Ozone production due to emissions from vegetation burning

Ozone has been observed in elevated concentrations by satellites over areas previously believed to be background. There is meteorological evidence, that these ozone plumes found over the Atlantic Ocean originate from vegetation fires on the African continent.In a previous study (DECAFE-88), we have investigated ozone and assumed precursor compounds over African tropical forest regions. Our measurements revealed large photosmog layers at altitudes from 1.5 to 4 km. Both chemical and meteorological evidence point to savanna fires up to several thousand km upwind as sources.Here we describe ozone mixing ratios observed over western Africa and compare ozone production ratios from different field measurement campaigns related to vegetation burning. We find that air masses containing photosmog ingredients require several days to develop their oxidation potential, similar to what is known from air polluted by emissions from fossil fuel burning. Finally, we estimate the global ozone production due to vegetation fires and conclude that this source is comparable in strength to the stratospheric input.     

Carbonyl sulfide emissions from biomass burning in the tropics

Carbonyl sulfide emissions from biomass burning have been studied during field experiments conducted both in an African savanna area (Ivory Coast) and rice fields, central highland pine forest and savanna areas in Viet-Nam. During these experiments CO₂, CO and C₂H₂ or CH₄ have also been also monitored. COS values range from 0.6 ppbv outside the fires to 73 ppbv in the plumes. Significant correlations have been observed between concentrations of COS and CO (R ²=0.92,n=25) and COS and C₂H₂ (R ²=0.79,n=26) indicating a COS production during the smoldering combustion. COS/CO₂ emission factors (COS/CO₂) during field experiments ranged from 1.2 to 61×10^–6 (11.4×10^–6 mean value). COS emission by biomass burning was estimated to be up to 0.05 Tg S/yr in tropics and up to 0.07 Tg S/yr on a global basis, contributing thus about 10% to the global COS flux. Based on the S/C ratio measured in the dry plant biomass and the COS/CO₂ emission factor, COS can account for only about 7% of the sulfur emitted in the atmosphere by biomass burning.     

On uncertainty in the computation of global emissions from biomass burning

Estimation of global atmospheric emissions from biomass burning has used a variety of procedures, most of which involve chain multiplication. The terms in the chain of inference are often poorly quantified, and in many cases there is reason to suspect bias and intercorrelation between terms. The leading estimates appear to have been conservative; however, uncertainty explodes when imprecisely known (coefficient of variation >0.3) terms are multiplied. Thus little confidence can be had in the precision of current best estimates. The situation can be improved through a combination of spatial disaggregation and process-oriented modeling.     

Atmospheric abundance of HULIS during wintertime in Indo-Gangetic Plain: impact of biomass burning emissions

This study reports for the first-time the ambient concentrations of HULIS mass (HULIS-OM, Humic-like substances) and HULIS-C (carbon) in PM₁₀ (particulate matter with aerodynamic diameter?≤?10 μm) from the Indo-Gangetic Plain (IGP at Kanpur, wintertime). HULIS extraction followed by purification and isolation protocol with methanol: acetonitrile (1:1 v/v) on HLB (Hydrophilic-Lipophilic Balanced) cartridge has been established. Quantification of HULIS-C was achieved on a total organic carbon (TOC) analyser whereas HULIS-OM was determined gravimetrically. Consistently high recovery (> 90%) of HULIS-C based on analysis of Humic standard (sodium salt of Humic acid) suggested suitability of our established analytical protocol involving solvent extraction, purification and accurate quantification of HULIS. HULIS-OM varied from 17.3–38 μg m^?3 during daytime and from 19.8–40.6 μg m^?3 during night in this study. During daytime the HULIS-OM constituted 20–30% mass fraction of OM_Total and 10–15% of PM₁₀ mass. However, a relatively low contribution of HULIS-OM has been observed during the night. This observation has been attributed to higher concentrations of OM and PM₁₀ in night owing to nighttime chemical reactivity and condensation of organics in conjunction with shallower planetary boundary layer height. Strong correlation of HULIS-C with K⁺_BB (R²?>?0.80) and significant day-night variability of HULIS-C/WSOC ratio in conjunction with air-mass back trajectories (showing transport of pollutants from upwind IGP) suggest biomass burning emission and secondary transformations as important sources of HULIS over IGP. High-loading of atmospheric PM₁₀ (as high as 440 μg m^?3) with significant contribution of water-soluble organic aerosols (WSOC/OC: ~ 0.40–0.80) during wintertime highlights their plausible potential role in fog and haze formation and their impact on regional-scale atmospheric radiative forcing over the IGP.     

