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1.
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   

2.
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   

3.
A detailed set of reactions treating the gas and aqueous phase chemistry of the most important iodine species in the marine boundary layer (MBL) has been added to a box model which describes Br and Cl chemistry in the MBL. While Br and Cl originate from seasalt, the I compounds are largely derived photochemically from several biogenic alkyl iodides, in particular CH2I2, CH2ClI, C2H5I, C3H7I, or CH3I which are released from the sea. Their photodissociation produces some inorganic iodine gases which can rapidly react in the gas and aqueous phase with other halogen compounds. Scavenging of the iodine species HI, HOI, INO2, and IONO2 by aerosol particles is not a permanent sink as assumed in previous modeling studies. Aqueous-phase chemical reactions can produce the compounds IBr, ICl, and I2, which will be released back into the gas phase due to their low solubility. Our study, although highly theoretical, suggests that almost all particulate iodine is in the chemical form of IO-3. Other aqueous-phase species are only temporary reservoirs and can be re-activated to yield gas phase iodine. Assuming release rates of the organic iodine compounds which yield atmospheric concentrations similar to some measurements, we calculate significant concentrations of reactive halogen gases. The addition of iodine chemistry to our reaction scheme has the effect of accelerating photochemical Br and Cl release from the seasalt. This causes an enhancement in ozone destruction rates in the MBL over that arising from the well established reactions O(1D) + H2O 2OH, HO2 + O3 OH + 2O2, and OH + O3 HO2 + O2. The given reaction scheme accounts for the formation of particulate iodine which is preferably accumulated in the smaller sulfate aerosol particles.  相似文献   

4.
Concentrations of aerosol methanesulfonic acid (MSA) and non-sea-salt (nss) sulfate were measured at six island stations in the Pacific Ocean to investigate regional and seasonal patterns of organosulfur emissions and the origin of nss sulfate over the Pacific. The mean MSA concentrations, in g/m3, at the stations were: Shemya, 0.097±0.098; Midway, 0.029±0.021; Fanning, 0.044±0.012; American Samoa, 0.026±0.012; New Caledonia, 0.021±0.009; Norfolk, 0.024±0.019. The extremely high MSA levels found at Shemya indicate a major source of organosulfur emissions in the western North Pacific. Significant seasonal trends in MSA were observed, with higher MSA occurring during warm months. The amplitude of the seasonal variation was greatest at higher latitude stations. At Fanning and American Samoa, which have minimal input of continental material, there is a significant positive correlation between MSA and nss sulfate. MSA/nss sulfate ratios at other Pacific stations exhibit greater variability, which may be related to variations in: the input of continentally derived sulfate, the composition of oceanic organosulfur emissions, and atmospheric reaction pathways.  相似文献   

5.
Vertical distributions of dimethylsulfide (DMS), sulfur dioxide (SO2), aerosol methane-sulfonate (MSA), non-sea-salt sulfate (nss-SO4 2-), and other aerosol ions were measured in maritime air west of Tasmania (Australia) during December 1986. A few cloudwater and rainwater samples were also collected and analyzed for major anions and cations. DMS concentrations in the mixed layer (ML) were typically between 15–60 ppt (parts per trillion, 10–12; 24 ppt=1 nmol m–3 (20°C, 1013 hPa)) and decreased in the free troposphere (FT) to about <1–2.4 ppt at 3 km. One profile study showed elevated DMS concentrations at cloud level consistent with turbulent transport (cloud pumping) of air below convective cloud cells. In another case, a diel variation of DMS was observed in the ML. Our data suggest that meteorological rather than photochemical processes were responsible for this behavior. Based on model calculations we estimate a DMS lifetime in the ML of 0.9 days and a DMS sea-to-air flux of 2–3 mol m–2 d–1. These estimates pertain to early austral summer conditions and southern mid-ocean latitudes. Typical MSA concentrations were 11 ppt in the ML and 4.7–6.8 ppt in the FT. Sulfur-dioxide values were almost constant in the ML and the lower FT within a range of 4–22 ppt between individual flight days. A strong increase of the SO2 concentration in the middle FT (5.3 km) was observed. We estimate the residence time of SO2 in the ML to be about 1 day. Aqueous-phase oxidation in clouds is probably the major removal process for SO2. The corresponding removal rate is estimated to be a factor of 3 larger than the rate of homogeneous oxidation of SO2 by OH. Model calculations suggest that roughly two-thirds of DMS in the ML are converted to SO2 and one-third to MSA. On the other hand, MSA/nss-SO4 2- mole ratios were significantly higher compared to values previously reported for other ocean areas suggesting a relatively higher production of MSA from DMS oxidation over the Southern Ocean. Nss-SO4 2- profiles were mostly parallel to those of MSA, except when air was advected partially from continental areas (Africa, Australia). In contrast to SO2, nss-SO4 2- values decreased significantly in the middle FT. NH4 +/nss-SO4 2- mole ratios indicate that most non-sea-salt sulfate particles in the ML were neutralized by ammonium.  相似文献   

