With industries, private vehicles and public transport shut during the lockdown, air in Delhi and NCR, among the worst in the country, was the least polluted in March since air quality records have been maintained.
On Sunday, however, air quality settled in the ‘moderate’ category at 102 – down down from a ‘satisfactory’ 87 on Saturday — demonstrating the impact of weather on AQI.
The Central Pollution Control Board’s AQI is based on air quality data from different monitoring stations across the city. Delhi’s data on Sunday was calculated based on 30 stations.
Experts said the sudden increase was because of a dip in wind speed. “Last week, the wind speed was an average of 25 km/ hour. This is because there was an active Western Disturbance blocking the flow of wind from the northwest direction. The average wind speed on Sunday was 10-12 km/ hour. Because the input load (of pollutants is so less) the change is only marginal but meteorology is a major factor,” said Kuldeep Srivastava, who heads the Regional Weather Forecasting Centre, Delhi.
The air quality along the Indo-Gangetic Plains is amongst the worst in the world due to a variety of factors – including meteorology. Winters see a steady accumulation of pollutants while high temperatures and wind speed in summer months means the dispersal of pollutants is quicker.
“Had this dip in wind speed been observed outside of a lockdown situation, the AQI would likely have been in the higher range of ‘poor’ or ‘very poor’. The conditions we are observing right now are extremely unique and have never been seen in the modern world. It will help us understand the nature of Delhi’s air and the extent of the impact of changes in different parameters,” said a Pollution Control Board official, who did not want to be named.
According to Srivastava, the wind speed will be low on Monday as well. “The city is expected to see thundershowers on Tuesday, when the impact of the disturbance will be felt in the city,” he said.
Delhi’s temperature has been below normal for most of March and the first five days of April as well because of frequent Western Disturbances.
