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1.
Aerosol and rain samples were collected between 48°N and 55°S during the KH-08-2 and MR08-06 cruises conducted over the North
and South Pacific Ocean in 2008 and 2009, to estimate dry and wet deposition fluxes of atmospheric inorganic nitrogen (N).
Inorganic N in aerosols was composed of ~68% NH4+ and ~32% NO3– (median values for all data), with ~81% and ~45% of each species being present on fine mode aerosol, respectively. Concentrations
of NH4+ and NO3− in rainwater ranged from 1.7–55 μmol L−1 and 0.16–18 μmol L−1, respectively, accounting for ~87% by NH4+ and ~13% by NO3− of total inorganic N (median values for all data). A significant correlation (r = 0.74, p < 0.05, n = 10) between NH4+ and methanesulfonic acid (MSA) was found in rainwater samples collected over the South Pacific, whereas no significant correlations
were found between NH4+ and MSA in rainwater collected over the subarctic (r = 0.42, p > 0.1, n = 6) and subtropical (r = 0.33, p > 0.5, n = 6) western North Pacific, suggesting that emissions of ammonia (NH3) by marine biological activity from the ocean could become a significant source of NH4+ over the South Pacific. While NO3− was the dominant inorganic N species in dry deposition, inorganic N supplied to surface waters by wet deposition was predominantly
by NH4+ (42–99% of the wet deposition fluxes for total inorganic N). We estimated mean total (dry + wet) deposition fluxes of atmospheric
total inorganic N in the Pacific Ocean to be 32–64 μmol m−2 d−1, with 66–99% of this by wet deposition, indicating that wet deposition plays a more important role in the supply of atmospheric
inorganic N than dry deposition. 相似文献
2.
Both aerosol and rainwater samples were collected and analyzed for ionic species at a coastal site in Southeast Asia over
a period of 9 months (January–September 2006) covering different monsoons. In general, the occurrence and distribution of
ionic species showed a distinct seasonal variation in response to changes in air mass origins. Real-time physical characterization
of aerosol particles during rain events showed changes in particle number distributions which were used to assess particle
removal processes associated with precipitation, or scavenging. The mean scavenging coefficients for particles in the range
10–500 nm and 500–10 μm were 7.0 × 10−5 ± 2.8 × 10−5 s−1 and 1.9 × 10−4 ± 1.6 × 10−5 s−1, respectively. A critical analysis of the scavenging coefficients obtained from this study suggested that the wet removal
of aerosol particles was greatly influenced by rain intensity, and was particle size-dependent as well. The scavenging ratios,
another parameter used to characterize particle removal processes by precipitation, for NH4
+, Cl−, SO4
2−, and NO3
− were found to be higher than those of Na+, K+, and Ca2+ of oceanic and crustal origins. This enrichment implied that gaseous species NH3, HCl, and HNO3 could also be washed out readily. These additional sources of ions in precipitation presumably counter-balanced the dilution
effect caused by high total precipitation volume in the marine and tropical area. 相似文献
3.
Joan D. Willey Robert J. Kieber G. Brooks Avery Jr. 《Journal of Atmospheric Chemistry》2004,47(3):209-222
Rainwater is a major source of dissolved iron to much of the world's oceans, including regions where iron may be a limiting
nutrient for marine phytoplankton primary production. Rainwater iron is therefore potentially important in regulating global
photosynthetic uptake of CO2, and hence climate. Two rainwater addition bioassay experiments (2% rain) conducted at the Bermuda Atlantic Time-series Station
(BATS) during March 2000 using 50 or 100 nM FeCl2 or FeCl3 in synthetic rain (pH 4.5 H2SO4) showed an increase in chlorophyll a 50% greater than controls after three days. Addition of 20 μM hydrogen peroxide, a typical rainwater concentration at BATS,
completely removed the chlorophyll a increase with both forms of iron additions, suggesting stimulation of phytoplankton growth by rainwater iron can be limited
by rainwater H2O2. In laboratory experiments using Gulf Stream seawater, iron-enriched (100 nM Fe(III)) synthetic rain was mixed with seawater
in a 5% rain 95% seawater ratio. Dissolved iron concentrations increased two times above concentrations predicted based on
dilution alone. The increase in soluble iron probably resulted from release from seawater particles and was maintained for
more than 24 hours. No increase was observed in controls that did not have iron added to the synthetic rain, or with synthetic
rainwater containing both added iron and H2O2. The increase in iron concentration above that predicted by dilution indicates rain may have a larger effect on seawater
iron concentrations than that calculated for rainwater iron addition alone. 相似文献
4.
