Emissions of Polycyclic aromatic hydrocarbons by savanna fires

Although Polycyclic aromatic hydrocarbons (PAH) are known as anthropogenic compounds arising from the combustion or the pyrolysis of fossil fuels, they may be also emitted by the combustion of vegetation. A field study was carried out in January 1991 at Lamto (Ivory Coast) as part of the FOS DECAFE experiment (Fire Of Savanna). Some ground samplings were devoted to the qualitative and quantitative characterization of atmospheric emissions by savanna fires during prescribed burns and under background conditions. Specific collections for gaseous and particulate PAHs have shown that the African practice of burning the savanna biomass during the winter months is an important source of PAHs. These compounds are emitted mainly in gaseous form but a significant fraction, essentially heavy PAHs, is associated with fine carbonaceous particles and can therefore represent a hazard for human health, since some of these compounds are mutagenic and carcinogenic. Twelve compounds were identified during the fire episodes and in the atmospheric background. The total concentration in the fires is of the order of 10 ng m^–3 for the gas phase and from 0.1 to 1 ng m^–3 in the aerosols. In the atmospheric background the mean concentrations are regular, 0.15 ng m^–3 and 2 pg m^–3, respectively. These concentrations are comparable with what is observed in European rural zones. The particulate emissions of PAHs by the savanna fires are distinguished by the abundance of some compounds which can be considered as tracers, although they are also slightly emitted by fossil fuel sources. These compounds are essentially pyrene, chrysene and coronene. In the gas phase, although no individual PAH may be considered as specific of the biomass combustion emissions, the relative abundances of the main PAHs are characteristic of the biomass burning. The concentrations of pyrene and fluorene are always predominant; these compounds could be considered as characteristic emission products of smoldering and flaming episodes, respectively. In the background the PAH composition shows that in a tropical region the air consists of a mixture coming from the various sources, but the biomass combustion is by far the most important source.The fluxes of total PAH emitted by savanna biomass burning in Africa were estimated to be of the order of 17 and 600 ton yr^–1, respectively, for the particulate PAHs and the gaseous PAHs, respectively.     

气溶胶辐射特性的观测研究

利用一个简化的辐射平衡模式,讨论了气溶胶直接辐射强迫和气溶胶辐射特性以及与地面反射率之间的关系。模式分析表明,增加气溶胶层以后,地气系统对太阳辐射的反射率可能增大,也可能减少,取决于气溶胶的单散射反射率~ω0、不对称度因子g与地面反射率αg之间的配置,但与气溶胶光学厚度δ没有直接的关系。气溶胶光学厚度值仅和反射率变化的幅度成正比。从辐射平衡模式的结果可知,为了定量地研究气溶胶直接辐射强迫作用,需要有系统的有关气溶胶辐射特性的观测资料。从地面和空间对中国地区气溶胶的辐射特性开展了观测研究,包括从地面用太阳光度计测量气溶胶的光学厚度、用浊度计测量气溶胶的散射系数、黑碳仪测量气溶胶的吸收系数,并且利用MODIS资料反演气溶胶的光学厚度。地面太阳光度计观测的气溶胶光学厚度用于检验卫星遥感的气溶胶光学厚度值,对中国东部地区,遥感的结果是可以接受的,主要是由于这一地区存在较低的地表反射率;但对中国北方植被条件不很好的地区,在遥感反演时对地面反射率的估计可能偏低,如做适当的修改还有可能提高遥感反演的精度。从地面直接测量气溶胶的散射系数和吸收系数算出的气溶胶单散射反射率在0.8左右,需要有更多的观测,以便进一步查清这一问题。     

撒哈拉地区沙尘气溶胶南北空间型分布特征及其成因

本次研究利用MODIS、CALIPSO等卫星观测资料以及MERRA-2再分析资料分析了2007–2017年撒哈拉地区气溶胶光学厚度的空间分布特征。结果表明,撒哈拉地区气溶胶光学厚度的空间分布具有明显的季节变化,夏季沙尘气溶胶光学厚度高值区位于撒哈拉北部地区,高达0.6以上;而冬季沙尘气溶胶光学厚度高值区位于撒哈拉南部地区,最大值约为0.5。此外,撒哈拉地区在不同季节的主要气溶胶类型均为沙尘,但在撒哈拉南部地区沙尘气溶胶光学厚度对总气溶胶光学厚度的贡献有明显的季节性差异。基于CALIPSO体积退偏比的研究结果表明,在撒哈拉南部地区,夏季人为气溶胶占比大,气溶胶粒子趋于球形,冬季气溶胶粒子的退偏比则明显高于夏季,粒子非球形程度更高。夏季撒哈拉北部地区位于脊前槽后的位置,以南地区近地面主要为偏西风,携带了大量水汽的气流由大西洋吹向撒哈拉地区,使撒哈拉南部地区进入雨季,增强了沙尘气溶胶的沉降,因此夏季撒哈拉地区沙尘气溶胶光学厚度分布北高南低;冬季高压控制着撒哈拉北部地区,撒哈拉南部地区近地面盛行偏东风,且冬季温度偏低,容易形成逆温,不利于沙尘气溶胶和局地污染物扩散,导致沙尘气溶胶光学厚度南高北...     

