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An estimation of emissions from domestic biofuel combustion over southern AfricaMulaudzi, Silas Khakhathi 22 February 2007 (has links)
Student Number : 0306319G -
MSc Research Report -
School of Geography, Archaeology and Environmental Studies -
Faculty of Science / Combustion of fuel wood, charcoal and non-woody biofuels is a daily practice for
about half of the world’s population. Combustion of biofuel is a major source of trace
gases, with domestic biomass burning contributing about 17% carbon dioxide (CO2),
13% carbon monoxide (CO) and 6% nitrous oxide (N2O) to the global budget. In
Africa, where there is a growing population, domestic biofuel emissions are a
particularly important source of trace gases. The most important source of biomass
fuels in Africa is wood fuel (wood and charcoal), crop residues and animal dung. In
this project, the amount of domestic biofuel used in rural households across southern
Africa was measured daily over a nine month period. This data was used to estimate
the trace gas production from domestic fires throughout Southern Africa. Results
indicate that RSA contributed the most trace gases to the regional budget (9.12 Tg C
yr-1 of CO2, 0.89 Tg C yr-1 of CO, 10.77 Gg N yr-1 of NO and 30.25 Gg C yr-1 of CH4)
and Botswana the least (0.25 Tg yr-1 of CO2, 0.02 Tg yr-1 of CO, 0.29 Gg yr-1 of NO
and 0.83 Gg yr-1 of CH4). Fuel wood is the dominant fuel type used in all southern
African countries, whereas charcoal was used in RSA, Mozambique and Zambia and
maize residues in Malawi only. CO2 was the gas emitted in the largest quantities, with
fuel wood and charcoal in RSA contributing the most (8.71 Tg yr-1 and 0.41 Tg yr-1
respectively), while CO2 from maize residue was highest in Malawi (0.82 Tg yr-1).
More trace gases were emitted in the dry season than wet season particularly in
Malawi and Mozambique. For the entire region the annual CO2, CO, NO and CH4
emissions produced 23.0 Tg C, 2.2 Tg C, 29.4 Gg N and 81.4 Gg C, respectively.
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Poluição atmosférica derivada de queimadas de cana-de-açúcar no estado de São Paulo / Air Pollution Derivate from Sugarcane Burning in Sao Paulo StateSilveira, Thiago Souza 12 September 2014 (has links)
O presente trabalho teve como objetivo a análise do transporte de poluentes atmosféricos gerados na queima da cana-de-açúcar no estado de São Paulo durante o ano de 2010, pois a cultura canavieira no estado é muito forte, abastecendo o mercado alimentício, energético e de bebidas. Porém, apresenta um grave problema com a queima da plantação antes da colheita, gerando poluição e enfraquecendo o argumento de energia limpa. Baseado nas teorias: dos Sistemas e dos Geossistemas, na dinâmica atmosférica e no uso de modelagem como instrumento de análise; além do levantamento dos dados atmosféricos e de poluição aferidos, mapeamento da área e das queimadas, concluiu-se que há áreas com picos de poluição ao longo do ano; a pluma de poluentes normalmente vai para outros estados como Minas Gerais e Mato Grosso do Sul e ocorreram eventos generalizados de queima de biomassa, principalmente entre agosto e setembro, porém com a mudança na direção do vento, geralmente quando está prestes a chegar uma frente fria, quando esses poluentes são direcionados para a Região Metropolitana de São Paulo e Campinas; confirmando a hipótese observando a distribuição e concentração de poluentes segundo os dados de circulação atmosférica e de poluição / This study has the objective to analyze the air pollution transport from sugarcane burn in Sao Paulo State in 2010, as the planted areas are very vast, it supplies the food, energy and beverage industry. By the other hand, it presents severe problem of burning culture before the harvest period, it causes air pollution and disqualify the clean energy argument. Based on the System and Geosystem theories, on atmospheric dynamic and using models as analysis instrument; in addiction getting atmospheric and pollution data observed, mapping sugarcane and the burned area, it was concluded there were parts with peaks of pollution during this year, the plume of pollutants normally are transported to other States as Minas Gerais and Mato Grosso do Sul and also there were several and generalized events of biomass burn principally in August and September, despite the wind change generally when it is upcoming a cold front, those pollutants are directed to Metropolitan Region of Sao Paulo and Campinas; confirming the hypothesis observing the concentration and distribution of them by the air circulation and pollutants data