J. N. Mphepya C. Galy-Lacaux J. P. Lacaux G. Held J. J. Pienaar 《Journal of Atmospheric Chemistry》2006,53(2):169-183
The chemical composition, as well as the sources contributing to rainwater chemistry have been determined at Skukuza, in the Kruger National Park, South Africa. Major inorganic and organic ions were determined in 93 rainwater samples collected using an automated wet-only sampler from July 1999 to June 2002. The results indicate that the rain is acidic and the averaged precipitation pH was 4.72. This acidity results from a mixture of mineral acids (82%, of which 50% is H2SO4) and organic acids (18%). Most of the H2SO4 component can be attributed to the emissions of sulphur dioxide from the industrial region on the Highveld. The wet deposition of S and N is 5.9 kgS⋅ha−1⋅yr−1 and 2.8 kgN⋅ha−1⋅yr−1, respectively. The N deposition was mainly in the form of NH4
+. Terrigenous, sea salt component, nitrogenous and anthropogenic pollutants have been identified as potential sources of chemical components in rainwater. The results are compared to observations from other African regions. 相似文献
5.
Ambient respirable particles (PM10; aerodynamic diameter ≤10 μm) collected in a tropical urban environment (Delhi, India) during December 2008-November 2009
were characterized with respect to 16 US EPA priority polycyclic aromatic hydrocarbons (PAHs) and 8 major and trace metals
(Fe, Mn, Cd, Cu, Ni, Pb, Zn and Cr). Concentrations of Σ16PAHs (annual mean: 74.7 ± 50.7 ng m−3, range 22.1–258.4 ng m−3) and most metallic species were at least an order of magnitude greater than values reported from similar locations worldwide.
Seasonal variations in Σ16PAHs were significant (p < 0.001) with highest levels in winter while crustal and anthropogenic metals showed significant but mutually opposite seasonal
dependence. Statistically significant associations were observed between chemical species and various meteorological parameters.
The PAH profile was dominated by combustion-derived large-ring species (~85%) that were essentially local in origin. Principal
component analysis–multiple linear regression (PCA-MLR) apportioned four sources: crustal dust (73%), vehicular emission (21%),
coal combustion (4%) and industrial emission (2%) that was further validated by hierarchical cluster analysis (HCA). Temporal
trend analysis showed that crustal sources were predominant in summer (p < 0.05) while the remaining sources were most active in winter. Summertime intrusions of Saharan dust were identified with
the help of aerosol maps and air parcel backward trajectories. Inhalation cancer risk assessment showed that up to 3,907 excess
cancer cases (357 for PAHs, 122 for Cd, 2040 for Cr (VI) and 1387 for Ni) are likely in Delhi considering lifetime inhalation
exposure to these chemicals at their current concentrations. 相似文献
6.
Melanie Louise Inez Witt Stephen Skrabal Robert Kieber Joan Willey 《Journal of Atmospheric Chemistry》2007,58(2):89-109
Significant quenching of fluorescence by Cu in rainwater samples from southeastern North Carolina demonstrates that chromophoric
dissolved organic matter (CDOM) is an effective ligand for Cu in rainwater. A strong inverse correlation between the decrease
in fluorescence upon Cu addition and CDOM abundance suggests the presence of excess binding sites for Cu in high CDOM samples.
Electroanalytical studies indicate that CDOM extracted from C18 cartridges formed Cu complexes with concentrations and conditional stability constants similar to ligands found in ambient
rainwater. When authentic rainwater samples were photolyzed with simulated sunlight both photoproduction and photodestruction
of ligands were observed, suggesting the photochemical response of Cu-complexing ligands in rainwater is the result of two
competing reactions. The rate of CDOM photobleaching was directly related to changes in strong ligands (KCuL ∼ 1015) whereas weaker ligands (KCuL < 1013) were not correlated, suggesting the photolabile CDOM resides in the strong ligand class. A photolysis study comparing filtered
and unfiltered rainwater samples indicated that Cu-complexing ligands adsorbed onto or otherwise associated with particles
are photodegraded much more rapidly than dissolved ligands. Photolysis with UV radiation appears to be most effective at engendering
changes in Cu ligands, however a significant photochemical response was also observed when samples were exposed to photosynthetically
active radiation with wavelengths greater than 400 nm. Results from this study demonstrate that complexation of Cu by CDOM
has important ramifications for controlling both the speciation of the metal and the reactivity of CDOM in rainwater. 相似文献
7.
