ROBERTO SCHMIDT via Getty Images To go with Climate-warming-UN-COP21-India,FOCUS by Trudy HarrisIn this November 6, 2015 photo, an Indian farmer feeds a controlled fire of spent rice stalks as he prepares the field for a new crop in the southeastern part of the state of Punjab, some 120 km north of New Delhi. India's capital, with 18 million residents, has the world's most polluted air with six times the amount of small particulate matter (pm2.5) than what is considered safe, according to the World Health Organization (WHO). The air's hazardous amount of pm2.5 can reach deep into the lungs and enter the blood, causing serious long term health effect, with the WHO warning India has the world's highest death rate from chronic respiratory diseases. India, home to 13 of the world's top 20 polluted cities, is also the third largest emitter of greenhouse gases behind the United States and China. In Delhi, the air pollution is due to vehicle traffic including cargo trucks running on low-grade diesel, individual fires that residents burn in winter, crop being burnt by farmers in neighboring states, and construction site dust. Burning coal in power plants is also major contributor that is expected to increase hugely in the coming decades to match electricity needs of the ever-growing city and its booming satellite towns. AFP PHOTO / ROBERTO SCHMIDT (Photo credit should read ROBERTO SCHMIDT/AFP/Getty Images)

On November 27th, one of the US Embassy's pollution-monitoring stations in New Delhi recorded a chart-breaking reading of 999 on its custom-developed Air Quality Index. To put that in perspective, any reading above 150 is considered unhealthy, with the range 351-500 classified as 'hazardous'.

Delhi pollution off the scale today at 999 in RK Puram. In most countries this would be a public health emergency. pic.twitter.com/kzXRhtAWqT — Meru Gokhale (@MeruGokhale) November 27, 2015

The agency's definition of hazardous specifies: 'Serious aggravation of heart or lung disease and premature mortality in persons with cardiopulmonary disease and the elderly; serious risk of respiratory effects in general population.'

The latest readings across air quality monitors such as the Indian Institute Of Tropical Meteorology-run SAFAR or the government's central pollution control body unanimously point to the harmful and according to some commentators, enervating, air of Delhi.

While it is possible to immediately blame construction, cars and industries for Delhi's toxic air, the city's geography has a disproportionate role to play. As a landlocked megacity, Delhi has fewer avenues for flushing polluted air out of the city. Coastal cities such as Mumbai have a shot at 'replacing' polluted air with relatively unpolluted sea breezes, whereas Delhi's surrounding regions are sometimes even more polluted than the city. For example, most of the brick kilns used for making bricks are not located in the city, but in predominantly upwind surrounding industrial areas.

Other contributors to pollution are low-quality fuels such as raw wood, agricultural and plastic waste in industrial settings, cow dung for cooking stoves and widespread use of diesel generators due to unreliable infrastructure. These sources release fine particle pollutants such as PM10 and PM 2.5. These are fine smidgens of practically-indestructible matter, able to lodge themselves in the lung and impede breathing as well as contribute to cancer.

The impetus on economic growth necessitates more buildings and roads and thereby, more dust. However, traditional agricultural practices too are to blame. October and November are the months when farmers in Punjab raze the remnant stubble of their paddy fields to prepare them for the winter sowing.

The ensuing smoke, which has been captured by satellite imagery over the years, then wafts to Delhi and significantly increases the levels of toxic particulate matter.