Associate Professor Sunil Kumar Joshi

Dahl A

Joshi Sk

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Kathmandu University Medical Journal (2010), Vol. 8, No. 2, Issue 30, 276-280
Short Communication
Received Date: 14 Feb, 2010 Accepted Date: 19 June, 2010
Correspondence
Dr. Sunil Kumar Joshi
Associate Professor
Department of Community Medicine
Kathmandu Medical College
E-mail: drsunilkj@gmail.com
Biomass combustion and potential health effects in the developing 
countries
Joshi SK1, Dahl A2, Kristensen T3, Roldin P4
1Department of Community Medicine, Kathmandu Medical College, Sinamagal, Nepal, 2Ergonomics and Aerosol 
Technology, Lund University, Sweden, 3Department of Chemistry, University of Copenhagen, Denmark, 4Division of 
Nuclear Physics, Lund University, Sweden 
Biomass combustion is a very large source of aerosol particles on a global scale. It is estimated 
that 20 % of the black carbon and 30 % of the organic 
carbon aerosol mass emissions are due to wild land fi res 
and intentional burning of agricultural waste in Asia. 
However in those numbers residential fuel combustion 
is not included, which is considered a larger source of 
black carbon and organic carbon aerosol particles in 
developing countries. When it comes to residential fuel 
combustion it covers combustion of coal, kerosene, gas 
and biofuel in stoves, cookers and heaters1. In regions 
where the climate forces people to preserve heat in their 
houses, food is often cooked over open fi re indoors. 
The hot emissions from the fi re are then directly used to 
heat the house, instead of using a heat exchanger such 
as a chimney. When wood or coal is used as fuel the 
particle concentration indoor reach hazardous levels. 
Especially women and their small children are exposed 
to the emissions, since they spend much time inside and 
often close to the fi re place2-7. This article elucidates 
the health effects related to biomass combustion in 
developing countries with focus on aerosol particles 
and the current knowledge in this fi eld.
Chemical and physical properties of biomass 
combustion aerosols
It is hard to characterise the chemical and physical 
properties of the aerosol from biomass combustion in 
general since it depends on the regional composition of 
the biomass, the temperature of the combustion and the 
amount of oxygen available for the process. In addition 
the aging of the aerosol particles depends on ambient 
conditions. For instance the condensation or evaporation 
of semi-volatile organic and inorganic vapors are 
strongly temperature and concentration dependant, and 
the lifetime of the nucleation and Aitken mode particles 
will depend on the coagulation sink of the background 
aerosol. To shed some light on this topic, focus will be 
on situations where people are exposed to the aerosol 
close to where the biomass combustion takes place e.g. 
in homes during cooking and heating. In the developing 
countries solid fuel is dominating in the households 
and consists primarily of wood and agricultural 
residues8. It can be seen from fi g. 1 that use of solid 
fuel dominates in developing countries such as India, 
Afghanistan, Bangladesh and most African countries. 
The airborne particle mass concentration, measured as 
total suspended particulate matter (TSP), in households 
with open fi re is often in the order of milligrams per 
cubic meter. As reference, the occupational TSP limit in 
Sweden is 5 mg/m3.
Wood consists primarily of the two polymers cellulose 
(50-70 % by weight) and lignin (~30 % by weight)9. 
In addition organic compounds with low molar mass 
and inorganic salts are present in wood. During 
combustion, pyrolysis occurs and the polymers break 
apart and produce a variety of smaller molecules. If the 
combustion is very effi cient most of the carbonaceous 
matter will be transformed into CO2. However wood 
combustion in homes is seldom effi cient and lots of 
partially oxidised organic compounds will be present 
both in the particle and gas phase. 
To investigate the physical composition of the aerosol 
people are exposed to, measurements should ideally 
be performed in the households. A study conducted in 
the households in Costa Rica during cooking period 
revealed that a stack was connected to the stove where 
wood was combusted10. A typical mass size distribution 
of the measured aerosol particles with two modes can 
be seen in fi g 2.
With regard to health impact it is probably of high 
relevance also to investigate the particle number 
concentrations down to ~10 nm since the smallest 
particles are effi ciently deposited in the lungs and may 
277
Fig 2: Size distribution of aerosol particles in Costa Rican rural households measured with an Aerodynamic Particle 
Sizer (APS)10
Fig 1: Map of solid fuel use2
Fig 3: Particle number size distribution from birch wood combustion with a stove. Circles indicate average values and 
the solid line median values. 90- and 10- percentile covered by the gray area12
Particle diameter (nm)
10 100
278
reach all the way to the alveoli11. A typical particle 
number size distribution from birch wood combustion 
in a stove can be seen in fi g. 3. There seems to be a 
(broad) maximum in the number concentration for 
diameters around 50 nm but with lots of smaller 
particles present. It is however questionable how much 
this size distribution resembles the combustion in open 
fi re places in homes in developing countries. Often 
the fuel is combusted under poor conditions. In many 
households in the developing countries there is no stack 
or chimney. This will lead to a larger fraction of bigger 
aerosol particles and due to the large coagulation sink 
probably to less smaller particles.
To assess the health effects of the aerosol particles it is 
also necessary to know the chemical composition. The 
chemical composition is very important with regard to 
toxicity of the particles. Most wood combustion in homes 
will lead to production of soot in the particle phase. In 
addition to soot a great variety of organic compounds 
will be present in the particle phase. Among the organic 
compounds that can be found in the particle phase are 
the Polycyclic Aromatic Hydrocarbons (PAHs) that 
are known to be mutagenic and carcinogenic. Among 
the multitude of oxygenated organics are the phenols 
found in the particle phase. Several of the phenols 
are known to be irritant, carcinogenic, mutagenic and 
teratogenic. In addition inorganic elements (e.g. KCl) 
are often present in the particle phase2. These salts will 
make the particles grow to larger sizes when exposed 
