Have you heard of PM2.5? If not, you should read this
PM2.5 is a unit of measurement of a particular kind of air pollution.
It refers to particles so small (2.5 microns in diameter) that they can penetrate deep into the lungs, and have been linked to a wide variety of diseases.
In fact, a recent study out of the UK (https://bbc.in/2vgyvZo) revealed that even low levels of exposure to PM2.5 (8 to 12 micrograms / cubic meters).
What they found was that people exposed to PM2.5 were beginning to suffer from enlargement of the left ventricle of the heart: an early stage in the development of heart diseases, REGARDLESS of their lifestyle (diet, exercise, smoking, etc).
In fact, they found that for every additional 1 microgram/m3 of PM2.5, the heart enlarged by 1%. For example, if you live in city with a PM2.5 score of 30 micrograms / m3, your heart is likely to be 10% enlarged compared to someone in a city with a score of 20.
The good news is that this enlargement of the heart is likely reversible by spending time in clean air, exercise, and giving your body what it needs to fight environmental pollutants (anti-oxidants from fruits and vegetables, Omega 3, etc).
Remember that those effects were seen in areas where PM2.5 scores were above 10. The World Health Organisation recommends a limit of 10 too for health.
Here are the PM2.5 score of some countries of interest (in micrograms / m3):
Lebanon: 33 (probably much much higher on the coast).