Key facts
- One cigarette per day ≈ a PM2.5 concentration of 22 µg/m³ sustained for a day.
- The equivalence is based on matched health outcomes, not on the weight of particles inhaled.
- The figure comes from Berkeley Earth’s 2015 analysis of air pollution mortality in China.
- Unlike smoking, this exposure reaches every age group and cannot be opted out of.
Cigarette Equivalent
How the conversion works
The calculator takes the current AQI for the city you select, converts it back to a PM2.5 concentration using the US EPA breakpoint table, and divides by 22 µg/m³ — the concentration Berkeley Earth equates to one cigarette per day.
Richard and Elizabeth Muller derived that ratio by comparing deaths rather than dose. Starting from roughly 1.37 deaths per million cigarettes smoked, and from an estimated 1.6 million annual deaths in China at a mean exposure of 52 µg/m³, they found the average Chinese resident was absorbing a health impact comparable to 2.4 cigarettes a day. That works out to one cigarette per 22 µg/m³.
Reference values from the original analysis
| Location | Cigarettes per day equivalent |
|---|---|
| United States, average | 0.4 |
| European Union, average | 1.6 |
| China, average | 2.4 |
| Beijing, annual average | 4.0 |
| Beijing, bad day | 25.0 |
| Shenyang, worst recorded | 63.0 |
What the comparison does not mean
It does not mean the particles are identical. The researcher Arden Pope previously published a far lower figure — around 0.3 cigarettes per day for Beijing — because he compared the mass of PM2.5 inhaled rather than the resulting health effects. Both calculations are internally correct; they answer different questions.
It also does not mean the two exposures are interchangeable in a clinical sense. Tobacco smoke and ambient particulate matter differ in composition and toxicity, and the relationship between exposure and outcome is a population-level statistic rather than a prediction about any individual.
- The number describes a population-average risk, not your personal risk.
- It assumes the concentration is sustained for a full day.
- It does not account for time spent indoors, filtration, or mask use.
- It is a communication device, not a diagnostic or clinical measure.
Reducing your own figure
- Most people spend the large majority of the day indoors, where filtration can cut the concentration substantially.
- A well-fitted N95 or FFP2 respirator removes most fine particles during outdoor time and commutes.
- Shifting outdoor exercise away from peak traffic hours lowers both concentration and breathing rate.
- The personal exposure calculator models these adjustments rather than assuming constant outdoor exposure.
Frequently asked questions
How many cigarettes a day is Delhi’s air equivalent to?
It depends entirely on the day. At a PM2.5 concentration of 110 µg/m³ the equivalent is about 5 cigarettes per day; during a severe winter episode above 300 µg/m³ it exceeds 13. Enter Delhi in the calculator above for the current figure.
Where does the 22 µg/m³ per cigarette figure come from?
From a 2015 Berkeley Earth memo by Richard and Elizabeth Muller, which equated the health impact of air pollution deaths in China with the health impact of cigarette smoking in the United States.
Is breathing polluted air really the same as smoking?
No. The equivalence matches statistical health impact at a population level. The particles differ in composition and toxicity, and unlike smoking, air pollution exposure is involuntary and affects infants and elderly people alongside everyone else.
Does staying indoors lower the equivalent number?
Usually yes. Indoor PM2.5 is typically a fraction of outdoor levels, and a HEPA purifier lowers it further. The calculator on this page uses ambient outdoor concentration, so it represents an upper bound for most people.
Sources
This reference was prepared from the following primary public-health and regulatory sources:
- Air Pollution and Cigarette EquivalenceBerkeley Earth
- WHO Global Air Quality GuidelinesWorld Health Organization
- Health and Environmental Effects of Particulate MatterUnited States Environmental Protection Agency