All six north Indian cities for which data was available had worse air quality than Beijing in 2015, The Hindu’s analysis of official data shows. However the south’s comparatively better air quality levels hide some lethal truths.
Launched in April 2015, India’s National Air Quality Index portal produces an Air Quality Index (AQI) value for around 15 cities based on the most prominent pollutant at that time for that city. Pollution monitoring stations measure the concentration of six different pollutants – PM2.5 (particulate matter of diameter less than 2.5 micrometres), PM10, sulphur dioxide, nitrogen dioxide, carbon monoxide and ozone.
For the AQI to be calculated, a station needs to have values for three or more pollutants, one of which needs to be particulate matter. The AQI is then classified along one of six categories – good, satisfactory, moderate, poor, very poor or severe.
Analysing AQI data for 2015, The Hindu found that Anand Vihar in east Delhi measured the worst air quality of any of the 25 monitoring stations for which adequate data was available, with just 15 per cent of its days being good, satisfactory or moderate.
Airoli in Navi Mumbai, on the other hand, had the best air quality – all of the days for which it recorded data were of good to moderate air quality. Averaging for multiple stations across cities, Varanasi had the fewest clean air days (52 per cent), followed by Delhi, Faridabad, Agra, Kanpur and Lucknow.
However, the index numbers might not capture the actual magnitude of pollution cities occasionally experience. BTM Layout in Bengaluru had the highest annual average concentration of PM2.5, The Hindu found, owing to massive intermittent spikes. The station’s annual average was a whopping 378 microgrammes per cubic metre in 2015 as against 157 for Anand Vihar.
CPCB officials in Bengaluru claimed that the spikes, however, are not due to construction or the increasing vehicular movement, but due to erratic power supply. “Every time the power supply is cut, our system shuts down. On restarting, erratic values start to be generated and this is sent directly to the AQI,” K. Karunakaran, Senior Technical Officer for the Bengaluru Zonal division told The Hindu. In April last year, meanwhile, state officials had claimed that the high numbers were a result of PM2.5 values being interchanged with carbon monoxide values.
On PM2.5, tiny particulate matter which is highly damaging to the lungs, the six north Indian cities were far worse off than Beijing was in 2015, a comparison with US Department of State data for China showed.
“The north has higher concentration of particulate matter due to dust and biomass burning, while the impact of combustion sources would be higher in the south”, Anumita Roychowdhury, executive director of the Centre for Science and Environment explained. Combustion sources, particularly from vehicles, are more toxic, and therefore, lower values of AQI in the south should not be ignored from a public health perspective. Particulate matter is the dominant pollutant in Indian cities, The Hindu found, followed by carbon monoxide. “Carbon monoxide is almost entirely from traffic,” Ms. Roychowdhury said.
(With inputs from Mohit Rao)
See what the air quality was like in 2015 at a station closest to you: