Experimental investigation of the scavenging of gaseous mercury by sea salt aerosol

Sea salt aerosol may be an important sink for reactive gaseous mercury (RGM) in the marine boundary layer, reducing ambient RGM concentrations and transferring the mercury (Hg) to the oceans and coastal ecosystems. The goal of this study was to determine the affinity of gaseous mercury for sea salt aerosol (SSA) by conducting adsorption experiments with sea salt-coated sampling denuders. In the first set of experiments, ambient outdoor air was passed through denuders coated with either KCl, as in the widely accepted method to sample RGM, or with NaCl, a primary component of sea salt aerosols. On the one sampling day in which RGM was above the MDL, the NaCl coated denuders removed Hg from the ambient air, equivalent to 87% of the RGM in the air (as determined by KCl denuders). For the second set of experiments HgCl₂ generated in the laboratory was passed through denuders coated with KCl and either NaCl or sea salt. The NaCl denuders collected an average of 99 ± 16% of the mercury that the KCl denuders collected. Newly coated sea salt denuders collected 88 ± 17% of the amount of mercury that the KCl denuders collected, but interestingly the sea salt denuders capacity decreased with repeated use. These experiments demonstrate that HgCl₂, a major component of RGM has a strong affinity for NaCl and sea salt and is therefore likely to be scavenged by SSA. This study adds to the growing evidence that RGM is scavenged by sea salt aerosols and therefore more quickly deposited to the ocean and coastal environment.     

Climate model sensitivity to sea ice albedo parameterization

Summary Three one-year experimental simulations with the National Center for Atmospheric Research Community Climate Model (NCAR CCM) were performed with three sea ice albedo parameterizations and compared with control run results to examine their impact on polar surface temperature, planetary albedo and clouds. The first integration utilized sea ice albedos of the Arctic Basin for the spring and summer of 1977 derived from defence Meteorological Satellite Imagery (DMSP). The second simulation employed prescribed lead and melt pond fractions and an albedo weighting scheme. The third simulation involved the coupling of an interactive sea ice/snow albedo parameterization made a function of surface state.Results show that prescribed, and assumed true satellite sea ice albedos produced higher planetary albedos than those calculated with the standard CCM sea ice albedo scheme in the control run. As a result, lower temperatures (up to 0.5 K) and increased cloudiness are generated for the Arctic region. The standard CCM sea ice albedo scheme is used as an adjustment to maintain normal temperatures for the polar oceans. The radiative impact of leads and melt ponds warmed sea ice regions only for short time periods. The third scheme generated markedly lower planetary albedos (reductions of 0.07 to 0.17) and higher surface temperatures (up to 2.0 K) than control values.The CCM simulates a gradual decrease in spring and summer Arctic cloud cover whereas observations show a sharp spring increase. Examination of the CCM code, particularly the cloud parameterization, is required to address this problem.With 12 Figures     

Climatic responses to the shortwave and longwave direct radiative effects of sea salt aerosol in present day and the last glacial maximum

