Planning on wandering down Pragues picturesque Václavské náměstí this summer? A four-day stay in the Czech capital will be as bad for your health as smoking four cigarettes.

Brussels-based NGO Transport & Environment ranked the 10 most popular tourist cities in Europe and found that the air pollution in many is poor enough to turn city dwellers into smokers. A four-day stay in Istanbul carries the same health risks as puffing on four cigarettes; that figure is three cigarettes for a mini-break in London or Milan.

T&E is using the ranking to draw a link between the well-known dangers of cigarette smoking and the less obvious peril of living in a big city, where the only way of avoiding pollution is to stop breathing.

With air pollution credited with shortening the lives of 400,000 Europeans every year, the NGO argues that “city bosses need to get a grip on air pollution or risk a tourist backlash,” said Jens Müller, an air quality campaigner with T&E.

Pointing out that car emissions are the main source of particulate matter in cities during summer months, T&E said carmakers should be held responsible for reducing pollution by complying with industry limits or else face bans on older diesel cars accessing city centers.

From air to smoke

The idea for a simple polluted air-to-cigarette equivalence comes from researchers at Berkeley Earth, a scientific nonprofit started by Richard and Elizabeth Muller. The father-daughter duo crunched the data and calculated the link.

They first cross-referenced the data on smoke-related lung cancer deaths with the number of cigarettes sold in the U.S. — finding that 1.37 people die annually per million cigarettes smoked.

They then took the average exposure to particulate matter 2.5 (PM 2.5) in China — a fine pollutant that burrows deep into lungs and causes lung cancer, asthma, heart attack and stroke — and the related number of deaths, and calculated that the health impact of one cigarette is equivalent to inhaling 22 micrograms per cubic metre of PM 2.5 for one day.

In other words, anywhere average exposure levels to PM 2.5 are that level or higher, everyone — from babies to grannies to strict non-smokers — is effectively smoking at least one cigarette per day.

Thats a level that many European cities easily exceed. Cities from Paris to Madrid and Hamburg are trying to tackle the problem, often by considering plans that would ban the most polluting cars. The European Commission is also cracking down on countries that fail to meet EU clean air standards, earlier this year referring six members to Europes highest court over the issue.

For people wanting to get a daily read on how much bad air theyre breathing, theres an app for that called Sh**t! I smoke. It says that anyone out and about in Brussels on Friday will be breathing in the equivalent of 2.1 cigarettes.

But any perturbed pedestrian in Prague or Brussels might spare a thought for the poor local in Chinas northern industrial hub of Shenyang, where the Mullers found that on the worst-recorded day, air pollution was equivalent to smoking 63 cigarettes.

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