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Issue Profile

Air Quality

Air Quality measures population-weighted exposure to fine particulate matter and percentage of the population burning solid fuel for cooking.

What it measures: This issue category includes three indicators: Air Pollution- Average Exposure to PM2.5 (fine particulate matter); PM2.5 Exceedance; and Household Air Quality – Indoor Solid Fuel Usage. Respectively, the first two indicators measure: Population-weighted exposure to PM2.5 in micrograms per cubic meter (µg/m3); an average of the percentage of the population exposed to PM2.5 levels at 10 µg/m3, 15 µg/m3, 25 µg/m3, and 35 µg/m3. These exposure levels represent the World Health Organization’s (WHO) air quality guidelines and interim I, II, and III targets specified to help countries gauge progress over time to reduce population exposure to particulate matter. Household Air Quality measures the percentage of the population burning solid fuel (biomass such as wood, crop residues, dung, charcoal and coal) for cooking.

What the targets are: 10 µg/m3 for Average Exposure to PM2.5 (fine particulate matter); 0% for PM2.5 Exceedance; 0% for Household Air Quality – Indoor Solid Fuel Usage. For more information, click here

Why we include it: Suspended particulates contribute to acute lower respiratory infections and other diseases such as cancer. They can penetrate human lung and blood tissue, leading to higher incidences of cardiovascular and lung disease. Most countries currently monitor and report coarse particulate pollution, or PM10 (particles between 2.5 and 10 microns in diameter). However, fine particulates or PM2.5 (2.5 microns and smaller) lodge deep in lung tissue and are far more injurious to health than coarser particulates. PM2.5 also travel farther from their source than PM10 and can have a more toxic composition, including heavy metals and carcinogenic compounds.

Cooking with solid fuels over open fires or in simple stoves exposes households to daily pollutant concentrations that lie between those of second-hand smoke exposure and active smoking. (See: Considering Smoking as an Air Pollution Problem for Environmental Health). Solid fuel combustion is associated with increased mortality from pneumonia and other acute lower respiratory diseases among children. Among adults it is connected to increased mortality from chronic obstructive pulmonary disease and, where coal is used, lung cancer. The most recent Global Burden of Disease project (GBD 2010) found household air pollution responsible for around 3.5 million premature deaths worldwide .1, A measure of solid fuel use (as a useful proxy for household air pollution) served as an estimation of health impacts from household air pollution in the GBD 2010 and, until 2007, as an indicator of environmental sustainability in a MDG.

Where the data come from: The satellite-derived PM2.5 data were provided by Aaron van Donkelaar of Dalhousie University. Population data for population weighting of PM2.5 concentrations and measurement of the proportion of the population above various PM2.5 concentration thresholds were obtained from the Global Rural Urban Mapping Project, v.1 at the NASA Socioeconomic Data and Applications Center hosted by the Center for International Earth Science Information Network (CIESIN) at Columbia University. The Household Air Quality data came from the WHO Household Energy Database, which provides estimates of the percentage of households using solid fuels (coal, wood, charcoal, dung, and crop residues), liquid fuels (kerosene), gaseous fuels (LPG, natural gas, biogas) and electricity. The WHO data come from household surveys, with a total of 586 data points in 155 countries.

Description: Particles smaller than 2.5 microns in diameter, known in shorthand as PM2.5, are fine enough to lodge deep into human lung and blood tissue. They place exposed populations at risk of heart and lung diseases, ranging from stroke to lung cancer. In severe cases, they lead to direct fatalities..2 Airborne particulates originate from a variety of sources. PM2.5 is generally the product of combustion, whether anthropogenic, like car emissions and coal burning, or through forest fires and volcanoes. For vulnerable lungs, high concentrations of PM2.5 can be a particularly virulent killer. The leading cause of child mortality ages one to five worldwide is pneumonia, and fine particulates are a major global contributor to its incidence.

Despite its known health impacts, many countries do not monitor PM2.5, usually because of lack of capacity, resources, technology, or public demand. Monitoring gaps primarily occur in developing countries outside of North America and Western Europe, where air pollution is more severe (see Figure 1).3 Given the sparseness of ground-based monitors, the EPI collaborated with Dalhousie University researchers who use satellite data to assess global, national exposure to PM2.5.  Unlike ground-based monitors, which are primarily concentrated in urban areas and can be sporadically stationed, satellite data provide consistent and complete values using the same methods and technology for every country.

Figure 1. Number of monitoring stations in developed (North America and Western Europe, here called NAWE) versus developing countries (non-NAWE). (Data source: Rudolph Husar and Stefan Falke, for GEO Task US-09-01a. Figure from Hsu et al., 2013.4)

With this satellite data, the 2014 EPI can include the only national indicator of population exposure to PM2.5 on a global scale. More than half of the population in 71 countries lives in regions with annual mean PM2.5 concentrations in excess of the WHO guideline of a 10 µg/m3 annual mean. Large, urbanizing centers with heavy industrial activity and high concentrations of vehicles suffer from heavy contamination. In Beijing, for instance, dangerous air pollution levels have dominated international headlines and incited citizens to protest.

