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1.
Precipitation samples collected at Erdemli, Turkey, during February 1996–June 1997 were analysed to determine iron content and speciation. The purpose of the measurements was to examine the atmospheric abundance of iron and to quantify its solubility in the region. Spectrophotometric analyses of Fe(II) and reducible Fe(III) in precipitation samples, along with measurements of pH, conductivity, filterable iron (Fefilt), particulate aluminium (Alpar) and particulateiron (Fepar) were performed to determine iron solubility, which principally affects its bioavailability. Backward trajectories corresponding to the sampling dates were analysed to determine the sources of atmospheric constituents arriving at the site. Among these, the mineral dust transported from the Great Sahara to the region is considered to be a rich source of iron. The concentration of Fe(II) varied from below detection limit (0.02 M) up to 0.42 M,while the maximum concentration of total reactive Fe (referred as Fe(II) + reducible Fe(III) = Fereac) was found to be 1.0 M in precipitation. A strong correlation was found between particulate Fe and Al fractions, both of crustal origin. No correlation was observed between the soluble and insoluble fractions of iron. The soluble iron fraction, Fe(II) concentration varied independently from the concentrations of reducible Fe(III), Fefilt, Fepar, and from the pH of the precipitation. The Fefilt fraction (size < 0.45 m), measuredby Atomic Absorption Spectrophotometer, and frequently interpreted to be the soluble iron fraction in the literature, was found to be significantly higher than the corresponding Fereac fraction inprecipitation samples, most likely due to the colloidal iron content of the Fefilt fraction passing through the 0.45 m pore size filter. The volume weighted mean Fefilt concentration of the precipitation samples collected during the episodic `red rain' events was found to be relatively higher. The geometric mean ratios of soluble Fe(II) and of Fereac to Total Fe (Fefilt + Fepar), werefound to be 1.6% and 2.1%, respectively, while the mean ratioof Fefilt to Total Fe was 9.6%. The flux of bioavailable iron (Fereac)fraction in most atmospheric wet deposition events was found to be sufficient for supporting the maximum primary production rates that are typical for the Eastern Mediterranean Sea.  相似文献   

2.
The photochemical activation of chlorine by dissolved iron in artificial sea-salt aerosol droplets and by highly dispersed iron oxide (Fe2O3) aerosol particles (mainly hematite, specific surface ~150 m2 g?1) exposed to gaseous HCl, was investigated in humidified air in a Teflon simulation chamber. Employing the radical-clock technique, we quantified the production of gaseous atomic chlorine (Cl) from the irradiated aerosol. When the salt aerosol contained Fe2O3 at pH 6, no significant Cl production was observed, even if the dissolution of iron was forced by “weathering” (repeatedly freezing and thawing for five times). Adjusting the pH in the stock suspension to 2.6, 2.2, and 1.9 and equilibrating for one week resulted in a quantifiable amount of dissolved iron (0.03, 0.2, and 0.6 mmol L?1, respectively) and in gaseous Cl production rates of ~1.6, 6, and 8?×?1021 atoms cm?2 h?1, respectively. In a further series of experiments, the pure Fe2O3 aerosol was exposed to various levels of gaseous hydrogen chloride (HCl). The resulting Cl production rates ranged from 8?×?1020 Cl atoms cm?2 h?1 (at ~4 ppb HCl) to 5?×?1022 Cl atoms cm?2 h?1 (at ~350 ppb HCl) and confirmed the uptake and conversion of HCl to atomic Cl (at HCl to Cl conversion yields of 2–5 %, depending on the relative humidity). The Fe2O3 experiments indicate that iron-induced Cl formation may be important for highly soluble combustion-aerosol particles in marine environments in the presence of gaseous HCl.  相似文献   

