An Examination of the Atmospheric Chemistry of Mercury Using 210Pb and 7Be

Measurements of Hg (total gas-phase, precipitation-phase andparticulate-phase), aerosol mass, particulate ²¹⁰Pb and⁷Be and precipitation ²¹⁰Pb were made at an atmosphericcollection station located in a near remote area of northcentral Wisconsin,U.S.A. (46°10N, 89°50W) during the summers of 1993, 1994and 1995. Total Hg and ²¹⁰Pb were observed to correlate strongly(slope = 0.06 ± 0.03 ng mBq^-1; r ² =0.72) in rainwater. Mercury to ²¹⁰Pb ratios in particulate matter(0.03 ± 0.02 ng mBq^-1; r ² = 0.06) wereconsistent with the ratio in rain. Enrichment of the Hg/mass ratio (approx.5–50×) relative to soil and primary pollutant aerosols indicatedthat gas-to-particle conversion had taken place during transport. Comparisonof these results with models for the incorporation of Hg into precipitationindicates that atmospheric particles deliver more Hg to precipitation than canbe explained by the presence of soot. A lack of correlation between totalgas-phase Hg (TGM) and a ⁷Be/²¹⁰Pb function suggests novertical concentration gradient within the troposphere, and allows an estimateof TGM residence time of 1.5 ± 0.6 yr be made based on surface airsamples.     

Measurement and meteorological analysis of 7Be and 210Pb in aerosol at Waliguan Observatory

Beryllium-7(~7Be)and lead-210(~(210)pb)activities were measured from October 2002 to January 2004 at Waliguan Observatory(WO:36.287°N,100.898°E,3816 m a.s.l(above sea level)in northwest China.~7Be and ~(210)Pb activities are high with overall averages of 14.7±3.5 mBq m~(3)and 1.8±0.8 mBq m~(-3)respectively. For both ~7Be and ~(210)Pb,there are significant short-term and seasonal variations with a commonly low value in summer(May September)and a monthly maximum in april(for ~7Be)and in December(for~(210)Pb). The ratio of ~7Be/~(210)pb showed a broad maximum extending from April to July,coinciding with a seasonal peak in surface ozone(O_3).The seasonal cycles of ~7Be and ~(210)Pb activities were greatly influenced by precipitation and thermal dynamical conditions over the boundary layer,especially for ~(210)Pb.The vertical mixing process between the boundary layer and the aloft air modulates the variations of ~7Be and ~(210)pb at WO in summer.It is indicated that air mass had longer residence time and originated from higher altitudes at WO in the spring-summer time and the winter in 2003.During an event with extremely high weekly- averaged ~7Be concentration(24.8 mBq m~(-3))together with high O_3 levels and low water mixing ratio,we found that air masses had been convectively transported a long distance to WO from high latitude source regions in central Asia,where significant subsiding motions were observed.In another case with the extreme ~(210)pb activity of 5.7 mBq m~(-3)high CO_2 level and specific humidity(in winter),air masses had come from south China and north Indian regions where ~(222)Rn activities were high.This study,using ~7Be and ~(210)Pb as atmospheric tracers,has revealed that complex interactions of convective mixing from the upper troposphere and long-range transports exist at WO.     

Beryllium-7 Deposition and Its Relation to Sulfate Deposition

Deposition of ⁷Be, a cosmogenic radionuclide, was observed at the Meteorological Research Institute in Tsukuba, Japan from 1986 to 1993 and compared with those of several chemical species observed in Tsukuba over the same period. We found a correlation between the monthly depositions of ⁷ Be and SO ₄ ² -, a major acidic species. The correlation was especially strong for late spring and fall, when both species had high depositional fluxes. This correlation was also observed in precipitation samples collected daily in 1992 at the same site. The cause of this correlation is discussed in connection with the fact that the stratospheric aerosol is composed largely of SO ₄ ² -. ⁷ Be is produced in the upper atmosphere, and detection of ⁷Be, especially in spring and fall in Japan, can be regarded as detection of stratospheric aerosol. However, we conclude that the bulk of the SO ₄ ² - observed did not have a stratospheric or an upper tropospheric origin. The correlation, therefore, may present a new question regarding acidic deposition: Why does the deposition of stratospheric aerosol in Japan coincide with that of nss-SO ₄ ² - originally from anthropogenic sources on the Earth's surface?     