Field study of the emissions of methyl chloride and other halocarbons from biomass burning in Western Africa

A field study of trace gas emissions from biomass burning in Equatorial Africa gave methyl chloride emission ratios of 4.3×10^–5±0.8×10^–5 mol CH₃Cl/mol CO₂. Based on the global emission rates for CO₂ from biomass burning we estimate a range of 226–904×10⁹ g/y as global emission rate with a best estimate of 515×10⁹ g/y. This is somewhat lower than a previous estimate which has been based on laboratory studies. Nevertheless, our emission rate estimates correspond to 10–40% of the global turnover of methyl chloride and thus support the importance of biomass burning as methyl chloride source. The emission ratios for other halocarbons (CH₂Cl₂, CHCl₃, CCl₄, CH₃CCl₃, C₂HCl₃, C₂Cl₄, F-113) are lower. In general there seems to be a substantial decrease with increasing complexity of the compounds and number of halogen atoms. For dichloromethane biomass burning still contributes significantly to the total global budget and in the Southern Hemisphere biomass burning is probably the most important source for atmospheric dichloromethane. For the global budgets of other halocarbons biomass burning is of very limited relevance.     

Multispectral remote sensing of biomass burning in West Africa

Remote sensing measurements provide a vauable means of determining the extent of burning areas and of estimating the overall distribution of pollutant sources (identified from experimental studies) in time and space. This distribution has to be taken into account in the boundary conditions of chemistry atmospheric models.Recent methods developed for the remote sensing of active fires in tropical or temperated forest zones, have been found to be completely inadequate for fire detection on West African savannas. In order to accurately estimate the active fire distribution in the function of different sorts of West African savannas (Sahelian, Sudanian and Guinean) and forests, a multispectral methodology has been developed based on NOAA/11-AVHRR satellite data, with the purpose of eliminating as much as possible the problems related to large surface heterogeneity, confusion and bias, produced by clouds, smoke, haze, background emissivities, etc.Unlike other methods, the results show that the multispectral method, in spite of its selectivity, provides realistic results, and does not under- or over-estimate the number of fires that can be sensed by the satellite. Consequently, this methodology is more appropriate than the simplest ones for a systematic sensing of this phenomenon.     

Spatio-temporal variation of biomass burning sources over South and Southeast Asia

In this study, we have investigated the seasonality and long-term trends of major biomass burning (BB) sources over South and Southeast Asia (S-SE Asia). The activities of BB and related emissions show bi-modal seasonality in S-SE Asia. From January to May period, the BB dominates in the northern hemisphere parts of S-SE Asia. From July to September, the activities shift to the southern hemisphere where the emissions from Indonesian and Malaysian islands make largest contributions. Overall, the activities of BB are lowest during October–December period in S-SE Asia. The seasonality of BB intensity and rain are just opposite in the phase over India. The climatological (1997–2008) emissions of carbon monoxide (CO), oxides of nitrogen (NOx) and non-methane hydrocarbons (NMHCs) show strong spatio-temporal variation. The trends show large inter-annual variations with highest and lowest values during years 1997 and 2000, respectively. In the southern hemisphere parts of S-SE Asia mainly in Indonesia, the intensity of biomass fires has been modulated by the large scale climatic phenomena like El Niño and Southern Oscillation (ENSO). The annual emissions of trace gases in southern hemisphere region during the El Niño years exceed to those for the normal years. The estimates for northern hemisphere region during the La Niña years were significantly higher than those for the normal years. The Model for Ozone And Related Chemical Tracers (MOZART) simulations of columnar CO and NOx tend to capture the prominent features of BB emissions in S-SE Asia. The impacts of extensive fires in Indonesia during El Niño year of 2006 compared to a normal year of 2005 were clearly seen in the MOZART-4 simulations of both CO and NOx.     

