Delhi’s air quality improves from ‘severe’ to ‘very poor’ due to wind

Delhi witnessed a change in the wind direction from north-westerly to easterly and a marginal increase in wind speed

The residents of Delhi woke up to a significantly better morning on Saturday as the average Air Quality Index (AQI) reduced to 339 at 9am, the lower half of ‘very poor’ category, thanks to a change in the wind direction from north-westerly to easterly and a marginal increase in wind speed.

People shop for the 'Chhath Puja' celebrations at Azadpur Mandi in New Delhi on Saturday (PTI)

The 24-hour average AQI on Friday evening was 405, still in the severe category. However, a change in wind direction started later in the evening, bringing down pollution levels from later in the night. The pollution levels have come down to poor after staying in the ‘severe’ category for the past three days.

Though winds were calm in the early hours of Friday, they increased to a maximum speed of 6 km/hr during the day that led to the dispersal of pollutants by late evening. The Met department has forecast easterly winds to remain dominant over the next three days, but said significant relief is only expected from November 21 onwards, when strong winds of up to 15 km/hr are expected in the capital.

Data as per Delhi government’s real-time source apportionment on Friday showed vehicles were contributing by 44% to Delhi’s PM 2.5, followed by 22% from biomass burning. The impact of stubble burning is expected to reduce over Delhi in the next three days now, firstly due to the change in wind direction, as well as a gradual drop in farm fire numbers. Data from the Indian Agricultural Research Institute (IARI) showed Punjab recorded 1,150 fires on Friday and Haryana 45.

Delhi’s minimum temperature, meanwhile, was recorded at 12°C and the maximum was about 28 degrees. IMD forecasted a rise in the minimum temperature to 13°C by Saturday.

While pollution level has reduced, measures under stage 4 of the Graded Response Action Plan (GRAP) will continue to remain in place on Saturday. The measures under it include a ban on diesel light commercial vehicles that are registered outside Delhi and are non BS VI, from entering the capital. Similarly, there is a ban on entry of trucks into Delhi, alongside a ban on plying of all diesel-Medium Goods Vehicles (MGV) and Heavy Goods Vehicles (HGV) in the capital. Under this category, all linear construction projects such as highways, roads and flyovers have also been stopped.