by Richard A. Muller and Elizabeth A. Muller
For many people, comparing air pollution to cigarette smoking is more vivid and meaningful than is citing the numbers of yearly deaths. When we published our scientific paper on air pollution in China in August 20151, we were surprised by the attention we got for a quick comparison we made comparing air pollution on a particularly bad day in Beijing to smoking 1.5 cigarettes every hour. We were also surprised to find that a prominent researcher, Arden Pope, had previously calculated that average pollution in Beijing is similar to smoking 0.3 cigarettes per day – and that this comparison is used to reassure people that the pollution really isn’t that bad.
In this memo, we will derive the rough value of conversion, so people can think of air pollution in terms of cigarettes equivalent. The sole goal of this calculation is to help give people an appreciation for the health effects of air pollution. We will also discuss the apparent discrepancy with Arden Pope (now resolved), which stems from our comparing the health impacts of cigarettes, rather than the amount of PM2.5 (the most deadly pollutant) delivered.
In summary, we find that air pollution can be approximated as cigarettes equivalent as follows:
|Air Pollution Location
|Equivalent in cigarettes
|Beijing, bad day
|Harbin, very bad day
|Shenyang, worst recorded
We start with some numbers estimated by the US Center for Disease Control: 480,000 people die in the US every year due to smoking.2 The number of cigarettes sold in the US has been dropping, from 470 billion per year in 1998, to 280 billion per year in 2013. For the purpose of our rough estimate, we will take an average number of 350 billion; it is easy to adjust the numbers using different values.
Now we combine these numbers. The ratio of deaths per year, to cigarettes per year, is 0.00000137, expressed in scientific notation as 1.37 x10-6. Put another way, there are 1.37 deaths every year for every million cigarettes smoked. We note that this figure agrees with the value of 1.4 published by Bernard Cohen in 1991.3
Now let’s consider air pollution. The most harmful pollution consists of small particulate matter, 2.5 microns in size or less, called PM2.5. These particles are small enough to work their way deep into the lungs and into the bloodstream, where they trigger heart attack, stroke, lung cancer and asthma. In the Berkeley Earth review of deaths in China we showed that 1.6 million people die every year from an average exposure of 52 μg/m3 of PM2.5. To kill 1.6 million people would require, assuming 1.37 x10-6 deaths per cigarette, 1.1 trillion cigarettes. Since the population of China is 1.35 billion, that comes to 864 cigarettes every year per person, or about 2.4 cigarettes per day.
Thus the average person in China, who typically breathes 52 μg/m3 of air pollution, is receiving a health impact equivalent to smoking 2.4 cigarettes per day. Put another way, 1 cigarette is equivalent to an air pollution of 22 μg/m3 for one day.
The average PM2.5 in Beijing over the year is about 85 μg/m3, equivalent to about 4 cigarettes per day. The average value in the industrial city of Handan, about 200 km south of Beijing, is about 120 μg/m3, equivalent to 5.5 cigarettes/day. We were in Beijing when the level rose to 550 μg/m3, equivalent to 25 cigarettes per day. In Harbin, the air pollution has reached the limit of the scale, 999 μg/m3. That would be equivalent to 45 cigarettes per day. As we are writing this, the air pollution in New Delhi, India, is 547 μg/m3, equivalent to about 25 cigarettes each day. A recent peak reported in the Washington Post for the city of Shenyang4 set a new record of 1400 μg/m3, equivalent to over three packs of cigarettes per day for every man, woman, and child living there.
Here is the rule of thumb: one cigarette per day is the rough equivalent of a PM2.5 level of 22 μg/m3. Double that level, and it is equivalent to 2 cigarettes per day. Of course, unlike cigarette smoking, the pollution reaches every age group.
The EPA estimates5 that the average air pollution in the United States in 2013 was 9.0 μg/m3. That is equivalent to 0.41 cigarettes per day for every person in the US. From our crude calculation, and taking into account the US population, that average exposure would be expected to lead to 66,000 deaths per year in the US. That is in reasonable agreement with the value of 52,000 per year published by Caiazzo et al. 6
Europe’s Environment Commissioner, Janez Potocnik, noted that pollution caused 400,000 premature deaths in 2010 in Europe.7 That’s equivalent, for the EU population of 508 million, to everyone smoking 1.6 cigarettes per day.
This sounds bad, but it may be even worse. The US EPA estimates that for every smoking death, there are 30 other people who suffer significant smoking- related health impairment.
Comparison of methods with Arden Pope
Arden Pope had published a number equating the average pollution in Beijing to about 0.3 cigarettes per day, nearly a factor of 10 lower than our value. His value was based on the comparison of the weight of the inhaled component of PM2.5 from smoking cigarettes, not on observed health effects. We discussed his number at some length with him, and he has subsequently gave us permission to quote his current stand as follows: “Although the potential differential toxicity of fine particulate matter air pollution from various sources is not fully understood, fine PM from the burning of coal, diesel, and other fossil fuels as well as high temperature industrial processes may be more toxic than particles from the burning of tobacco.”
For the current memo, rather than just compare the amount of material absorbed in the body, we considered the equivalence of health effects from air pollution and smoking, and that is what our table represents.
Air Pollution kills more people worldwide each year than does AIDS, malaria, diabetes or tuberculosis. For the United States and Europe, air pollution is equivalent in detrimental health effects to smoking 0.4 to 1.6 cigarettes per day. In China the numbers are far worse; on bad days the health effects of air pollution are comparable to the harm done smoking three packs per day (60 cigarettes) by every man, woman, and child. Air pollution is arguably the greatest environmental catastrophe in the world today.
- Rohde and Muller, 2015, Air Pollution in China: Mapping of Concentrations and Sources, PLOSONE
- Bernard L. Cohen, 1991, Catalog of Risks Extended and Updated, Health Physics vol. 61, pp. 317-335.
- http://news.nationalpost.com/news/doomsday-smog-shenyang-records-worst- air-pollution-reading-since-china-started-monitoring-smog