Introduction

According to the WHO, the risks from air pollution are now far greater than previously thought or understood, particularly for heart disease and strokes. Many people are exposed to both indoor and outdoor air pollution. Due to this overlap, mortality attributable to the two sources cannot simply be added together, hence the total estimate of around 7 million deaths in 2012, which is 12% of all global deaths.

The sources of air pollution are industries, households and automotive vehicles. They emit complex mixtures of pollutants, primarily particulate matter (PM), ozone (03), nitrogen dioxide (NO2), and sulphur

dioxide (SO2). Of all of these pollutants, fine particulate matter has the greatest effect on human health. Many studies have reported associations between ambient particulate matter and adverse health effects. Globally PM10, which is the concentration of particles with a diameter of 10 microns (µ), has been the standard measure of particulate pollution. More recently PM2.5, which measures fine particulate matter with a diameter of 2.5 microns, is being used more frequently because the finer the particles the more hazardous they are to human health. Concentrations are reported as micrograms per cubic metre (µg/m3).

Linking diseases to air pollution

The major diseases and causes of death are the same for both outdoor and indoor air pollution. The disease groups are ischaemic heart disease (IHD adults) including coronary artery diseases, stroke (adults), lung cancer (adults), chronic obstructive pulmonary disease (COPD in adults) – including bronchitis, emphysema and influenza, and acute lower respiratory infection (ALRI in children under 5 years) including pneumonia.

Death certificates do not give air pollution as a cause of death. Attributing deaths to air pollution requires research that links, through exposure-response functions, the incidence of diseases to exposures to air pollution. WHO uses a methodology called Comparative Risk Assessment (CRA), which uses the best exposure and/or exposure-response data. The CRA methodology now cover 68% of deaths attributable to the environment. For some diseases and many developing regions of the world, reliable research is not available. In these cases estimating the proportion of incidences of diseases attributable to air pollution is based on expert opinion.

A sense of the magnitude of the uncertainty in these estimates can be gained by comparing the latest 2012 estimates with the previous estimates from 2008. Globally, WHO estimated that 3.7 million deaths were attributable to outdoor or ambient air pollution (AAP) in 2012 more than double the 2008 estimate of only 1.3 million deaths. Similarly with respect to indoor pollution, in 2012 WHO estimated 4.3 million deaths a year were attributable to indoor or household air pollution (HAP) again more than double WHO’s 2004 estimate of around 2 million deaths In both cases the reasons provided by WHO for the much larger 2012 estimates are primarily methodological.

A separate article on this site titled Changes in methodology doubles WHO estimates of deaths linked to environmental risk factors examines this issue and concludes that “while the latest WHO report is based on the best evidence available, there are still important gaps and concerns with the data underlying the estimates.”

Out door or ambient air pollution (AAP) 

88% of the 3.7 million deaths annually attributable to outdoor air pollution occur in low- and middle-middle income countries, with the greatest number in Western Pacific (including China) and SE Asia regions. While the health impacts of AAP occur in both cities and rural areas, the problem and resulting mortality is generally far higher in many fast developing cities than in more stable developed cities and rural areas. Ambient (outdoor) air quality and health. UN WHO, 2014

Components and sources of outdoor air pollution (AAP)

The prime sources of outdoor air pollution are fossil fuel exhaust from automobiles, trucks, trains and planes; power generation from burning fossil fuels, particularly coal; manufacturing and processing industries; and outdoor fires including forest fires and slash and burn agriculture.

The major components of PM are sulfate, nitrates, ammonia, sodium chloride, black carbon, mineral dust and water. These combine in a complex mixture of solid and liquid particles (both organic and inorganic) which are suspended in the air. PM10 particles can penetrate and remain in the lungs and contribute to cardiovascular and respiratory diseases and to lung cancer.

Mortality from AAP by region, country and city

Approximately 1.67 million deaths attributable to outdoor pollution occur in the Western Pacific region (which includes China) and around 940,000 occur in South East Asia. Total deaths linked to AAP in High Income Countries total around 454,000.

Outdoor air pollution (AAP) attributable deaths by global region – 2012
Region	Deaths – ‘000s (error range)	Deaths per 100,000 children under 5 years	Deaths per 100,000 population
Africa	175.7 (145.1 – 211.1)	31	20
Low – mid income countries of Americas	57.6 (16.6 – 135.8)	2	10
Southeast Asia	936.3 (761.5 – 1,157.5)	23	51
Low – mid income countries European Region	202.7 (168.3 – 248.3)	7	75
Low and mid income countries Eastern Mediterraneum Region	236.0 (202.0 – 277.4)	35	42
Low – mid income countries Western Pacific Region (inc China)	1,669.4 (1,289.4 – 1,955.7)	12	102
Global	3,732.5	19	53
Source: WHO Global Health Observatory data repository

The WHO data base for AAP data covers some 1600 cities/urban areas in 91 countries for the 2008-2013 period (although not every country or city has data for every year).

