Seasonal variation of atmospheric dimethylsulfide at Amsterdam Island in the southern Indian Ocean

Daily measurements of atmospheric concentrations of dimethylsulfide (DMS) were carried out for two years in a marine site at remote area: the Amsterdam Island (37°50S–77°31E) located in the southern Indian Ocean. DMS concentrations were also measured in seawater. A seasonal variation is observed for both DMS in the atmosphere and in the sea-surface. The monthly averages of DMS concentrations in the surface coastal seawater and in the atmosphere ranged, respectively, from 0.3 to 2.0 nmol l^-1 and from 1.4 to 11.3 nmol m^-3 (34 to 274 pptv), with the highest values in summer. The monthly variation of sea-to-air flux of DMS from the southern Indian Ocean ranges from 0.7 to 4.4 mol m^-2 d^-1. A factor of 2.3 is observed between summer and winter with mean DMS fluxes of 3.0 and 1.3 mol m^-2 d^-1, respectively.     

Seasonal Variation of Dimethylsulfoxide in Rainwater at Amsterdam Island in the Southern Indian Ocean: Implications on the Biogenic Sulfur Cycle

A continuous record of dimethylsulfoxide (DMSO) in rainwater was performed at Amsterdam island (37°S 77°E) from December 1995 to February 1997. Eighty one rainwater samples were collected. DMSO, methanesulfonic acid (MSA), the major anions, and cations were analyzed. DMSO concentrations ranged from 7.0 to 369 nM, with a distinct seasonal variation. The mean concentrations during the summer and the winter periods were 90 nM and 25.6 nM respectively. The observed DMSO seasonal cycle is in line with the observations of DMS in the atmosphere and MSA in rainwater, measured simultaneously during the reported period. However, the summer to winter ratio of DMSO is significantly lower than that observed for DMS and MSA. The DMSO to MSA ratio and its observed seasonal variability are also presented. The implications on the biogenic sulfur cycle are discussed.     

Airborne measurements of dimethylsulfide,sulfur dioxide,and aerosol ions over the Southern Ocean South of Australia

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.     

Vertical distribution of dimethylsulfide,sulfur dioxide,aerosol ions,and radon over the Northeast Pacific Ocean

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.     

Simulations of seasonal variations of sulfur compounds in the remote marine atmosphere

A photochemical box model is used to simulate seasonal variations in concentrations of sulfur compounds at latitude 40° S. It is assumed that the hydroxyl radical (OH) addition reaction to sulfur in the dimethyl sulfide (DMS) molecule is the predominant pathway for methanesulfonic acid (MSA) production, and that the rate constant increases as the air temperature decreases. Concentration of the nitrate radical (NO₃) is a function of the DMS flux, because the reaction of DMS with NO₃ is the most important loss mechanism of NO₃. While the diurnally averaged concentration of OH in winter is a factor of about 8 smaller than in summer, due to the weak photolysis process, the diurnally averaged concentration of NO₃ in winter is a factor of about 4–5 larger than in summer, due to the decrease of DMS flux. Therefore, at middle and high latitudes in winter, atmospheric DMS is mainly oxidized by the reaction with NO₃. The calculated ratio of the MSA to SO₂ production rates is smaller in winter than in summer, and the MSA to non-sea-salt sulfate (nssSO₄ ^2-) molar ratio varies seasonally. This result agrees with data on the seasonal variation of the MSA/nssSO₄ ^2- molar ratio obtained at middle and high latitudes. The calculations indicate that during winter the reaction of DMS with NO₃ is likely to be a more important sink of NO_x (NO+NO₂) than the reaction of NO₂ with OH, and to serve as a significant pathway of the HNO₃ production. If dimethyl sulfoxide (DMSO) is produced through the OH addition reaction and is heterogeneously oxidized in aqueous solutions, half of the nssSO₄ ^2- produced in summer may be through the oxidation process of DMSO. It is necessary to further investigate the oxidation products by the reaction of DMS with OH, and the possibility of the reaction of DMS with NO₃ during winter.     

