India, Oct. 18 -- New Delhi

Delhi's air quality index (AQI) remained in the "poor" category for a fourth consecutive day on Friday, according to the Central Pollution Control Board's (CPCB's) daily bulletin. Forecasts suggest that air quality may further deteriorate over the next few days.

On Friday, the 24-hour average AQI was 254 (poor), continuing the "poor" air streak of 245 on Thursday, 233 on Wednesday and 211 on Tuesday. Before that, Delhi had been enjoying a continuous streak of "moderate" and "satisfactory" air days from June 12.

CPCB classifies an AQI of 0-50 as "good", 51-100 as "satisfactory", 101-200 as "moderate", 201-300 as "poor", 301-400 as "very poor" and 401-500 as "severe".

Data on Friday evening showed that of the...