3.
The impacts of aerosol loading on surface precipitation from mid-latitude deep convective systems are examined using a bin microphysics model. For this, a precipitation case over north central Mongolia, which is a high-altitude inland region, on 21 August 2014 is simulated with aerosol number concentrations of 150, 300, 600, 1200, 2400, and 4800 cm?3. The surface precipitation amount slightly decreases with increasing aerosol number concentration in the range of 150–600 cm?3, while it notably increases in the range of 600–4800 cm?3 (22% increase with eightfold aerosol loading). We attempt to explain why the surface precipitation amount increases with increasing aerosol number concentration in the range of 600–4800 cm?3. A higher aerosol number concentration results in more drops of small sizes. More drops of small sizes grow through condensation while being transported upward and some of them freeze, thus increasing the mass content of ice crystals. The increased ice crystal mass content leads to an increase in the mass content of small-sized snow particles largely through deposition, and the increased mass content of small-sized snow particles leads to an increase in the mass content of large-sized snow particles largely through riming. In addition, more drops of small sizes increase the mass content of supercooled drops, which also leads to an increase in the mass content of large-sized snow particles through riming. The increased mass content of large-sized snow particles resulting from these pathways contributes to a larger surface precipitation amount through melting and collision-coalescence.  相似文献   

4.
Using the multi-source observation data from wind-profiling radar, microwave radiometer, Doppler weather radar, etc. during the blizzard event in 19–20 March 2012 in Urumqi, this paper analyzed the detailed characteristics of the atmospheric dynamics, thermodynamics, intensity and water vapor during the process of this blizzard weather. The findings suggest: (1) in the course of the blizzard weather, the near-surface atmosphere is mainly dominated by northwest airflows, the wind speed and relative humidity increase rapidly, temperature drops and air pressure ascends; (2) the blizzard weather this time is accompanied by cold front system whose entering time is about 16:00 BT 19 March; the shear line that develops from low to high is the position height of the frontal zone, and the variation of the high-level frontal zone directly reflects the altitude and layers where cold and warm air masses interact; (3) the radar equivalent reflectivity factor of the snowstorm process changes within the range 8–25 dBZe and its large-value zone is correlated well with the blizzard duration, the height for the formation of rain (snow) particles and the snow intensity; (4) before the occurrence of the blizzard, atmosphere is in the state of high temperature and high humidity, the maximum vapor density is around 6 g m?3, water vapor mainly stays under the height of 5,000 m; affected by cold front system, cold airs gradually lift warm and moist airs so that the vapor condenses and deposits into water drops and snow particles, forming the snowstorm in the end.  相似文献   

5.
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   

6.
齐宇轩  周杨 《山东气象》2021,41(2):1-13
生物活性铁(Fe) 进入生物地球化学循环中能够调节碳循环,影响海洋初级生产力,间接影响全球气候变化。决定 Fe生物可利用度的关键因子是可溶Fe含量,其中大气气溶胶的长距离传输是上层海洋获取生物可利用Fe的重要来源。近年来,对气溶胶中的Fe及溶解度的研究取得了重要进展,包括对不同区域Fe质量浓度和溶解度的观测以及对Fe溶解度影响因素的讨论。基于以上研究成果,汇总了近二十年全球部分陆地和海洋站点观测所得的不同粒径气溶胶颗粒物中的Fe质量浓度及其溶解度数据;重点介绍了气溶胶沉降入海洋前影响Fe溶解度的主要因素,包括Fe的来源、大气物理过程以及大气化学和传输混合过程等,并就各影响因素间的关联及相对重要性展开讨论;对未来气溶胶 Fe的研究方向和方法提出建议。  相似文献   

7.
Ground-based aerosol instrumentation covering particle size diameters from 25 nm to 32 µm was deployed to determine aerosol concentration and cloud condensation nuclei (CCN)-activation properties at water vapor supersaturations in the range of S = 0.20–1.50 % in the remote Brazilian northeast semi-arid region (NEB) in coastal (maritime) and continental (inland) regimes. The instruments measured aerosol number concentration and activation spectra for CCN and revealed that aerosol properties are sensitive with respect to the sources as a function of the local wind circulation system. The observations show that coastal aerosol total number concentrations are above 3,000 cm?3 on average, exhibiting concentration peaks depending on the time of the day in a consistent daily pattern. The variation on aerosol concentration has also influences on the fraction of particles active as CCN. At 1.0 % water vapor supersaturation, the fraction can reach as high as 80 %. Inland aerosol total concentrations were about 1,800–1,900 cm?3 and did not show much diurnal variation. The fraction of particles active as CCN observed inland depend on the history of the air masses, and was much higher when air masses were originated over the sea. It was found that (NH4)2SO4 and NaCl are the major soluble inorganic fraction of the aerosols at the coast. The major fraction of NaCl was present in the coarse mode, while ammonium sulfate dominates the inorganic fraction at the submicron range, with about 10 % of the total aerosol mass at 0.32 µm. Inorganic compounds are almost absent in particles with sizes around 0.1 μm. The study suggests that the air masses with high concentration of CCN originate at the sea. The feasible explanation lies in the fact that the NEB’s beaches have a particular morphology that produces a wide surf zone and creates a large load of aerosols when combined with strong and permanent winds of the region.  相似文献   

