I've never been to the US. Wow, that is 2 decades ago. Does LA still have such issues? If not, how did they improve the air quality?
California has been working on this since the late 60s. They were the first state to require better emissions controls on cars, they have tightened regulations on businesses and industries that would normally negatively contribute, and the push the problems of dirty power generation into other states.
> It took decades. Los Angeles had its first real smog attack during World War II, a smog strong enough that some people suspected a Japanese chemical attack. But it wasn’t until 1975 that the U.S. required new cars to have catalytic converters, “the key piece of technology that allowed everything to change,” according to Mary Nichols, chairman of California’s Air Resources Board.
It feels like (after having lived there) these cities have crossed the threshold for number of people/cars/houses/offices per unit area and the way forward is to force expansion of cities - - reduce number of high rises that can be built - reduce number of cars that can be produced or sold - force/incentivize offices and industries to move out of these big cities - large, safe and economical state owned public transport
If they had left it up to the individual, as India has, we would experience similar air quality.
I should add that California has tighter emissions standards than the federal government, and some vehicles will be sold with special emissions control equipment in California. For example, I had a GMC C1500 truck, which shipped with an optional Air Injection Reactor if you bought it in California.
This has some relevant statistics from the South Coast Air Quality Management District which is larger larger than just LA County but includes it:
http://www.latimes.com/local/lanow/la-me-ln-summer-smog-2016...
It's an uphill battle. There are more hybrid vehicles on the road these days and California has pretty stringent emissions requirements, the Dept. of Motor Vehicles requires you to have a smog check every two years on your car. However the population of L.A has been booming for over a decade now and despite investment in mass transit it hasn't put much any appreciable dent in automobile traffic.
p.s. it's also overcrowded, and there's no public transit. did i mention the food is terrible?