Indoor Air Pollution (IAP)

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Cooking on open fire, Indonesia 2011, Katharina Wiedemann.jpg

Indoor air pollution (IAP) also called household air pollution (HAP) in developing countries is a major environmental and public health challenge. According to data from the World Health organisation[1] as many as 3.8 million people die each year as a result of it worldwide. This can be compared with one death every 8 seconds. Most of the death occur in middle and low income countries in South East Asia with 1.69 million death, followed by the Western Pacific regions 1.62 million, Africa 600,000, Eastern Mediterranean region 200,000, Europe 99,000, and in the Americas 81,000 death. In high income countries 19,000 people died because of IAP. IAP/HAP has to be distinguished from outdoor ambient air pollution (AAP) which supposedly caused the death of another 3.7 million people in 2012.
Indoor sources of IAP/HAP are cooking and heating with solid fuels, burning candles or oil lamps, fuel-burning space heaters and tobacco smoke. Of special importance is inefficient and insufficiently vented cooking and heating with solid fuels (biomass and coal) on simple stoves or open fires. Burning these fuels in inefficient stoves results in poor combustion efficiency and high levels of emissions of health-damaging pollutants including both fine and coarse particulate matter, carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), and a variety of organic air pollutants (e.g., formaldehyde, 1,3-butadiene, benzene, acetaldehyde, acrolein, phenols, pyrene, benzopyrene, benzo(a)pyrene, dibenzopyrenes, dibenzocarbazoles, and cresols). In a typical solid fuel stove, about 6–20% of the solid fuel is converted into toxic emissions (by mass). The exact quantity and relative composition of the emissions is determined by various factors such as the fuel type and moisture content, stove type and the way the stove and fuel is used by the cook. [2] Most measurements of emissions and the corresponding literature focus on the concentration of particulate matter of different sizes (e.g., PM2.5, PM10) and carbon monoxide (CO), which are main products of incomplete combustion and are considered to pose the greatest health risk. According to estimations 2.9 billion people used solid fuels (mainly biomass, in the form of wood, charcol, dung, and crop residue) for cooking and other heating purposes in 2012 [3]. Around 80% of them reside in rural and 20% in urban areas. Because much of the burning of solid fuels is carried out indoors in environments with insufficient ventilation, millions of people, primarily poor women and children face serious health risks.

Health Effects

According to WHO there is consistent evidence that exposure to household air pollution is a major risk factor leading to acute lower respiratory infections (ALRI) in children under five, and ischaemic heart disease (IHD), stroke, chronic obstructive pulmonary disease (COPD) and lung cancer (LC) in adults.[4]In addition, the smoke from burning biomass is also causing eye irritations.
Smoke in form of particulate matter with particle diameters of less than 10 micrometers in diameter penetrate deep into the lungs. At sizes of 2.5 micrometers particles can enter the finest parts of the lungs. Ultrafine particles get even into the bloodstream. Exposure to particulate matter has short-term effects such as nose, throat and lung irritation, coughing, sneezing, runny nose and shortness of breath as well as more severe effects on the respiratory system such as pneumonia and asthma. Children are especially affected by ALRI. A child exposed to smoke in the home is two to three times more likely to catch pneumonia. Globally, pneumonia and other acute lower respiratory infections represent the single most important cause of death in children under five years. Exposure to IAP more than doubles the risk of pneumonia. Women exposed to indoor smoke are three times as likely to suffer from chronic bronchitis and other obstructive pulmonary diseases (COPD) than women who cook and heat with electricity, gas and other cleaner fuels. In addition, there are indications, that indoor smoke is also causing tuberculosis, cataracts, low birth weight and high infant mortality. Most of the victims of IAP are women and children, as they are exposed to the source of indoor smoke and the large associated health risks the most. Women spend daily three to seven hours near the stove with their kids breathing polluted air during cooking. At the early age of the children, when they are newborns or infants, their immature lungs and immune systems make them particularly vulnerable. Over 10 million children aged under five years die every year – 99% of them in developing countries.[5] According to Global Disease Study 2010 the relationship between exposure to pollutants and health effects is often not linear. In the case of PM2.5 an exposure response model estimating health effects by using relative risk (RR) information for ALRI, IHD,stroke, COPD, and LC is assuming a kind of exponential saturation curve. The health risks rise significantly with increasing concentrations of PM2.5at lower levels. The effect becomes less pronounced at higher PM2.5 exposure levels. This has major implications for strategies to reduce health risks by controlling air pollution at high exposure concentration levels.
The actual health impacts of pollutants depends on the inhaled dose which is the result of the inhalation rate (m³/hr) x the average exposure concentration (mg/m³)x exposure duration (hr).

