Delhi recorded its air quality in the "poor" category for the third consecutive day on Tuesday, and no improvement is likely in the next six days, forecasting agencies said here.
Delhi's 24-hour average air quality index (AQI) stood at 241 at 4 pm. It was 254 in Ghaziabad, 258 in Faridabad, 216 in Greater Noida, 258 in Gurugram and 242 in Noida.
Air pollution rose to the "severe" category at Anand Vihar (AQI 438) and "very poor" levels at Shadipur (AQI 361) and Wazirpur (AQI 308).
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'.
According to the Decision Support System of the Indian Institute of Tropical Meteorology (IITM), the transport sector accounted for 18.5 per cent of PM2.5 pollution in Delhi on Tuesday.
The Early Warning System of the IITM said the air quality was likely to remain in the "poor" and "very poor" categories over the next six days.
Data from the Indian Agricultural Research Institute showed a spike in the incidents of stubble burning in Punjab.
The agrarian state reported 169 farm fires on Saturday, 206 on Sunday, 403 on Monday and 342 on Tuesday.
According to experts, the delay in paddy harvesting due to two prolonged spells of rains -- in late September and October -- could lead to a spike in stubble burning incidents as farmers would be in a race against time to prepare their fields for the next crop.
Along with unfavourable meteorological conditions, paddy straw burning in Punjab and Haryana is a major reason behind the alarming spike in air pollution levels in the capital in October and November. Farmers set their fields on fire to quickly clear off the crop residue before cultivating wheat and vegetables.
On Sunday, the Commission for Air Quality Management (CAQM) asked agencies to strictly implement measures under Stage I of the Graded Response Action Plan (GRAP) as the air quality in Delhi and neighbouring areas slipped to the poor level.
GRAP is a set of anti-air pollution measures followed in the capital and its vicinity according to the severity of the situation.
Under Stage 1 (poor air quality), the CAQM recommends stopping construction and demolition activities at sites having plot size equal to or more than 500 square metres that are not registered on the "web portal" of the respective states for remote monitoring of air pollution levels.
Project proponents are required to ensure proper implementation of guidelines for dust mitigation, management of construction and demolition waste and use of anti-smog guns at construction sites.
-With PTI Input
