Use Of Firewood Research Articles

Unapređenje korišćenja biomase iz šumarstva u energetske svrhe u Srbiji

Serbia is one of the countries of Southeastern Europe with significant potentials for using biomass from forests and wood processing industry in the form of wood residues for the production of modern fuels. This type of biomass has not been used efficiently. One of the reasons is the traditional use of firewood for domestic heating needs despite its lower energy efficiency compared to pellets and briquettes. According to FAO methodology, the estimated energy potential of the available biomass derived from forests and wood processing industry in Serbia amounts to 1.53 Mtoe/year. According to the Energy Sector Development Strategy of the Republic of Serbia for the period by 2025 with projections by 2030 together with relevant Decisions on the energy balance determination, the degree of the use of potentially available biomass from forests and wood processing industry is around 1.02 Mtoe/year (66.7%). The remaining unused potential of this biomass is estimated at around 0.51Mtoe / year. Besides the study of the state of biomass from forests and wood processing industry, the paper provides recommendations on how to increase the utilization rate of this biomass in Serbia.

Study of C/N Ratio Effect on Biogas Production of Carica Solid Waste by SS-AD Method And LS-AD

Biogas is a renewable energy which can be used as an alternative source to replace fossil fuels. Recently, the use of energy has become an important issue because the oil sources and natural gas are depleting. Utilization of carica waste to produce biogas can reduce the consumption of commercial energy sources such as kerosene as well as the use of firewood. Biogas is produced by the process of organic material digestion by certain anaerobic bacterial activity in anaerobic digester. In this study we studied the influence of LS-AD and SS-AD methods, the effect of C / N ratio on biogas yield obtained and kinetics of biogas production reaction. The study was conducted by making a total solid variation of 7%, 9%, 11%, 13%, 19%, 21%, 23% and C/N ratio 25 and 30. The study started with carica waste collection process and examination of the total composition of solids and water content. Thereafter, calculation and determination of variation of C / N ratio by mixing the substrate with inoculum and urea into the reactor. Observe the volume of biogas produced every two-day intervals. The highest biogas production rate of 1.7825 ml/g TS day was obtained from carica solid waste variable by liquid state anaerobic disgestion and C/N 25.

The Anthropogenic Use of Firewood During the European Middle Pleistocene: Charcoal Evidence from Levels XIII and XI of Bolomor Cave, Eastern Iberia (230–160 ka)

ABSTRACTHuman control of fire is a widely debated issue in the field of Palaeolithic archaeology, since it involved significant technological innovations for human subsistence. Although fire evidence has been the subject of intense debate regarding its natural or anthropogenic nature, most authors agree that combustion structures represent the most direct evidence of human control of fire. Wood charcoal fragments from these contexts represent the fuel remains that result from humans’ collection of firewood, which means they can reveal significant behavioural and palaeoenvironmental information relevant to our understanding of Middle Palaeolithic societies. In this work, we present anthracological data derived from combustion structure 2 (level XIII, ca. 230 ka, MIS 7) and combustion structure 4 (level XI, ca. 160 ka, MIS 6) from Bolomor Cave, which are chronologically among the earliest combustion structures found in Europe. The present work discusses how the presence of black pine and / or scots pine in both levels sheds light on the characterisation of the local landscape. Additional analyses focussing on the pre- and post-depositional processes affecting charcoal preservation point to biodegradation patterns. The aim of this work is to provide the first discussion concerning the anthracological data derived from Bolomor Cave in order to contribute to the general debate regarding the use of fire during the European Middle Pleistocene.

Influence of roasting of shea kernels on their fat content and some quality characteristics of shea butter

In shea production zones in Sub-Saharan Africa, shea butter is mostly produced by women using traditional methods. Improvement of their practices would allow them to obtain better monetary returns for their activities. Roasting of crushed shea kernels is a processing step that has a major influence on the quantity and quality of extracted shea butter. Using a central composite face-centered design (CCFD), the effect of roasting, specifically roasting time and temperature was investigated. Both factors influenced fat content (44-53% dw) of the crushed kernels; colour characteristics and free fatty acid (FFA) content (0.5-3%) of the butter. In shea butter from differently roasted kernels, 58 volatile compounds were identified, of which 11 were quantitatively dominant, against 27 compounds in butter from unroasted kernels. The ideal practice according to the CCFD model is roasting at 171 ºC for 15 min, which resulted in a fat content of 49% dw of the kernels, a butter yield of 32%, a FFA of 1.2% of the butter, and a peroxide value of 3.2 meq O2/kg. This optimum roasting time is appreciably shorter than the current practice, suggesting that the use of firewood during traditional processing can be reduced.