Aerosol removal coefficients based on 7Be, 210Pb,and 210Po radionuclides in the urban atmosphere

Journal of Atmospheric Chemistry - In this study, the aerosol removal coefficients based on 7Be, 210Pb and 210Po radionuclides in the urban air, in Lodz, Poland, were investigated over 3 years,...     

Nitrous Oxide Flux Estimates for South-Eastern Australia

Nitrous oxide (N₂O) fluxes for south-easternAustralia have been estimated using a combination ofthe in situ N₂O and radon (Rn) measurementsmade at the Cape Grim Baseline Air Pollution Station,in north-west Tasmania. The average N₂O fluxesfrom the south-eastern mainland of Australia and fromTasmania over the nine years of record analysed (1985–1993) have beenfound to be 130 ± 30 kgN km^-2yr^-1 and 160 ± 45 kgN km^-2yr^-1respectively. These fluxes are larger than expectedand a significant dependence of the flux on rainfallis observed, with greater fluxes in the spring (October–December) andduring periods of positive SouthernOscillation Index. A large flux (1,300 ± 500kgN km^-2 yr^-1) from a nearby island (KingIsland) was also estimated from the data record,indicating a strong source, although the small size ofthe island means that it is not a significant sourcefor Australia.     

Nitrogen and sulfur species in acrosols at Mawson,Antarctica, and their relationship to natural radionuclides

High volume aerosol samples were collected continuously at Mawson, Antarctica (67°36'S, 62°30'E), from February 1987 through October 1989. All samples were analyzed for Na⁺, Cl^-, SO₄ ⁼, NO₃ ^-, methanesulfonate (MSA), NH₄ ⁺,⁷Be, and²¹⁰Pb. The annual mean concentrations of many of the species are very low, substantially lower than even those over the relatively pristine regions of the tropical and subtropical South Pacific. The concentrations at Mawson are comparable both in magnitude and in seasonality to those which have been measured in long term studies at the South Pole and at the coastal German Antarctic research station, Georg von Neumayer (GvN). This comparability suggests that the aerosol composition may be relatively uniform over a broad sector of the Antarctic. The concentrations of most of the species exhibit very strong and sharply-defined seasonal cycles. MSA, non-sea-salt (nss) SO₄ ⁼ and NH₄ ⁺ all exhibit similar cycles, with maxima during the austral summer (December through February) being more than an order of magnitude higher than the winter minima. The limited⁷Be data appears to exhibit a similar cycle. Although nitrate and²¹⁰Pb also exhibit relatively high concentrations during the austral summer, their cycles are far more complex than those of the previous species with indications of multiple peaks. As expected, the concentration of sea-salt (as indicated by Na⁺ and Cl^-) peaks during the winter. The results from multiple variable regression analyses indicate that the dominant source of nss SO₄ ⁼ is the oxidation of dimethylsulfide (DMS) which produces MSA and nss SO₄ ⁼ in a ratio of about 0.31 (about five times higher than that over the tropical and subtropical oceans). However, a very significant fraction (about 25%) of the nss SO₄ ⁼ is associated with NO₃ ^-, The seasonal cycle of NO₃ ^- is similar to that of²¹⁰Pb and distinctly different from that of⁷Be and MSA. These results indicate that the major source of NO₃ ^- over Antarctica is probably continental as opposed to stratospheric or marine biogenic.     

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.     

Forest-Air Fluxes Of Carbon, Water And Energy Over Non-Flat Terrain

A field study of surface-air exchange of carbon, water, and energy was conducted at a mid-latitude, mixed forest on non-flat terrain to investigate how to best interpret biological signals from the eddy flux data that may be subject to advective influences. It is shown that during periods of Southwest winds (sector with mild topography), the eddy fluxes are well-behaved in terms of energy balance closure, the existence of a constant flux layer, consistency with chamber observations and the expected abiotic controls on the fluxes. Advective influences are evident during periods with wind from a steep (15%) slope to the Northeast of the tower. These influences appear more severe on CO₂ flux, particularly in stable air, than on the energy fluxes. Large positive flux of CO₂ (> 23 mol m^-2 s^-1) occurs frequently at night. The annual sum of the carbon flux is positive, but the issue about whether the forest is a source of atmospheric carbon remains inconclusive.Attempts are made to assess vertical advectionusing the data collected on a single tower. Over the Southwestsector, vertical advection makes a statistically significant but small contribution to the 30-min energy imbalance and CO₂ flux variations. Contributions by horizontal advection may be larger but cannot be verified directly by the current experimental method.     