to high relative humidity in the lung, and thereby affect 
the deposition probability of the particles. Apart from 
the particles the bio-mass smoke is reported to contain 
a large number of harmful gas phase species, mainly 
carbon monoxide (CO), Sulfur Dioxide (SO2), Oxides 
of Nitrogen (NOx), Ozone (O3), Formaldehyde (HCHO) 
and PAHs14. 
Techniques for health relevant particle 
characterisation and exposures
The reference method for measuring airborne particles 
mass concentration is fi lter sampling. Often fi lter 
sampling is replaced by light scattering instruments, 
because it provide less labor intense handling. One 
serious problem with light scattering techniques is that 
they must be calibrated to the target aerosol. Therefore 
less skill demanding methods, such as fi lter sampling, 
probably are more robust and less prone to error. 
Observed health effects
Biomass smoke exposure increases the diseases such as 
Acute Lower Respiratory Illness (ALRI) in childhood 
(pneumonia); Asthma, Chronic Bronchitis (CB); and 
Chronic Obstructive Pulmonary diseases (COPD); 
etc. in children and adults13. The pollutants from the 
biomass smoke cause infl ammation of lungs, reduce 
ciliary clearance, and impair immune response15. 
Similarly, particulate matter, gaseous pollutants, and 
other chemicals present in the indoor air may cause 
damage to nasal olfactory and respiratory mucosa16. 
Exposure of pregnant women to high level of CO may 
cause intrauterine growth retardation of the foetus17. 
There are evidences that exposure to ultrafi ne particles 
may lead to development of cardiovascular diseases18,19. 
Housewives and small children, who stay in front of the 
fi re, for even a short period of time, are potential targets 
for serious health outcomes in the long run. Exposure 
to CO, O3 and NO2 are known to be asphyxiant and 
irritants respectively. Whether there is reason to expect 
synergistic effects together with aerosol particles is not 
well investigated.
Biological mechanisms
There are several mechanisms anticipated to elucidate 
the adverse health effects of particles. It has been 
assumed that exposure to particles lead to infl ammation, 
cytokine and chemokine release, production of white 
blood cells, production of oxygen free radicals in 
the lungs leading to endotoxin mediated cellular and 
tissue responses, stimulation of irritant receptors and 
covalent modifi cation of key cellular enzymes. PM 
exposure is likely linked to infl ammation through the 
generation of reactive oxygen species and oxidative 
stress. It is still not clear which particle components 
are responsible for producing reactive oxygen species, 
but there is increasing evidence that pro-oxidative 
organic hydrocarbons, such as polycyclic aromatic 
hydrocarbons, quinines, and transition metals such as 
copper, vanadium, chromium, nickel, cobalt and iron 
have important role20, 21. Those reactive oxygen species 
can damage cellular proteins, lipids, membranes, and 
DNA. In order to prevent this damage, cells utilise 
stored up antioxidant such as glutathione. Depletion of 
glutathione can induce a state of cellular stress, called 
oxidative stress. Such an oxidative stress can increase the 
production of antioxidant enzymes through activation 
of a transcription factor Nrf222. If the organism fails 
to overcome oxidative stress, it leads to the activation 
of additional intracellular chemicals that regulate the 
expression of cytokine and chemokine genes21,23. These 
cytokine and chemokine are produced locally in target 
tissues as well as systemically, and initiate widespread 
pro infl ammatory effects. 
Control measures
There is a large need for improved technologies 
and education in developing countries to be able to 
reduce the exposure to biomass combustion in indoor 
environments. Actions that can improve the situation 
are better ventilation, stoves, fuels and behaviour 
changes24. Most research has focused on how to make 
the stoves more effi cient and emit less smoke. However 
279
there is also a need to study the actual conditions at 
which the stoves are operated. Often the conditions are 
far from optimal and the gain which better technology 
may not be as good as it could be25. Another action that 
is believed to have large potential benefi ts is to shift 
fuel from unprocessed biomass fuels to charcoal25-26. It 
would be even better, in a health perspective, if the solid 
fuels were replaced with nonsolid fuels. However this is 
not likely within the near future25. 
Conclusions
Although the biological mechanism that can explain 
the health effects related to PM exposure is not well 
known there are a large number of studies which has 
linked severe health effects to PM exposure from 
biomass combustion in indoor environments. These 
fi ndings should be more than enough to perform 
control measures to improve the indoor environment in 
developing countries. It can also be argued against the 
necessity to conduct fi eld measurements when particle 
levels are clearly hazardous, but different governmental 
programmes targeting the health of poor people compete 
against each other. Pure water and disease prevention 
often catches most attention, as acute effects are more 
obvious to the public and policy makers. Poor indoor 
air is a problem that the exposed population has lived 
with for generation and therefore the problem is not 
clearly noticed. It is therefore important to conduct fi eld 
measurements even if the results are obvious. Especially 
measurement should be conducted in conjunction with 
programmes on indoor air improvements, in order to 
observe and quantify the effects. Research has been 
focussed on technological improvements of stoves and 
chimneys however little attention has been drawn on 
how the technologies are implemented in the homes. 
In developing countries the most vulnerable groups 
are generally children and women who spend much of 
their time indoor preparing the food. We should address 
the need for research on cost-effi cient technologies 
which improve the indoor environment, especially 
during cooking which generally cause the highest PM 
exposure levels. This together with education of women 
and children has the potential to save hundred thousand 
of lives every year in the developing countries.
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Biomass combustion and potential health effects in the developing countries

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Biomass combustion and potential health effects in the developing countries

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