8.
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   

9.
The Fe(II)/Fe(III)-partition in cloudwater samples collected during two field campaigns is evaluated. It turned out that the simultaneous occurrence of complexing and reducing substances in the atmosphere and the cloud processing increase the solubility of iron compounds present in aerosol particles. A correlation between the concentration of iron(II) in the liquid phase and the intensity of the solar irradiation was observed for most of the cloudwater samples. This could be due to the fact that both the photochemical reduction of the iron(III) complexes and the photochemical reductive dissolution of iron(III)(hydr)oxides are depending on the pH-value. Iron(II) seems to be oxidised back to iron(III) preferably by hydrogen peroxide during the night. Positive correlations were received e.g. between the concentration of dissolved iron and the concentration of oxalate and between the percentage of iron(III) and the concentration of hydrogen peroxide. A negative correlation was found e.g. between the concentration of dissolved iron and the pH-value. The uncertainty of the whole process of sampling and analysis was investigated and the conformity of the results was satisfying considering the sometimes difficult conditions during a field campaign.  相似文献   

10.
Laboratory experiments were carried out in the Mainz vertical wind tunnel to determine the retention of the trace gases ammonia and sulfur dioxide dissolved in supercooled cloud droplets during riming. The conditions during riming were similar to the ones in atmospheric mixed phase clouds: temperatures from ?18 °C to ?5 °C, liquid water contents between 1 and 1.5 g m?3, liquid drop radii between 10 and 20 μm, liquid phase concentrations from 1 to 22 mg/l. As collectors, floating ice particles and snow flakes with diameters between 6 mm and 1.5 cm were used. After riming the retention coefficients, i.e. the fractions of the species which remained in the ice phase after freezing were determined. Retention coefficients lying between 0.1 and 1.0 were measured depending on the solubility and dissociation of the trace gas, liquid phase concentration, ambient air temperature, and shape of rimed collector. This can be explained from the chemists’ point of view by the effective Henry’s law constant of the species and physically with the rate of latent heat removal from the rimed collector during freezing. Parameterizations derived from the different experimental cases describe the retention coefficients as a function of temperature. In general, an average retention of ammonia of 92?±?21 % was determined independently of liquid phase concentration while mean values for sulfur dioxide were 53?±?10 % at low liquid phase concentrations and 29?±?7 % at high liquid phase concentrations.  相似文献   

11.
长江中下游一次暴雪冻雨微物理过程模拟研究   总被引：2，自引：2，他引：0       下载免费PDF全文
根据NECP1°×1°客观再分析资料和常规观测资料,利用中尺度数值模式WRF对2008年1月25—29日长江中下游暴雪冻雨过程进行了数值模拟,结果表明：WRF模式可以很好地模拟出此次强降雪过程高低空环流形势演变特征以及降水带的分布。分析表明,中层西南急流对暖湿空气的输送以及低层冷空气的持续扩散为暴雪和冻雨的发生提供了很好的温度层结条件。云微物理过程特征分析表明,此次暴雪冻雨过程存在多种云系共同降水,中低空600—850 hpa强逆温层尤其是0 ℃层的存在使得雪、冰晶等冰相粒子融化形成过冷却水,是大范围冻雨形成的必要条件,同时也是区分大范围冻雨暴雪形成的重要条件。  相似文献   