锡林浩特草原CO2通量特征及其影响因素分析

利用锡林浩特国家气候观象台开路涡度相关系统、辐射土壤观测系统,测得的长期连续通量观测数据,对锡林浩特草原2009—2011年期间的CO₂通量观测特征进行了分析。结果表明:CO₂通量存在明显的年际、季节和日变化特征。3 a中NEE年际变率达到200 g·m^-2,季节变率最大达到460 g·m^-2,日变化幅度生长季最大达到0.25 mg·m^-2·s^-1。通过不同时间尺度碳通量与温度、水分、辐射等环境因子的分析,认为CO₂通量日变化主要受温度和光合有效辐射影响,而季节变化和年变化主要受降水和土壤含水量的影响。降水强度及时间分布是制约牧草CO₂吸收的关键因素,大于15%的土壤含水量有利于促进牧草生长。     

7Be deposition in a high-rainfall area of New Zealand

Concentrations of natural ⁷Be in air and rainwater were monitored for one year at Hokitika, New Zealand. The mean airborne concentration was 3.1±1.3 mBq m^–3, the mean Hokitika, New Zealand. The mean airborne concentration was 3.1±1.3 mBq m^–3, the mean concentration in rainwater was 2600±1200 Bq m^–3, and the mean total deposition was estimated to be 130±99 Bq m^–2 wk^–1. Most of the ⁷Be was wet deposited and the washout ratio was independent of precipitation amount. A significant linear relationship exists between the weekly wet deposition flux and weekly precipitation at this high-rainfall site.     

Free tropospheric reservoir of natural sulfate

¹⁰Be is used as a spike of the natural background atmospheric aerosol to calculate the global flux of sulfur (F_S) into the free troposphere. The sulfate and¹⁰Be concentrations determined in polar snow are compared. On the basis of an annual¹⁰Be production rate of 1.21 10⁶ at.cm^-2, a very low figure of 2.9 Tg S a^-1 is calculated for F_S, which suggests that most of the sulfur emitted at ground level remains in the boundary layer. The role of OCS in the upper tropospheric sulfur budget is reviewed. It is also shown that cataclysmic volcanic eruptions may disturb considerably for 1–2 years this vast background tropospheric sulfur reservoir.     

Evaluation of turbulent fluxes over Maitri,Antarctica

Turbulent fluxes have been evaluated for clear sunny days over the Indian Antarctic station, Maitri, using the basic meteorological data recorded at four levels of a 28 m tower. The data are supplemented with radiation data. The surface layer over Maitri remains thermally stratified during the hours of minimum solar insolation, the so-called nighttime period. The surface winds during this period are generally very strong resulting in high momentum fluxes. In particular, for high winds (>12 m s^–1), the temperature gradient is found to be less positive than for moderate winds (4 to 7 m s^–1). Solar insolation provided the daytime heating necessary for the diurnal variation of atmospheric stability, and hence, for the turbulent fluxes. Thus, on clear days daytime conditions are marked by upward transport of heat with reduced momentum flux, while stable nighttime conditions are marked by a downward heat flux with increased momentum fluxes.     

Production of N2O,CH4, and CO2 from soils in the tropical savanna during the dry season

Emissions of N₂O, CH₄, and CO₂ from soils at two sites in the tropical savanna of central Venezuela were determined during the dry season in February 1987. Measured arithmetic mean fluxes of N₂O, CH₄, and CO₂ from undisturbed soil plots to the atmosphere were 2.5×10⁹, 4.3×10¹⁰, and 3.0×10¹³ molecules cm^-2 s^-1, respectively. These fluxes were not significantly affected by burning the grass layer. Emissions of N₂O increased fourfold after simulated rainfall, suggesting that production of N₂O in savanna soils during the rainy season may be an important source for atmospheric N₂O. The CH₄ flux measurements indicate that these savanna soils were not a sink, but a small source, for atmospheric methane. Fluxes of CO₂ from savanna soils increased ninefold two hours after simulated rainfall, and remained three times higher than normal after 16 hours. More research is needed to clarify the significance of savannas in the global cycles of N₂O, CH₄, CO₂, and other trace gases, especially during the rainy season.     