Regulations and Recommended Maximum Concentrations of PM and CO

Due to the severe health risks of air pollutants, many governments and international organisations have defined maximum concentrations of pollutants for emissions allowed from certain types of pollution sources, for the ambient air (immissions) and for workplaces or short periods of exposure. This chapter only presents the data for PM and CO as they are most widely used to measure the degree of air pollution.
The following table gives an overview about current standards.[6]

Pollutant Standard Averaging Time Country/Region
150 μg/m³

50 μg/m³

40 μg/m³

150 μg/m³
24 hrs

70 μg/m³

50 μg/m³ 24 hrs WHO

20 μg/m³ annual WHO
35 μg/m³

15 μg/m³c

25 μg/m³c
annual EU

75 μg/m³c
24 hours

35 μg/m³c
annual China

25 μg/m³c 24 hrs WHO

10 μg/m³c annual WHO
35 ppm (40 mg/m³)

9 ppm (10 mg/m³)
8-hour USA

9 ppm (10 mg/m³)

10-20 mg/m³

35 mg/m³ 1-hour WHO

10 mg/m³ 8-hours WHO

The table shows a certain variability of the air quality standards in different countries and regions. The variability is mainly caused by different short and long term air quality targets of the countries, the path to obtain these targets considering resources, location, economic structure etc..
In the case of PM2.5 WHO has defined three interim air quality targets for annual outdoor PM2.5., taking into consideration that achieving the full target will not be realistic for most developing countries in a short period of time. The interim air quality targets are: Level 1: 35, level 2: 25, and level 3: 15 μg/m3 per year.

IAP/HAP, KAP and Cooking Systems

The term indoor air pollution (IAP) refers to toxic contaminations of the air in buildings (homes and workplaces). It is identifical with the term household air pollution (HAP) if referred to the air quality of dwellings.  The concentration of pollutants is higher indoors compared to the ambient air pollution, if sources inside the house emit pollutants that do not diffuse rapidly to the outside.

The level of exposure to IAP is not uniform in dwellings but depends on the air quality in the different rooms or areas in the building and the time a person is spending in the different rooms. Thus, the term kitchen air pollution refers specifically to the cooking place where concentrations of pollutants can be significantly higher than in the living room.
In many industrial countries maximum concentrations of pollutants are defined for the air quality at workplaces but not for household situations under diferent denominations such as  AGW (Arbeitsplatzgrenzwerte), MAK (Maximale Arbeitsplatzkonzentration), MAC (Maximaal Aanvaardbare Concentratie) VLEP (Valeur limites d'exposition professionelle), WEL (Workplace Exposure Limits), PEL (Permissible Exposure Limit) and TLV (Threshold Limit Values). An overview about the different regulations are given by the International Labour Organisation on the following website 

In several countries different types of maximum workspace concentrations are defined:

  1. maximum average exposure values on the basis of a 8h/day, 40h/week work schedule
  2. maximum short-term exposure limits for a duration of 1h, 15-30 minutes or less
  3. maximum absolute exposure limits that should not be exceeded at any time. 

Most occupational exposure limits refer to the average values. This means that concentrations can be higher for periods lower than 8 hours. As a general rule: worker exposure levels may exceed 3 times the average level  for no more than a total of 30 minutes during a workday, and under no circumstances should they exceed 5 times the average. [7] 

For respirable dust, which penetrates the alveoles (comparable to PM2.5), occupational exposure limits in industrialized countries generally vary between 1.25 mg/m3 and 5 mg/m3.. For inhalable dust (comparable to PM10) the respective values are between 10 and 15 mg/m3.

