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1.
Electrical charges on aerosol particles and droplets modify the droplet–particle collision efficiencies involved in scavenging, and the droplet–droplet and particle–particle collision efficiencies involved in coalescence of droplets and particles, even in only weakly electrified clouds and aerosol layers. This work places electrically enhanced scavenging, and the electrical inhibition of scavenging in the context of the microphysics of weakly electrified clouds.Collision efficiencies are calculated by numerical integration to obtain particle trajectories, that are determined by the complex interplay of electrical, gravitational and phoretic forces together with inertia. These modify the trajectory of a particle as it is carried by flow around the falling droplet. Conversely, the flow around the particle also modifies the trajectory of the droplet. The flows are specified analytically, using a hybrid of the Proudman–Pearson stream function for that region close to the droplet or particle, where it is accurate, merging into the exact Oseen stream function for larger distances, where that becomes accurate. The effect of the flow around the particle on the motion of the droplet was simulated using Langmuir's superposition technique on the hybrid stream functions. The treatment of inertia in the present calculations allows an extension of the scope of our previous work by a factor of 10 larger in particle size (103 in mass). The coverage is extended to a wide range of atmospheric conditions and particle densities.The pressures and temperatures used in the models ranged from a representation of the lower troposphere at  1 km altitude (900 hPa, 10 °C) to that of the middle stratosphere at  30 km altitude (12 hPa, − 47 °C). The particles considered range from 0.1 μm to 10 μm radius; the droplet radii range from 4 μm to 50 μm; particle densities range from 300 kg m− 3 to 2500 kg m− 3; particle charges range from 2e to 100e with droplet charges of like sign of 100e; and relative humidities range from 10% to 100%.For the larger particles (radii greater than about 3 μm) interacting with the larger droplets (radii greater than about 15 μm) the effects of inertia increase with particle density and dominate at the larger densities. For particles with radii in the range 1–3 μm the ‘Greenfield Gap’ of very low collision efficiencies was found, and was determined to be due to the effects of the gravitational force causing a reduction of collisions of particles with the front of the droplet, and the effect of inertia overcoming the tendency for the weight to produce a collision in the slow velocity region in the rear. When the electrical or phoretic forces are sufficiently large the Greenfield Gap is closed.When the particles have radii < 3 μm inertial effects no longer dominate the collisions, although inertia modifies the weight effects for particles with radii down to about 0.5 μm. For charged aerosol particles with radii smaller than about 0.1 μm interacting with droplets or background aerosol particles smaller than a radius of about 15 μm, the long range electrical repulsive force is effective in opposing the phoretic forces and keeping the particle out of range of the short range attractive image force. Thus ‘electroscavenging’ gives way to ‘electroprotection’ against the scavenging or coagulation processes otherwise caused by Browninan diffusion or phoretic forces.In an atmosphere of temperature 10 °C and pressure 900 hPa the net phoretic force reduces to zero and becomes repulsive for particles with radii above about 2 μm (depending on particle conductivity). This enhances the development of the Greenfield Gap. However, the value of this radius (at which the net phoretic force is zero) increases strongly with decreasing temperature and pressure (increasing altitude) as expected from theory, and is about 5 μm in the middle troposphere and more than 10 μm in the stratosphere. Thus a net attractive phoretic force on particles extends into the 1–3 μm radius range in the upper troposphere; however, the weight and inertial effects can ensure the presence of the Greenfield Gap in that range for 2000 kg m− 3 particles up to the middle stratosphere.  相似文献   