Assessment of Major Pools and Fluxes of Carbon in Indian Forests

The major pools including phytomass, soil, litter, and fluxes of carbon (C)due to litterfall and landuse changes were estimated for Indian forests. Basedon growing stock-volume approach at the state and district levels, the Indianforest phytomass was estimated in the range of 3.8–4.3 PgC. The totalsoil organic pool in the top 1m depth was estimated as 6.8 PgC, usingestimated soil organic carbon densities and Remote Sensing (RS) based area byforest types. Based on 122 published Indian studies and RS-based forest area,the total litterfall carbon flux was estimated as 208.8 MgCha^–1 yr^–1.The cumulative net carbon flux (1880–1996) from Indian forests(1880–1996) due to landuse changes (deforestation, afforestation andphytomass degradation) was estimated as 5.4 PgC, using a simple book-keepingapproach. The mean annual net C flux due to landuse changes during1985–1996 was estimated as 9.0 TgC yr^–1. For the recentperiod, the Indian forests are nationally a small source with some regionsacting as small sinks of carbon as well. The improved quantification of poolsand fluxes related to forest carbon cycle is important for understanding thecontribution of Indian forests to net carbon emissions as well as theirpotential for carbon sequestration in the context of the Kyoto protocol.     

Field measurement of small ozone fluxes to snow,wet bare soil,and lake water

Eddy-correlation measurements over snow, wet bare soil, and lake water indicate very small vertical ozone fluxes. Adjustments to the small vertical fluxes are needed to take into account the effect of mean Stefan flow associated with evaporation at the surface and the effects of correlation between density variations and vertical wind fluctuations. For snow, the residual resistance calculated for the surface is about 34 s cm^-1, indicating that the maximum deposition velocity is abut 0.03 cm s^-1. For cold bare soil well saturated with water, the surface resistance is about 10 s cm^-1 (maximum deposition velocity of about 0.1 cm s^-1). The highest resistances obtained are for transfer to the surface of Lake Michigan, yielding values near 90 s cm^-1 for resistance (0.01 cm s^-1 for deposition velocity).Work supported by the U.S. Dept. of Energy and the U.S. Environmental Protection Agency.     

Pb isotopic ratios in airborne PM10 of an iron/metal industrial complex area and nearby residential areas: Implications for ambient sources of Pb pollution

This study examined four stable isotopic compositions of Pb in the PM₁₀ (²⁰⁴Pb, ²⁰⁶Pb, ²⁰⁷Pb and ²⁰⁸Pb) along with the ambient Pb concentrations in two residences relative to their proximity to an iron and metal industrial complex (IMIC) as well as an industrial site located within the boundary of the IMIC. In addition, eight potential emission sources were investigated for stable isotopic compositions of Pb. The wintertime Pb isotopic ratios for ²⁰⁸Pb/²⁰⁶Pb for ambient samples of an industrial sampling site (ISS) were closer to those of the residential ambient air concentrations measured at closer proximity to the IMIC (RA1) compared to another residential area located further away (RA2). This finding suggests that the ambient Pb sources were more similar between RA1 and the ISS than between RA2 and the ISS. In contrast, the summertime Pb isotopic ratios for the ambient samples of the ISS were not similar to those for RA1, which in turn were similar to those for RA2. During the summer, it is suggested that motor vehicle emissions appear to be a potential source of Pb in the two residential areas. For the ISS, neither ²⁰⁷Pb/²⁰⁶Pb nor ²⁰⁸Pb/²⁰⁶Pb ratios showed a clear seasonal pattern. However for the ambient samples of the two residential areas, both the ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb ratios exhibited a seasonal pattern, with relatively higher mean ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb ratios during the summer season. It was further confirmed that the ambient Pb concentrations were significantly higher at the ISS than those for RA1, which in turn were significantly higher than those for RA2. At all three sampling sites, high enrichment factor values (≥ 475) were found for Pb.     

210Po in savanna burning plumes

During the FOS-DECAFE experiment at Lamto (Ivory Coast) in January 1991 aerosols samples were collected at ground level above fires in order to investigate the possibility of using²¹⁰Po as a tracer of biomass burning. The concentration of this radionuclide in plants is studied as a function of its content in soils and in the atmospheric background. It is shown that it depends strongly on the atmospheric content in²¹⁰Po, due to dry deposition of the aerosols. The mean concentration of plants at Lamto is found to be about 4.4 pCi of²¹⁰Po/gC during the fire season and falls down to less than 1pCi/gC outside this period. The budget of²¹⁰Po is evaluated taking into account its complete volatilization during the flaming phase, the (²¹⁰Po)_ash/(²¹⁰Po)_plants ratio, which is measured to be about 14% and the percentage of submicron particles in the plume, about 91%. The inferred flux of²¹⁰Po is 3850 Ci/yr for the African savanna, and 5800 Ci/yr for the global savanna. From this flux, fluxes of Ct and Cs are estimated to be 8.4 and 1.1 Tg of C/yr for the worldwide savanna.     