Acid rain and alkalization in southwestern China: chemical and strontium isotope evidence in rainwater from Guiyang 总被引:1,自引:0,他引:1
A comprehensive study on the chemical compositions of rainwater was carried out from June 2007 to December 2008 in Guiyang,
a city located on the acid rain control zone of southwest China. All samples were analyzed for pH, major anions (F−, Cl−, NO3−, SO42−), major cations (K+, Na+, Ca2+, Mg2+, NH4+), Sr2+ and Sr isotope. The pH increase is due to the result of neutralization caused by the alkaline dust which contain large amount
of CaCO3. It was observed that Ca2+ was the most abundant cation with a volume-weighted mean (VWM) value of 217.6 μeq/L (52.7–1928 μeq/L), accounting for 66%
(39%–88%) of the total cations. SO42− was the most abundant anion with VWM value of 237.8 μeq/L (49.6-1643 μeq/L). SO42− and NO3− were dominant among the anions, accounting for 66%–97% of the total measured anions. The Sr concentrations vary from 0.01
to 0.92 μmol/L, and strontium isotopic ratios vary in the range of 0.707684–0.710094, with an average of 0.708092. The elements
ratios and the 87Sr/86Sr ratios showed that the solutes of rainwater mainly come from weathering of carbonate and secondary dust input. Moreover,
urbanization results in the calcium-rich dust increased and the high concentrations of alkaline ions (mainly Ca2+) have played an important role to neutralize the acidity of rainwater, leading to the increase of arithmetic pH mean value
by 0.5 units since 2002. It is worth noting that the emission of SO2 and NOx from the automobile exhaust is increasing and is becoming another important precursor of acid rain now. 相似文献
8.
Absorption and fluorescence properties of rainwater during the cold season at a town in Western Portugal 总被引:1,自引:0,他引:1
Patrícia S. M. Santos Regina M. B. O. Duarte Armando C. Duarte 《Journal of Atmospheric Chemistry》2009,62(1):45-57
This study aims at evaluating the variability of the optical properties of chromophoric dissolved organic matter (CDOM) of
rainwater during the cold season, specifically between Autumn and Winter periods. The spectroscopic characteristics of rainwater
samples collected at a town (Aveiro) in western Portugal were assessed by UV-Vis absorbance and three-dimensional excitation-emission
matrix (EEM) fluorescence spectroscopies. Rainwater samples showed similar characteristics to those of natural humic substances
when analysed by UV-Vis absorbance spectroscopy, but a significant difference was observed in the volume weight average (VWA)
of absorbances between Autumn and Winter. In general, the EEM fluorescence spectra of the Autumn and Winter samples disclosed
the presence of six fluorophores with different VWA specific fluorescence intensities: three humic-like (λ
excitation/λ
emission ≈ 230/415 nm; 290/415 nm; and 340/415 nm) and three protein-like (λ
excitation/λ
emission ≈ 230/350 nm; 280/340 nm; and 225/300 nm), but one of the humic-like peaks (≈340/415 nm) does not always appear in the EEM
fluorescence spectra of the Winter samples. During the cold season, chromophoric compounds are important constituents of rainwater
dissolved organic matter and the presence of these highly absorbing and fluorescing compounds may exert a determining effect
in atmospheric absorption of solar radiation. 相似文献
9.