The impact of a household biogas programme on energy use and expenditure in East Java

Biogas has been promoted as a renewable, cleaner and cheaper energy source. While there are several initiatives promoting the use of biogas, credible analyses of its effects on the use of alternative energy sources and energy related expenditure are limited. This study uses panel data from households engaged in dairy farming in rural East Java to assess the impact of a household level programme, which promotes the construction of digesters that produce biogas, on energy use and expenditures. Both a difference-in-difference analysis and a pipeline comparison show that the use of digesters leads to a sharp reduction in energy related expenditures and a reduction in the use of firewood and liquefied petroleum gas. However, without subsidies, the payback period of between 11 and 14years, albeit based only on reductions in energy costs accruing from investing in a digester, is perhaps too long to justify the investment.

Polusi udara dan kejadian penyakit kardiometabolik di Indonesia: analisis data IFLS tahun 2014

PurposeThe purpose of this study was to determine the relationship between indoor air pollution due to the use of firewood with cardiometabolic disease.MethodsThis research was a prospective cohort study conducted by comparing secondary data of the Indonesian Family Life Survey (IFLS) 2 to IFLS 5. Bivariate analysis used logistic regression and simple Cox regression tests. Multivariate analysis used Cox regression tests.ResultsResults showed exposure to air pollution due to the use of firewood accelerated the incidence of diabetes mellitus by 1.32 times, after controlling for the variables of smoking status, education level, body mass index, waist circumference, and domicile areas. The use of firewood was not correlated to the rate of onset of cardiovascular disease such as CHD and stroke.ConclusionThis research recommends LPG as a replacement fuel.

EVOLUÇÃO E CONCENTRAÇÃO DA PRODUÇÃO DE LENHA E CARVÃO VEGETAL DA SILVICULTURA NO BRASIL

O uso de lenha e carvão vegetal produzido a partir de plantios florestais tem apresentado tendências de crescimento na matriz energética brasileira. Essas fontes de energia renováveis têm sido foco de estudos e políticas públicas, visando à reestruturação das cadeias produtivas para o suprimento da demanda. O objetivo desse trabalho foi analisar a dinâmica mercadológica da lenha e carvão vegetal da silvicultura no Brasil, considerando a evolução da produção e dos preços, a concentração da produção e sua localização geográfica nos municípios e estados brasileiros. Utilizou-se como base de dados, a produção e o valor da produção municipal, obtidos junto ao Instituto Brasileiro de Geografia e Estatística (IBGE) e da Pesquisa da Extração Vegetal e Silvicultura (PEVS), considerando o período entre os anos 2001 e 2011. A taxa de crescimento da produção, a curva de Lorenz, o índice de Gini e a distribuição espacial em mapas da produção de lenha e carvão vegetal no Brasil foram as ferramentas de análise utilizadas. Os principais resultados evidenciam uma concentração da produção de lenha nos três estados do Sul do Brasil e do carvão vegetal em Minas Gerais. O aumento dos preços indica que a demanda não está sendo suficientemente suprida, sobretudo nos estados em que a produção ainda é insipiente.

An exploration into the household energy choice and expenditure in Bangladesh

Globally 1.3 billion people have no access to electricity, and 3.0 billion people rely on biomass and firewood for cooking. It is projected that by 2030, 1 billion people will have no access to electricity, and 2.4 billion people will continue to depend on firewood and biomass for cooking. It is widely documented that the use of firewood and biomass for household chores can have detrimental impacts on human health from indoor air pollution. The massive use of firewood and biomass can lead to deforestation and environmental degradation. Therefore, it is imperative to ensure the use of clean energy, such as electricity and gas for household chores. To encourage the use of clean energy, the factors that affect a household's choice of energy must be understood. Using information collected from more than 29,000 households in Bangladesh, the study econometrically demonstrates that the incidence and reliance on clean energy is high among the households headed by relatively highly-educated and wealthy heads and spouses. Particularly, households use clean energy progressively with an increase in income. Based on the findings, this study suggests specific policies to encourage the use of clean energy for household chores.