12.
《Atmospheric Research》2007,83(3-4):622-632
Electron paramagnetic resonance (EPR) was used to study the chemical form of iron, manganese and other paramagnetic species in airborne particles collected on southern coastal part of the North Sea, located in France. In parallel, chemical analysis was performed to obtain the metal concentrations in samples whereas an individual analysis of particles was provided by scanning electron microscopy coupled to an energy-dispersive X-ray spectrometer (SEM-EDX). EPR spectra have evidenced Fe3+ and Mn2+ ions in the form of isolated or agglomerated species, as well as carbonaceous products with variable signal intensities according to the wind direction. The monitoring of a signal of isolated Mn2+ ions on a distance close to 90 km was proposed as tracer of particles from a Mn local emission source. Fe3+ signals are relative to agglomerated species and differences in the type of interaction between these species were evidenced following the wind direction. Fe3+ EPR signals parameters revealing antiferromagnetic contribution in Fe-rich particles were found for an industrial origin at Dunkerque.  相似文献   

13.
Electron paramagnetic resonance (EPR) was used to study the chemical form of iron, manganese and other paramagnetic species in airborne particles collected on southern coastal part of the North Sea, located in France. In parallel, chemical analysis was performed to obtain the metal concentrations in samples whereas an individual analysis of particles was provided by scanning electron microscopy coupled to an energy-dispersive X-ray spectrometer (SEM-EDX). EPR spectra have evidenced Fe3+ and Mn2+ ions in the form of isolated or agglomerated species, as well as carbonaceous products with variable signal intensities according to the wind direction. The monitoring of a signal of isolated Mn2+ ions on a distance close to 90 km was proposed as tracer of particles from a Mn local emission source. Fe3+ signals are relative to agglomerated species and differences in the type of interaction between these species were evidenced following the wind direction. Fe3+ EPR signals parameters revealing antiferromagnetic contribution in Fe-rich particles were found for an industrial origin at Dunkerque.  相似文献   

14.
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   

15.
黄钦  牛生杰  吕晶晶  周悦  张小鹏 《大气科学》2018,42(5):1023-1037
利用PARSIVEL激光雨滴谱仪和自动气象站观测资料及MICAPS数据,对2014年2月7~15日庐山地区积冰天气期间持续时间在5 h以上的2次冻雨过程[2月10日（个例1）和2月13日（个例2）]降水谱分布特征及下落末速度粒径分布进行研究。所观测到的两次个例均是以冻雨为主体的混合相态降水,下落末速度粒径分布偏离G-K曲线,与常规液态降水存在差异,低落速的冻雨滴随降水过程会逐渐向冰粒和干雪转化。结果表明:（1）个例1总降水粒子谱谱宽大于个例2,但峰值数密度比个例2小:个例1谱宽为10 mm,个例2谱宽为4.25 mm,两者峰值粒径均为0.5 mm;个例1降水粒子谱宽为干雪>冻雨>冰粒,个例2降水粒子谱宽为冻雨>干雪>冰粒。（2）Gamma分布更适合描述混合相态降水粒子谱以及冻雨滴谱,个例1中总降水粒子谱Gamma分布为:N（D）=20D-3.61exp（-0.08D）,冻雨Gamma分布:N（D）=76D-2.18exp（-1.11D）;个例2中总降水粒子谱Gamma分布为:N（D）=30D-4.68exp（-0.75D）,冻雨Gamma分布:N（D）=30D-4.67exp（-0.75D）。（3）混合相态降水因混有干雪或冰粒而使得下落末速度粒径谱分布表现出不同程度地向大粒径小落速方向或小粒径大落速方向延展的趋势,这为今后依据下落末速度粒径谱区分同时期降水类型提供了新的思路。  相似文献   

16.
Extraordinary blowing snow transport events in East Antarctica   总被引：1，自引：1，他引：0  
In the convergence slope/coastal areas of Antarctica, a large fraction of snow is continuously eroded and exported by wind to the atmosphere and into the ocean. Snow transport observations from instruments and satellite images were acquired at the wind convergence zone of Terra Nova Bay (East Antarctica) throughout 2006 and 2007. Snow transport features are well-distinguished in satellite images and can extend vertically up to 200 m as first-order quantitatively estimated by driftometer sensor FlowCapt?. Maximum snow transportation occurs in the fall and winter seasons. Snow transportation (drift/blowing) was recorded for ~80% of the time, and 20% of time recorded, the flux is >10?2 kg m?2 s?1 with particle density increasing with height. Cumulative snow transportation is ~4 orders of magnitude higher than snow precipitation at the site. An increase in wind speed and transportation (~30%) was observed in 2007, which is in agreement with a reduction in observed snow accumulation. Extensive presence of ablation surface (blue ice and wind crust) upwind and downwind of the measurement site suggest that the combine processes of blowing snow sublimation and snow transport remove up to 50% of the precipitation in the coastal and slope convergence area. These phenomena represent a major negative effect on the snow accumulation, and they are not sufficiently taken into account in studies of surface mass balance. The observed wind-driven ablation explains the inconsistency between atmospheric model precipitation and measured snow accumulation value.  相似文献   

17.
Iron is the most abundant transition metal in the atmosphere and can play a significant role in cloudwater chemistry where its reactivity is closely related to the partitioning between Fe(II) and Fe(III). The objective of this work is to determine the total iron content and the iron speciation in a free tropospheric site, and to understand which factors influence these parameters. We collected 147 samples of cloudwater during 34 cloud events over a period of four years at the puy de Dôme summit. Besides iron we measured other chemical compounds, solar radiation, physico-chemical and meteorological parameters potentially connected with iron reactivity. The total iron concentrations ranged from 0.1 to 9.1 μM with the major frequency occurring at low levels. The pH and presence of organic complexants seem to be the most significant factors connected with total dissolved iron; while the iron oxidation state seems to be an independent factor. Light intensity, presence of complexants or oxidants (H2O2) do not influence the Fe(II)/Fe(Total) ratio, that was quite constant at about 0.75. This could be due to the potential redox that forces the Fe(II)-Fe(III) couple to the reduced form or, more probably to the complexation by Natural Organic Matter, that can stabilize iron in its reduced form and prevent further oxidation. Our field measurements did not show the diurnal cycle observed in surface water and predicted by models of atmospheric chemistry. This result prompts a more careful review of the role of iron and, by analogy, all the transition metals in atmospheric liquid phase, often over-estimated in the literature.  相似文献   

18.
Observations of the tropical atmosphere are fundamental to the understanding of global changes in air quality, atmospheric oxidation capacity and climate, yet the tropics are under-populated with long-term measurements. The first three years (October 2006–September 2009) of meteorological, trace gas and particulate data from the global WMO/Global Atmospheric Watch (GAW) Cape Verde Atmospheric Observatory Humberto Duarte Fonseca (CVAO; 16° 51′ N, 24° 52′ W) are presented, along with a characterisation of the origin and pathways of air masses arriving at the station using the NAME dispersion model and simulations of dust deposition using the COSMO-MUSCAT dust model. The observations show a strong influence from Saharan dust in winter with a maximum in super-micron aerosol and particulate iron and aluminium. The dust model results match the magnitude and daily variations of dust events, but in the region of the CVAO underestimate the measured aerosol optical thickness (AOT) because of contributions from other aerosol. The NAME model also captured the dust events, giving confidence in its ability to correctly identify air mass origins and pathways in this region. Dissolution experiments on collected dust samples showed a strong correlation between soluble Fe and Al and measured solubilities were lower at high atmospheric dust concentrations. Fine mode aerosol at the CVAO contains a significant fraction of non-sea salt components including dicarboxylic acids, methanesulfonic acid and aliphatic amines, all believed to be of oceanic origin. A marine influence is also apparent in the year-round presence of iodine and bromine monoxide (IO and BrO), with IO suggested to be confined mainly to the surface few hundred metres but BrO well mixed in the boundary layer. Enhanced CO2 and CH4 and depleted oxygen concentrations are markers for air-sea exchange over the nearby northwest African coastal upwelling area. Long-range transport results in generally higher levels of O3 and anthropogenic non-methane hydrocarbons (NMHC) in air originating from North America. Ozone/CO ratios were highest (up to 0.42) in relatively fresh European air masses. In air heavily influenced by Saharan dust the O3/CO ratio was as low as 0.13, possibly indicating O3 uptake to dust. Nitrogen oxides (NOx and NOy) show generally higher concentrations in winter when air mass origins are predominantly from Africa. High photochemical activity at the site is shown by maximum spring/summer concentrations of OH and HO2 of 9?×?106 molecule cm?3 and 6?×?108 molecule cm?3, respectively. After the primary photolysis source, the most important controls on the HOx budget in this region are IO and BrO chemistry, the abundance of HCHO, and uptake of HOx to aerosol.  相似文献   