Kinetics of the reactions of soot surface-bound polycyclic aromatic hydrocarbons with NO<Subscript>2</Subscript> 总被引:1,自引:0,他引:1
Mai Lan Nguyen Yuri Bedjanian Angélique Guilloteau 《Journal of Atmospheric Chemistry》2009,62(2):139-150
The kinetics of heterogeneous reactions of NO2 with 17 polycyclic aromatic hydrocarbons (PAHs) adsorbed on laboratory generated kerosene soot surface was studied over the
temperature range (255–330) K in a low pressure flow reactor combined with an electron-impact mass spectrometer. The kinetics
of soot-bound PAH consumption due to their desorption and reaction with NO2 were monitored using off-line HPLC measurements of their concentrations in soot samples as a function of reaction time, NO2 concentrations in the gas phase being analyzed by mass spectrometer. No measurable decay of PAHs due to the reaction with
NO2 was observed under experimental conditions of the study (maximum NO2 concentration of 5.5 × 1014 molecule cm−3 and reaction time of 45 min), which allowed to determine the upper limits of the first-order rate constants for the heterogeneous
reactions of 17 soot-bound PAHs with NO2: k < 5.0 × 10−5 s−1 (for most PAHs studied). Comparison of these results to previous studies carried on different carbonaceous substrates, showed
that heterogeneous reactivity of PAHs towards NO2 is, probably, dependent on the substrate nature even for resembling, although different carbonaceous materials. Results show
that particulate PAHs degradation by NO2 alone is of minor importance in the atmosphere 相似文献
10.
Particle composition and size distributions in and around a deep-pit swine operation,Ames, IA 总被引:1,自引:0,他引:1
Randal S. Martin Philip J. Silva Kori Moore Mark Erupe Vishal S. Doshi 《Journal of Atmospheric Chemistry》2008,59(2):135-150
The contribution of emissions from agricultural facilities is rapidly becoming a major concern for local and regional air
quality. Characterization of particle properties such as physical size distribution and chemical composition can be valuable
in understanding the processes contributing to emissions and ultimate fate of particulate matter from agricultural facilities.
A measurement campaign was conducted at an Iowa, deep-pit, three-barn swine finishing facility to characterize near-source
ambient particulate matter. Size-specific mass concentrations were determined using minivol samplers, with additional size
distribution information obtain using optical particle counters. Particulate composition was determined via ion chromatographic
analysis of the collected filters. A thermal-CO2 elemental/organic carbon analyzer measured particulate carbon. The chemical composition and size distribution of sub-micron
particles were determined via real-time aerosol mass spectrometry. Primary particulate was not found to be a major emission
from the examined facility, with filter-based impactor samples showing average near-source increases (~15–50 m) in ambient
PM10 of 5.8 ± 2.9 μg m−3 above background levels. PM2.5 also showed contribution attributable to the facility (1.7 ± 1.1 μg m−3). Optical particle counter analysis of the numerical size distributions showed bimodal distributions for both the upwind
and downwind conditions, with maximums around 2.5 μm and below the minimum quantified diameter of 0.3 μm. The distributions
showed increased numbers of coarse particles (PM10) during periods when wind transport came from the barns, but the differences were not statistically significant at the 95%
confidence level. The PM10 aerosols showed statistically increased concentrations of sulfate, nitrate, ammonium, calcium, organic carbon, and elemental
carbon when the samplers were downwind from the pig barns. Organic carbon was the major constituent of the barn-impacted particulate
matter in both sub-micron (54%) and coarse size (20%) ranges. The AMS PM1 chemical speciation showed similar species increases, with the exception of and Ca+2, the latter not quantified by the AMS. 相似文献
11.
Robert J. Kieber Nichole E. Parler Stephen A. Skrabal Joan D. Willey 《Journal of Atmospheric Chemistry》2008,60(2):153-168
Mercury speciation was determined in rainwater from 76 storms in southeastern North Carolina between September 1, 2003 and
September 30, 2005. Volume-weighted average concentrations of total Hg (THg), total dissolved Hg (TDHg), particulate Hg (Hgpart) and dissolved monomethyl Hg (MMHg) were 45.5 pM, 34.8 pM, 12.0 pM and 1.1 pM respectively. TDHg accounted for 77% of THg
in precipitation which is similar to Cu but significantly higher than Cr or Fe. Concentrations of the various Hg species were
very similar during summer and winter indicating that there was not a dominant seasonal influence on Hg speciation in rainwater
at this location. THg, TDHg, and MMHg concentrations were also not significantly impacted by storm origin suggesting that
they are relatively well mixed regionally and that air mass back trajectory is not the dominant factor controlling their concentration
at this location. Concentrations of TDHg and Hgpart were inversely correlated in rainwater samples subjected to irradiation with simulated sunlight, suggesting the distribution
between dissolved and particulate Hg may be controlled by photochemical transformations. Unlike TDHg and Hgpart, no significant changes in MMHg were observed upon photolysis of rainwater indicating that its distribution is not significantly
driven by sunlight-mediated reactions, in contrast to what has been observed in surface waters. Results presented in this
study indicate that the speciation of Hg in rainwater is dynamic and is driven by a complex combination of natural and anthropogenic
processes as well as interactions with sunlight. 相似文献
12.
