Living in an area with PM2.5 levels of 18.6 µg/m3 is equivalent of smoking one cigarette every day.
Read the article below to understand the science behind this scary number. The article lists top 150 of the world’s most polluted cities and their annual average PM2.5 levels.
I know that most of you are non–smokers. However, what if I told you that depending on where you live, you are inhaling enough air pollutants that your health risks are on par with, or worse than, those of smokers?
Read on to find out exactly how many ‘cigarettes’ you smoke daily.
Air pollution has various components, such as coarse and rough particles, toxic gases, and biological contaminants. Here is a brief primer on these: Air pollution – various acronyms, numbers and units.
The most insidious of the common air pollutants are fine particles called PM2.5. These are airborne particles smaller than 2.5 µm in size. They are at least 20 times smaller than the width of your hair.
Due to their very small size, your body has no defense against them. They enter your bloodstream unhindered, via your nose and lungs. And, through blood, they travel all around your body, triggering allergy and asthma attacks, lung cancer, stroke, and heart attacks.
They have been designated Grade I Carcinogen by the World Health Organisation (WHO). That means, there is sufficient evidence to show that they can cause various cancers.
Since PM2.5 is the main pollutant present outdoors as well as indoors, the level of air pollution at any place is mostly the result of the ambient PM2.5 values.
PM2.5 and mortality
Every day, there are many deaths worldwide that are attributed to air pollution. To know this number, scientists measure the normal death rate in an unpolluted region. The increase in the death rate, if any, in a polluted town is, then, attributed to air pollution.
Researchers have found that as the average pollution in a locality rises, the death rate increases in a continuous manner. Exhibit 1 at the end of this article shows how death rate increases with rising PM2.5 levels.
However, for ordinary people, it is difficult to visualize this deadly effect of PM2.5. So, to offer some perspective, researchers at Berkeley Earth came up with an ingenuous method.
Berkeley Earth is an independent, non–profit organisation specialising in climate science. It is based in California, USA.
They compared the mortality, or the chance of death, from PM2.5 with that from cigarette smoke. They found that an annual average PM2.5 level of 22 µg/m3 was equivalent to smoking one cigarette a day.
Both of these lead to roughly the same increase in one’s chances of dying.
Thus, by converting your local PM2.5 pollution levels into an equivalent ‘cigarettes smoked in the day’ number, you can visualise how severe the effects of air pollution will be on you and your family.
Calculating PM2.5 and cigarette equivalence
As per the US Center for Disease Control (CDC), 480,000 people die in the USA every year due to smoking.
As per the US Environmental Protection Agency (EPA) estimates, 100,000 people die in the USA every year due to air pollution.
Roughly, 249 billion cigarettes are sold in the USA every year. The population of the USA is 325 million. So, on an average, each American person smokes 766 cigarettes a year, or 2.1 cigarettes a day.
As per the EPA, an American lives in air with annual average PM2.5 levels of 8.16 µg/m3.
Thus, smoking 2.1 cigarettes a day is equivalent to getting PM2.5 exposure of 4.8 x 8.16 µg/m3 or 39.2 µg/m3.
In other words, smoking 1 cigarette a day is equivalent to getting PM2.5 exposure of 18.6 µg/m3.
Living in an area with annual average PM2.5 levels of 18.6 µg/m3 would lead to the same risk of death (mortality) as with smoking one cigarette a day.
Thus, for every additional PM2.5 increase of 18.6 µg/m3, you can visualise yourself and each of your family members to be smoking one cigarette a day.
This calculation is done with the latest available data. Using somewhat older data — 3 to 14 years old — Berkeley Earth scientists came up with the number 22 µg/m3. As per their scientists, living in PM2.5 levels of 22 µg/m3 is equivalent to smoking a cigarette a day.
If your local PM2.5 level is, say, 100 µg/m3, you can calculate the cigarette equivalence of the air pollution as follows:
100 µg/m3 / 18.6 ≡ 5.4 cigarettes a day.
Thus, if you live in an area where the annual average PM2.5 levels are 100 µg/m3, your risk of death is roughly equal to that if you were smoking 5.4 cigarettes every day.
The table 1 below gives the list of most polluted 150 cities in the world and their annual average PM2.5 values. Using the above equivalence, the table also shows how many ‘equivalent’ cigarettes a day a typical resident of that city is smoking.Table 1. World's most polluted cities, ranked by annual average PM2.5 values, and equivalent number of cigarettes smoked by the residents of those cities.
|Rank||City||Country||Average PM2.5||≡ Cigarettes/day|
|93||Dubai||United Arab Emirates||55.3||3.0|
|136||Abu Dhabi||United Arab Emirates||48.8||2.6|
You will notice that even the 150th most polluted city has annual average PM2.5 levels of 46.3 µg/m3, which is equivalent of smoking 2.5 cigarettes every day.