Oligomerization of levoglucosan by Fenton chemistry in proxies of biomass burning aerosols

Reactions of levoglucosan with produced from Fenton chemistry were studied in solution serving as a proxy for biomass burning aerosols. Two modes of oligomerization (≤2000 u) were observed for reaction times between 1 and 7 days using matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOF-MS) and laser desorption ionization time-of-flight mass spectrometry (LDI-TOF-MS). Single-mass unit continuum mass distributions with dominant −2 u patterns were measured and superimposed by a +176/+162 u oligomer series. This latter oligomer pattern was attributed to a Criegee rearrangement (+14 u) of levoglucosan, initiated by , forming a lactone (176 u). The acid-catalyzed reaction of any ROH from levoglucosan (+162 u) forms an ester through transesterification of the lactone functionality, whereupon propagation forms polyesters. Proposed products and chemical mechanisms are suggested as sources and precursors of humic-like substances (HULIS), which are known to possess a large saccharic component and are possibly formed from biomass burning aerosols (Andreae, Global Biomass Burning, MIT Press, Cambridge, Massachusetts, 3–21, 1991).     

Aging of savanna biomass burning aerosols: Consequences on their optical properties

During the FOS-DECAFE experiment at Lamto, Ivory Coast, in January 1991, various ground studies were undertaken simultaneously in order to investigate the physical and chemical characteristics of smoke emitted by savanna biomass burning. Here we present sunphotometer ground-based results which allow the measurements of the spectral optical depth between 450 and 850 nm, the atmospheric water vapour content and the particle size distribution spectrum. The carbonaceous content of the savanna biomass burning aerosols is also investigated. This is the first time that the physical characteristics of particles emitted by savanna plumes are obtained from ground-field studies. All the results suggest that a rapid aging of the smoke occurs first hundred metres from the savanna fire èmission source. They show a relationship between the optical properties of smoke and the chemical aging of the aerosols primarily due to particle growth and a loss of organic material relative to the black carbon content.     

The balance and redistribution of potential vorticity within the ocean

The balance and redistribution of potential vorticity in a turbulent, inhomogeneous ocean is examined analytically. In the first part of the paper, we derive a vorticity conservation law describing the way in which vorticity is lost and gained in a closed ocean basin. We show that the potential vorticity within the ocean can only be altered by molecular diffusion at the bounding surfaces, or by the advective input of vorticity via the turbulent velocity at the free upper surface. An imbalance between these two effects within the body of the ocean leads to a net temporal change in the total potential vorticity, which we are able to express in terms of the temporal changes in the magnitude and orientation of a vector formed by the surface velocity and density and the earth's rotation. Finally, the steady-state balance of integrated vorticity is found to be between the surface wind-stress curl and the molecular diffusion at the solid boundaries.We then consider the localized redistribution of potential vorticity in detail. In recent papers, Green (1970) and Welander (1973) have purported to show that an internal redistribution of potential vorticity can give rise to important forces in the atmosphere (Green) and the ocean (Welander). Using their recipe leads in some cases to such unphysical results as a breakdown of the laws of conservation of angular momentum. Such consequences cause us to question the validity of the argument, and lead us to a close examination' of Welander's mechanism. (Green's argument is more general and does not lend itself to such close examination.) Our investigation reveals important flaws not only in Welander's argument, but also in the classical mixing-length theory of Prandtl (1925) and of Taylor (1915) on which it is modelled. More specifically, the internal redistribution process presented in these theories is found to be incomplete since it fails to take into account the lift force exerted on individual parcels of fluid as they are transported by the turbulent motions. Inclusion of these lift forces not only permits the unification of the classical mixing-length theories, but also shows that the forces claimed by Welander do not in fact arise.     

