delhi

Updated: Dec 26, 2017 12:04 IST

Delhi’s air quality entered the ‘very poor’ zone on Christmas Day on Monday.

The situation deteriorated after sunset with nine out of 17 stations of the Central Pollution Control Board (CPCB) in the city recording ‘severe’ air quality.

Monday’s average Air Quality Index (AQI) was 372, classified under the ‘very poor’ category of the CPCB. On Sunday, the reading was 305. The AQI is calculated on a scale of 0-500. An AQI between 0-50 is considered good, 51-100 satisfactory, 101-200 moderate, 201-300 poor, 301-400 very poor and 401-500 severe.

The levels of PM10 and PM2.5, too, saw a substantial increase throughout Monday. The PM10 concentration went up from 365.8 microgrammes per cubic metre (μg/m3) at 6am to 403.6 μg/m3 at 6pm. The level of PM2.5 saw an increase from 226.9 μg/m3 at 6am to 268.9 μg/m3 at 6pm.

Both PM10 and PM2.5 are ultra-fine particles, the dominant pollutants in Delhi. The acceptable levels of PM10, the larger particulate matter, and PM 2.5, which measures the finer and more dangerous particulate matter, are 100 μg/m3 and 60 μg/m3, respectively.

According to Met officials, the particulate matter concentration rose due to a fall in wind speed and presence of high-level of moisture — factors which trap pollutants. Humidity was recorded at a maximum 100% by the India Meteorological Department (IMD).

“The wind speed was poor throughout the day. At one point, it picked up to 15-17km/hour for some time. However, in the evening it significantly went down to 5-6km/hour. On Tuesday too, not much improvement is expected in terms of air quality. Wind speed will pick up during the day and then will go down again,” Kuldeep Srivastava, a senior Met department scientist, said.

On Tuesday, clear sky is expected with shallow fog in the morning. The maximum and minimum temperatures would be around 23 and 07 degrees Celsius respectively.

On Monday, the maximum temperature was 22.8, a degree above normal, while the minimum temperature was recorded at 7 degrees Celsius, a notch below what is normal this time of the year.

Sunday was the coldest day yet this December with minimum temperature hitting a low of 6.3 degree Celsius. The previous lowest in December 2017 was on 15th with the minimum recording of 7.3 degrees Celsius. The maximum temperature on Sunday stayed at 25.1, four degrees above what is normal this time of the month.