Level of pollutants commonly associated with vehicular pollution were higher Friday than on April 15 last year, showed data from Delhi Pollution Control Committee’s (DPCC’s) six ambient air quality stations. A comparison of the central-run AQI also showed similar trends.
Scientists, however, cautioned that due to high rains during this period last year, such a daily short-term comparison may not give an understanding of the impact of the scheme.
On the first day of the second phase of the odd-even scheme, Delhi government did not release any results from the ambient or the 74 mobile monitoring units deployed. Here are some of the comparative trends based on the data of DPCC and Central Pollution Control Board’s (CPCB’s) ambient air quality stations:
PM 2.5 is the pollutant experts associate most directly with vehicles. According to DPCC data, at RK Puram, PM 2.5 peaks this day last year were 85 micrograms per cubic metre (µg/m³) at 10 am, 75 µg/m³ at 9 am, and 73 µg/m³ at 6 pm. On Friday, a peak of 298 µg/m³ was recorded at 8.30 am, followed by 213 µg/m³ at 9.30 am, and 173 µg/m³ at 6 pm.
PM 10 are particles of larger sizes of less than 10 microns. According to DPCC data, at Mandir Marg, PM 10 peaks this day last year were 219 µg/m³ at 9 am; 291 µg/m³ at 12.10 pm; 158 µg/m³ at 8.10 pm. On Friday, a peak of 482 µg/m³ was recorded at 8.55 am, followed by 234 µg/m³ at 10.55 am.
Ozone is formed through a photochemical reaction to combine different pollutants including PM 2.5. Data from Punjabi Bagh station shows that on April 15 last year, levels peaked at 162 µg/m³ at 2.30 pm, followed by 154 µg/m³ at 3.30 pm. On Friday, the peak for ozone at the station stood at 177 µg/m³ at 3.30 pm, and 169 µg/m³ at 5.30 pm.
CPCB’s National AQI IHBAS was the only station where there was sufficient data for computing AQI on April 15 last year. This day last year, an AQI of 193 was recorded with PM 2.5 as the prominent pollutant. On Friday, at 6 pm, an AQI of 265 was recorded with PM 2.5 as the prominent pollutant.
A senior scientist at CPCB said, “On April 14, the AQI across stations in Delhi was 209, and on April 15 it is at 291. Both days were holidays. The spike can probably be attributed to weather factors like reduction in wind speeds on Friday.” An IMD official said, “On Friday, the wind speeds were comparatively lower, so more particulate matter could collect in the air.”
Anumita Roychowdhury from the Centre for Science and Environment said meteorological conditions last year were different. “Summer pollutant patterns as such are different from winter pollutants… Last year, there were also a lot of rainy days during this period, which could have led to the apparently low pollutant levels.”