19.
Beijing is one of the largest and most densely populated cities in China. PM2.5 (fine particulates with aerodynamic diameters less than 2.5 μm) pollution has been a serious problem in Beijing in recent years. To study the temporal and spatial variations in the chemical components of PM2.5 and to discuss the formation mechanisms of secondary particles, SO2, NO2, PM2.5, and chemical components of PM2.5 were measured at four sites in Beijing, Dingling (DL), Chegongzhuang (CG), Fangshan (FS), and Yufa (YF), over four seasons from 2012 to 2013. Fifteen chemical components, including organic carbon (OC), elemental carbon (EC), K+, NH4 +, NO3 ?, SO4 2?, Cl?, Al, Ca, Fe, Mg, Na, Pb, Si, and Zn, were selected for analysis. Overall, OC, SO4 2?, NO3 ?, and NH4 + were dominant among 15 components, the annual average concentrations of which were 22.62 ± 21.86, 19.39 ± 21.06, 18.89 ± 19.82, and 13.20 ± 12.80 μg·m?3, respectively. Compared with previous studies, the concentrations of NH4 + were significantly higher in this study. In winter, the average concentrations of OC and EC were, respectively, 3 and 2.5 times higher than in summer, a result of coal combustion during winter. The average OC/EC ratios over the four sites were 4.9, 7.0, 8.1, and 8.4 in spring, summer, autumn, and winter, respectively. The annual average [NO3 ?]/[SO4 2?] ratios in DL, CG, FS, and YF were 1.01, 1.25, 1.08, and 1.12, respectively, which were significantly higher than previous studies in Beijing, indicating that the contribution ratio of mobile source increased in recent years in Beijing. Analysis of correlations between temperature and relative humidity and between SOR ([SO4 2?]/([SO4 2?] + [SO2])) and NOR ([NO3 ?]/([NO3 ?] + [NO2])) indicated that gas-phase oxidation reactions were the major formation mechanism of SO4 2? in spring and summer in urban Beijing, whereas slow gas-phase oxidation reactions and heterogeneous reactions both occurred in autumn and winter. NO3 ? was mainly formed through year-round heterogeneous reactions in urban Beijing.  相似文献   

20.
Existing simple but theoretically based clear-sky models for longwave down-welling radiation (LDRc) and cloud impact algorithms transforming them to all-sky radiation (LDR) are checked against locally calibrated empirical algorithms. They are evaluated for daylight hours based on measurements in regionally differing climates of Germany. The Prata clear-sky scheme is additionally tested with adjusted coefficients so that LDRc converges against a realistic emissivity for a completely dry atmosphere. This version is characterised by an improved modelled variance. Compared with locally calibrated schemes, bias and root mean square error (RMSE) of the more theoretical clear-sky schemes do not differ significantly and yield even better results at a mountain site. In contrast, the locally calibrated algorithms yield biases up to 9% and an increase in RMSE between 6% and 67%, if applied for other sites. For daylight hours, the cloud impact on LDR can be calculated via the ratio of observed to clear-sky global irradiation (CMFsol). With CMFsol, the Crawford and Duchon scheme reveals the lowest bias and a decrease in RMSE by 22% against the next best performing algorithms. Compared with synoptic cloud observations as input, the bias is reduced by 9 to 28 W m?2 and the scattering of the residuals decreases by 20% to 30%. Based on published results for also non-European sites, it is inferred that the more theoretically based LDRc schemes and cloud impact evaluated via CMFsol are universally applicable and perform at least in the order of magnitude of locally calibrated empirical algorithms.  相似文献   

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