Seasonal carbon dioxide balance and respiration of a high-arctic fen ecosystem in NE-Greenland 总被引:2,自引:0,他引:2
C. Nordstroem H. Soegaard T. R. Christensen T. Friborg B. U. Hansen 《Theoretical and Applied Climatology》2001,70(1-4):149-166
Summary Turbulent fluxes of CO2 were continuously measured by eddy correlation for three months in 1997 over a gramineous fen in a high-arctic environment
at Zackenberg (74°28′12″N, 20°34′23″W) in NE-Greenland. The measurements started on 1 June, when there was still a 1–2 m cover
of dry snow, and ended 26 August at a time that corresponds to late autumn at this high-arctic site. During the 20-day period
with snow cover, fluxes of CO2 to the atmosphere were small, typically 0.005 mg CO2 m−2 s−1 (0.41 g CO2 m−2 d−1), wheres during the thawed period, the fluxes displayed a clear diurnal variation. During the snow-free period, before the
onset of vegetation growth, fluxes of CO2 to the atmosphere were typically 0.1 mg CO2 m−2 s−1 in the afternoon, and daily sums reached values up to almost 9 g CO2 m−2 d−1. After 4 July, downward fluxes of CO2 increased, and on sunny days in the middle of the growing season, the net ecosystem exchange rates attained typical values
of about −0.23 mg m−2 s−1 at midday and max values of daily sums of −12 g CO2 m−2 d−1. Throughout the measured period the fen ecosystem acted as a net-sink of 130 g CO2 m−2. Modelling the ecosystem respiration during the season corresponded well with eddy correlation and chamber measurements.
On the basis of the eddy correlation data and the predicted respiration effluxes, an estimate of the annual CO2 balance the calender year 1997 was calculated to be a net-sink of 20 g CO2 m−2 yr−1.
Received October 6, 1999 Revised May 2, 2000 相似文献
13.
Joan D. Willey Robert J. Kieber Kelly H. Williams Jamie S. Crozier Stephen A. Skrabal G. Brooks Avery Jr. 《Journal of Atmospheric Chemistry》2000,37(2):185-205
Iron occurs in rain as particulateand dissolved Fe and includes both Fe(II) and Fe(III)species. Model calculations and correlation analysisindicate Fe(II)(aq) occurs almost exclusively as thefree ion whereas Fe(III)(aq) occurs as both ironoxalate and Fe(OH)2
+(aq) with largevariations over the pH range from 4.0 to 5.0. Complexation with humic-like compounds may also beimportant for Fe(III)(aq); however, the concentrationand structural characteristics of these compounds haveyet to be determined. 112 rain samples were collectedfor iron analysis in Wilmington, North Carolina,between 1 July 1997, and 30 June 1999. Total iron,particulate iron and Fe(III)(aq) were higher inconcentration in summer and spring rain relative towinter and autumn rain. Fe(II)(aq) concentrations, incontrast, did not vary seasonally. Particulate iron,which was approximately half the total rainwater iron,was highest between noon and 6 p.m. (EST), probably dueto more intense regional convection including land-seabreezes during that time. The ratio ofFe(II)(aq)/Fe(III)(aq) was also highest in rainreceived between noon and 6 p.m., which most likelyreflects photochemical reduction of Fe(III)(aq)complexes to form Fe(II)(aq). A conceptual modeldepicting the interplay between iron species, lightintensity and organic ligands in rainwater ispresented. 相似文献
14.