Developed countries are not immune from pollution, however. While the United States meets air quality standards at the national level, some sites reveal discrepancies. Bakersfield, California, for example, had the highest level of particulate pollution out of 277 metropolitan areas in the United States in 2013. There, annual average PM2.5 concentrations have been nearly two times the WHO recommended guideline over the last decade. Salt Lake City, Utah, experienced temperature inversions on 57 percent of winter days from 1994 through 2008, leading to spikes in particulate matter pollution exceeding National Ambient Air Quality Standards.5 

While air pollution in developed countries is primarily the product of industrialization and urbanization, air pollution in many developing countries generally has a different source: biomass burning. The combustion of organic refuse, charcoal, wood, animal dung, and agricultural waste, such as straw, nut shells, or rice husks, is prevalent in rural and urban areas of the developing world. In India, where 60 percent of the population is agrarian, biomass is burned to clear fields, releasing pollutants that drift into nearby cities. In June 2012, Wuhan, a major city in central China, experienced the worst air pollution in a decade. Levels exceeded the top range of measurement indices, and the city was engulfed in a dense, greenish cloud of smoke. Satellite imaging revealed fires in rural areas across the region, suggesting biomass burning as a likely culprit for the extreme pollution spikes.

Acknowledging the contribution of biomass burning to local and regional air pollution, some governments in developing countries have started to provide farmers alternatives to harness otherwise wasted biomass for cleaner energy production (See: Alternatives to Biomass Burning to Address Air Quality.) These include the construction of waste-to-energy plants, which produce electricity by burning biomass with less pollution than outdoor fires.

Contributions to air pollution are not restricted to industrial or agricultural sources. Biomass and coal are often burned in simple stoves or open fires in poorly ventilated cooking spaces. In fact, chronic exposure to air pollution produced by the combustion of cooking fuels is among the world’s most significant and most silent killers. And its effects are not isolated to kitchens. Data have shown that smoke may pervade the rest of the house and the outdoors. Families that cook outdoors also experience adverse health effects, though at a lower rate. Households using clean fuel sources amidst a community of solid fuel users may still be exposed to harmful smoke by their neighbors.

The burning of solid fuels is far more prevalent in developing countries and in places where a majority of the population lacks access to modern cooking technology. The 2014 EPI indicator for Household Air Pollution reveals a clear correlation between national income and household air pollution. The population most significantly affected by solid fuel contamination, low-income households from developing countries, is likely even larger than the data indicate, as families in developing countries tend to be larger. At 77 percent, sub-Saharan Africa has the highest proportion of households using solid fuels. It is also the region with the least improvement over a 30-year period of measurement. There, the absolute number of people using solid fuels has roughly doubled from 333 to 646 million, reflecting both explosive population growth and the marginal changeover to modern fuels.6

Solutions to address household air pollution must focus on reducing emissions through the use of cleaner fuels, such as liquid petroleum gas and electricity. While installing chimneys or smoke hoods on simple stoves might seem an easy fix, the scarcity of wood and the potential risks to the environment posed by the collection of biomass are yet another argument against in-home biomass use. Largely prompted by these environmental concerns, China in the early 1980s undertook a large-scale attempt at improved rural household stoves. Since then the country has installed nearly 200 million improved stoves, reducing household air pollution and easing the environmental burden of biomass demand.7 An initiative called the Global Alliance for Clean Cookstoves has tried to foster public and private cooperation to make clean cookstoves and fuels widely available in the greater developing world.

Ultimately, policy has an important role to play in reducing both outdoor and household air pollution. (See: Toward a New Generation of Air Quality Monitoring.) Efforts to address outdoor air pollution have surfaced during the latter half of the 20th century. National and international laws aimed at phasing out dirty industrial fuels such as coal, regulating auto emissions, and incentivizing better energy efficiency have all proven effective at improving air quality. While the MDGs have to some extent encouraged policy interventions to reduce household air pollution, the 2014 EPI shows one-third of countries ranked still have more than 50 percent of their population using solid fuels indoors. However, unlike other environmental health issues included in the EPI that improve with economic growth, air pollution for many countries worsens with industrialization and urbanization, making the call for policymakers to address it all the more urgent. 

PM2.5 - The Invisible Killer, by Yinan Song from YCELP on Vimeo.
Yinan Song, Yale College '14, designed and animated a video that explains fine particulate matter air pollution.

1 Lim S. S., Vos, T., Flaxman, A. D., et al. (2012) A comparative risk assessment of burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions, 1990-2010: a systematic analysis for the Global Burden of Disease Study 2010. The Lancet 380:2224–2260.

2 Goldberg, M. (2008) A systematic review of the relation between long-term exposure to ambient air pollution and chronic diseases. Reviews on environmental health23:243-298.

3 Engel-Cox, J., Kim Oanh, N. T., van Donkelaar, A., et al. (2013) Toward the next generation of air quality monitoring: Particulate Matter. Atmospheric Environment, 80:584-590.

4 Hsu, A., Reuben, A., Shindell, D., et al. (2013) Toward the next generation of air quality monitoring indicators. Atmospheric Environment, 80:561-570.

5 Bailey, A., Chase, T. N., Cassano, J. J., et al. (2011) Changing temperature inversion characteristics in the US southwest and relationships to large-scale atmospheric circulation. Journal of Applied Meteorology and Climatology50:1307-1323.

6 Bonjour, S., Adair-Rohani, H., Wolf, J., et al. (2013) Solid fuel use for household cooking: Country and regional estimates for 1980-2010. Environmental Health Perspectives 121:784-790.

7 Sinton, J. E., Smith, K. R., Peabody, J. W., et al. (2004) An assessment of programs to promote improved household stoves in China. Energy for Sustainable Development 8:33-52.


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