6.
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   

7.
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   

8.
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   

9.
Use of an airborne quartz crystal microbalance cascade impactor instrument together with a correlation spectrometer has allowed the flux of particles and their size distribution to be determined at Mount Erebus. The plume contributes 21±3 metric tomnes/day of aerosol particles to the Antarctic upper troposphere. The aerosol particles consist of larger (5–25 m) particles of elemental sulfur and silica, a middle sized group of iron oxides and smaller particles (less than 1 m) of complex liquids. Unlike many volcanic plumes, the Erebus plume has only a small amount of sulfate particles. The concentrations of particles in the Erebus plumes was 70–370 m/m3. Limited sampling of the Antarctic atmosphere at 8 km altitude but hundreds of km away from Erebus obtained a few large particles of sulfur and silicates, suggesting a similarity with the Erebus plume. The fallout of these particles occurs slowly over a broad area of the Antarctic continent.  相似文献   

10.
Individual aerosol particles collected in the Negev desert in Israel during a summer and winter campaign in 1996–1997 were analysed by scanning electron microscopy with energy-dispersive X-ray analysis. Hierarchical cluster analysis was performed to interpret the data on the basis of particle diameter and composition. Eleven particle classes (groups) provided clues on sources and/or particle formation. The summer samples were enriched in sulphates and mineral dusts; the winter samples contained more sea salts, aged sea salts, and industrial particles. The fine size fraction below 1 m diameter was enriched in secondary particles and showed evidence of atmospheric processing. The secondary sulphate particles were mainly attributed to long-range transport. A regional conversion from calcite to calcium sulphate occurred during summer. Industrial particles originating from local pollution appeared during winter.  相似文献   

11.
An investigation of the influence of mineral dust ontrace gas cycles in the troposphere is carried out inthis study. A 3D regional scale atmospheric chemistrymodel (STEM-III) which includes aerosol processes isused for the numerical simulations for May 1987.Heterogeneous interactions between gaseous species(SO2, N2O5, HNO3, HO2andH2O2) and the dust particles are considered.Emissions of dust behind convective cold fronts aremodeled. The transport and distribution of mineraldust predicted from the model is compared withsatellite measurements (aerosol index from TOMS). Themodel is shown to capture the synoptic variability inthe observed aerosol index. Calculations show twomajor dust events in May 1987, during which thedust levels close to the source reach more than500 g/m3. The transport of dust is mostlyrestricted towards the north, with the net continentaloutflow of 6 Tg for the entire month. Results showthat the presence of mineral aerosol can greatlyimpact sulfate and nitrate distributions. Averagedover the month of May, the presence of dust isestimated to increase particulate sulfate and nitratelevels in east Asia by 40%. Furthermore, the sulfateand nitrate on the dust particles are predicted to beassociated with the coarse mode (3–5 m particlediameter), consistent with observations over Japan.The influence of mineral dust on the photochemicaloxidant cycle is also investigated. For the entiremonth, a5–10% decrease in boundary layer ozone ispredicted by the model closer to regions of higherdust levels. The ratio of nitric acid to NOx overmarine regions is reduced by a factor between 1 and 2in the boundary layer to more than 2 in the freetroposphere as a result of aerosol processes.  相似文献   