Multiple Regression Analysis on Influence Factors of Household Cooking Fuels in Indonesia

<em>One of the causes of the energy crisis is that the number of people is positively correlated with increased consumption of energy, especially fuel and electricity. The need for energy sources, especially for household purposes such as cooking, can be fulfilled by using LPG gas and firewood, as is well known, the LPG and firewood have been used by households in Indonesia since a long time. The variables that affect the use of LPG and firewood by households are "per capita GRDP", poor population, total area, number of islands, forests, and waters. By using multiple linear regression analysis, the prediction of the effect of these variables on the use of LPG and firewood can be obtained. Accuracy results obtained are 64% for both types of fuel. Meanwhile, the completeness of the data and the addition of other variables can improve the results of prediction accuracy.</em>

Dead wood gathering among Neanderthal groups: Charcoal evidence from Abric del Pastor and El Salt (Eastern Iberia)

We present here a new approach combining the microscopic characterization of fungal decay features and the fragmentation degree of the charcoal remains from Middle Palaeolithic combustion structures: features H4 and H11 from Abric del Pastor, unit IV (>75 ka BP) and features H50 and H57 from El Salt, unit Xb (ca. 52 ka BP), Eastern Iberia. The observation of wood degradation patterns that occurred prior to charring followed by their quantitative analysis according to previous experimental studies revealed differences between the alteration degrees of the firewood used in the hearths, highlighting the existence of firewood acquisition criteria based on dead wood gathering and also suggesting smoke-related functions. Coupled with fragmentation analyses, this method highlighted possible post-depositional processes affecting the higher degraded charcoals. These results lead us to propose a quantitative analysis of the fungal decay patterns on Middle Palaeolithic charcoal reinforcing the previous hypotheses about dead wood gathering among Neanderthal groups as an accessible and available resource in the surroundings. These data have significant implications for the interpretation of firewood use and management by Palaeolithic hunter-gatherers which was traditionally defined as an opportunistic activity according to the absence of selection criteria based on specific taxa.

Iron Age ovens and hearths from the hilltop of Quinta de Crestelos, Sabor Valley (NE Portugal): An archaeobotanical approach on typology, functionality and firewood use

The construction of Baixo Sabor Dam (NE Portugal), led to the discovery and excavation of the site of Quinta de Crestelos, with a human occupation ranging from the Early Palaeolithic to mid-20th century. Its Iron Age phase, found at the site's hilltop, revealed an unprecedented large number of combustion structures, comprehending several typologies of ovens and hearths, as well as refuse deposits in which archaeobotanical samples were recovered.Given the number and interpretative importance of these structures to the general understanding of the site, a holistic approach to their study was devised. This research combines the analysis of archaeobotanical samples with the morphological study of archaeological features comprising typological analysis. Such corpus of data is finally compared with ethnographical examples. The objectives of this study were to identify the main firewood species used inside the ovens, to define patterns of fuel use, to evaluate the existence of firewood selection - including both taxonomic outcomes and dendrological attributes - and their possible determining factors, as well as these structures functional purposes and patterns of use.The analysis of the carbonized plant content in these combustion structures displayed a diverse range of 15 taxa, with the majority of the ovens and hearths revealing predominance of Arbutus unedo, Cistus sp., Fraxinus sp., Juniperus sp. or Quercus evergreen. Triticum aestivum/durum is the main crop recovered in the studied samples, followed by Panicum miliaceum. Residual presences of Hordeum vulgare, Vicia faba, Vitis vinifera and Papaver sp. were recovered as well.The archaeobotanical results, together with the typology of the ovens and hearths, their spatial distribution and ethnographical examples, allowed the discussion of the structure's functionality, the identification of patterns and trends of their use according to different typologies and contexts and the recognition of possible firewood selection and storage practices. This study also provides a preliminary approach to the paleolandscape of the site during the Iron Age of NW Iberia.