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\"Os efeitos de aerossóis emitidos por queimadas na formação de gotas de nuvens e na composição da precipitação na Amazônia\" / Effect of biomass-burning emitted aerosols on cloud droplets formation and rainwater chemistry in the Amazon BasinPauliquevis Junior, Theotonio Mendes 18 November 2005 (has links)
Este trabalho teve como objetivo investigar a relação entre produtos de atividades antropogênicas na Amazônia e sua influência no efeito indireto dos aerossóis no clima. Para isso, foi feita uma caracterização físico-química detalhada dos aerossóis naturais e de queimadas na Amazônia e procurou-se compreender como estes diferentes tipos de aerossóis se comportam como Núcleos de Condensação de Nuvens. Foi estudado também a influência dos aerossóis de queimadas na composição química da precipitação e no transporte de nutrientes. Visando atingir estes objetivos, foram feitas medidas em regiões distintas da Amazônia com relação ao impacto por atividades antropogênicas, principalmente queimadas. Foi possível observar em várias circunstâncias uma relação entre a composição do material particulado e da precipitação, o que nos permitiu concluir que as emissões antropogênicas influenciam significativamente a composição da precipitação. Foram identificadas as principais componentes que afetam a composição do material particulado em suspensão na Amazônia, e concluimos que o material particulado originado de emissões biogênicas é predominante em regiões preservadas, com pequena contribuição também de poeira de solo e transporte de aerossóis marinhos. Em regiões sob influência de atividades antropogênicas, observou-se que a composição dos aerossóis e da precipitação é afetada mesmo na estação úmida. No estudo das propriedades físicas e químicas das partículas de aerossol que são relevantes para o seu papel como Núcleos de Condensação de Nuvens, concluiu-se que a distribuição de tamanho é mais importante do que a composição química das partículas, devido ao fato das emissões de novas partículas por queimadas ocorrer predominantemente acima do diâmetro seco de ativação. A composição química só foi importante em valores de supersaturação baixos (< 0.2%), o que significa que esse efeito pode ser importante para nuvens estratiformes, onde o valor máximo de supersaturação é baixo, devido a baixa velocidade de ascensão das parcelas. A exportação de nutrientes devido ao transporte em larga escala de aerossóis de emissões de queimadas se mostrou particularmente crítica com relação às quantidades de fósforo que estão sendo perdidas irreversivelmente pela floresta amazônica, que foi cerca de 7 vezes maior do que a quantidade reposta por deposição úmida. Essa perda de fósforo pode ser crítica para o ecossistema em longo prazo. / The main objective of this study was to investigate the relationship between anthropogenic emissions in the Amazon basin and the indirect aerosol effect on climate. A detailed study of physical and chemical properties of natural and biomass burning aerosols was conducted, in order to understand how these completely different aerosols behave as Cloud Condensation Nuclei (CCN). It was also investigated the influence of biomass burning aerosols in chemical composition of precipitation, and transport of nutrients. The measurements were carried out in completely different regions respect to the impact of anthropogenic activities, especially biomass burning emissions. The analysis of aerosols and rainwater chemistry showed that anthropogenic emissions have a significant influence in the composition of precipitation. Factor analysis was applied to perform source identification, and the conclusion is that at remote and free of anthropogenic emission areas, the most important contribution was from biogenic emissions, with a small contribution of soil dust and marine aerosols advection. It was quite different at regions under influence of anthropogenic activities, where measurements showed a clear anthropogenic influence even during wet season both in aerosols and precipitation chemistry. In the study of hygroscopic properties of aerosol particles, the main conclusion was that size distribution of particles is the most important parameter to determine the ability of aerosols to act as CCN, because most of biomass burning emission are particles bigger than the activation diameter. Chemical composition was an important factor only if supersaturation is below 0.2%, because in this supersaturation range the activation diameter is extremely sensible to small changes in supersaturation. Transport of nutrients due to largescale transport of biomass burning aerosols was specially critical concerning phosphorus exportation, estimated as 7 times the apportionment through wet deposition. Continuous exportation of phosphorus can be a long term limitation to the forest ecosystem, if biomass burning activity maintain its present levels.
