NEW DELHI: The average air quality index (AQI) in Delhi in April this year was 256, the worst for the month since 2016, according to Central Pollution Control Board (CPCB) data.
The city saw 29 "poor" air quality days in April, the highest in the month since the CPCB started maintaining AQI data in 2015.
This was also the first time that Delhi did not record a single day with "moderate" or better air quality in April, the data showed.
"Generally, during the second half of April, wind direction shifts from south and southeast to west and northwest and picks up speed with intermittent rains.
"This time, the wind speed was higher the entire month and there was no rainfall. This caused lifting of dry local dust and particulate matter resulting in higher AQI throughout the month," former CPCB Air Lab chief Dr Dipankar Saha said.
An AQI between zero and 50 is considered 'good', 51 and 100 'satisfactory', 101 and 200 'moderate', 201 and 300 'poor', 301 and 400 'very poor', and 401 and 500 'severe'.
Delhi recorded an average AQI of 197 in April last year and 110 in 2020, the lowest in the last six years on account of a Covid-induced lockdown.
The city logged an average AQI of 211 in April of 2019; 222 in 2018; 224 in 2017 and 269 in 2016.
In April 2020, Delhi experienced 14 days of "satisfactory" air quality and 16 days of "moderate air quality.