Interdisciplinary approach to the landscape and firewood exploitation during the Holocene at La Garrotxa (Girona, NE Iberia)

This paper assesses the landscape and management of firewood resources during the Holocene at La Garrotxa (Girona, NE Iberia), a middle mountain region (400-1600 m a.s.l.) located within a volcanic area in the Pre-Pyrenees. Anthracological and palynological data from archaeological sites and lacustrine and peat deposits in this area have been considered in an interdisciplinary approach to the landscape and use of resources. According to Early Holocene palynological data, the landscape was characterised by the progressive expansion of forests, mainly dominated by conifers (pine and juniper) and deciduous trees (oak and hazel). The Holocene Climatic Optimum led to the culmination of forest expansion, with the dominance of dense oak forests, the landscape that the first farming societies found on arrival in this area. During the Middle to Late Holocene transition (c. 4000 cal BP), the expansion of evergreen sclerophyllous trees and the regression of broadleaf deciduous trees are recorded, in response to both climatic and anthropic causes. Deciduous Quercus and Buxus sempervirens were the most important taxa in all periods and areas, as shown in charcoal data from 26 archaeological levels. However, some other taxa had certain importance in some periods and sites. The variability observed between sites is discussed in terms of the availability of resources and the transformation of landscape evidenced in pollen records. This could explain the appearance of evergreen Quercus and other Mediterranean taxa in the Middle-Late Holocene anthracological record. The characteristics of the sites and socio-historical processes have also been considered in order to understand the use of firewood. In that sense, social necessities would have been the determining factor in planning timber and firewood procurement strategies rather than adapting to the environmental availability.

Study of prevalence of bronchial asthma in school children of 6–12 years of age in rural schools of Tumakuru district

Context: Pediatric asthma is a serious global health problem. The recent rise in the prevalence of asthma was associated with environmental pollution, urbanization, and the change in demography. Aims: The present study was undertaken to determine the prevalence of asthma in school children of rural parts of Tumakuru district and to study its association with different epidemiological factors. Settings And Design: This study is a questionnaire-based study (International Study of Asthma and Allergies in Childhood-Questionnaire) carried out in four randomly selected rural schools of Tumakuru district. Subjects And Methods: The questionnaire was distributed to all the children (n = 1750) and asked to fill the questionnaire with the help of their parents. These questionnaires were given standard scores to diagnose asthma. Other epidemiological factors were also recorded in the questionnaire and studied. Statistical Analysis Used: The statistical analysis was done using MSTAT software. Chi-square test was used to get the P value. P Results: The prevalence of asthma in our study was 3.12% (n = 51). Boys had a slightly higher prevalence 3.36% (n = 32) than girls 2.8% (n = 19). We found 58.8% (n = 30) of these asthmatics had allergic rhinitis and 19.6% (n = 10) had a history of atopy. Overall prevalence of allergic rhinitis was 8.3% (n = 137) and atopy was 1.13% (n = 23). Conclusions: The study showed 3.12% of children are affected with asthma, and its prevalence is significantly associated with epidemiological factors such as family history of allergy, high socioeconomic status, and use of fire wood for cooking.

O impacto da queima doméstica de biomassa lenhosa nos níveis de PM2,5 na cidade de Bragança, Portugal

We evaluated the influence of residential firewood combustion in the PM2,5 fraction of the atmospheric particulate matter in the city of Bragança, Portugal. Day and night time measurements were carried out between December 2013 and May 2014 in 35 urban sampling points. We also collected data on potential influencing factors of air particle concentration which we related statistically with PM2,5 observation data. Temporal variation and spatial patterning of atmospheric PM2,5 concentrations highlighted the contribution of PM2,5 emissions from domestic firewood use. Night time levels of PM2,5 were in general higher in areas of lower altitude, higher population density and higher firewood combustion intensity. Our results also indicated that during the study period, mean daily PM2,5concentrations were higher than the World Health Organization reference level in more than half of the city area. This study strengthened the importance of monitoring and controlling this source of atmospheric pollution in cities of high use of firewood for energy.

Potential of biogas production to reduce firewood consumption in remote high-elevation Himalayan communities in Nepal