生物质燃烧颗粒物中有机质及源解析研究进展

对近年来有关生物质燃烧排放的颗粒物中有机化合物和有机示踪物的研究进展进行了综述,分析了各国学者根据有机示踪物研究城市大气颗粒物中生物质燃烧和其他排放源对空气污染的贡献,对以后的相关研究具有借鉴意义．     

Estimates of gross and net fluxes of carbon between the biosphere and the atmosphere from biomass burning

In order to estimate the production of charcoal and the atmospheric emissions of trace gases volatilized by burning we have estimated the global amounts of biomass which are affected by fires. We have roughly calculated annual gross burning rates ranging between about 5 Pg and 9 Pg (1 Pg = 10¹⁵ g) of dry matter (2–4 Pg C). In comparison, about 9–17 Pg of above-ground dry matter (4–8 Pg C) is exposed to fires, indicating a worldwide average burning efficiency of about 50%. The production of dead below-ground dry matter varies between 6–9 Pg per year. We have tentatively indicated the possibility of a large production of elemental carbon (0.5–1.7 Pg C/yr) due to the incomplete combustion of biomass to charcoal. This provides a sink for atmospheric CO₂, which would have been particularly important during the past centuries. From meager statistical information and often ill-documented statements in the literature, it is extremely difficult to calculate the net carbon release rates to the atmosphere from the biomass changes which take place, especially in the tropics. All together, we calculate an overall effect lof the biosphere on the atmospheric carbon dioxide budget which may range between the possibilities of a net uptake or a net release of about 2 Pg C/yr. The release of CO₂ to the atmosphere by deforestation projects may well be balanced by reforestation and by the production of charcoal. Better information is needed, however, to make these estimates more reliable.Now at the Max-Planck-Institute for Chemistry, Mainz, FRG.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

湿位涡在陕西一次强对流天气中的应用分析

利用常规观测资料、NCEP再分析资料、云顶亮温资料,对2006年6月24—25日陕西强对流天气过程分析,结果表明：高空低槽、中低层切变线是这次强对流天气的主要影响系统,中尺度对流云团是造成此次强对流天气的直接原因。强对流发生前,近地面存在逆温层。强对流发生发展与湿位涡的时空演变有很好的对应关系,对流层高低层湿位涡“正负区垂直叠加”的配置是强对流天气发展的有利形势。强对流天气发生在低层湿位涡正压项等值线密集的零线附近及湿斜压项的正值区。     

Sustainable agriculture and the production of biomass for energy use

Modern bioenergy is seen as a promising option to curb greenhouse gas emissions. There is, however, a potential competition for land and water between bioenergy and food crops. Another question is whether biomass for energy use can be produced in a sustainable manner given the current conventional agricultural production practices. Other than the land and water competition, this question is often neglected in scenarios to meet a significant part of global energy demand with bioenergy. In the following, I address this question. There are sustainable alternatives, for example organic agriculture, to avoid the negative environmental effects of conventional agriculture. Yet, meeting a significant part of global energy demand with biomass grown sustainably may not be possible, as burning significant quantities of organic matter—inherent in bioenergy use—is likely to be incompatible with the principles of such alternatives, which often rely on biomass input for nutrient balance. There may therefore be a trade-off between policies and practices to increase bioenergy and those to increase sustainability in agriculture via practices such as organic farming. This is not a general critique of bioenergy but it points to additional potential dangers of modern bioenergy as a strategy to meet significant parts of world energy demand.