We examine the climatic responses to the shortwave (SW) and longwave (LW) direct radiative effects (RE) of sea salt aerosol in present day and the last glacial maximum (LGM) using a general circulation model with online simulation of sea salt cycle. The 30-year control simulation predicts a present-day annual emission of sea salt of 4,253?Tg and a global burden of 8.1?Tg for the particles with dry radii smaller than 10?μm. Predicted annual and global mean SW and LW REs of sea salt are, respectively, ?1.06 and +0.14?W?m^?2 at the top of atmosphere (TOA), and ?1.10 and +0.54?W?m^?2 at the surface. The LW warming of sea salt is found to decrease with altitude, which leads to a stronger net sea salt cooling in the upper troposphere. The changes in global mean air temperature by the present-day sea salt are simulated to be ?0.55, ?0.63, ?0.86, and ?0.91°K at the surface, 850, 500a, and 200?hPa, respectively. The emission of sea salt at the LGM is estimated to be 4,075?Tg?year^?1. Relative to present day, the LGM sea salt emission is higher by about 18% over the tropical and subtropical oceans, and is lower by about 35% in the mid- and high-latitudes in both hemispheres because of the expansion of sea ice. As a result of the weakened LGM water cycle, the LGM annual and global mean burden of sea salt is predicted to be higher by 4% as compared to the present-day value. Compared with the climatic effect of sea salt in present day, the sea-salt-induced reductions in surface air temperature at the LGM have similar magnitude in the tropics but are weakened by about 0.18 and 0.14°K in the high latitudes of the Southern and Northern Hemispheres, respectively. We also perform a sensitivity study to explore the upper limit of the climatic effect of the LGM sea salt. We assume an across-the-board 30% increase in the glacial wind speed and consider sea salt emissions over sea ice, so that the model can reproduce the ratio of sea salt deposition between the LGM and present day in the high latitudes of the Southern Hemisphere as suggested by the ice core records. This sensitivity run predicts a global emission of sea salt of 11,941?Tg?year^?1 with a global burden of 20.9?Tg. With such a high loading, sea salt aerosol at the LGM can have a net RE of ?2.28?W?m^?2 at the TOA and lead to an annual and global mean cooling of 1.27°K at the surface.     

Effect of sea salt on dust settling to the ocean

Dust particles frequently become mixtures of mineral dust and sea salt during their transport in the marine boundary layer, consequently growing in size, which causes changes in their settling velocities. In this study, the effect of sea salt on the gravitational settling of dust particles is investigated. Results show that the adhering of sea salt to dust particles can dramatically increase the gravitational settling of the particles, in particular if the particles become larger than 3–4 μm. Estimates with the observational data from six dust events in southwestern Japan revealed that, due to sea salt adhering, the gravitational settling flux of mineral dust increased approximately 14–17% in well-mixed events and 4–6% in less-mixed events, indicating a potential significant effect of sea salt on dust settling and the importance of considering this effect in the schemata of particle gravitational settling when mapping dust flux to the ocean.     

The effect of an oil slick on the albedo of the sea surface

Values of sea surface albedo estimated from a 3-day data set agree reasonably well with the findings of Payne (1972). However, when an oil slick moved over the observational site, the value of albedo suddenly jumped to 0.57. The effect of turbidity on the albedo over a lake has already been reported (Sadhuram et al., 1988).     

Spatiotemporal characteristics and driving factors of global planetary albedo: an analysis using the Geodetector method

Theoretical and Applied Climatology - As an important parameter of the Earth’s energy budget, the planetary albedo of Earth varies with the dynamics of atmospheric and surface variables. In...     

CICE海冰模式中反照率相关参数对北极海冰模拟的影响

国家气候中心气候系统模式BCC_CSM2.0最新耦合了美国Los Alamos国家实验室发展的海冰模式CICE5.0,为试验模式中与反照率相关参数的敏感性及其对模拟结果的影响,提高模式对北极海冰的模拟能力,选取海冰模式中3个主要参数进行了敏感性试验。利用以BCC_CSM2.0耦合框架为基础建立的海冰-海洋耦合模式,选取CORE资料为大气强迫场开展试验,试验的3个参数分别为冰/雪表面反射率、雪粒半径和雪粒半径参考温度。结果表明,参数取值的不同对北极海冰的模拟有显著的影响,优化后的取值组合极大提高了模式的模拟能力,主要表现在:（1）改善了对北极冬季海冰厚度的模拟,海冰厚度增大,与观测资料更为吻合;（2）显著提高了对北极夏季海冰密集度的模拟能力,从而模拟的北极海冰范围年际循环与观测更为一致。参数取值的优化改进了模式对海冰反照率的模拟,进而影响了冰面短波辐射的吸收和海冰表层的融化,最终提高了模式对海冰密集度和厚度的模拟效果。      

Modeling of aerosol induced snow albedo feedbacks over the Himalayas and its implications on regional climate

Climate Dynamics - Regional climate model (RegCM-4.6.0) coupled with Community Land Model (CLM4.5), which includes SNow, ICe and Aerosol Radiation (SNICAR) model was used to investigate the effect...     