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Estudo do perfil atmosférico com as técnicas lidar e análise de filtros de impactação no período de queimadas e relação com internações por doenças respiratórias em Porto Nacional e estado do Tocantins (2008-2016) / Study of atmospheric profile with lidar and analysis of impactation filters on the burning season and relation with hospitalizations for respiratory diseases in Porto Nacional and Tocantins State (2008-2016)Moraes, Ana Paula Faria 27 April 2017 (has links)
A relação entre a poluição atmosférica e a saúde vem sendo estudada há muitos anos em grandes cidades ao redor de todo o mundo e recentemente em regiões de intensa queima de biomassa. Porto Nacional é um município do estado do Tocantins que vem sofrendo expressivo crescimento em decorrência da expansão da cultura de grãos. Está incluso no bioma cerrado, onde é costume o uso do fogo para limpeza dos campos de agricultura. O lidar é uma ferramenta que vem sendo usada para estudo do perfil óptico atmosférico mundialmente, não havendo registros de sua utilização no cerrado. Junto com o lidar, costuma-se também utilizar a análise de filtros de impactação de aerossóis para determinação da composição e concentração de material particulado, o qual está relacionado ao desenvolvimento de doenças respiratórias.Também não havia sido investigada a correlação das queimadas no Tocantins com a saúde respiratória da população. Esse estudo visa analisar o perfil óptico e químico dos aerossóis provenientes das queimadas na região e correlacionar as internações por doenças respiratórias com o número de focos de incêndio no município de Porto Nacional e no estado do Tocantins. Para isso, foram utilizados um sistema lidar móvel, dados dos sistemas MODIS e CALIPSO e filtros de impactação de aerossóis instalados em Porto Nacional, dados de queimadas do Instituto Nacional de Pesquisas Espaciais e de saúde do banco de dados do Departamento de Informática do Sistema Único de Saúde. Foram registradas com o uso do lidar camadas de aerossóis em agosto de 2015 a uma altitude de 2 a 3,5 km, com predomínio de poeira contaminada, resultado da mistura de poeira da crosta e produto de queimadas. A análise química dos aerossóis mostrou aumento de black carbon e óxidos de alumínio e sílicio em setembro/2013 e aumento de óxido de enxofre em dezembro de 2015. Através das análises de modelos lineares generalizados e correlação de Pearson, não foi encontrada relação entre o número de focos de incêndio e as internações por doenças respiratórias, apesar da significância estatística dos dados colhidos ter sido confirmada pelo stepwise. Sugere-se aprofundamento do estudo através da coleta direta de dados de saúde respiratória diários e de atendimento em pronto socorro. / The relationship between air polution and health has been studied for many years in big cities worldwide and in biomass burning regions more recently. Porto Nacional is a city from Tocantins state where the grain culture is promoting an expressive development. It is included in the cerrado biome (brazilian savanna), where the use of fire to clean the agriculture fields is a custom. Lidar is a tool that has been worldwide used to study the optical atmosphere profile, but there wasnt found registers of its use at cerrado Along with lidar, it has also been used the analysis of aerosol impactation filters to determinate the composition and concentration of particulate material, which is related to the development of respiratory diseases. The correlation between burnings and respiratory health also had not being investigated in Tocantins. This study aim to analyse the optical and chemical profile of the burning aerosols at the region and to co-relate the respiratory diseases hospitalizations to the burning spots at Porto Nacional and Tocantins state. For this, a mobile lidar system and aerosol impactation filters were installed in Porto Nacional. Data from MODIS and CALIPSO were also used. The burning data were extrated from the National Institute of Spacial Researches and the health data from the database of Unic System of Health TI. Aerosol layers were registered by lidar at an altitude of 2-3.5 km, predominating polluted dust, resulting from a mix of crust dust and burning aerosol. The aerosol chemical analysis showed an increase of black carbon and aluminum and silicon oxides in september 2013 and an increase of sulfur oxide in december 2015. It wasnt found relation between the burning spots and respiratory diseases hospitalizations, using generalized linear models, despite of the statistical significance of collected data be assured by stepwise analysis. It is suggested the study deepening through of the daily and direct respiratory health data collection and from admissions instead of hospitalizations.
