OK, next story. Air pollution, it's well-documented that it can cause lung problems. But can it hurt the human brain. Researchers at Lancaster University in the United Kingdom say yes. They took a look at brain samples from dozens of people who live in polluted areas and they say they found the same kind of particles in the brain that are found in polluted air. They say these particles are toxic. They believe the particles entered the brain when people breathe in polluted air, and they think these pollution particles could increase people's risk of developing Alzheimer's disease.
But there is room for doubt. For one thing, similar particles are produced naturally in the brain and an expert from University College London says any correlation between pollution particles and Alzheimer's disease is weak. Scientists agree that more research needs to be done on this.
Still, experts in several major cities are taking steps to help lower levels of air pollution.
ANDREW GRIEVE, SENIOR AIR QUALITY ANALYST, KINGS'S COLLEGE LONDON: Although you don't feel it day to day, it's a cumulative effect. Everyone is exposed to it, from your first breath to your last breath, you know, little kids, older people, people who respiratory conditions.
But also, if you reduce it just a little bit, because you're affecting the whole population, they can have a huge effect, beneficial effect.
REPORTER: In January of 2016, London took just over one week to reach its own annual limits of nitrogen dioxide. That's a toxic gas which comes from vehicle exhaust.
RUTH CALDERWOOD, CITY OF LONDON CORPORATION: We see drivers who are parked with their engines idling as an unnecessary source of local pollution. So, what we do is we go out, speak to drivers, ask them if they can turn their engines off. We have evidence that it does make a difference here locally.
UNIDENTIFIED MALE: Good morning. Hi. We're doing some volunteer work this morning on air quality on the city.
REPORTER: Switching off engines may seem like a small action. But experts have tracked an improvement in pollution levels on the days when air quality worsens are actually active.
UNIDENTIFIED MALE: So, thank you for turning it off.
REPORTER: Andrew Grieve suffered from asthma as a child. Now, he's a scientist who analyzes air quality and one of his jobs has been building city air that's enough which helps people navigate pollution hot spots.
GRIEVE: I've got kind of like a pollution map overlaid on the top of map, which is updated every hour. So, here, I plotted the route from Liverpool Street Station to Bank Station. There's a route here through the backstreets, which is 28 percent less polluted than behind it.
REPORTER: Individual actions are creating localized solutions which benefit everyone.