Potential decadal predictability and its sensitivity to sea ice albedo parameterization in a global coupled model

Decadal prediction is one focus of the upcoming 5th IPCC Assessment report. To be able to interpret the results and to further improve the decadal predictions it is important to investigate the potential predictability in the participating climate models. This study analyzes the upper limit of climate predictability on decadal time scales and its dependency on sea ice albedo parameterization by performing two perfect ensemble experiments with the global coupled climate model EC-Earth. In the first experiment, the standard albedo formulation of EC-Earth is used, in the second experiment sea ice albedo is reduced. The potential prognostic predictability is analyzed for a set of oceanic and atmospheric parameters. The decadal predictability of the atmospheric circulation is small. The highest potential predictability was found in air temperature at 2?m height over the northern North Atlantic and the southern South Atlantic. Over land, only a few areas are significantly predictable. The predictability for continental size averages of air temperature is relatively good in all northern hemisphere regions. Sea ice thickness is highly predictable along the ice edges in the North Atlantic Arctic Sector. The meridional overturning circulation is highly predictable in both experiments and governs most of the decadal climate predictability in the northern hemisphere. The experiments using reduced sea ice albedo show some important differences like a generally higher predictability of atmospheric variables in the Arctic or higher predictability of air temperature in Europe. Furthermore, decadal variations are substantially smaller in the simulations with reduced ice albedo, which can be explained by reduced sea ice thickness in these simulations.     

尺度自适应大气边界层参数化改进及其对一次海雾的数值模拟研究

大气边界层湍流运动是地球大气运动最重要的能量输送过程之一.当数值模式分辨率接近活跃含能湍涡长度尺度时,湍流运动被部分解析,被称为"灰色区域",传统的边界层方案不适合此时模式湍流问题的描述.为了提高模式边界层方案在包括"灰色区域"的不同网格尺度上的描述能力,适应不同分辨率模式的需要,在雷诺平均湍流理论基础上,修正Mell...     

Observed dependence of the water vapor and clear-sky greenhouse effect on sea surface temperature: comparison with climate warming experiments

This study presents a comparison of the water vapor and clear-sky greenhouse effect dependence on sea surface temperature for climate variations of different types. Firstly, coincident satellite observations and meteorological analyses are used to examine seasonal and interannual variations and to evaluate the performance of a general circulation model. Then, this model is used to compare the results inferred from the analysis of observed climate variability with those derived from global climate warming experiments. One part of the coupling between the surface temperature, the water vapor and the clear-sky greenhouse effect is explained by the dependence of the saturation water vapor pressure on the atmospheric temperature. However, the analysis of observed and simulated fields shows that the coupling is very different according to the type of region under consideration and the type of climate forcing that is applied to the Earth-atmosphere system. This difference, due to the variability of the vertical structure of the atmosphere, is analyzed in detail by considering the temperature lapse rate and the vertical profile of relative humidity. Our results suggest that extrapolating the feedbacks inferred from seasonal and short-term interannual climate variability to longer-term climate changes requires great caution. It is argued that our confidence in climate models' predictions would be increased significantly if the basic physical processes that govern the variability of the vertical structure of the atmosphere, and its relation to the large-scale circulation, were better understood and simulated. For this purpose, combined observational and numerical studies focusing on physical processes are needed.     