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Experimental Constraints on Fe Concentrations in Biomass Burning AerosolsJanuary 2019 (has links)
abstract: Atmospheric deposition of iron (Fe) can limit primary productivity and carbon dioxide uptake in some marine ecosystems. Recent modeling studies suggest that biomass burning aerosols may contribute a significant amount of soluble Fe to the surface ocean. Existing studies of burn-induced trace element mobilization have often collected both entrained soil particles along with material from biomass burning, making it difficult to determine the actual source of aerosolized trace metals.
In order to better constrain the importance of biomass versus entrained soil as a source of trace metals in burn aerosols, small-scale burn experiments were conducted using soil-free foliage representative of a variety of fire-impacted ecosystems. The resulting burn aerosols were collected in two stages (PM > 2.5 μm and PM < 2.5 μm) on cellulose filters using a high-volume air sampler equipped with an all-Teflon impactor. Unburned foliage and burn aerosols were analyzed for Fe and other trace metals using inductively coupled plasma mass spectrometry (ICP-MS).
Results of this analysis show that less than 2% of Fe in plant biomass is likely mobilized as atmospheric aerosols during biomass burning events. The results of this study and estimates of annual global wildfire area were used to estimate the impact of biomass burning aerosols on total atmospheric Fe flux to the ocean. I estimate that foliage-derived Fe contributes 114 ± 57 Gg annually. Prior studies, which implicitly include both biomass and soil-derived Fe, concluded that biomass burning contributes approximately 690 Gg of Fe. Together, these studies suggest that fire-entrained soil particles contribute 83% (576 Gg) of Fe in biomass burning emissions, while plant derived iron only accounts for at most 17%. / Dissertation/Thesis / Masters Thesis Chemistry 2019
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Chemical characterization of biomass burning and sea spray aerosolJayarathne, Thilina 01 May 2017 (has links)
Particulate matter (PM) suspended in air varies in size from nanometers to micrometers and contains a wide range of chemical components, including organic compounds, black carbon (soot), inorganic minerals and metals. Atmospheric aerosols are generated from either primary sources like volcanic eruptions, re-suspended soil dust, sea spray, vegetative detritus, fossil fuel and biomass combustion emissions; or secondary atmospheric reactions via gas-to-particle conversion of atmospheric gases. Particle size, abundance, and chemical composition determine how a particle interacts with light and other atmospheric constituents (e.g. gases, water vapor) in addition to its impact on human health. While atmospheric scientists have been working on characterizing atmospheric aerosols for many years, major gaps persist in understanding the properties of many globally-important sources. This dissertation provides new understanding of the chemical composition of biomass burning and sea spray aerosols.
PM emissions from biomass burning vary by fuel, and depend on fuel type and composition, moisture content, and combustion conditions. Although biomass smoke is critically important in global climate and local-regional health impacts, the physical and chemical composition of biomass burning aerosol is still not fully understood in the case of peat, agricultural residues and cooking fires. The Fire Laboratory at Missoula Experiments (FLAME) were designed to fulfill these gaps to improve our understanding in both historically undersampled and well-studied fuels while adding new instrumentation and experimental methods to provide previously unavailable information on chemical properties of biomass burning emissions. Globally-important biomass fuels were combusted in a controlled environment, and PM was chemically characterized to compute fuel based emission factors (EF) as the amount of chemical species released per unit mass of fuel burned. We showed that chemical composition of PM varies for different fuel types and certain fuels types (e.g., peat and ocote) emit considerably high concentrations of polycyclic aromatic compounds that are associated with negative health effects. We also showed that PM from biomass smoke contains fluoride for the first time, at approximately 0.1% by weight. With respect to the annual global emissions of PM due to biomass burning, this makes biomass burning an important source of fluoride to the atmosphere. Further, peatland fire emissions are one of the most understudied atmospheric aerosol sources but are a major source of greenhouse gases globally and cause severe air quality problems in Asia. This thesis provides the first field-based emissions characterization study, for samples collected at peat burning sites in Central Kalimantan, Indonesia. Using these EFs and estimates of the mass of fuel burned, it was estimated that 3.2 - 11 Tg of PM2.5 were emitted to atmosphere during 2015 El Niño peat fire episode which is ~10 % of estimated total annual PM flux for biomass burning. Overall, these studies computed more representative EFs for previously undersampled sources like peat, and previously unidentified chemical species like fluoride that can be used to update regional and global emission inventories.