Organic matter of the troposphere — V: Application of molecular marker analysis to biogenic emissions into the troposphere for source reconciliations

Organic matter in tropospheric aerosols is derived from two major sources and is admixed depending on the geographic area. These sources are biogenic detritus and anthropogenic emissions. The biogenic materials in the solvent-extractable organic matter are comprised predominantly of higher plant waxes, with lesser amounts of resin and microbial detritus and the anthropogenic components are primarily vehicular emissions (e.g. oils, soot, etc.) and input from combustion (e.g. charcoal, thermally-altered biogenic matter, etc.). Both biogenic detritus and anthropogenic emissions contain organic compounds (C₁₂–C₄₀₊), which can be identified with unique and distinguishable distribution patterns. Molecular composition analysis has been applied to such extracts after suitable chemical separation into subfractions (i.e. hydrocarbons, ketones, aldehydes, carboxylic acids, alcohols, and wax esters). Both homologous compound series and specific natural products (e.g. phytosterols, terpenes, etc.) are identified as molecular markers.Aerosols from rural and remote areas in the western United States, South America, Nigeria and Australia have been analyzed and all contained predominantly plant waxes. The loadings of hydrocarbons ranged approximately from 10–1400 ng/m³ of air, of fatty acids from 10–450 ng/m³ and of fatty alcohols from 10–1650 ng/m³. These higher molecular weight lipids primarily from flora comprise a major component of the organic carbon in rural and remote aerosols. They are thus important indicators for regional biogenic sources in the global cycling of organic carbon.Presented in part at the International Symposium on Biosphere-Atmosphere Exchange, Mainz, E.R. Germany, March 16–22, 1986, for Part IV see Simoneit et al. (1988) Atmos. Environ. 22, 983–1004.     

Organosulfates – A New Component of Humic-Like Substances in Atmospheric Aerosols?

Ion trap mass spectrometry (ITMS) was used to obtain further qualitative information about the chemical composition of humic-like substances (HULIS) in atmospheric particulate matter. Particles ≤10 μm (PM₁₀) were collected on quartz fiber filters for 24 h in the region of Basel (Switzerland) and extracted with water. HULIS were separated from inorganic salts by size exclusion chromatography (SEC) and detected by electrospray ionization in the negative ion mode (ESI(−)). Series of consecutive fragment ion spectra (MSⁿ) were recorded by ITMS. Full scan mass spectra of the extracts showed a mass distribution pattern characteristic for HULIS. Different molecular ions were selected from this pattern for further fragmentations. Among them the molecular ion m/z 299 was considered as representative and intensively studied. Many MS² and MS³ fragment spectra contained a fragment m/z 97 and a neutral loss of 80 u. Time-of-flight (TOF) MS and deuterium exchange experiments identified m/z 97 as hydrogen sulfate. MS² and MS³ fragment spectra supported the existence of sulfate covalently bound to HULIS. The fragmentation behavior of sulfated HULIS could be confirmed by model compounds.     

Effects of additional HONO sources on visibility over the North China Plain

The objective of the present study was to better understand the impacts of the additional sources of nitrous acid （HONO） on visibility, which is an aspect not considered in current air quality models. Simulations of HONO contributions to visibility over the North China Plain （NCP） during August 2007 using the fully coupled Weather Research and Forecasting/Chemistry （WRF/Chem） model were performed, including three additional HONO sources： （1） the reaction of photo-excited nitrogen dioxide （NO~） with water vapor; （2） the NO2 heterogeneous reaction on aerosol surfaces; and （3） HONO emissions. The model generally reproduced the spatial patterns and diurnal variations of visibility over the NCP well. When the additional HONO sources were included in the simulations, the visibility was occasionally decreased by 20%-30% （3-4 km） in local urban areas of the NCP. Monthly-mean concentrations of NO3, NH＋, SO]- and PM2.5 were increased by 20%-52% （3-11μg m-3）, 10%-38%, 6%-10%, and 6%-11% （9-17 μg m-3）, respectively; and in urban areas, monthly-mean accumulation- mode number concentrations （AMNC） and surface concentrations of aerosols were enhanced by 15%-20% and 10%-20%, respectively. Overall, the results suggest that increases in concentrations of PM2.5, its hydrophilic components, and AMNC, are key factors for visibility degradation. A proposed conceptual model for the impacts of additional HONO sources on visibility also suggests that visibility estimation should consider the heterogeneous reaction on aerosol surfaces and the enhanced atmospheric oxidation capacity due to additional HONO sources, especially in areas with high mass concentrations of NOx and aerosols.     