Remote communities in the Nepalese mountains above 2500 m a.s.l. belong to the most precarious in the world. Inhabitants struggle for the minimum in terms of safe drinking water, food and sanitation. Reliable, affordable and clean energy for cooking, room heating and warm water for personal hygiene is often lacking and dependency on firewood very high. The remoteness and unlikeliness of electric grid connection in the coming decades make a diversified energy supply from renewable local resources crucial. Small-scale anaerobic digestion (AD) of organic substrates has been used for long in rural areas of developing countries to produce biogas as energy source and recover residue as organic fertilizer. AD is challenging at high elevations due to year around lower ambient temperatures and lower annual biomass production per area compared to lowlands. Nevertheless, examples of operational household AD exist even above 3000 m a.s.l. in the Andes. Here we compare firewood consumption with biogas potential from organic substrates in a community with 39 households at 3150 m a.s.l. in Jumla District, Nepal. In five households with varying numbers of members and animals kept, mean firewood use and its energy content per capita (cap) and day (d) were 2.1 kg or ca. 25 MJ in spring and 2.3 kg or ca. 28 MJ in winter. Easily available substrates include cow, sheep and horse dung from overnight shelters and human excrements from pit latrines, amounting on average to 1.7 kg wet weight (kgww ) cap−1 d−1 in spring and 2.2 kgww cap−1 d−1 in winter. Adjusted to normal conditions (Nm3 at 0 °C, 1013.15 hPa), these substrates yielded on average 0.08 Nm3 cap−1 d−1 biogas in spring and 0.12 Nm3 cap−1 d−1 in winter (35–60% methane content) in biochemical methane potential (BMPs) tests at 36 °C. This could provide up to 60% of basic cooking needs on average and up to 75% in a “typical” household in terms of members and animals kept. Of the overall thermal energy needs including also room heating ca. 10–20% could be covered, substituting 0.1–0.4 (mean: 0.2) kg firewood cap−1 d−1 . If only animal dung and human excrements are considered, no competition for resources arises as residues can still be used as organic fertilizer. This study supports the design and introduction of planned pilot digesters integrated into on-going community development including pit latrines for substrate availability, greenhouses as possible way of thermal insulation, and planned pico-hydropower plants to use excess electricity during the night for digester heating.

PM<sub>10</sub> Emissions from Cooking Fuels in Nigerian Households and Their Impact on Women and Children

A study was carried out on the type of fuels being used by households in Ibadan, a highly populated city in south-west Nigeria. Ekotedo, Agbeni, Bodija and Agbowo communities were selected through stratified random sampling, keeping in view of their socioeconomic background and population density. The study monitored 186 households for the type of fuel used for cooking and measured PM10 and the lung function of the respondents. The study population involved 130 women and 130 children. In addition, a community nurse carried out a physical and clinical examination of both the mothers and the children for respiratory and non-respiratory symptoms. The results showed that 37.7% used firewood, 33.1% used kerosene, 17.7% used charcoal and 11.5% used liquefied natural gas. Firewood use followed by charcoal emitted high PM10 at a level of 1640 μg/m3 and 1159 μg/m3, respectively. Charcoal users showed the lowest lung function values and gas users the highest value. A majority (78.5%) of the respondents complained of having cough during and after cooking. Some of them reported breathing problems, eyes and skin irritations. It is recommended that the communities be advised to switch over from the use of biomass fuels to natural gas so as to sustained the natural resources and again, reduced the health impacts of these cooking fuels on the population.

Biogas Stoves Reduce Firewood Use, Household Air Pollution, and Hospital Visits in Odisha, India

Traditional cooking using biomass is associated with ill health, local environmental degradation, and regional climate change. Clean stoves (liquefied petroleum gas (LPG), biogas, and electric) are heralded as a solution, but few studies have demonstrated their environmental health benefits in field settings. We analyzed the impact of mainly biogas (as well as electric and LPG) stove use on social, environmental, and health outcomes in two districts in Odisha, India, where the Indian government has promoted household biogas. We established a cross-sectional observational cohort of 105 households that use either traditional mud stoves or improved cookstoves (ICS). Our multidisciplinary team conducted surveys, environmental air sampling, fuel weighing, and health measurements. We examined associations between traditional or improved stove use and primary outcomes, stratifying households by proximity to major industrial plants. ICS use was associated with 91% reduced use of firewood (p < 0.01), substantial time savings for primary cooks, a 72% reduction in PM2.5, a 78% reduction in PAH levels, and significant reductions in water-soluble organic carbon and nitrogen (p < 0.01) in household air samples. ICS use was associated with reduced time in the hospital with acute respiratory infection and reduced diastolic blood pressure but not with other health measurements. We find many significant gains from promoting rural biogas stoves in a context in which traditional stove use persists, although pollution levels in ICS households still remained above WHO guidelines.

Biomass Cooking Fuels and Health Outcomes for Women in Malawi.