The concentration and composition of organic compounds in sea spray aerosol (SSA) alters its optical properties, hygroscopicity, cloud condensation, and ice nucleation properties and thus affects Earth’s radiative budget. In the past, SSA has been difficult to characterize, because of low concentrations relative to background pollutants. Nascent SSA was generated during a mesocosm, using a wave-flume at the University of California, San Diego and was characterized for saccharides and inorganic ions in order to assess their relative enrichment in fine (PM2.5) and coarse (PM10-2.5) SSA and sea surface microlayer (SSML) relative to seawater. For the first time, we showed that saccharides comprise a significant fraction of organic matter in fine and coarse SSA contributing 11 % and 27 %, respectively. Relative to sodium, saccharides were enriched 14-1314 times in fine SSA, 3-138 times in coarse SSA, but only up to 1.0-16.2 times in SSML. The saccharide and ion concentration in SSML and persistent whitecap foam was quantitatively assessed by another mesocosm study performed under controlled conditions. We demonstrated that relative to sodium, saccharides were enriched 1.7-6.4 times in SSML and 2.1-12 times in foam. Higher enrichment of saccharides in foam over the SSML indicates that surface active organic compounds become increasingly enriched on aged bubble film surfaces. Similarly, we showed that fine SSA contains saccharides characteristic of energy-related polysaccharides, while coarse SSA contains saccharides that are characteristic of structure-related polysaccharides. The ultrafiltration studies showed that structure-related polysaccharides effectively coagulate to form large particulate organic matter and size is likely the reason for their exclusion from small SSA. The enrichment of organic species in SSML, foam and SSA led to an enrichment of inorganic ions probably through chelation with organic molecules. Mean enrichment factors for major ions demonstrated the highest enrichment in fine SSA for potassium (1.3), magnesium (1.4), and calcium (1.7). Consequently, due to these organic and inorganic enrichments, SSA develops a significantly different chemical profile compared to seawater. These improved chemical profiles of SSA should be used to develop laboratory proxies to further study the transfer of organic matter across the ocean-air interface and the physical properties of SSA. .
Overall, the results presented in this dissertation provide new chemical profiles for previously understudied emission sources like peatland fire emissions, and previously unquantified chemical species like F- in biomass burning emissions and enrichment of saccharides and ions in SSA. These data could be used in updating regional and global emission inventories, atmospheric modeling and human exposure studies.
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Investigating water soluble organic aerosols: sources and evolutionHecobian, Arsineh N. 05 April 2010 (has links)
An existing method for the measurement of atmospheric gaseous species was modified to collect data on aerosol concentrations. Data from biomass burning events in different regions (Canada, the Arctic and California) were collected during April to July, 2008 and the concentrations and evolution of secondary organic aerosols were discussed. And finally, data on the light absorbing properties of water soluble organic aerosols were collected in Atlanta, GA and compared with filter data for the same properties. The results presented in this thesis showed that a negative ion chemical ionization mass spectrometer (CIMS), can be modified by the addition of a thermally denuded inlet to measure aerosol phase sulfuric acid. This system can also be used to measure other aerosol phase organic acids. In the biomass burning plumes studied in the second part, no clear indication of formation of secondary aerosol or gaseous species was observed, except for peroxyacetyl nitrate (PAN). Filter data collected from FRM sites in the Southeastern U.S. showed that biomass burning is the most dominant source of water soluble light absorbing carbonaceous aerosol in this region. The data from a study in Atlanta, GA showed that the online PILS-LWCC-WSOC system might be used for measurements of light absorbing properties of aerosols and WSOC.
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The sources, formation and properties of soluble organic aerosols: results from ambient measurements in the southeastern united states and the los angeles basinZhang, Xiaolu 03 July 2012 (has links)
900 archived FRM filters from 15 sites over the southeast during 2007 were analyzed for PM2.5 chemical composition and physical properties. Secondary components (i.e. sulfate aerosol and SOA) were the major contributors to the PM2.5 mass over the southeast, whereas the contribution from biomass burning varied with season and was negligible (2%) during summer. Excluding biomass burning influence, FRM WSOC was spatially homogeneous throughout the region, similar to sulfate, yet WSOC was moderately enhanced in locations of greater predicted isoprene emissions in summer. On smaller spatial scale, a substantial urban/rural gradient of WSOC was found through comparisons of online WSOC measurements at one urban/rural pair (Atlanta/Yorkville) in August 2008, indicating important contribution from anthropogenic emissions.