2.
On February 8, 1993, the NASA DC-8 aircraft profiled from 10,000 to 37,000 feet (3.1–11.3 km) pressure altitude in a stratified section of tropical cyclone “Oliver” over the Coral Sea northeast of Australia. Size, shape and phase of cloud and precipitation particles were measured with a 2-D Greyscale probe. Cloud/ precipitation particles changed from liquid to ice as soon as the freezing level was reached near 17,000 feet (5.2 km) pressure altitude. The cloud was completely glaciated at −5°C. There was no correlation between ice particle habit and ambient temperature. In the liquid phase, the precipitation-cloud drop concentration was 4.0 × 103 m−3, the geometric mean diameter Dg=0.5−0.7 mm, and the liquid water content 0.7−1.9 g m−3. The largest particles anywhere in the cloud, dominated by fused dendrites at concentrations similar to that of raindrops (2.5 × 103 m−3) but a higher condensed water content (5.4 g m−3 estimated) were found in the mixed phase; condensed water is removed very effectively from the mixed layer due to high settling velocities of the large mixed particles. The highest number concentration (4.9 × 104 m−3), smallest size (Dg=0.3−0.4 mm), largest surface area (up to 2.6 × 102 cm2 m−3 at 0.4−1.0 g m−3 of condensate) existed in the ice phase at the coldest temperature (−40°C) at 35,000 feet (10.7 km). Each cloud contained aerosol (haze particles) in addition to cloud particles. The aerosol total surface area exceeded that of the cirrus particles at the coldest temperature. Thus, aerosols must play a significant role in the upscattering of solar radiation. Light extinction (6.2 km−1) and backscatter (0.8 sr−1 km−1) was highest in the coldest portion of the cirrus cloud at the highest altitude.  相似文献   

3.
In this study bulk airborne aerosol composition measured by the PILS-IC (integration time of 3 min 24 s) during TRACE-P P3B Flight 10 are used to investigate the ionic chemical composition and mixing state of biomass burning particles. A biomass burning plume, roughly 3–4 days old, moderately influenced by urban pollution aerosols recorded in the Philippine Sea is investigated. Focusing on the fine particle NO3−, SO42−, K+, NH4+, and water-soluble organics, the observed correlations and nearly 1-to-1 molar ratios between K+ and NO3− and between NH4+ and (SO42−+ inferred Organics) suggest the presence of fine-mode KNO3, (NH4)2SO4, and NH4(Organics) aerosols. Under the assumption that these ion pairs existed, and because KNO3 is thermodynamically less favored than K2SO4 in a mixture of NO3−, SO42−, K+, NH4+, and Organic anions, the measurements suggest that aerosols could be composed of biomass burning particles (KNO3) mixed to a large degree externally with the (NH4)2SO4 aerosols. A “closed-mode” thermodynamic aerosol simulation predicts that a degree of external mixing (by SO42− mass) of 60 to 100% is necessary to achieve the observed ionic associations in terms of the existence of KNO3. However, the degree of external mixing is most likely larger than 90%, based on both the presence of KNO3 and the amounts of NH4NO3. Calculations are also shown that the aerosol mixing state significantly impacts particle growth by water condensation/evaporation. In the case of P3B Flight #10, the internal mixture is generally more hygroscopic than the external mixture. This method for estimating particle mixing state from bulk aerosol data is less definitive than single particle analysis, but because the data are quantitative, it may provide a complementary method to single particle chemical analysis.  相似文献   

4.
Terry Deshler   《Atmospheric Research》2008,90(2-4):223-ICNAA07
Stratospheric aerosol, noted after large volcanic eruptions since at least the late 1800s, were first measured in the late 1950s, with the modern continuous record beginning in the 1970s. Stratospheric aerosol, both volcanic and non-volcanic are sulfuric acid droplets with radii (concentrations) on the order of 0.1–0.5 µm (0.5–0.005 cm− 3), increasing by factors of 2–4 (10–103) after large volcanic eruptions. The source of the sulfur for the aerosol is either through direct injection from sulfur-rich volcanic eruptions, or from tropical injection of tropospheric air containing OCS, SO2, and sulfate particles. The life cycle of non-volcanic stratospheric aerosol, consisting of photo-dissociation and oxidation of sulfur source gases, nucleation/condensation in the tropics, transport pole-ward and downward in the global planetary wave driven tropical pump, leads to a quasi steady state relative maximum in particle number concentration at around 20 km in the mid latitudes. Stratospheric aerosol have significant impacts on the Earth's radiation balance for several years following volcanic eruptions. Away from large eruptions, the direct radiation impact is small and well characterized; however, these particles also may play a role in the nucleation of near tropopause cirrus, and thus indirectly affect radiation. Stratospheric aerosol play a larger role in the chemical, particularly ozone, balance of the stratosphere. In the mid latitudes they interact with both nitrous oxides and chlorine reservoirs, thus indirectly affecting ozone. In the polar regions they provide condensation sites for polar stratospheric clouds which then provide the surfaces necessary to convert inactive to active chlorine leading to polar ozone loss. Until the mid 1990s the modern record has been dominated by three large sulfur-rich eruptions: Fuego (1974), El Chichón (1982) and Pinatubo (1991), thus definitive conclusions concerning the trend of non-volcanic stratospheric aerosol could only recently be made. Although anthropogenic emissions of SO2 have changed somewhat over the past 30 years, the measurements during volcanically quiescent periods indicate no long term trend in non-volcanic stratospheric aerosol.  相似文献   