A global three-dimensional model of the tropospheric sulfur cycle

The tropospheric part of the atmospheric sulfur cycle has been simulated in a global three-dimensional model. The model treats the emission, transport, chemistry, and removal processes for three sulfur components; DMS (dimethyl sulfide), SO₂ and SO₄ ^2– (sulfate). These processes are resolved using an Eulerian transport model, the MOGUNTIA model, with a horizontal resolution of 10° longitude by 10° latitude and with 10 layers in the vertical between the surface and 100 hPa. Advection takes place by climatological monthly mean winds. Transport processes occurring on smaller space and time scales are parameterized as eddy diffusion except for transport in deep convective clouds which is treated separately. The simulations are broadly consistent with observations of concentrations in air and precipitation in and over polluted regions in Europe and North America. Oxidation of DMS by OH radicals together with a global emission of 16 Tg DMS-S yr^–1 from the oceans result in DMS concentrations consistent with observations in the marine boundary layer. The average turn-over times were estimated to be 3, 1.2–1.8, and 3.2–6.1 days for DMS, SO₂, and SO₄ ^2– respectively.     

Summertime Seawater Concentrations of Dimethylsulfide in the Western Indian Ocean: Reconciliation of Fluxes and Spatial Variability with Long-Term Atmospheric Observations

Dimethylsulfide (DMS) measurements in the seawater of the subtropical and the temperate western Indian Ocean were conducted for the first time from 3 December to 20 December 1997. In total, 443 surface seawater DMS determinations were performed between 24°–49° S and 50° E–77° E with a frequency of 1 sample every 10 km. An important spatial variability was observed in seawater DMS concentrations with values ranging from 0.9 to 35.8 nM. DMS maxima coincided in most cases with thermal fronts and were in reasonable agreement with mean pigment figures obtained from satellite observations. The deduced DMS fluxes are consistent with long-term observations of atmospheric DMS and rainwater concentrations of nss- SO4= and MSA measured at Amsterdam island (37° S, 77° E); then account for the differences observed in atmospheric DMS concentrations between Amsterdam island and Cape Grim, Indian Ocean monitoring stations.     

Annual variation of atmospheric carbonyl sulfide in the marine atmosphere in the Southern Indian Ocean

Measurements of the concentrations of carbonyl sulfide (COS) in the marine atmosphere were made over a period of two years in the southern Indian Ocean (Amsterdam Island, 37°50 S–77°31 E; March 1987–February 1988 and April 1989–February 1990). The mean atmospheric COS concentration for the whole period was 475±48 pptv (n=544). Atmospheric COS concentrations show no significant seasonal variation with a summer to winter ratio of 1.05. Taking into account the observed variability of the atmospheric COS concentration (10%), a value of 1.4 yr is estimated as a lower limit for the atmospheric COS lifetime. A comparison of the COS data at Amsterdam Island with those obtained in the Southern Hemisphere in the past 12 yr does not reveal any significant trend in the tropospheric background COS mixing ratio.     

A Study of DMS Oxidation in the Tropics: Comparison of Christmas Island Field Observations of DMS, SO2, and DMSO with Model Simulations

This study reports comparisonsbetween model simulations, based on current sulfurmechanisms, with the DMS, SO₂ and DMSOobservational data reported by Bandy et al.(1996) in their 1994 Christmas Island field study. For both DMS and SO₂, the model results werefound to be in excellent agreement with theobservations when the observations were filtered so asto establish a common meteorological environment. Thisfiltered DMS and SO₂ data encompassedapproximately half of the total sampled days. Basedon these composite profiles, it was shown thatoxidation of DMS via OH was the dominant pathway withno more than 5 to 15% proceeding through Cl atoms andless than 3% through NO₃. This analysis wasbased on an estimated DMS sea-to-air flux of 3.4 ×10⁹ molecs cm^-2 s^-1. The dominant sourceof BL SO₂ was oxidation of DMS, the overallconversion efficiency being evaluated at 0.65 ± 0.15. The major loss of SO₂ was deposition to theocean's surface and scavenging by aerosol. Theresulting combined first order k value was estimated at 1.6 × 10^-5 s^-1. In contrast to the DMSand SO₂ simulations, the model under-predictedthe observed DMSO levels by nearly a factor of 50. Although DMSO instrument measurement problems can notbe totally ruled out, the possibility of DMSO sourcesother than gas phase oxidation of DMS must beseriously considered and should be explored in futurestudies.     

Field study of dimethylsulfide oxibation in the boundary layer: Variations of dimethylsulfide,methanesulfonic acid,sulfur dioxide,non-sea-salt sulfate and aitken nuclei at a coastal site

Measurements of atmospheric dimethylsulfide (DMS) and its oxidation products, sulfur dioxide (SO₂), methanesulfonic acid (MSA) and non-sea-salt sulfate (nss-SO₄ ^2-) were monitored during the period June 9–26, 1989 at a coastal site in Brittany. As indicated by the radon (Rn-222) activities and the high concentrations of NOx the air masses, for most of the experiment, were continental in origin. The observed concentrations range from 1.9 to 65 nmol/m³ for DMS (n=157), 0.6 to 94.2 nmol/m³ for SO₂ (n=50), 0.6 to 11.6 nmol/m³ for MSA (n=44) and 42 to 350 nmol/m³ for nss-SO₄ ^2- (n=44). Aitken nuclei reached values as high as 4.5 × 10⁵ particles/m³. When continental conditions predominated, the measured SO₂ concentrations were lower than those expected from a consideration of the observed DMS concentrations and the existence of SO₂ background of the continental air masses. Similarly, compared to the MSA/DMS ratio in the marine atmosphere, higher concentrations of MSA were observed than those expected from the measured levels of DMS. The presence of enhanced levels of MSA was also endorsed by the observation that the measured mean MSA/nss-SO₄ ^2- ratio of 6±3% was similar to the mean value of 6.9% observed in the marine atmosphere. These above observations are in line with recent laboratory findings by Barnes et al. (1988), which show an increase of the MSA/DMS yield with a simultaneous decrease of the SO₂/DMS yield in the presence of NOx.     

Features of the atmospheric cycle of aerosol trace elements and sulphur dioxide revealed by baseline observations in Canada

Selected applications of baseline aerosol, SO₂ and deposition chemistry observations in Canada are reviewed to illustrate how new insight can be gained into features of the atmospheric pathway of trace substances such as sources, transformation and removal. A strong annual variation in Arctic aerosol concentration is a manifestation of particle residence times that are much longer in winter than in summer. Differences in the variation of SO₄ ⁼ and V concentrations in the Arctic winter are due to SO₂ oxidation. The mean rate of oxidation between November and April ranges from 0.04 to 0.25%/h and is a minimum in December, January and February. Br measured on filters in the Arctic peaks in concentration later (March and April) than anthropogenic particulate matter suggesting photochemical production. Acidity in Arctic aerosol and in glacial ice are correlated. The relationship yields a best estimate of acidity in the absence of anthropogenic influences of 5.8 mole/l. Coincident air and precipitation measurements of sulphur oxides indicate that on average in eastern Canada 60% of SO₄ ⁼ in rain originates from SO₂ oxidation in the storm. Trends in Arctic ice core acidity and SO₂ emissions in Europe are similar, that is, little variation in the first half of the century and a marked increase since the mid 1950's. This is consistent with meteorological and chemical evidence linking Arctic air pollution with Eurasian sources.     

Covariations in oceanic dimethyl sulfide,its oxidation products and rain acidity at Amsterdam Island in the Southern Indian Ocean

Simultaneous measurements of rain acidity and dimethyl sulfide (DMS) at the ocean surface and in the atmosphere were performed at Amsterdam Island over a 4 year period. During the last 2 years, measurements of sulfur dioxide (SO₂) in the atmosphere and of methane sulfonic acid (MSA) and non-sea-salt-sulfate (nss-SO₄ ^2-) in rainwater were also performed. Covariations are observed between the oceanic and atmospheric DMS concentrations, atmospheric SO₂ concentrations, wet deposition of MSA, nss-SO₄ ^2-, and rain acidity. A comparable summer to winter ratio of DMS and SO₂ in the atmosphere and MSA in precipitation were also observed. From the chemical composition of precipitation we estimate that DMS oxidation products contribute approximately 40% of the rain acidity. If we consider the acidity in excess, then DMS oxidation products contribute about 55%.     

Seasonal variation of atmospheric 210Pb and Al in the western North Pacific region

The atmospheric concentration of ²¹⁰Pb was determined for two years at six stations in the western North Pacific region. The following results were obtained and discussed by comparing them with those of Al. The atmospheric concentration of ²¹⁰Pb varied widely from week to week, but the degree of variation was about a half that of Al. Contrary to Al, the year-to-year variation of ²¹⁰Pb was not pronounced and its seasonal variation was well expressed by a sine curve. The ²¹⁰Pb concentration did not show a marked latitudinal variation and its base-line concentration was high in the surface air over the North Pacific. These suggest that atmospheric ²¹⁰Pb has a longer residence time, due to its transportation through higher altitudes and deposits much more evenly onto the Earth's surface and the ocean, as compared with Al in mineral dust which is larger in size in the source region.     

Variations in atmospheric CO2 at the Meteorological Research Institute, Tsukuba, Japan

Since April 1986, measurements of the CO₂ concentration in the surface air have been conducted at the Meteorological Research Institure (MRI, 36°04 N, 140°07 E, 25 m above sea level) in Tsukuba, located 50 km northeast of Tokyo, Japan. The CO₂ data measured over times between 11:00 Japan Standard Time (JST) and 16:00 JST (C _N ) were considered to be representative of the air (within a few ppmv) in the planetary boundary layer. To evaluate the representative CO₂ level on a spatial scale larger than that of the C _N record, the CO₂ data with hour-to-hour variation less than 1 ppmv were selected (C _P ). Comparison of these data with those of Ryori (39°02 N, 141°50 E), a continental station operated by the Japan Meteorological Agency, indicates that the C _P record provides a representative CO₂ level in the air on spatial scales of at least a few hundred kilometers.The C _N record allows an investigation of the internanual changes in photosynthesis/respiration against changes in climatological parameters. Within a small temperature anomaly (ca.±1 °C) respiration is sensitive to the temperature change, while photosynthesis is less sensitive. When the temperature anomaly is large, however, photosynthesis and respiration tend to be competitive.     

The solubility of SO2 and the dissociation of H2SO3 in NaCl solutions

The pK ₁ ^* and pK ₂ ^* of H₂SO₃ have been determined in NaCl solutions as a function of ionic strength (0.1 to 6 m) and temperature (5 and 25 °C). The extrapolated values in water were found to be in good agreement with literature data. The experimental results have been used to determine the Pitzer interaction parameters for SO₂, HSO ₃ ^- and SO ₃ ^- in NaCl solutions. The resultant parameters for NaHSO₃ and Na₂SO₃ were found to be in reasonable agreement with the values for NaHSO₄ and Na₂SO₄. It, thus, seems reasonable to assume that the interactions of Mg²⁺ and Ca²⁺ with HSO ₃ ^- and SO ₃ ^- can be estimated from the values with HSO ₄ ^- and SO ₄ ^- until experimental values are available. Measurements of pK ₁ ^* and pK ₂ ^* in artificial seawater were found to be in good agreement with the calculated values using the derived Pitzer parameters. It is, thus, possible to make reasonable estimates of the activity coefficients of HSO ₃ ^- and SO ₃ ^- ions and pK ₁ ^* and pK ₂ ^* for the ionization of H₂SO₃ in marine aerosols.     

On the Spatial Distribution and Seasonal Variation of Lower-Troposphere Ozone over Europe

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 O_x(= 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.     

临安冬夏季SO2、NO2和O3体积分数特征及与气象条件的关系

对临安大气本底站2003-2004年冬、夏季二氧化氮(NO2)、二氧化硫(SO2)、臭氧(O3)进行了分析.结果表明:冬季NO2和SO2平均体积分数分别为19.48×10-9和35.74 x10-9,而夏季的平均体积分数分别为4.81×10-9和8.12×10-9,冬季高于夏季;O3在夏季的平均体积分数为33.55×10-9,略高于冬季的25.44×10-9;夜间NO2和SO2体积分数比白天高,并且NO2呈明显的单峰单谷型分布,O3也呈单峰型但峰值出现在白天.NO2、SO2体积分数存在着明显的“假日效应”,假日比非假日低,周五高于假日和非假日;但O3体积分数没有明显的假日效应.降水对SO2有明显的清除作用,但对NO2的清除作用不明显.与风向对比发现,夏季高体积分数的NO2、SO2都受到NW、WNW风的影响,冬季则分别受NE和SW、SSW风的影响;而O3受风向的影响较复杂,与局地光化学反应有关.     

东印度洋水体输运的季节变化及相关盐度变化

利用20年（1992-2012年）的ECCO2模式模拟数据,主要研究了东印度洋（EIO）水体输运的季节变化.在EIO选取3个断面,分别为赤道、80°E和6°N.研究结果表明,跨赤道和80°E的季节输运主体部分大致相补偿.跨赤道的大部分水体输运局限在上层100 m,80°E的水体输运具有复杂结构,与显著的季风流、Wyrtki Jets（WJs）、赤道潜流（EUC）等有关.6°N上层水体净输运较小,但存在较强的边界流和相对较弱的内区流.纬向流的显著变化发生在80°E.在季风盛行季节,由于WJs减弱,赤道附近的水体输运以西向的梯度流为主,上层100 m的其余区域则主要受季风流控制.同样,由于EUC减弱,西向的梯度流与次表层东向的EUC之间也存在转换.在季风转换季节,季风流减弱,WJs与EUC分别在上层100 m和次表层占主导地位.此外,本研究还讨论了与季风流、WJs和EUC相关的盐水和暖水交换,有助于了解研究区域内温度和盐度的水平和垂直结构.