A comparative study between Atlanta and LA reveals a number of contrasting features between two cities. WSOC gas-particle partitioning, investigated through the fraction of total WSOC in the particle phase, Fp, exhibited differing relationships with ambient RH and organic aerosols. In Atlanta, both particle water and organic aerosol (OA) can serve as an absorbing phase. In contrast, in LA the aerosol water was not an important absorbing phase, instead, Fp was correlated with OA mass. Fresh LA WSOC had a consistent brown color and a bulk absorption per soluble carbon mass at 365 nm that was 4 to 6 times higher than freshly-formed Atlanta soluble organic carbon. Interpreting soluble brown carbon as a property of freshly-formed anthropogenic SOA, the difference in absorption per carbon mass between the two cities suggests most WSOC formed within Atlanta is not from an anthropogenic process similar to LA.
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The suitability of the IASI instrument for observing CO from spaceIllingworth, Samuel Michael January 2011 (has links)
This thesis presents a methodological approach to developing the capability of the Infrared Atmospheric Sounding Interferometer (IASI) instrument to inform on the atmospheric concentrations of carbon monoxide (CO), focussing on three key studies: 1) an assessment of the radiometric accuracy of the instrument; 2) the development of the University of Leicester IASI Retrieval Scheme (ULIRS) to convert measured radiances into a CO product; and 3) an investigation into the reliability and possible use of the ULIRS product. An intercomparison between the radiances as measured by the IASI and Advanced Along Track Scanning Radiometer (AATSR) instruments is performed, and absolute differences at 11 µm of less than 0:1K are observed. Given the radiometric behaviour across the IASI instrument as a whole, it is also concluded that the IASI instrument is radiometrically accurate to < 0.3K in the 12 and 4.7 µm spectral regions. A retrieval scheme, the ULIRS, is developed with explicit digital elevation and emissivity information, and a correction for solar surface reflection with a high resolution solar spectrum. Typical random errors over the African region relating to the profiles are found to be ~10% at 5 and 12 km, and on the total columns to be ~12 %. The ULIRS dataset and the operational CO products from the Measurements Of Pollution In The Troposphere (MOPITT) are inter-compared. A methodology which uses the same a priori statistics, and which reduces the smoothing bias between the two sets of data shows that there is only a small bias between the ULIRS and MOPITT V4 products. A simplified top-down approach to estimating CO emissions from fires is also presented, highlighting the need for a better understanding of the correct detection of burnt area from space-based measurements.
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Transport pathways of fire generated tracers to the upper troposphere as determined by A-Train satellite measurementsHuang, Lei, active 2013 15 July 2013 (has links)
Convective and long-range transport of air mass controls the global distributions and impacts of the pollutants generated in limited source regions. However, an observational characterization of such transport based on long-term satellite data has been difficult in part because adequate satellite measurements were not available until recent years and lack of an automated method for identifying the transport pathways. My dissertation addresses this problem through three steps: First, I developed a method to automate the identification of two pathways that are responsible for the transport of biomass burning generated tracers from the surface to the upper troposphere (UT). I focused on carbon monoxide (CO) because it has a relatively long lifetime in the atmosphere, and thus it is commonly used as a tracer of convective and long-range mass transport. Next, I applied this method to investigate the relative importance of the two pathways in determining the seasonal pattern of UT CO distribution. Results show that the seasonality of CO concentrations in the tropical UT mainly reflects the seasonality of the “local convection” pathway, because the “local convection” pathway typically transports significantly more CO to the UT than the “advection within the lower troposphere followed by convective transport” pathway. Then, I investigated the impacts of transport pathways on the interannual variation of tropical UT CO concentration. Results show that the interannual variation of CO in the tropical UT is dominated by UT CO anomaly over Southeast Asia related to the El Niño-Southern Oscillation, and the average mass of CO transported per event of “local convection” is the factor that accounts for the UT CO difference between two El Niño periods.
After that, I began to address the transport of more complex pollutants such as aerosols. First, the seasonal and diurnal variations of the vertical distributions of aerosol properties were characterized through a statistical analysis of aerosol profile data. Then, the transport pathways associated with the aerosol layer at the tropopause level over Asian area during boreal summer were investigated through back-trajectory model analyses. Three major pathways were found and the occurrence frequency of each pathway was analyzed and discussed. / text
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