Simulation and Evaluation of Terrestrial Ecosystem NPP with M-SDGVM over Continental China

Using the regional terrestrial Net Primary Production (NPP) from different observations and models over China, we validated the NPP simulations and explored the relationship between NPP and climate variation at interannual and decadal scales in the Modified Sheffield Dynamic Global Vegetation Model (M-SDGVM) during 1981–2000. M-SDGVM shows agreement with the NPP data from 743 sites under the Global Primary Production Data Initiative (GPPDI). The spatial and the zonal averaged NPP of M-SDGVM agree well with ...     

Accumulation over the Greenland Ice Sheet as Represented in Reanalysis Data

Annual precipitation,evaporation,and calculated accumulation from reanalysis model outputs have been investigated for the Greenland Ice Sheet (GrIS),based on the common period of 1989-2001.The ERA-40 and ERA-interim reanalysis data showed better agreement with observations than do NCEP-1 and NCEP-2 reanalyses.Further,ERA-interim showed the closest spatial distribution of accumulation to the observation.Concerning temporal variations,ERA-interim showed the best correlation with precipitation observations at five synoptic stations,and the best correlation with in situ measurements of accumulation at nine ice core sites.The mean annual precipitation averaged over the whole GrIS from ERA-interim (363 mm yr 1) and mean annual accumulation (319 mm yr 1) are very close to the observations.The validation of accumulation calculated from reanalysis data against ice-core measurements suggests that further improvements to reanalysis models are needed.     

Nitrogen and sulfur species in Antarctic aerosols at Mawson,Palmer Station,and Marsh (King George Island)

High volume bulk aerosol samples were collected continuously at three Antarctic sites: Mawson (67.60° S, 62.50° E) from 20 February 1987 to 6 January 1992; Palmer Station (64.77° S, 64.06° W) from 3 April 1990 to 15 June 1991; and Marsh (62.18° S, 58.30° W) from 28 March 1990, to 1 May 1991. All samples were analyzed for Na⁺, SO ₄ ^2– , NO ₃ ^– , methanesulfonate (MSA), NH ₄ ⁺ ,²¹⁰Pb, and⁷Be. At Mawson for which we have a multiple year data set, the annual mean concentration of each species sometimes vary significantly from one year to the next: Na⁺, 68–151 ng m^–3; NO ₃ ^– , 25–30 ng m^–3; nss SO ₄ ^2– , 81–97 ng m^–3; MSA, 19–28 ng m^–3; NH ₄ ⁺ , 16–21 ng m^–3;²¹⁰Pb, 0.75–0.86 fCi m^–3. Results from multiple variable regression of non-sea-salt (nss) SO ₄ ^2– with MSA and NO ₃ ^– as the independent variables indicates that, at Mawson, the nss SO ₄ ^2– /MSA ratio resulting from the oxidation of dimethylsulfide (DMS) is 2.80±0.13, about 13% lower than our earlier estimate (3.22) that was based on 2.5 years of data. A similar analysis indicates that the ratio at Palmer is about 40% lower, 1.71±0.10, and more comparable to previous results over the southern oceans. These results when combined with previously published data suggest that the differences in the ratio may reflect a more rapid loss of MSA relative to nss SO ₄ ^2– during transport over Antarctica from the oceanic source region. The mean²¹⁰Pb concentrations at Palmer and Marsh and the mean NO ₃ ^– concentration at Palmer are about a factor of two lower than those at Mawson. The²¹⁰Pb distributions are consistent with a²¹⁰Pb minimum in the marine boundary layer in the region of 40°–60° S. These features and the similar seasonalities of NO ₃ ^– and²¹⁰Pb at Mawson support the conclusion that the primary source regions for NO ₃ ^– are continental. In contrast, the mean concentrations of MSA, nss SO ₄ ^2– , and NH ₄ ⁺ at Palmer are all higher than those at Mawson: MSA by a factor of 2; nss SO ₄ ^2– by 10%; and NH ₄ ⁺ by more than 50%. However, the factor differences exhibit substantial seasonal variability; the largest differences generally occur during the austral summer when the concentrations of most of the species are highest. NH ₄ ⁺ /(nss SO ₄ ^2– +MSA) equivalent ratios indicate that NH₃ neutralizes about 60% of the sulfur acids during December at both Mawson and Palmer, but only about 30% at Mawson during February and March.