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Despite lower diesel consumption, concentration of NO2 dangerously high

NEW DELHI: The concentration of nitrogen dioxide (NO2) substantially rose in Delhi in 2017, despite a fall in diesel consumption, official data shows.
The Delhi government on Thursday attributed the fall in levels of particulate matter in the city to the fall in diesel consumption. However, last year, annual NO2 level breached 50 micrograms per cubic metre (μg/m3) for the first time since 2013.
According to data compiled from the six National Air Quality Monitoring (NAMP) stations in Delhi, the annual concentration of NO2, primarily a product of diesel combustion, has been steadily rising since 2015.
The data shows that annual NO2 average in 2013 was 49.8 μg/m3, 46.3 μg/m3 in 2014, 48.3 μg/m3 in 2015, 49.8 μg/m3 in 2016 and 51.83 μg/m3 in 2017; as against the annual safe average standard of 40 μg/m3.
Surprisingly, the concentration of NO2 increased despite a fall in diesel consumption – from 15.08 lakh metric tonnes in 2015-16 to 12.67 lakh metric tonnes 2016-17 – and a dip of 11 per cent in the registration of new vehicles in 2017 as against 2016 in the city.
Explaining the reason for this, Anumita Rowchowdhury, executive director of Centre for Science and Environment (CSE), said it may be due to a massive number of vehicles entering Delhi from neighbouring states.
"In 2015, we found that the daily total influx of vehicles in Delhi from outside was nearly similar to the annual registration figures," she said.
Meanwhile, data from the same Central Pollution Control Board (CPCB) report also showed that levels of PM2.5 and PM10 in the city's air-dropped marginally in 2017, the first time since 2013.
The levels of PM2.5 in 2013, 2014, 2015, 2016 and 2017 were - 73, 80, 81.5, 118.9 and 101.3 ug/m3 as against the annual prescribed standard of 40. Annual PM10 levels during the corresponding years were -- 211, 215.8, 227.8, 301 and 260.6 ug/m3. The annual prescribed limit is 60.
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