5.
A high-volume cascade impactor, equipped with a PM10 inlet, was used to collect size-segregated aerosol samples during the summer of 2004 at two Portuguese locations: a coastal-rural area (Moitinhos) and an urban area (Oporto). Concentrations of airborne particulate matter (PM), total carbon (TC), organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon (WSOC) were determined for the following particle size ranges: < 0.49, 0.49–0.95, 0.95–3.0, and 3.0–10 µm. The total PM mass concentrations at the urban and coastal-rural sites ranged from 22.8 to 79.6 μg m− 3 and 19.9 to 28.2 μg m− 3, respectively, and more than 56% of the total aerosol mass was found in the fractions below 3.0 μm. At both locations the highest concentrations of OC and EC were found in the submicrometer size range. The regional variability for the OC and EC concentrations, with the highest concentrations being found in the urban area, was related to the contribution of local primary sources (mostly traffic emissions). It was also verified an enrichment of the small size particles in WSOC, representing on average 37.3(± 12.4)% and 59.7(± 18.0)% of OC in the very fine aerosol at the coastal-rural and urban areas, respectively. The amount of secondary OC calculated by the minimum OC/EC ratio method indicates that secondary organic aerosol formation was important throughout the study at both sites. The obtained results suggest that long-range transport and favourable summer conditions for photochemical oxidation are key factors determining secondary OC formation in the coastal-rural and urban areas. The ultraviolet absorption properties of the chromophoric constituents of the WSOC fractions were also different among the different particle size ranges and also between the two sampling locations, thus suggesting the strong impact of the diverse emission sources into the composition of the size-segregated organic aerosol.  相似文献   

6.
Chemical characteristics of haze during summer and winter in Guangzhou   总被引：33，自引：0，他引：33  
Airborne particles were collected with a 10-stage MOUDI and a PM10 sampler in Guangzhou, China, during both haze and normal days in the summer of 2002 and 2003, and winter 2002. The characteristics of PAHs, organic carbon, elemental carbon and water-soluble inorganic ions were studied under four periods (summer normal, summer haze, winter normal and winter haze). In this study, secondary pollutants (OC, SO42−, NO3− and NH4+) were the major chemical components and appeared to show a remarkably rapid increase from normal to haze days. The particle mass size distributions were bimodal and dominated by fine particles in haze days. A significantly higher OC/EC ratio was found in haze days (3.2–4.7) compared to normal days (1.8–2.8), indicating secondary organic aerosol formation might be significant during haze days. Correlation analysis between visibility and chemical species showed that the major scattering species were TC (total carbon) and sulfate in normal days and nitrate and TC in haze days, respectively. Simultaneously, correlation analysis between visibility and meteorological factors demonstrated that visibility increased with both temperature and wind speed, while it decreased with relative humidity. Furthermore, the relatively higher value of IcdP/(BghiP + IcdP) and the low value of Cmax, CPI, and BghiP/BeP in winter haze could be due to the growth of motor vehicle usage and energy consumption in winter.  相似文献   

7.
Black carbon aerosols plays an important role in the earth's radiative balance and little is known of their concentrations, distributions, source strength, and especially the aerosol chemistry of the developing world. The present study addresses the impact of back carbon aerosols on different atmospheric species like CO and tropospheric ozone over an urban environment, namely Hyderabad, India. Ozone concentration varies from 14 to 63 ppbv over the study area. Diurnal variations of ozone suggest that ozone concentration starts increasing gradually after sunrise, attaining a maximum value by evening time and decreasing gradually thereafter. Black carbon (BC) aerosol mass concentrations varies from 1471 to 11,175 ng m−3. The diurnal variations of BC suggest that the concentrations are increased by a factor of 2 during morning (06:00–09:00 h) and evening hours (18:00 to 22:00 h) compared to afternoon hours. Positive correlation has been observed between BC and CO (r2=0.74) with an average slope of 6.4×10−3 g BC/g CO. The slope between black carbon aerosol mass concentration and tropospheric ozone suggests that every 1 μg m−3 increase in black carbon aerosol mass concentration causes a 3.5 μg m−3 reduction in tropospheric ozone. The results have been discussed in detail in the paper.  相似文献   

8.
Coastal nucleation events and behavior of cluster ions were characterized through the measurements of air ion mobility distributions at the Mace Head research station on the west coast of Ireland in 2006. We measured concentrations of cluster ions and charged aerosol particles in the size range of 0.34–40 nm. These measurements allow us to characterize freshly nucleated charged particles with diameters smaller than 3 nm. The analysis shows that bursts of intermediate ions (1.6–7 nm) are a frequent phenomenon in the marine coastal environment. Intermediate ion concentrations were generally close to zero, but during some nucleation episodes the concentrations increased to several hundreds per cm3. Nucleation events occurred during most of the measurement days. We classified all days into one of seven classes according to the occurrence and type of new particle formation. Nucleation events were observed during 207 days in 2006, most prominently in the spring and summer months. Rain-induced events, in turn, were observed during 132 days. Particle formation and growth events mostly coincided with the presence of low tide. Also small cluster ions (0.34–1.6 nm) were characterized. Average concentrations of small ions were 440 cm− 3 for the negative ions and 423 cm− 3 for the positive ions. Average mean mobilities of small ions were 1.86 cm2V− 1s− 1 and 1.49 cm2V− 1s− 1 for the negative and positive polarities, respectively. Concentrations of small ions were observed to be strongly dependent on the variations of meteorological parameters including wind speed and direction.  相似文献   

9.
The non-polar organic composition of airborne particulate matter was analysed over a two year period in an urban area under oceanic climate conditions (Errenteria, Basque Country, Spain). In addition, the distribution of polycyclic aromatic hydrocarbons (PAH) among different aerosol particle sizes was determined. Clues as to the origin of various particle types were gained by using scanning electron microscopy to view the morphology of the particulates in each size fraction. Samples were collected on glass fibre filters and analysed by means of soxhlet extraction and gas chromatography (either with a flame ionization detector or coupled to a mass spectrometry). In general, total PAH levels were moderate (0.96–50 ng m− 3) as compared to other studies conducted in Europe, and showed clear seasonal variation with maxima in winter and minima in summer. Vehicular traffic was identified as a major source of PAHs in the study area. Regarding particle size, a bimodal distribution was observed. The large sized particles exhibited an apparent seasonal variation with higher concentrations in winter than in summer. The dependences between particle size, PAH distribution and meteorological variables were studied with multivariate statistics. Three main sources of organic compounds were identified: combustion, vegetation, and atmospheric oxidation.  相似文献   

10.
Measurements of fog and rain water chemistry at the summit of Mt. Fuji, the highest peak in Japan, as well as at Tarobo, the ESE slope of Mt. Fuji in September 2002. The pH of fog and rain water sampled at Mt. Fuji varied over a range of 4.0–6.8. Acidic fogs (pH < 5.0) were observed at the summit when the air mass came from the industrial regions on the Asian continent. The ratio of [SO42−]/[NO3−] in the fog water was lower at Tarobo than at the summit. High concentrations of Na+ and Cl− were determined in the rain water sampled at the summit, possibly because of the long-range transport of sea-salt particles raised by a typhoon through the middle troposphere. The vertical transport of sea-salt particles would influence the cloud microphysical properties in the middle troposphere. Significant loss of Mg2+ was seen in the rain water at the summit. The concentrations of peroxides in the fog and rain water were relatively large (10–105 μM). The potential capacity for SO2 oxidation seems to be strong from summer to early autumn at Mt. Fuji. The fog water peroxide concentrations displayed diurnal variability. The peroxide concentrations in the nighttime were significantly higher than those in the daytime.  相似文献   

11.
As a component of the Canadian Arctic Haze Study, held coincident with the second Arctic Gas and Aerosol Sampling Program (AGASP II), vertical profiles of aerosol size distribution (0.17 m), light scattering parameters and cloud particle concentrations were obtained with an instrumented aircraft and ground-based lidar system during April 1986 at Alert. Northwest Territories. Average aerosol number concentrations range from about 200 cm–3 over the Arctic ice cap to about 100 cm–3 at 6 km. The aerosol size spectrum is virtually free of giant or coarse aerosol particles, and does not vary significantly with altitude. Most of the aerosol volume is concentrated in the 0.17–0.50 m size range, and the aerosol number concentration is found to be a good surrogate for the SO4 = concentration of the Arctic haze aerosol. Comparison of the aircraft and lidar data show that, when iced crystal scattering is excluded, the aerosol light scattering coefficient and the lidar backscattering coefficient are proportional to the Arctic haze aerosol concentration. Ratios of scattering to backscattering, scattering to aerosol number concentration, and backscattering to aerosol number concentration are 15.3 steradians, 1.1×10–13 m2, and 4.8×10–15 m2 sr–1, respectively. Aerosol scattering coefficients calculated from the measured size distributions using Mie scattering agree well with measured values. The calculations indicate the aerosol absorption optical depth over 6 km to range between 0.011 and 0.018. The presence of small numbers of ice crystals (10–20 crystals 1–1 measured) increased light scattering by over a factor of ten.  相似文献   

12.
Direct physical measurements of particle mass and number concentration indicate an increase in overall aerosol mass resulting from cloud processing, most likely through aqueous-phase chemistry (e.g., SO2 oxidation). Measurements conducted in the Pennines of Northern England reveal an average increase of 14 to 20% in dry aerosol mass (0.003<particle diameter<0.9 μm) after aerosol passage through an orographic cloud. The rate of in-cloud mass production is most sensitive to changes in upwind particle size distributions, SO2 concentration, and cloud water acidity. Newly-formed mass appears in size range between 200 and 600 nm and enhances the bimodality of the particle number distribution after cloud processing. Furthermore, the cloud-produced mass is estimated to increase total light scattering, bsp, by 18 to 24%. The scattering efficiency of the dry, cloud-generated aerosol is 5.0±0.3 m2 g−1 and increases to 7.4±0.7 m2 g−1 when adjusted to 90% relative humidity by incorporating particle hygroscopicity data.  相似文献   

13.
The potential resources on the ion-stimulated syntheses effects of aerosol particles of lower troposphere in test sites in the arctic, mountain, arid and forest areas as the function of irradiation time and gas-precursor concentration were experimentally and theoretically evaluated. The dust-free outdoor air was irradiated with an ionization current of 10− 6 A by α-rays from isotope 239Pu. The total output of radiolytic aerosols (RA) with a diameter of 3–1000 nm was found to be 0.05–0.1 molecules per 1 eV of absorbed radiation, while the physical upper limit is 0.25–0.4 molecules/eV. In an interval of exposition time from 6 to 800 s (adsorbed energy is 3 · 1012–1014 eV/cm3) the RA mass concentration at different sites was increased from 1–10 to 50–500 μg/m3. According to the liquid chromatography data the major RA material is the H2O/HNO3 solution with acid concentration  25%. The used physical model presents new aerosols as a product from small and intermediate ion association through formation of neutral clusters and describes adequately some of the peculiarities in field experiment data. Introducing SO2, NH3, and also hydrochloric, nitric and sulphuric acid vapours with concentration 0.1–1 mg/m3 in the irradiated air stimulated an increase of mass aerosol concentration by a factor of 8–30. The mean size also decreased by a factor of 3–5. These facts allowed us to expect that the chemical composition of radiolytic aerosols generated in outdoor air would noticeably differ after addition of the gas-precursors.  相似文献   

14.
The change of the chemical composition of the near-ground level atmospheric aerosol was studied during two summer episodes by a Lagrangian type of experimental approach. Bulk and single-particle chemical analyses of ions and elements in the particulate phase were deployed. N(-III) and N(V) components were also measured in the gas-phase. The measurements were completed by particle size distributions.Secondary inorganic aerosols (SIA) and fine particles of ≈0.2–0.4 μm size were still elevated 50 km downwind of the city. The direct comparison of transport over the city in contrast to transport over the surrounding areas showed that SIA was formed from emission from the city within less than 3 h. Relative increases, i.e., enrichment during transport were observed for primary and secondary aerosol components. The degree of mixing on the individual particle level increased significantly during transport in the area. In particular, newly emitted carbonaceous particles became internally mixed within hours with pre-existing sulphate particles. Mostly due to secondary aerosol formation the average particle size (mass median diameter) of major constituents of the aerosol was significantly decreased while being transported over 13 h. Given recent insights which link fine particles number and mass concentrations with health risks, the results suggest that rural populations in areas which frequently are located within an urban plume might run an elevated health risk relative to populations in areas not affected by urban plumes.  相似文献   

15.
A field study was conducted at a mountain-top site in northwestern Colorado. Supercooled cloud water, collected as a function of droplet size, was analyzed for anions, cations and trace elements. Enrichment factors (EF) of SO 4 2– , K+, Na+ and Cl– relative to crustal and marine reference elements (Al and Na) were calculated to determine whether chemical fractionation of the aerosol occurs during cloud droplet formation. The largest EF's for all ions were found for droplets less than 10–15 µm diameter. Ratios of the small to large droplet mean EF's ranged from 1 to 2, for SO 4 2– relative to both Al and Na+, to 10 to 12 for Na+, Cl– and K+, relative to Al. EF's of K+ and Cl– in the bulk cloud water were in crustal and marine proportions, respectively. It was concluded that although bulk could chemistry may indicate a lack of enrichment of a species, this may not be true throughout the droplet size distribution. The higher enrichments in small droplets is likely a result of their formation on small aerosol particles whereas the large droplets form on the largest aerosol particles. This may suppress EF's in precipitation relative to the total aerosol.  相似文献   

16.
In the present study, the wet and dry depositions of particulate NO3−, SO42−, Cl− and NH4+ were measured using a wet/dry sampler as a surrogate surface. Gas phase compounds of nitrogen, sulfur and chloride (HNO3, NH3, SO2 and HCl) were measured by an annular denuder system (ADS) equipped with a back up filter for the collection of particles with diameter ≤ 5 μm. Ambient concentrations of NO, NO2 and SO2 were also taken into consideration. Sampling was conducted at an urban site in the center of the city of Thessaloniki, northern Greece. The presence of the aerosol species was examined by cold/warm period and the possible compounds in dry deposits were also considered. Dry deposition fluxes were found to be well correlated with ambient particle concentrations in order to be used for the calculation of particle deposition velocity. Average particulate deposition velocities calculated were 0.36, 0.20, 0.20 and 0.10 cm s− 1 for Cl−, NO3−, SO42− and NH4+, respectively. Total dry deposition fluxes (gas and particles) were estimated at 3.24 kg ha− 1 year− 1 for chloride (HCl + p-Cl), 9.97 kg ha− 1 year− 1 for nitrogen oxidized (NO + NO2 + HNO3 + p-NO3), 5.32 kg ha− 1 year− 1 for nitrogen reduced (NH3 + p-NH4) and 15.77 kg ha− 1 year− 1 for sulfur (SO2 + p-SO4). 70–90% total dry deposition was due to gaseous species deposition. The contribution of dry deposition to the total (wet + dry) was at the level of 60–70% for sulfur and nitrogen (oxidized and reduced), whereas dry chloride deposition contributed 35% to the total. The dry-to-wet deposition ratio of all the studied species was found to be significantly associated with the precipitation amount, with nitrogen species being better and higher correlated. Wet, dry and total depositions measured in Thessaloniki, were compared with other countries of Europe, US and Asia.  相似文献   

17.
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   

18.
An electrically based ion spectrometer is described, capable of measuring particle sizes and mobilities from molecular ions (small ions) to aerosol particles across a size range of 0.4 to 30 nm in diameter. It consists of a single cylindrical capacitor divided into three electrically insulated sections. The current arriving at the central section is measured by an electrometer and represents the ion flux over a known range of mobilities determined by the applied voltage. The applied voltage is scanned in steps to measure the ion fluxes over a large number of overlapping mobility ranges. The recorded signal and the response function of the instrument are unfolded using a maximum entropy procedure to give a high-resolution measured mobility spectrum. The maximum entropy approach offers a considerable improvement over traditional aspiration collectors and can approach the resolution of a drift tube system. In this way, the spectrometer successfully overcomes the diffusion limit to small ion resolution. Illustrative spectra are shown, demonstrating for the first time the presence of some resolved structure within the small ion spectrum at the highest mobilities. It is demonstrated that the actual mobility spectrum of small ions falls in the range 0.8–2.0 × 10−4 m2 V−1 s−1. This represents a narrower range than that previously measured which is attributed to improved spectral resolution in the present work.  相似文献   

19.
Throughfall (TF) and wet only (WO) deposition along with SO2 and sulfate (SO42−) concentration in air at 4 urban and rural sites in southwestern China were monitored in order to understand the role of different forms of sulfur (S) emission to the S deposition and its effect in China. The sites were located in Chongqing, Hunan, and Guizhou provinces. S deposition at the most polluted site reached 15 g S m− 2 yr− 1. At three of the sites, located in the vicinity of several emission sources, dry S deposition is 2.1–4.2 times that of wet deposition, which is significantly higher than what is found in most other parts of the world.Main components in airborne particles (PM10) are (NH4)2SO4 and CaSO4 at the highly polluted Tie Shan Ping (TSP) site. Dust particles of gypsum (CaSO4) in the air are partly due to direct emission and partly from the reaction of calcium oxides and carbonates with sulfuric acid in the air. To illustrate the importance of sulfate emission to total S deposition we analyzed the source of S deposition based on both measurements and models. Results indicated that direct emission of SO42− particles could account for high proportion in total S deposition at the three most polluted sites.  相似文献   

20.
Although it is believed that organic aerosols play a key role in cloud nucleation and make an important contribution to the cloud condensation nuclei (CCN) population, their specific species remain poorly characterized. This paper reviews the current knowledge of organic acids (mainly formic, acetic, pyruvic and oxalic acids). Without specification, organic acids in this paper refer to these four organic acids in the gas and aerosol phases. This paper analyzes the extent to which organic acids act as CCN and compares the physical and chemical properties of organic acids with those of CCN. The results show that aerosol formate and acetate concentrations range from 0.02 to 5.3 nmol m−3 and from 0.03 to 12.4 nmol m−3, respectively, and that between 34 to 77% of formate and between 21 to 66% of acetate are present in the fine fraction of aerosols. It was found that although most (98–99%) of these volatile organic acids are present in the gas phase, their concentrations in the aerosol particles are sufficient to make them a good candidate for CCN. The results also show that organic acids may make an important contribution to the formation of CCN in some special sources such as vegetation emissions and biomass-burning. Organic acids are expected to contribute significantly to the estimates of indirect (cloud-mediated) forcing due to aerosols.  相似文献   

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