Kinetic Study of the Reactions of Ozone with Polycyclic Aromatic Hydrocarbons Adsorbed on Atmospheric Model Particles 总被引:1,自引:0,他引:1
In this experimental study, rate constants were measured for the reactions of ozone with 13 polycyclic aromatic hydrocarbons (PAHs) adsorbed on different types of particles. Graphite and silica were chosen to model, respectively, carbonaceous and mineral atmospheric particles. The pseudo-first order rate constants were obtained from the fit of the experimental decay of particulate PAH concentrations versus time. Second order rate constants were calculated considering the ozone gaseous concentration. At room temperature, rate constants varied, in the case of graphite particles, between (1.5 ± 0.5) × 10−17 and (1.3 ± 0.7) × 10−16 cm3 molecule−1 s−1 for chrysene and dibenzo[a,l]pyrene, respectively, and, in the case of silica particles, between (1.5 ± 0.3) × 10−17 and (1.4 ± 0.3) × 10−16 cm3 molecule−1 s−1 for fluoranthene and benzo[a]pyrene, respectively. Different granulometric parameters (particle size, pore size) and different PAH concentrations were tested in the case of silica particles. Heterogeneous reactions of ozone with particulate PAHs are shown to be more rapid than those occurring in the gas-phase, and may be competitive with atmospheric photodegradation. 相似文献
15.
Summary Net ecosystem CO2 exchange was measured over a mountain birch forest in northern Finland throughout the growing season. The maximal net CO2 uptake rate of about − 0.5 mg(CO2) m−2 s−1 was observed at the end of July. The highest nocturnal respiration rates in early August were 0.2 mg(CO2) m−2 s−1. The daily CO2 balances during the time of maximal photosynthesis were about −15 g(CO2) m−2 d−1. The mountain birch forest acted as a net sink of CO2 from 30 June to 28 August. During that period the net CO2 balance was −448 g(CO2)m−2. The interannual representativeness of the observed balances was studied using a simplified daily balance model, with daily
mean global radiation and air temperature as the input parameters. The year-to-year variation in the phenological development
was parameterised as a function of the cumulative effective temperature sum. The daily balance model was used for estimating
the variability in the seasonal CO2 balances due to the timing of spring and meteorological factors. The sink term of CO2 in 1996 was lower than the 15-year mean, mainly due to the relatively late emergence of the leaves.
Received October 11, 1999 Revised April 25, 2000 相似文献
16.
Guillaume Bertrand Hélène Celle-Jeanton Paolo Laj Jérôme Rangognio Gilles Chazot 《Journal of Atmospheric Chemistry》2008,60(3):253-271
The present study investigates the chemical composition of wet atmospheric precipitation samples on a daily and an intra-event
timescales in Opme, an experimental meteorological station located near Clermont-Ferrand, France. The samples have been collected
from November 2005 to October 2007. A total of 217 rainwater samples, integrated for 24 h, were collected and analyzed for
pH, conductivity, Na+, K+, Mg2+, NH4+, Ca2+, Cl−, NO3− , SO42− , PO43− and HCO3−. The composition of the rainwater collected appeared to be controlled by the following potential sources: neutralisation
process (association among calcium, ammonium with nitrate and sulphate), marine and terrestrial sources. In order to determine
the role of long-range transport, the integrated events were classified according to four origins of air-masses: (1) West,
(2) North and East, (3) South including Iberian and Italian Peninsulae and (4) local. This analysis allows identifying the
source areas of the different association of elements defined. Although calcium is always dominant, total content of rainfall
is variable and neutralisation process can be more or less efficient and specific. Rainout (long-range transport) and washout
(below-cloud scavenging) were investigated through intra-event measurements of chemical species. Four rain-events have been
selected according to the four classes of origins of air-masses. It appears that the first fractions are responsible for an
important part of the chemical content of the whole event. Terrestrial species, locally emitted, induce the neutralisation
process of acid species. Local meteorological conditions, such as wind’s speed and direction, play an important role as they
could provoke recharges of the below cloud air column during the event. 相似文献
17.