12.
A method for determining the distribution of supermicrometer nitrate between size-segregated sea-salt and soil derived particles is presented. The analysis is based on field data from six measurements at a coastal site in southern Finland, and on a theoretical treatment taking into account the transfer of gaseous species onto particle surfaces and their subsequent reaction. Significant amounts of nitrate were found in both the particle types, with the fraction of nitrate associated with soil particles varying from 20–50% in the 1–2 m size to near 90% in particles larger than 10 m. Overall, the nitrate accumulation followed closely the relative abundances of these two particle types. Two overlapping modes in supermicron nitrate mass size distributions could be identified. The lower mode, associated with sea-salt, was located between the surface-area and volume distribution of sodium peaking at about 2–3 m of EAD. The upper mode peaked at 3–5 m and followed more closely the surface-area distribution of calcium in all samples. At our site, the accumulation of nitrate into both particle types was shown to be limited by an effective surface reaction rate rather than by gas-phase diffusion. This rate was estimated to be considerably larger for sea-salt particles. Strong evidence in support of the saturation of nitrate in sea-salt particles were obtained.  相似文献   

13.
Systematic year-round observations of submicron aerosols were carried out at Syowa Station (69°00'S, 39°35'E) in 1978. On the basis of the results of these observations, it is concluded that two types of aerosols originating from different sources are present in the Antarctic croposphere. With the intrusion of maritime air, mostly in the polar night months, sea salt particles and ammonium sulfate particles contained originally in the clean maritime air are dominant. The size distribution of such aerosols is monomodal, having a single mode at around 0.03 m in radii. On the other hand, in the sunlit months, sulfuric acid droplets are predominant and the size distribution is bimodal, having an additional mode at around 0.005 m in radii. Those sulfuric acid particles seem to be formed photochemically within a specific layer in the mid to lower troposphere over Antarctica. Most Antarctic submicron particles are of tropospheric origin, not of stratospheric nor anthropogenic origin.  相似文献   

14.
Five years of turbidity data at Cape Grim have been analysed. The turbidity at 500 nm in clean maritime airmasses from the South to the West shows a seasonal variation, with a minimum in winter. There is also a variation in turbidity with wind speed. The winter minimum can be explained partially by a minimum in wind strength in that season. On the assumption, based on observations at Cape Grim and at other locations, that the boundary layer turbidity is caused by seasalt haze, an attempt is made to interpret the observed turbidity values and their seasonal changes. Optical extinction coefficients at the surface deduced from the measured values of optical depth are compared with extinction coefficients calculated from Mie theory using particle size distributions measured at Cape Grim. Reasonable agreement is obtained when the growth of salt particles in the high maritime humidity is considered, using both theoretical models and previous experimental results together with the rapid increase in salt concentration with wind speed.  相似文献   