For carbon monoxide, many countries established an average exposure limit of 35 mg/m3. The short-term maximum level for CO is generally higher,  in the UK for example 225 mg/m3.[8]   

Household air pollution caused by using solid fuels and simple inefficient stoves for cooking and heating, and by lighting  homes with kerosene and simple wick lamps, is in many ways comparable to occupational air pollution. Both household practices produce high levels of pollutant emissions in specific areas for a limited period of time during the day. Cooking is generally done 3-4 times a day with a total time of roughly 4 hours. The cook and other people in the kitchen area are exposed to the pollution level at the cooking place only during that time. When leaving the kitchen for the rest of the day they are exposed to air quality situations, where the emissions from the stove are diluted up to a insignificant level. The same is applicable for using kerosene as fuel for lighting. The lights are used for a limited period of time in the evening and early morning in specific rooms. The exposure to pollutants depends again on the length and frequency of a person using these rooms. Generally these are less than 8 hours a day. 

Based on this considerations, average maximum exposure limits of 5 - 10 mg/m3 for respirable dust, of 15 - 30 mg/m3 for inhalable dust and of 70 mg/m3 for carbon monoxide seem acceptable for the 2 billion people which use solid fuels for cooking

The typical 24-hour levels of PM10 in biomass-using homes (kitchen) in Africa, Asia or Latin America range from 300 to 3,000 μg/m3. Peaks during cooking may be as high as 10,000 μg/m3 especially during the beginning ignition process when combustion is especially incomplete.[9] Kitchen Air pollution for PM 2.5 average 100 - 1000 μg/m3  with peak levels of up to 2500 μg/m3.

Remote rural areas are likely to have better ambient air quality (even when biomass use is higher) than urban or periurban or well-connected rural locations where a more intensive use of commercial fuels and the higher traffic affect stronger the ambient air quality.

WHO Guidelines for Indoor Air Quality and Emission Rate Targets (ERTs)

Reducing Indoor Air Pollution (IAP)

Measures to reduce IAP in developing countries:

  • Changing the fuel, switching to cleaner alternatives, the so-called BLEENS (biogas, liquid petroleum gas(LPG), electricity, ethanol, natural gas or solar energy)
  • Improving the design and construction of traditional stoves to improve the combustion (improved stoves, advanced stoves clean stoves) 
  • Improving the ventilation in the kitchen (smoke hoods that vent pollutants to the outside, ventilation through windows, doors, chimney)
  • Inducing behavioral changes (using a pot lid when cooking to speeds up the cooking, drying wood before burning it, awareness-raising activities).

Cleaner Fuels / Improved Cookstoves

The most effective way to reduce smoke in the home is to switch to cleaner fuels (liquid petroleum gas, kerosene or biogas). It’s also possible to improve the air quality and promote energy efficiency and environmental sustainability by promoting improved cooking stoves.

Gasifier stove can reduce kitchen air pollution values to 100-200 μg/m3 with peak levels of up to 1500 μg/m3.

Chimney, Smoke Hoods

The huge majority of people in developing countries who are still cooking on open fires are often too poor to change to improved stoves and cleaner fuels or have no access to modern combustibles. Where the use of biomass, wood or charcoal remains predominant, and the indoor environment remains subject to high levels of smoke, other alternatives have to be found to improve air quality and related health issues.

The use of chimneys will remove all emissions from the stove away from the cooking space if there are no leaks in the stove and chimney. A functional chimney will thus protect household members from pollutants caused by burning fuels under the condition that it is regularly cleaned.   The installation of a smoke hood can aslo be extremely effective in improving the air quality in houses, too. This applies especially, when traditional biomass burning stoves are being used without a chimney. In addition, some efficient stoves may not be clean and therefore employing a smoke hood allows for health benefits coupled with lower operating costs. Moreover, in some cultures, an open fire plays a special social role as a place around which the family gathers, traditional meals are cooked or other important rituals. As a result the introduction of improved cookstoves is difficult and a smoke hood serves as the best alternative for improving indoor air quality.

