Air pollution kills 3.3 million people a year. In some parts of the world it's already so bad that people need pollution filters in their cars and homes. Pollution exposure in utero has been associated with increased risk of
neuro-developmental delay. Thirty one studies published between 2006 and 2015, from the Americas, Asia and Europe were reviewed by the National Center for Biotechnology Information (NCBI) and the review came to this conclusion:
"The evidence to date is coherent in that exposure to a
range of largely traffic-related pollutants has been associated with
quantifiable impairment of brain development in the young and cognitive decline
in the elderly. There is insufficient evidence at present to comment on
consistency, in view of the different indices of pollution and end-points
measured, the limited number of studies, and the probability at this stage of
publication bias. However, plausible toxicological mechanisms have been
demonstrated and the evidence as a whole suggests that vehicular pollution, at
least, contributes to cognitive impairment, adding to pressure on governments
and individuals to continue to reduce air pollution."