Devil is in the Details: 7 Charts That Show You How Bad Delhi's Air Was After Diwali

Delhi saw yet another polluted Diwali in 2018, in spite of the Supreme Court’s orders restricting the burning of firecrackers.

This year, the Air Quality Index (AQI) showed an overall improvement of 390, a day after Diwali at 4pm, compared to 445 last year. What this doesn’t reveal, however, is that the day before Diwali was unusually clean due to favourable weather conditions and post-Diwali AQI dropped 109 points this year — compared to 126 points last year. A marginal improvement, at best.

The devil inevitably lies in the details.

Data from the Delhi government showed that concentration of particulate matter (both PM 2.5 and PM 10) — fine particles impossible to see with the naked eye that clog the lungs — more than doubled. Sulphur dioxide, which is indicative of burning of firecrackers, showed only a slight decrease.

While last year the Supreme Court had banned the sale of firecrackers, which was openly flouted, this year it put in certain restrictions on the type of firecrackers to be burst. It also set a two-hour window for the crackers to be burst. This, too, was flouted.

Another key difference is that of weather. Last year, Diwali was on October 19 — a much warmer day. This year, the festival coincided with weather conditions ranging from stagnant surface winds to colder temperatures that trap pollutants closer to the surface.

Noise pollution was also more than last year, the Delhi government found. It conducted real-time noise monitoring at five locations in 2018 and the range observed is from 64.4 dB (A) to 74.0 dB (A), while in 2017, the range varied from 61.4 dB (A) to 68.2 dB (A).

PM 10

On Diwali this year, the average concentration (for 24 hrs) of PM10 ranged between 167 and 1859 micrograms per cubic metre. The minimum value was observed at 3pm and the maximum at 1am. Location-wise, the minimum concentration was observed at Najafgarh (241 µg/m3), while the maximum was at Ashok Vihar (1494 µg/m3).

The permissible concentration of PM 10 is 100 micrograms per cubic metre.

Last year, this ranged from 331 micrograms per cubic metre to 951 micrograms per cubic metre and in 2016, the average concentration of PM 10 ranged from 448 micrograms per cubic metre to 939 micrograms per cubic metre.

PM 2.5

On Diwali, the average concentration of PM 2.5 (for 24hrs) ranged from 69 to 1560 micrograms per cubic metre. The minimum value was observed at 3pm and maximum value was observed at 1am. The maximum concentration was observed at Ashok Vihar (1252 µg/m3) and minimum was at Najafgarh (143 µg/m3). The permissible concentration of PM 2.5 is 60 micrograms per cubic metre. In 2017, this was between 154 micrograms per cubic metre and 440 micrograms per cubic metre. In 2016, this range was 180 micrograms per cubic metre and 440 micrograms per cubic metre.

Carbon Monoxide (CO)

On Diwali this year, the average concentration of CO (for 24 hrs) ranged from 0.8 to 4.0 micrograms per cubic metre. The minimum value was observed at 2pm and maximum was observed at 11pm. The location-wise minimum concentration was observed at Najafgarh (0.6 mg/m³) and maximum concentration was observed at Anand Vihar (4.4 mg/m³).

The permissible range for the same is 2 micrograms per cubic metre.

In 2017, this had ranged from 3.0 micrograms per cubic metre to 3.7 micrograms per cubic metre, while in 2016, this was between 2.0 micrograms per cubic metre to 4.2 micrograms per cubic metre.

Oxides of nitrogen

The average concentration of NO2 (for 24 hrs) ranged from 29 µg/m3 to 83 µg/m3. The minimum value was observed at 1pm and maximum was observed at 11pm. The location-wise minimum concentration was observed at Okhla (7.6 µg/m3) and maximum at Punjabi Bagh (142 µg/m3). In 2017, this had ranged between 43 micrograms per cubic metre and 173 micrograms per cubic metre. In 2016, this was between 70 micrograms per cubic metre and 123 micrograms per cubic metre. The permissible amount is 80 micrograms per cubic metre.

Sulphur Dioxide (SO2)

On Diwali this year, the average concentration of SO2 (for 24 hrs) ranged from 15 to 81 micrograms per cubic metre. The minimum value was observed at 7am and maximum at 11pm. The location-wise minimum concentration was observed at Narela (3.1 µg/m3) and maximum concentration was observed at Karni Singh (50.8 µg/m3).

In 2017, this was between 20 to 89 micrograms per cubic metre and in 2016, this was between 20 to 131 micrograms per cubic metre.