However, chimneys and smoke hoods will have only limited effects in areas where homes are tightly clustered together with minimal space between adjacent houses as in the case of urban slums. Under such conditions, the emissions vented through the chimney or hood lead to significant outdoor air pollution around the houses which affects the indoor air quality, too.

What prevents households from applying the different methods to reduce IAP?

  • male and female sometimes like the smoky taste of food. Therefore, they are not interested in 100% smokeless cooking.
  • some household cook inside with little ventilation to avoid higher firewood consumption because of the wind;
  • households often do not have a stock of cut wood drying over months as the stock is difficult to be protected against theft;
  • the use of chimney is difficult for thatched roofs;


SDGs: Reaching the goal to reduce this extremely harmful IAP would significantly help to achieve several of the internationally agreed Sustainable Development Goals (see Energy and the SDGs), especially Goal 7, 2, 3, and 13.

Targets include

  • access to clean energy (Indicator 7.1.2 Proportion of population with primary reliance on clean fuels and technology),
  • improve nutrition (food needs to be cooked) and increase agricultural productivity (2.1.1 Prevalence of undernourishment),
  • health issues like the child mortality rate, (3.2.1 Children under 5 mortality rate and 3.9.1: Mortality rate attributed to household and ambient air pollution), and
  • climate change (Up to 25% of black carbon emissions come from burning solid fuels for household energy needs).

Many organizations are already working on this field to make improvements in this issue.

In absolute, the number of people relying on biomass has not decreased yet, and will not in the future neither.

Deaths due to IAP stay constant at around 3 million per year: Exposure to indoor air pollution from cooking with solid fuels has declined since 1990, but in 2013 still two-fifths of the world’s population was exposed. In low-income countries, population growth (exposing a growing number of people) offset the declines in death rates. This means that the overall death caused by indoor air pollution declined by 38% from 75 per 100,000 people in 1990 to 47 per 100,000 people in 2013. However, the total number of deaths associated with indoor air pollution has mostly remained constant at about 2.9 million per year, mostly in low and lower-middle-income countries.[10]

Child mortality rates dropped from 100 in 1990 to 72 per 1,000 live births in 2008, (not) reaching the MDG goal to decrease by two thirds (1990-2015).[11]

The Cost of Air Pollution

Indoor air pollution reduces development potentials and quality of life through the health related risks. Therefore, there is also a business case for Governments to invest in reducing IAP.

Global costs are very high: The cost of exposing people to air pollution amounted some $5.11 trillion in welfare losses of the world’s economy in 2013 (this figure includes ambient and household pollution). Welfare losses due to indoor air pollution grew by 63% since 1990, because the percentage of population depending on solid fuels for cooking did not change fast enough to (over)compensate other developments like population growth.[10]

Sub-Saharan Africa and South Asia are most affected by IAP: Indoor air pollution is the biggest cause of welfare losses (% of GDP) in South Asia and Sub-Saharan Africa (see green columns in figure below), while ambient air and ozone pollution are major drivers in America, North Africa, Europe and East Asia. [10]

In Sub-Saharan Africa, the costs due to IAP amount to 2.5% of GDP equivalent; in East Asia to 3.1% and in South Asia even to 4.9%. This is a higher percentage of losses in GDPs than in total for Latin America, Middle East and North America respectively.[10]

Figure: Welfare Losses Due to Air Pollution by Region, 2013 [10]


Since deaths rates due to IAP stay constant over the past decade, the costs will not decline either. Therefore, indoor air pollution remains a persistent challenge despite some gains in the past decades.

Further Information


  1. WHO (2021): Household air pollution and health.,27%25%20are%20due%20to%20pneumonia
  5. Fuel for Life - Household Energy and Health. Geneva: World Health Organization, 2006.
  6. Source:;;
  7.; ^ "437-002-0382 Oregon Rules for Air Contaminants" (PDF). Oregon Occupational Safety and Health Division. Retrieved 30 January 2014.
  9. WHO: Air quality and health, Fact sheet N°313fckLR
  10. 10.0 10.1 10.2 10.3 10.4 The World Bank. ‘The Cost of Air Pollution : Strengthening the Economic Case for Action’. Washington, DC: The World Bank, 2016. License: Creative Commons Attribution CC BY 3.0 IGO