It is not just the air around us that is polluted with carbon monoxide (CO), but even the upper layers of the troposphere, the first layer of atmosphere that extends up to 16 km from surface of the Earth, is polluted by carbon monoxide.

A study conducted by five researchers from Physical Research Laboratory, Ahmedabad, Indian Institute of Technology, Gandhinagar and Max-Planck Institute for Chemistry, Germany, found high levels of carbon monoxide as far as 10km from the surface of the earth in the troposphere in five Indian cities — Ahmedabad, New Delhi, Dibrugarh, Trivandrum and Hyderabad.

The researchers collected values of CO at 200 hectopacals (hPa), which is around 10 km from the surface and at 900hPa, around 800 meters from the earth’s surface over a period of 14 years, from 2001-2014 across four seasons winter, spring, monsoon and autumn.

The maximum value of CO, at 200hPa, was found to be highest, at 118 parts per billion volume (ppbv), over Ahmedabad followed by 115ppbv in Hyderabad during the monsoon season. The normal value for CO in troposphere is considered to be around 50ppbv.