For more interesting stuff, read an article on this website that compares air pollution due to firecrackers, cigarettes, and PM2.5 particles.
The difference between smoking and PM2.5
This cigarette equivalence is to make us understand and visualise the risk due to air pollution. While the risks due to smoking and air pollution are similar, there are still some differences, as discussed below.
You can skip the technical discussion below and directly go to the section at the end on relevance for air purifier selection.
Air pollution affects all family members
When we think of smoking, we consider a smoker or two in the family. The young children, and very senior adults are not viewed as smokers.
The main risk of smoking is borne by the primary smoker. The non–smoking family members end up with just secondary smoking. The risk from secondary smoke is relatively less compared to that faced by the smoker.
However, with the air pollution, every single member of the family faces the same risk. Thus, the small baby and the elderly grandmother also suffer as if they were smoking multiple cigarettes.
Mortality versus morbidity
For every person who dies (mortality) due to smoking, there are at least 30 people who live with a serious smoking–related illness (morbidity). Thus, the damage due to smoking happens not only in terms of death but also in the form of serious health disorders.
The disease pattern and their risks due to air pollution will be different from those due to cigarettes. To account for morbidity, we may need a different equivalence.
In our calculations, we consider only the risk of death (mortality) for comparison, and not mortality.
Smoking and mortality relation
The risk of death rises linearly with the number of cigarettes smoked per day. Doubling the number of cigarettes smoked doubles the mortality. However, men face slightly higher mortality for the same number of cigarettes smoked per day.
In our calculations, we consider men and women to be affected equally by smoking cigarettes.
PM2.5 and mortality relation
As you can see in exhibit 1 below, the risk of death rises logarithmically, and not linearly, with rising PM2.5 levels. Thus, doubling of pollution does not necessarily double the mortality.
At low levels of PM2.5, the equivalence calculated above is fairly accurate. However, the mortality increase with PM2.5 follows a different curve (logarithmic) than the mortality increase with cigarettes smoked (linear).
As a result, at very high levels of PM2.5, the exact equivalence number will increase. It will take more increase in PM2.5 to be as bad as smoking yet another cigarette.
For example, PM2.5 of 18.6 µg/m3 is equivalent of smoking 1 cigarette a day. But, five times higher PM2.5 of 93 µg/m3 might be equivalent of smoking just 3 cigarettes a day.
Incidentally, exhibit 2 below shows Air Quality Index (AQI) US versus PM2.5 levels. Can you guess why the graph is not a straight line? See if you can get a hint from exhibit 1.
As per the exhibit 1, the risk due to air pollution does not rise linearly with increasing PM2.5 levels. Initially, it rises sharply and then it kind of tapers off.
Air quality index (AQI), in a way, measures the quality of air as regards to its effects on health and mortality. Hence, it will not be surprising that exhibits 1 and 2 look similar to each other.
Relevance for air purifier selection
Key observations from Exhibits 1 and 2
The PM2.5 risk is concentrated mostly at the low levels. At high pollution levels, rising PM2.5 does not increase the health risk as rapidly.
Inverting the argument, if your city has half the pollution levels of a highly polluted city, such as New Delhi, India, your risk is not 50% that of a New Delhi resident. It will be 70% of the New Delhi risk.
It will take 4 times lesser pollution than in New Delhi for the risk to reduce to half (70% x 70% = 49%).
The health risk due to PM2.5 disappears completely below 5.8 µg/m3. While WHO standards suggest the safe levels of PM2.5 to be 10 µg/m3, exhibit 1 suggests that a better cutoff for safety should be 5.8 µg/m3.
If one were to use an indoor air purifier to lower PM2.5 levels, it is important to use a unit that completely removes the pollution.
Many inexpensive air purifier units lower PM2.5 level but they don’t bring the level below 5.8 µg/m3. Don’t ever go by marketing claims made in brochures.
Ask for a pollution measuring meter. Take it to the room where you want to keep the air purifier. Check the actual PM2.5 levels at the start. See if the levels go below 5.8 µg/m3 levels within a maximum of 20 minutes of operation at the highest speed of the unit.
At nights, most machines are kept on silent or quiet mode. The machine speed is low in this setting.
If your machine cannot bring the pollution down to safe levels, below 5.8 µg/m3, in 20 minutes of high speed operation, it will take hours at night (when it is in quiet or slow mode) to do the same.
- Spend as much time as possible in air with low PM2.5 levels.
Since the air pollution effect depends on the average time spent in the polluted air, reduce the average PM2.5 exposure.
- Choose air purifiers that can remove PM2.5 to 5.8 µg/m3 or below.
Test the purifier with PM2.5 measuring meter in the actual room, before deciding on it.
First published on: 1st September, 2019
Image credit: Gerd Altmann from Pixabay