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Measures to contain coronavirus disease, less vehicular movement brings down levels of NOx

According to the SAFAR report from March 5, there has been a reduction in the levels of NOx in Pune (45 per cent), Mumbai (45 per cent) and Ahmedabad (50 per cent) this year.

Written by Anuradha Mascarenhas | Pune | Updated: March 23, 2020 6:50:47 am
On ‘janata curfew’ day, areas of Hadapsar MG road, Kondhwa in Pune worn a deserted look. (Express photo by Ashish Kale)

Even as data on quality of air on Sunday, when citizens participated in the voluntary janata curfew — will be uploaded on Monday, researchers at the System of Air Quality Forecasting and Research (SAFAR) have said there has been considerable reduction in levels of nitrogen oxide (NOx) — an irritant gas which is released during fuel combustion and in high concentrations can cause inflammation in the airways.

According to the SAFAR report from March 5, there has been a reduction in the levels of NOx in Pune (45 per cent), Mumbai (45 per cent) and Ahmedabad (50 per cent) this year. In Delhi, there has been no significant change in NOx but since the last week, there has been a decline in levels of particulate matter (PM) 2.5 at various locations.

According to SAFAR)researchers, fossil fuel emissions, mainly coming from vehicular traffic, are one of the major sources of NOx (around 60-80 per cent) and PM 2.5 (35-50 per cent). Since coronavirus cases started being reported and measures were taken towards social distancing, SAFAR tried to understand the impact of vehicular traffic in March this year in comparison to 2018 and 2019 in Delhi, Pune, Mumbai and Ahmedabad.

NOx levels are mainly controlled by its major sources of emissions (vehicular traffic), although changes due to weather cannot be ruled out. So, if NOx levels are reduced significantly as compared to earlier years, it is likely to provide a qualitative/broader indication in reduction in emissions in major sources.

The oxides of nitrogen (NOx) have the highest level of emissions coming from vehicular sources (around 60-80 per cent). So for any change, the signal would be strongest in NOx levels. Vehicular traffic impacts PM 2.5 by fossil fuel and re-suspended dust emissions. Although the reduced vehicular traffic brings down PM 2.5 emission by fossil fuel source, it increases re-suspended dust emissions as faster speed of vehicles will accelerate lifting on roads. So, final PM 2.5 will be a delicate balance of two oppositely impacting sources, researchers said.


There appears to be a significant reduction in NOx pollution in Pune and Pimpri-Chinchwad regions from March 6 onwards (~ 50 per cent) but it is fluctuating. The levels of PM 2.5 show mixed impact depending on location.


There appears to be a significant reduction (by a factor of 2) in NOx pollution in overall Ahmedabad city.


There appears to be a reduction in NOx pollution levels in overall Mumbai from March 2 onwards (by ~30 per cent) but again it started to increase from March 16. No change in PM 2.5 .


There appears to be reduction in PM 2.5 pollution levels in overall Delhi-NCT from March 5 onwards. Slight reduction in NOx was seen between March 8-13 but no trend thereafter.

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