Impact of absorbing aerosol deposition on snow albedo reduction over the southern Tibetan plateau based on satellite observations

We investigate the snow albedo variation in spring over the southern Tibetan Plateau induced by the deposition of light-absorbing aerosols using remote sensing data from moderate resolution imaging spectroradiometer (MODIS) aboard Terra satellite during 2001–2012. We have selected pixels with 100 % snow cover for the entire period in March and April to avoid albedo contamination by other types of land surfaces. A model simulation using GEOS-Chem shows that aerosol optical depth (AOD) is a good indicator for black carbon and dust deposition on snow over the southern Tibetan Plateau. The monthly means of satellite-retrieved land surface temperature (LST) and AOD over 100 % snow-covered pixels during the 12 years are used in multiple linear regression analysis to derive the empirical relationship between snow albedo and these variables. Along with the LST effect, AOD is shown to be an important factor contributing to snow albedo reduction. We illustrate through statistical analysis that a 1-K increase in LST and a 0.1 increase in AOD indicate decreases in snow albedo by 0.75 and 2.1 % in the southern Tibetan Plateau, corresponding to local shortwave radiative forcing of 1.5 and 4.2 W m⁻², respectively.

     

Time-dependent uptake of NO3 by sea salt

Using a coated-insert flow tube reactor coupled to a low-energy electron-impact mass spectrometer with molecular beam sampling, we studied uptake of NO₃ by sea salt at room temperature and [NO₃]?=?8?10¹¹???4?10¹³ molecule cm^?3. The radical uptake coefficient γ(t) is time dependent: its initial value (γ _ini) decreases exponentially with the characteristic time (τ) to its steady-state value (γ _ss) at given [NO₃]. The parameters γ _ini, γ _ss and τ depend on [NO₃], whereas γ _ss is water vapor independent at [H₂O]?=?8?10¹²???1.6?10¹⁵ molecule cm^?3 and RH ≤ 0.5 %. HCl and NO₂ are uptake products detected in the gas phase. We used these findings to estimate γ values under tropospheric conditions for urban coastal and remote marine environments: at high NO₃ (~90 ppt), the time dependence becomes important, and the γ value averaged over the aerosol lifetime is 4?10^?3; at low NO₃ (~1 ppt), the radical uptake is time independent and proceeds faster with γ _ini?=?8?10^?3     

Turbidity measurements of Saharan aerosol and their effects on atmospheric heating and planetary reflectivity

Summary Eleven months of atmospheric turbidity measurements were made in Tozeur, Southern Tunisia, located at the northern edge of the Sahara. These measurements were done with a Linke-Feussner actinometer equipped with broad band Schott filters (OG1, RG2, RG8). These filters were chosen, as they have demonstrated a good stability with time. The lowest values of turbidity were found in winter, which is the rainy season for this area. In spring (April) the largest number of sand storms were observed, but the turbidity remained high for the whole summer. A mean Linke turbidity factor of 5.39 was derived, which is a value otherwise generally found only in industrial areas. Mean values of Ångström coefficients were = 0.34 and = 1.20.Aerosol particles were also sampled with nucleopore membrane filters. The chemical analyses of the particles with an X-ray spectrometer showed that most of the smaller ones had a chemical composition similar to sand. Other, larger ones showed high amounts of Ca and Cl; these are believed to have originated in Chott Djerid, the largest dried-out salt lake in Tunisia, which is located 20 km southeast of Tozeur.Model calculations of the radiative transfer for the solar spectrum were carried out, taking the turbidity measurements and ground truth measurements of albedo [33] into account. A perturbation experiment was carried out, changing turbidity and surface reflectivity. It was found that an increased surface reflectivity had a cooling effect at the surface, and a warming effect on the lowest kilometer of the atmosphere. Further, increases in turbidity resulted again in cooling at the surface, but with additional warming of the atmosphere. The combined increases of surface reflectivity and turbidity had a somewhat balancing effect as far as planetary albedo was concerned.