Detail for above graphic

Household air pollution (HAP) and health 

77% of the deaths attributable to household air pollution (HAP) are in South East Asia (1.69 million) and the low- and middle-middle income countries of Western Pacific (1.62 million). Another 600,000 deaths linked to HAP are in Africa and 200,000 in the Eastern Mediterranean region.

Source of Household Air Pollution

Around three billion people worldwide still cook and heat their homes with solid fuels (wood, coal and dung) in open fires and variable quality stoves. Most of these are in the low- and middle-income countries and regions.

The main source of HAP is smoke and black carbon (sooty particles), methane and kerosene fumes from indoor stoves and lamps. 1.2 billion people have no ready access to electricity and rely on kerosene lamps (with consequent fumes) for household lighting.

In some countries such as Ethiopia and Rwanda, WHO estimates that around 98% of the population relies on solid fuels. Around 1 billion people in China and India rely primarily on solid fuels for cooking.

Diseases and causes of death from HAP

The major diseases and cause of death linked to HAP and the per cent distribution attributable to each are; pneumonia – 12%, stroke – 34%, ischaemic heart disease – 26%, chronic obstructive pulmonary disease (COPD) – 22%, and lung cancer – 6%.

Deaths from HAP by age and sex

WHO reports that in poorly ventilated dwellings indoor smoke can be 100 times higher than acceptable guidelines for small particles. Moreover, women and young children are particularly exposed to this condition because of their proximity to the cook stove/fire. These results are clearly shown in the chart which indicates that the deaths of 534,000 children under 5 years were attributable to HAP. This represented 13% of the total in 2012.

Mortality from HAP by global region and cause of death

Approximately 1.62 million deaths attributable to HAP are in the Western Pacific region and around 1.69 million are in South East Asia. In Africa around 600,000 deaths were attributable to HAP in 2012. Compared to this, the total deaths attributable to HAP in high income countries were almost negligible at 19,000.

The estimates of people’s exposure to outdoor air pollution in different parts of the world were formulated through a new global data mapping. This incorporated satellite data, ground-level monitoring measurements and data on pollution emissions from key sources, as well as modelling of how pollution drifts in the air.

Interactive graphics relevant to this article

Interactive and infographics are increasingly being developed and shared online. The best of these can assist readers in visualizing, understanding and accessing some of the critical data, factors and relationships relating to the subject matter of data compilations and articles. The WHO has developed a strong set of such graphics and makes them available online through its Global Health Observatory (GHO).

In addition to WHO, over the past few years other international and national public agencies (as well as some academic institutions, NGOs and companies) have accelerated their efforts in this field and are developing more and visually more accessible interactive and other infographics over increasingly more subject areas and data fields.
The following three examples from WHO are directly relevant to this article.

* Mortality from outdoor air pollution by region and cause of death

Death attributable to AAP by global region is summarized in a WHO online interactive graphic. The graphic provides a filter by total deaths (‘000s) and deaths per capita (per 100,000) for each of the seven global regions (defined by WHO).

Deaths attributable to AAP by major disease/cause of death in ‘000s and per 100,000.

Ctrl + click to open the interactive version this WHO graphic in separate window.

* Exposure to Ambient Air Pollution by country and P10 concentration

WHO has published an interactive graphic that provides a global map with country data interactively linked to both a table and chart. This set enables a ready interrogation of the concentration of P10 by country with the year of the latest data available for each country. The bar chart indicates where each country (for which data is reported) falls on a global ranking of P10 concentration. Multiple selections can be made to study the data by user selected groups of countries.

Exposure to ambient air pollution (particulate matter less than 10 microns) in urban areas, 2008-2013.

Ctrl + click to open the interactive version of this WHO map/chart/table, which provides filters by global region and country.

* Mortality from HAP by global region and cause of death

The global distribution of deaths attributable to HAP by region is illustrated in an interactive graphic. The graphic provides a filter by total deaths (‘000s) and per capita deaths (per 100,000).

Deaths attributable to HAP by major disease/cause of death in ‘000s and per 100,000.

Ctrl + click to open the interactive version this WHO graphic in separate window.

Source:

Burden of disease from ambient and household air pollution. UN WHO

Ambient (outdoor) air quality and health. UN WHO Fact sheet 313, March 2014

Household air pollution and health. UN WHO Fact sheet 292, March 2014

Air pollution database and attributable mortality. UN WHO Presentation, 19 May,2014

Changes in methodology doubles WHO estimates of deaths linked to the environment. EnvironmentCounts.org, April, 2016

Global Health Observatory (GHO) data repository, WHO The GHO data repository contains an extensive list of indicators, which can be selected by theme or through a multi-dimension query functionality. It is the World Health Organization’s main health statistics repository and is online and searchable by the public through this link.