In sub-Saharan Africa, biomass fuels account for approximately 90% of household energy consumption. Limited evidence exists on the association between different biomass fuels and health outcomes. We report results from a cross-sectional sample of 655 households in Malawi. We calculated odds ratios between hypothesized determinants of household air pollution (HAP) exposure (fuel, stove type, and cooking location) and five categories of health outcomes (cardiopulmonary, respiratory, neurologic, eye health, and burns). Reliance on high- or low-quality firewood or crop residue (vs. charcoal) was associated with significantly higher odds of shortness of breath, difficulty breathing, chest pains, night phlegm, forgetfulness, dizziness, and dry irritated eyes. Use of high-quality firewood was associated with significantly lower odds of persistent phlegm. Cooks in rural areas (vs. urban areas) had significantly higher odds of experiencing shortness of breath, persistent cough, and phlegm, but significantly lower odds of phlegm, forgetfulness, and burns. With deforestation and population pressures increasing reliance on low-quality biomass fuels, prevalence of HAP-related cardiopulmonary and neurologic symptoms will likely increase among cooks. Short- to medium-term strategies are needed to secure access to high-quality biomass fuels given limited potential for scalable transitions to modern energy.

Problems with Biogas Implementation in Developing Countries from the Perspective of Labor Requirements

Most households in rural developing countries depend on firewood from public forests or agricultural bio-wastes for cooking. Public forests, though, are declining due to an increasing population and inefficient use of wood. Use of agricultural wastes on the other hand involves loss of soil nutrients since these resources are used as a substitute for inorganic fertilizers. Biogas energy can be an alternative in providing clean energy for cooking as well as improving soil fertility with the slurry. However, the labor spent on producing biogas can limit its use as a source of energy and fertilizers. Therefore, this study aims to determine the labor requirement of different mono and co-digestion biogas energy systems. The assessment is made by using simple models involving different schemes of resources collection and transportation based on reported relevant literature. The analysis shows that biogas production can be labor intensive when transportation of feedstock, water, and slurry is involved. Transporting these resources over a one kilometer (km) distance requires about ten times the amount of time spent on firewood collection and transportation. The largest part of the time for biogas production activities is spent on water collection and transportation. Low labor biogas production is possible only if all the resources are available nearby (not transported). One of the advantages of the biogas energy system is to use the slurry for soil enrichment. However, this can only be realized when the slurry is converted to compost or directly applied on nearby lands. In general, biogas production involving resources (feedstock, water and slurry) transportation is not a viable alternative to save the time spent on the traditional use of firewood. However, a community biogas system involving resource system integration is an option to provide clean energy with acceptable labor requirements of production.

Urban heat islands and damage to respiratory health in elderly in a high desert town in northern Chile.

Introduction Urbanization allows the generation of urban heat island (UHI). In the city of Calama, Chile, with high desert climate, UHI were identified in summer and winter. We examined possible associations between UHI and chronic diseases of the elderly people. Methods Environmental temperature data loggers (HOBO) were installed in different parts of the city during 2014. Interpolations according to IDW-Inverse Distance Weighting method using ArcGIS were performed. Two UHI were defined for summer and winter, defining two areas of highest risk for extreme temperatures People aged &gt; 65 years apparently healthy and living in Calama were eligible. All participants (n = 103) answered an epidemiological survey. The outcomes measured were asthma, chronic bronchitis, emphysema and chronic obstructive pulmonary diseases (COPD). We did logistic regressions to estimate the risk to being diagnosed with any of these diseases. The independent variable was the residence or not within the area defined by the UHIs; other covariates were particulate matter (PM), type of heating, smoking, and occupational history. Results We identified that residence in areas where to occur UHI is not related to increased risk for diagnosis of asthma, emphysema or COPD. Residing in the area of the city where UHI in winter is identified was associated with increased risk of chronic bronchitis (OR 0.97, 95% CI 0.3- 1.05). Other risk factors were defined: for asthma elderly that have used coal for heating in the past and exposure PM10 (lag -3 day); smoking for lung emphysema and use of firewood for heating in the past for COPD. Conclusions Various meteorological, geographic and urban morphologic factors can lead to the establishment of UHI. However, associations with health damage in elderly represent a methodological challenge. The weak association measured for chronic bronchitis may be due to sample size but also requires improved measurement of all historical exposures in this vulnerable group.