Maria Neira, head of the WHO's department of public health and environment, termed the report as a 'public health emergency'. She also urged governments to take up measures like cutting the number of vehicles on the road, improving waste management and promotion of clean cooking fuel.

The WHO report is based on data collected from more than 3000 sites across the globe. According to the report, poorer countries have much dirtier air than the developed world.

How the report was made?

The report is based on WHO’s new air quality model that is based on data derived from satellite measurements, air transport models and ground station monitors. The model was developed by WHO in collaboration with the University of Bath, United Kingdom.

Air pollution’s toll on human health

Some 3 million deaths a year are linked to exposure to outdoor air pollution. Indoor air pollution can be just as deadly. In 2012, an estimated 6.5 million deaths (11.6% of all global deaths) were associated with indoor and outdoor air pollution together.

Nearly 90 percent of air-pollution-related deaths occur in low and middle-income countries, with nearly 2 out of 3 occurring in WHO’s South-East Asia and Western Pacific regions.

WHO says that 94 percent are due to non-communicable diseases – notably cardiovascular diseases, stroke, chronic obstructive pulmonary disease and lung cancer. Air pollution also increases the risks for acute respiratory infections.

Sources of air pollution

Major sources of air pollution include inefficient modes of transport, household fuel and waste burning, coal-fired power plants, and industrial activities. However, not all air pollution originates from human activity. For example, air quality can also be influenced by dust storms, particularly in regions close to deserts.