The reaction kinetics of S(IV) autoxidation catalyzed by single metal ions of Mn(II) and Fe(II) or Fe(III) and by a mixture of Mn(II) and Fe(II) under the conditions representative for acidified atmospheric liquid water was investigated. A simple power law kinetic model based on the stability constants for metal-sulfito complexes formed during the first step of a radical chain mechanism predicts well the kinetics for the reactions catalyzed by single metal ions. The calculated stability constants for iron (5.7×103 dm3 mol–1) and manganese (10×104 dm3 mol–1) sulfito complexes are close to those reported in the literature. The catalytic synergism between Mn(II) and Fe(II) was confirmed. For this system the following power law rate equation was suggested:rtot = SFe · rFe + SMn · rMn ,where rFe and rMn are the reaction rates in the presence of Fe(II) and Mn(II), respectively. SFe and SMn are proportional factors, which account for the synergistic effect. The proposed power law rate equation predicts the reaction kinetics very well. The values of SFe (1.35) and SMn (15) indicate that the influence of Fe(II)/Fe(III) on Mn(II)/Mn(III) cycling is larger than, vice versa, agreeing with the reaction mechanism proposed for the S(IV) autoxidation catalyzed by mixed metal ions. 相似文献
18.
Annual methane emission from Finnish mires estimated from eddy covariance campaign measurements 总被引:4,自引:0,他引:4
K. J. Hargreaves D. Fowler C. E. R. Pitcairn M. Aurela 《Theoretical and Applied Climatology》2001,70(1-4):203-213
Summary Measurements of landscape-scale methane emission were made over an aapa mire near Kaamanen in Finnish Lapland (69° 8′ N,
27° 16′ E, 155 m ASL). Emissions were measured during the spring thaw, in summer and in autumn. No effect of water table position
on CH4 emission was found as the water table remained at or above the surface of the peat. Methane emission fluxes increased with
surface temperature from which an activation energy of −99 kJ mol−1 was obtained. Annual emission from the site, modelled from temperature regression and short-term flux measurements made in
three separate years, was calculated to be 5.5 ± 0.4 g CH4 m−2 y−1 of which 0.6 ± 0.1 g CH4 m−2 y−1 (11%) was released during the spring thaw which lasted 20 to 30 days.
The effect of global warming on the CH4 budget of the site was estimated using the central scenario of the SILMU (Finnish Research Programme on Climate Change) model
which predicts annual mean temperature increases of 1.2, 2.4 and 4.4 °C in 2020, 2050 and 2100, respectively. Maximum enhancements
in CH4 emission due to warming were calculated to be 18, 40 and 84% for 2020, 2050 and 2100, respectively. Actual increases may
be smaller because prediction of changes in water table are highly uncertain.
Received September 17, 1999 Revised October 16, 2000 相似文献
19.
The uptake of water vapor on MgCl2×6H2O and NaCl salt dry solid films was studied over the temperature range 240 to 340 K and at 1 Torr pressure of helium using
a flow reactor coupled to a modulated molecular beam mass spectrometer. The H2O to salt uptake data were obtained from the kinetics of H2O loss on salt coated Pyrex rods. The following Arrhenius expression was obtained for the initial uptake coefficient of H2O on MgCl2×6H2O films: γ
0
(MgCl2) = (6.5 ± 1.0) × 10−6 exp[(470 ± 40)/T] (calculated with specific BET surface area, quoted uncertainties are 1σ statistical). The rate of H2O adsorption on NaCl was found to be much lower than on MgCl2×6H2O, and only an upper limit was determined for the corresponding uptake coefficient: γ (NaCl) ≤ 5.6 × 10−6 at T = 300 K. The results show that the rate of H2O adsorption to salt surfaces is drastically dependent on the salt sample composition. 相似文献
20.
Summary Net Ecosystem CO2 Exchange (NEE) was studied during the summer season (June–August) at a high Arctic heath ecosystem for 5 years in Zackenberg,
NE Greenland. Integrated over the 80 day summer season, the heath is presently a sink ranging from −1.4 g C m−2 in 1997 to −23.3 g C m−2 in 2003. The results indicate that photosynthesis might be more variable than ecosystem respiration on the seasonal timescale.
The years focused on in this paper differ climatically, which is reflected in the measured fluxes. The environmental conditions
during the five years strongly indicated that time of snow-melt and air temperature during the growing season are closely
related to the interannual variation in the measured fluxes of CO2 at the heath. Our estimates suggest that net ecosystem CO2 uptake is enhanced by 0.16 g C m−2 per increase in growing degree-days during the period of growth. This study emphasises that increased summer time air temperatures
are favourable for this particular ecosystem in terms of carbon accumulation. 相似文献