AQI 299 to 376: What Delhi’s air around Diwali equals in cigarettes, day by day

Delhi’s AQI stood at 308 at 8:40 am on Wednesday, 11 November, IANS reported from CPCB data. That is ‘very poor’. Of 59 stations, 29 were ‘very poor’ and the rest ‘poor’, with none ‘severe’. The official 24-hour average had slipped to 299 on Tuesday, from 344 on Monday. GRAP Stage III curbs have been in force since 6 November.

Berkeley Earth’s Richard A Muller and Elizabeth A Muller estimated that a day of breathing 22 µg/m³ of PM2.5 does roughly as much harm as one cigarette. They worked it out by comparing deaths linked to smoking with deaths linked to air pollution. Double the pollution and you double the cigarettes. They call it a rough estimate, and it should be read that way.

We converted CPCB’s daily AQI into PM2.5 using the official band ranges. On 5 November, AQI 369 meant about 210 µg/m³, or 9.5 cigarettes. Diwali, 8 November, hit 376, Delhi’s worst Diwali-day reading since 2021, which works out to about 10 cigarettes. Monday’s 344 was about 8. Tuesday’s 299 was about 5.4. This assumes PM2.5 drove the AQI. Business Standard reported that it did at most stations on 11 November.

By the same rule, ‘good’ air, up to 30 µg/m³, is at most 1.4 cigarettes a day. ‘Satisfactory’ tops out at about 2.7, ‘moderately polluted’ at 4.1 and ‘poor’ at 5.5. ‘Very poor’ covers 121 to 250 µg/m³, or about 5.5 to 11.4 cigarettes. Anything above that is ‘severe’. All of these are full-day averages.

Single-hour readings ran far higher. Akshardham logged about 761 µg/m³ of PM2.5 at 11 pm on Diwali night, Business Standard reported. That is one hour, so it can’t be turned into a daily figure. CPCB also drops readings outside its analysers’ 0-1,000 range. Hindustan Times estimated that Monday’s 344 would be about 360 with missing data restored.

WHO’s 24-hour guideline for PM2.5 is 15 µg/m³, or about 0.7 of a cigarette on this rule. India’s own standard is 60 µg/m³, about 2.7 cigarettes. Tuesday was the cleanest day of the week, and our estimate of about 120 µg/m³ is still 8 times WHO’s limit and double India’s. On Diwali, Delhi’s air was about 15 times WHO’s limit.

IMD expects ‘very poor’ air from 11 to 13 November as winds slow, NewsBytes reported. IANS said stronger winds could bring some relief over the next few days. Another method, based on how much particle mass you breathe in, gives a figure nearly 10 times lower. Use the cigarette comparison for scale only. For health decisions, go by CPCB’s daily bulletin, GRAP advisories and your doctor.