The early phase of winter this year from October to November was the least polluted in Delhi in the past eight years, according to a report published by non-profit organisation Centre for Science and Environment.

“Diwali falling in warmer October, lower incidents of crop fires that otherwise tips the local pollution over the dangerous levels, pre-emptive action based on pollution forecasting, and favourable meteorological conditions including extended rainfall in October, have all contributed towards bending of the early winter pollution curve,” the report said.

The organisation, however, said that there may be spikes in pollution levels later, as has been the case in previous years.

According to the report by CSE, Delhi experienced the least smoke intrusion from stubble burning in five years.

The organisation referred to data from the Ministry of Earth Sciences’ SAFAR, or System of Air Quality and Weather Forecasting And Research, that showed that smoke from farm fires contributed to PM2.5 pollution in Delhi on 53 days this year from October 12 to December 3.

“This October-November, not only the quantity and intensity of farm stubble fires have been comparatively lower but also the meteorological conditions have been less conducive for the transport of the smoke,” the report said.

Particulate matter smaller than 2.5 microns (or about ten-thousandth of an inch) is particularly dangerous to human health. Such particles are small enough to travel deep into the respiratory system, potentially impairing lung function.

The National Capital recorded five good air days in the first two weeks of October, due to heavy rainfall during this period. This number was the highest in the last five years. A location is said to have an air quality index in the “good” category when PM2.5 levels are less than 30 µg/m3.

Last year, there was one good air day in Delhi in this period, while no good air days were recorded in the winters of 2018, 2019 and 2020.