporal changes during the last years.Presented at the Second Conference on Baseline Observations in Atmospheric Chemistry (SABOAC II) in Melbourne, Australia, November 1988.  相似文献   

12.
The chemical composition of regional background aerosols, and the time variability and sources in the Western Mediterranean are interpreted in this study. To this end 2002–2007 PM speciation data from an European Supersite for Atmospheric Aerosol Research (Montseny, MSY, located 40 km NNE of Barcelona in NE Spain) were evaluated, with these data being considered representative of regional background aerosols in the Western Mediterranean Basin. The mean PM10, PM2.5 and PM1 levels at MSY during 2002–2007 were 16, 14 and 11 µg/m3, respectively. After compiling data on regional background PM speciation from Europe to compare our data, it is evidenced that the Western Mediterranean aerosol is characterised by higher concentrations of crustal material but lower levels of OM + EC and ammonium nitrate than at central European sites. Relatively high PM2.5 concentrations due to the transport of anthropogenic aerosols (mostly carbonaceous and sulphate) from populated coastal areas were recorded, especially during winter anticyclonic episodes and summer midday PM highs (the latter associated with the transport of the breeze and the expansion of the mixing layer). Source apportionment analyses indicated that the major contributors to PM2.5 and PM10 were secondary sulphate, secondary nitrate and crustal material, whereas the higher load of the anthropogenic component in PM2.5 reflects the influence of regional (traffic and industrial) emissions. Levels of mineral, sulphate, sea spray and carbonaceous aerosols were higher in summer, whereas nitrate levels and Cl/Na were higher in winter. A considerably high OC/EC ratio (14 in summer, 10 in winter) was detected, which could be due to a combination of high biogenic emissions of secondary organic aerosol, SOA precursors, ozone levels and insolation, and intensive recirculation of aged air masses. Compared with more locally derived crustal geological dusts, African dust intrusions introduce relatively quartz-poor but clay mineral-rich silicate PM, with more kaolinitic clays from central North Africa in summer, and more smectitic clays from NW Africa in spring.  相似文献   

13.
The atmospheric concentration of peroxyacetylnitrate (PAN) was measured during a cruise of the R.S. Polarstern from Bremerhaven (Germany) to Rio Grande do Sul (Brazil) in September/ October 1988. The measurements were made in-situ by a combination of electron capture gaschromatography with a cryogenic preconcentration step. The theoretical lower limit of detection (3) was 0.4 ppt. The mixing ratios of PAN varied by more than three orders of magnitude from 2000 ppt in the English Channel to less than 0.4 ppt south of the Azores (38° N). South of 35° N, PAN levels were below the detection limit, except at 30–31° S off the eastern coast of South America. Here, PAN mixing ratios of 10 to 100 ppt were detected in continentally influenced air masses. Detectable levels of PAN were mostly observed in air masses of continental or high northern origin. Changes in the wind directions were usually associated with substantial changes in the PAN mixing ratios.  相似文献   

14.
We measured CO2, CO, CH4, H2, and NO2 in air masses polluted by savanna fires over Côte d'Ivoire, western Africa. Elevated concentrations of these trace gases were found in fire plumes and also in extensive haze layers. Trace gas mixing ratios ranged as high as 605 ppmv for CO2, 14.8 ppmv for CO, 2.7 ppmv for CH4, 4.2 ppmv for H2, and 25 ppbv for NO2. We compare our emission ratios to those obtained in previous field and laboratory studies. The emission ratios, expressed as an average and as a range or as an average only, were: dCO/dCO2 5.3×10–2 (3–18×10–2); dCH4/dCO 5.3×10–2; dH2/dCO 2.4×10–1 and dNO2/dCO2 1.8×10–4 (1.5–2.2×10–4). The values found match those found during similar measurements, though our results point to rather vigorous burning in the savanna of western Africa.  相似文献   

15.
A field study of trace gas emissions from biomass burning in Equatorial Africa gave methyl chloride emission ratios of 4.3×10–5±0.8×10–5 mol CH3Cl/mol CO2. Based on the global emission rates for CO2 from biomass burning we estimate a range of 226–904×109 g/y as global emission rate with a best estimate of 515×109 g/y. This is somewhat lower than a previous estimate which has been based on laboratory studies. Nevertheless, our emission rate estimates correspond to 10–40% of the global turnover of methyl chloride and thus support the importance of biomass burning as methyl chloride source. The emission ratios for other halocarbons (CH2Cl2, CHCl3, CCl4, CH3CCl3, C2HCl3, C2Cl4, F-113) are lower. In general there seems to be a substantial decrease with increasing complexity of the compounds and number of halogen atoms. For dichloromethane biomass burning still contributes significantly to the total global budget and in the Southern Hemisphere biomass burning is probably the most important source for atmospheric dichloromethane. For the global budgets of other halocarbons biomass burning is of very limited relevance.  相似文献   

16.
Measurements of NOx (NO +NO2) and the sum of reactive nitrogenconstituents, NOy, were made near the surface atAlert (82.5°N), Canada during March and April1998. In early March when solar insolation was absentor very low, NOx mixing ratios were frequentlynear zero. After polar sunrise when the sun was abovethe horizon for much or all of the day a diurnalvariation in NOx and NOy was observed withamplitudes as large as 30–40 pptv. The source ofactive nitrogen is attributed to release from the snowsurface by a process that is apparently sensitized bysunlight. If the source from the snowpack is a largescale feature of the Arctic then the diurnal trendsalso require a competing process for removal to thesurface. From the diurnal change in the NO/NO2ratio, mid-April mixing ratios for the sum of peroxyand halogen oxide radicals of 10 pptv werederived for periods when ozone mixing ratios were inthe normal range of 30–50 ppbv. Mid-day ozoneproduction and loss rates with the active nitrogensource were estimated to be 1–2 ppbv/day and in nearbalance. NOy mixing ratios which averaged only295±66 pptv do not support a large accumulation inthe high Arctic surface layer in the winter and springof 1998. The small abundance of NOy relative tothe elevated mixing ratios of other long-livedanthropogenic constituents requires that reactivenitrogen be removed to the surface during transport toor during residence within the high Arctic.  相似文献   

17.
As part of the second Arctic Gas and Aerosol Sampling Program (AGASP II) continuous measurements of atmospheric aerosol black carbon (BC) were made at the NOAA/GMCC observatory at Barrow, Alaska (71°19N, 156°36W) during the period March 21–April 22, 1986. Black carbon is produced only by incomplete combustion of carbonaceous materials and so is a particularly useful atmospheric indicator of anthropogenic activities. The BC data have been analyzed together with the concurrent measurements of carbon dioxide (CO2), methane (CH4), and condensation nuclei (CN) that are routinely made at the observatory. All four species showed elevated and highly variable concentrations due to local human activities, principally in the township of Barrow, 7 km to the southwest, and at the DEW Line radar installation 1 km to the northwest. We distinguish between those periods of the record that are affected by local activities and those that are not, on the basis of the short-term (periods of up to 1 hour) variability of the continuous CO2 and CN records, with large short-term variabilities indicating local sources. We identified seven periods of time (events) with durations ranging from 13 to 37 hours when the BC, CO2, and CH4 concentrations changed smoothly over time, were highly correlated with each other, and were not influenced by local activities. These events had BC/CO2 ratios in the range (50–103)×10–6. These ratios are dimensionless since we convert the CO2 concentrations to units of ng m–3 of carbon. Such values of BC/CO2 are characteristic of the combustion effluent from large installations burning heavy fuel oil or coal, automobiles, and domestic-scale natural gas usage. We conclude that these events are indicative of air masses that have been polluted with combustion emissions in a distant location and then transported to the Arctic. In the absence of species-selective loss mechanisms, these air masses will maintain their combustion effluent signatures during the transport. The BC/CO2 ratios found for the local combustion activities are consistent with those expected from known combustion processes.  相似文献   

18.
In situ AGAGE GC-MS measurements of methyl bromide (CH3Br) and methyl chloride (CH3Cl) at Mace Head, Ireland and Cape Grim, Tasmania (1998–2001) reveal a complex pattern of sources. At Mace Head both gases have well-defined seasonal cycles with similar average annual decreases of 3.0% yr−1 (CH3Br) and 2.6% yr−1 (CH3Cl), and mean northern hemisphere baseline mole fractions of 10.37 ± 0.05 ppt and 535.7 ± 2.2 ppt, respectively. We have used a Lagrangian dispersion model and local meteorological data to segregate the Mace Head observations into different source regions, and interpret the results in terms of the known sources and sinks of these two key halocarbons. At Cape Grim CH3Br and CH3Cl also show annual decreases in their baseline mixing ratios of 2.5% yr−1 and 1.5% yr−1, respectively. Mean baseline mole fractions were 7.94 ± 0.03 ppt (CH3Br) and 541.3 ± 1.1 ppt (CH3Cl). Although CH3Cl has astrong seasonal cycle there is no well-defined seasonal cycle in the Cape Grim CH3Br record. The fact that both gases are steadily decreasing in the atmosphere at both locations implies that a change has occurred which is affecting a common, major source of both gases (possibly biomass burning) and/or their major sink process (destruction by hydroxyl radical).  相似文献   

19.
A series of 72 measurements of the acetaldehyde (CH3CHO) mixing ratio were made in the lower troposphere during TROPOZ II. These measurements are the first ever made of the background level of this trace gas in the free troposphere. The data show a vertical decrease of the CH3CHO mixing ratio with increasing altitude and indicate higher CH3CHO concentrations in the Northern Hemisphere — in general agreement with a model-derived average CH3CHO distribution. Deviations of the observed CH3CHO mixing ratios from the modelled mean distribution are correlated with similar deviations in the corresponding HCHO mixing ratios.  相似文献   

20.
A global data set on the geographic distribution and seasonality of freshwater wetlands and rice paddies has been compiled, comprising information at a spatial resolution of 2.5° by latitude and 5° by longitude. Global coverage of these wetlands total 5.7×106 km2 and 1.3×106 km2, respectively. Natural wetlands have been grouped into six categories following common terminology, i.e. bog, fen, swamp, marsh, floodplain, and shallow lake. Net primary productivity (NPP) of natural wetlands is estimated to be in the range of 4–9×1015 g dry matter per year. Rice paddies have an NPP of about 1.4×1015 g y–1. Extrapolation of measured CH4 emissions in individual ecosystems lead to global methane emission estimates of 40–160 Teragram (1 Tg=1012 g) from natural wetlands and 60–140 Tg from rice paddies per year. The mean emission of 170–200 Tg may come in about equal proportions from natural wetlands and paddies. Major source regions are located in the subtropics between 20 and 30° N, the tropics between 0 and 10° S, and the temperate-boreal region between 50 and 70° N. Emissions are highly seasonal, maximizing during summer in both hemispheres. The wide range of possible CH4 emissions shows the large uncertainties associated with the extrapolation of measured flux rates to global scale. More investigations into ecophysiological principals of methane emissions is warranted to arrive at better source estimates.  相似文献   

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