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Messungen der Trübung des Aerosols der Sahara und ihre Auswirkungen auf die Erwärmung der Atmosphäre und auf die planetare Reflexionsfähigkeit

Zusammenfassung Elf Monate hindurch wurden in Tozeur in Süd-Tunesien am Nordrand der Sahara Messungen der atmosphärischen Trübung durchgeführt. Diese Messungen wurden mit einem Linke-Feussner gemacht, das mit Breitband Schott-Filter OG1, RG2 und RG8 ausgerüstet ist. Die kleinsten Trübungswerte wurden im Winter gefunden, der für dieses Gebiet die Regenzeit ist. Im Frühling (April) wurde die größte Zahl von Sandstürmen beobachtet und die Trübung blieb auch im ganzen Sommer groß. Es wurde ein mittlerer Trübungsfaktor nach Linke von 5.39 bestimmt. Das ist ein Wert, der im allgemeinen nur in Industriegebieten gefunden wird. Die Mittelwerte der Ångström-Koeffizienten betrugen = 0,34 und = 1,20.Mit Membranfiltern wurden auch Aerosolteilchen gesammelt. Die mit einem Röntgenstrahlen-Spektrometer durchgeführten chemischen Analysen der Teilchen zeigten, daß die kleineren Teilchen meist eine dem Sand ähnliche chemische Zusammensetzung haben. Größere Teilchen zeigten hohe Beträge von Ca und Cl. Diese haben ihren Ursprung scheinbar im Chott Djerid, dem größten ausgetrockneten Salzsee in Tunis, der 20 km südöstlich von Tozeur liegt.Es wurden Modellrechnungen der Strahlungsübertragung für das Sonnenspektrum durchgeführt, wobei die Trübungsmessungen und die Albedomessungen in Rechnung gezogen worden sind. Es wurden auch Störungsexperimente mit geänderter Trübung und Oberflächenreflexion durchgeführt. Es wurde gefunden, daß zunehmende Oberflächenreflexion einen Abkühlungseffekt an der Oberfläche und einen Erwärmungseffekt im untersten Kilometer der Atmosphäre zeigt. Ferner bewirkt eine Zunahme der Trübung ebenfalls eine Abkühlung der Oberfläche, aber zusätzliche Erwärmung der Atmosphäre. Die kombinierte Zunahme der Oberflächenreflexion und der Trübung hatte einen etwas ausgleichenden Effekt, soweit die planetare Albedo betroffen war.

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With 13 Figures     

西太平洋热带海域海盐粒子的观测和结果

1986年10月15日至12月15日西太平洋热带海域(6°30′N__5°00′S,127°00′__150°00′E)182份海盐粒子资料分析结果:该海域海盐粒子总平均数浓度为107个/l,总平均质量浓度为2.O×10~(-10)g/l,表明该海域可能是海盐粒子低产区;盐粒子浓度与风速有正相关趋势。小风速时的高粒子浓度可能是海盐粒子的1_2天滞留时间所致,也可能是经过本站的气团属性和经历不同造成的;海面流场对盐粒子浓度大小也有一定影响。     

δ函数在云的反射率计算中的应用

本文证明了二流模式和s-w模式,两种计算散射大气反射率的简化方法,都具有δ-相函数的特点.结合δ函数并通过由二流模式得到的计算结果作为一次近似再代入辐射传输方程中而导出一种更精确计算云层反照率的简单方法.     

The application of delta function to the albedo of clouds

It is verified that there is δ-phase function characteristic in both of TS and SW simplified models, and on the basis of TS model, a more accurate model calculating the albedo and transmissivity of cloud layers is derived.     

Sensitivity of the IAP two-level AGCM to surface albedo variations

Summary Two numerical experiments were performed for sensitivity study of surface albedo, one was a control run in which the albedo values for snow-free surfaces were prescribed as constant; the other was a sensitivity run in which an albedo with seasonal variation was incorporated into the model show that the simulation of precipitation is sensitive to the surface albedo variations, especially those over Eastern Asia and the Sahara. Changes in surface albedo also have an impact on the monthly mean sea level pressure, especially on the July-mean Western Pacific subtropical high. Surface air temperature decreased over most of the Eastern Asia but increases over most of the Antarctica in July.With 6 Figures