我国沙尘的来源、移动路径及对东部海域的影响

利用中国气象局提供的micaps天气资料,通过对2000—2002年发生的42次沙尘天气个例的分析,重点研究了沙尘的源地、移动路径、入海地点及对不同海域的影响概率。结果表明：影响我国的沙尘天气有70%起源于蒙古国,在经过境内沙漠地区时得以加强。沙尘粒子的移动和入海途径主要有3条：一是从内蒙古东部入侵的沙尘天气经浑善达克和科尔沁沙地后进入渤海和黄海;二是从内蒙古西部入侵的沙尘天气经内蒙古西部沙地和黄土高原后进入渤海、黄海和东海;三是从青海东部扬起的沙尘长距离输运进入黄海、东海及西北太平洋。2000—2002年,63.9％的沙尘天气会影响到海洋,其中,影响渤海、黄海和东海的概率分别为27.4％、30.9％和12.3％,影响朝鲜海峡和日本海的概率为20.2％和9.2％。     

东亚夏季风变化机理的模拟和未来变化的预估:成绩和问题、机遇和挑战

东亚夏季风对于我国东部气候具有重要影响,呈现出多种时间尺度的变化特征。在理解东亚夏季风过去和当前的变化机理、预测和预估其未来变化等方面,气候系统模式发挥着不可替代的作用。但是当前的气候模式在东亚夏季风的模拟上尚存在诸多不足,这使得其模拟结果存在不确定性,既制约了我们对过去和当前季风变化机理的准确理解,又降低了未来预测预估结果的可信度。关于造成季风模拟偏差的原因,既涉及模式本身的性能问题,又与模拟系统的构建、强迫资料的误差、乃至我们当前对季风变化规律自身的认知水平有关。本文以时间尺度为序,从气候态、日变化、年际变率、年代际变率、长期气候变化和未来预估等季风学界关注的热点问题角度,本着总结成绩、归纳问题、寻找机遇、面对挑战的目的,从七个方面系统总结了当前气候模式的水平,归纳了其主要偏差特征,讨论了影响模式性能的可能因素。内容涉及模式分辨率和地形效应、对流和云辐射效应的作用、与季风相关的热带海气相互作用关键过程、内部变率（太平洋年代际振荡）、自然变率（太阳辐照度变化和火山气溶胶强迫）和人为辐射强迫（人为温室气体和气溶胶排放）对季风变化的不同影响、热力和动力过程及气候敏感度对季风环流（副高）和降水预估不确定性的影响等。最后从优化参数、实现场地观测和过程模拟的协同、发展高分辨和对流解析模式等角度,讨论了提升东亚夏季风模拟能力的技术途径。     

CHEMICAL CHARACTERISTICS OF AEROSOLS IN THE KUROSHIO AREA——II.CHEMICAL FORMS AND SIZE DISTRIBUTIONS OF TRACE METALS

Aerosol samples were collected with a Sierrer Model 235 cascade impactor in the marine atmosphere over the Kuroshio area in consecutive four seasons from 1987 to 1988. Na, G, Al, V, and water soluble and acid soluble Mn, Fe, Pb, Cu, V, Cd were determined by neutron activation analysis and atomic absorption spectrophotometry, respectively. Seawater source chemical species in the aerosols appeared in high content in large over 3.6um diameter particles, and crustal source vanadium appeared in 3.6um diameter particles, but pollution source vanadium appeared in less than 0.52um diameter particles. Trace metals in the aerosols mostly had the highest concentration of water soluble metals on fine particles, and acid soluble metals on large particles. The concentrations of trace metals in the aerosols were higher in autumn and winter, lower in spring and summer.     

Direct Radiative Forcing of Anthropogenic Aerosols over Oceans from Satellite Observations

Anthropogenic aerosols play an important role in the atmospheric energy balance. Anthropogenic aerosol optical depth (AOD) and its accompanying shortwave radiative forcing (RF) are usually simulated by nu- merical models. Recently, with the development of space-borne instruments and sophisticated retrieval algorithms, it has become possible to estimate aerosol radiative forcing based on satellite observations. In this study, we have estimated shortwave direct radiative forcing due to anthropogenic aerosols over oceans in all-sky conditions by combining clouds and the Single Scanner Footprint data of the Clouds and Earth’s Radiant Energy System (CERES/SSF) experiment, which provide measurements of upward shortwave fluxes at the top of atmosphere, with Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol and cloud products. We found that globally averaged aerosol radiative forcing over oceans in the clear-sky conditions and all-sky conditions were -1.03±0.48 W m-2 and -0.34 ±0.16 W m-2, respectively. Direct radiative forcing by anthropogenic aerosols shows large regional and seasonal variations. In some regions and in particular seasons, the magnitude of direct forcing by anthropogenic aerosols can be comparable to the forcing of greenhouse gases. However, it shows that aerosols caused the cooling effect, rather than warming effect from global scale, which is different from greenhouse gases.