15.
Dimethylsulfide (DMS), sulfur dioxide (SO2), methanesulfonate (MSA), nonsea-salt sulfate (nss-SO4 2–), sodium (Na+), ammonium (NH4 +), and nitrate (NO3 –) were determined in samples collected by aircraft over the open ocean in postfrontal maritime air masses off the northwest coast of the United States (3–12 May 1985). Measurements of radon daughter concentrations and isentropic trajectory calculations suggested that these air masses had been over the Pacific for 4–8 days since leaving the Asian continent. The DMS and MSA profiles showed very similar structures, with typical concentrations of 0.3–1.2 and 0.25–0.31 nmol m–3 (STP) respectively in the mixed layer, decreasing to 0.01–0.12 and 0.03–0.13 nmol m–3 (STP) at 3.6 km. These low atmospheric DMS concentrations are consistent with low levels of DMS measured in the surface waters of the northeastern Pacific during the study period.The atmospheric SO2 concentrations always increased with altitude from <0.16–0.25 to 0.44–1.31 nmol m–3 (STP). The nonsea-salt sulfate (ns-SO4 2–) concentrations decreased with altitude in the boundary layer and increased again in the free troposphere. These data suggest that, at least under the conditions prevailing during our flights, the production of SO2 and nss-SO4 2– from DMS oxidation was significant only within the boundary layer and that transport from Asia dominated the sulfur cycle in the free troposphere. The existence of a sea-salt inversion layer was reflected in the profiles of those aerosol components, e.g., Na+ and NO3 –, which were predominantly present as coarse particles. Our results show that long-range transport at mid-tropospheric levels plays an important role in determining the chemical composition of the atmosphere even in apparently remote northern hemispheric regions.  相似文献   

16.
To stimulate a discussion on the role of tropical atmospheric circulation versus thermohaline circulation changes for tropical Atlantic sea-surface temperature (SST) variations, we present a record of the SST contrast (SST) between the tropical northwest and southeast Atlantic from the Last Glacial Maximum to the Late Holocene. The SST was calculated from two alkenone-derived SST records; one from the Caribbean Sea and the other from the Angola Basin. Changes in the cross-equatorial SST were then compared with an abundance record of Florisphaera profunda from the equatorial Atlantic, which is indicative of SE trade-wind induced variations in thermocline depth in the equatorial divergence zone. This comparison implies that the Last Glacial Maximum, the Younger Dryas, and the Mid to Late Holocene were periods of strong SE trade winds, which led to an intense upwelling-related cooling in the southeast Atlantic and concurrently enhanced advection of warm tropical South Atlantic waters into the western tropical Atlantic. Accordingly, a coupled ocean-atmospheric process has probably created a dipole-like SST distribution pattern in the tropical Atlantic during these three distinct climatic periods. In contrast, Heinrich Event 1, the Bølling-Allerød, and the Early Holocene were intervals of weakened SE trade winds, causing a warming in the southeast Atlantic. However, synchronous warming in both regions during Heinrich Event 1 can be partially attributed to a weakening of thermohaline overturning which caused a reduced northward heat transport from the low-latitude to the high-latitude North Atlantic.  相似文献   

17.
Aerosol samples were collected in the Atlantic marine boundary layer between the English Channel and Antarctica during November–December 1999. The composition of coarse (aerodynamic diameter 1–3 μm) individual aerosol particles was studied using the SEM/EDX method. The major particle types observed were fresh sea salt, sea-salt particles reacted partly or totally with sulphuric acid or nitric acid, Mg-sulphate, Ca-sulphate, mixed aluminosilicates and sea salt, aluminosilicates, Ca-rich particles and Fe-rich particles. The relative fractions of sea-salt particles with moderate or strong Cl depletion were high near the coasts of Europe (65–74%) and Northern Africa (44–87%), low far from the coast of Western Africa (10–20%) and very low in remote sea areas between Africa and Antarctica (1%). The Cl depletion was strongest when air masses arrived from the direction of anthropogenic pollution sources. The fractions of Mg-sulphate particles were high (18–25%) in 2 samples near Europe. The Mg-sulphate particles were probably formed as a result of fractional recrystallization of sea-salt particles in which Cl was substituted by sulphate. It remained unclear whether these particles were formed in the atmosphere or during and after sampling. The relative fractions of particles from continental sources were quite low (10–15%) near Europe, very high (25–78%) near the coast of Northwestern Africa and very low in the remote sea areas (0–2%). Most of the continental particles were aluminosilicates and some of them were internally mixed with sea salt. Near the coast of Northwestern Africa, the main source of aluminosilicates was Saharan dust, and near the Gulf of Guinea, emissions from biomass burning were also mixed with aluminosilicates and sea salt.  相似文献   

18.
Summary This work evaluates the impact of deforestation on the climate of the eastern portion of the Amazon basin. This region is primarily an area of native tropical rainforest, but also contains several other natural ecosystems such as mangroves and savanna. It is the most densely populated area in Amazonia, and has been significantly affected by deforestation. In this study, numerical simulations were performed with a high spatial resolution, regional model that allows for consideration of mesoscale aspects such as topography, coastlines and large rivers.To evaluate the present situation and to predict potential future effects of deforestation on the climatic conditions of this region, two, one-year model simulations were made. In the first, control simulation, an attempt was made to match the existing surface vegetation. The biophysical parameters used were derived from recent studies of similar Amazon-region ecosystems. In the second run, deforested simulation, the forested-area biophysical parameters were replaced by those corresponding to the pasture areas of the region.The higher-resolution regional modelling revealed important climatic features of the deforestation process, displaying some associated mesoscale effects that are not typically represented in similar Global Circulation Model simulations. Near coastal zones and along large rivers, deforestation resulted in reduced cloud cover and precipitation. However, increased cloud cover and precipitation was predicted over upland areas, especially on slopes facing river valleys. The modelled surface sensible and latent heat fluxes also presented both positive and negative anomalies. The magnitudes of these anomalies were greater during the dry season. Windspeed near the surface was the meteorological variable that presented the most significant change due to deforestation. The reduction in roughness coefficient resulting from the shift from forest to pasture produced increased windspeeds near the Atlantic coast. The greater windspeeds diminished local humidity convergence and consequently reduced rainfall totals in nearby regions.The results obtained from these higher-resolution simulations show that, in general, orography, coastline profile and the distribution of large rivers play important roles in determining anomaly patterns of precipitation, wind, and energy exchange associated with deforestation in eastern Amazonia.  相似文献   

19.
Ambient particulate sulfate measurements have been intermittently performed at a rural site in Israel over a period of more than two years. Concurrent measurements of ambient pollutants (SO2, NO–NOx, and O3), as well as meteorological data, were also carried out. The daily data included four particulate sulfate samples representing four successive 6 h accumulating periods. The measured concentrations of sulfate ions ranged from a low 2 g m-3 observed during the winter season to a high of >50 g m-3 obtained during the summer. Little correlation was obtained between the sulfate concentration and either O3 or SO2, although sulfate and O3 showed a similar diurnal and annual trend. Based on the data distribution and on a photochemical model, it was concluded that a large part of the particulate sulfate observed at the eastern coast of the Mediterranean Sea must be related to long-range transport from distant sources.  相似文献   

20.
A model with spectral microphysics was developed to describe the scavenging of nitrate aerosol particles and HNO3 gas. This model was incorporated into the dynamic framework of an entraining air parcel model with which we computed the uptake of nitrate by cloud drops whose size distribution changes with time because of condensation, collision-coalescence and break-up. Significant differences were found between the scavenging behavior of nitrate and our former results on the scavenging behavior of sulfate. These reflect the following chemical and microphysical differences between the two systems:
  1. nitrate particles occur in a larger size range than sulfate particles.
  2. HNO3 has a much greater solubility than SO2 and is taken up irreversibly inside the drops in contrast to SO2.
  3. nitric acid in the cloud water is formed directly on uptake of HNO3 gas whereas on uptake of SO2 sulfuric acid is formed only after the reaction with oxidizing agents such as e.g., H2O2 or O3.
  4. nitrate resulting from uptake of HNO3 is confined mainly to small drops, whereas sulfate resulting from uptake of SO2 is most concentrated in the largest, oldest drops, which have had the greatest time for reaction.
Sensitivity studies showed that the nitrate concentration of small drops is significantly affected by the mass accommodation coefficient.  相似文献   

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