Less heavy industry in the LA Basin and much cleaner internal combustion. In those days both gas and diesel used to belch black smoke.

It is like Lake Erie got a lot cleaner when the industry went overseas.

But one thing I believe was environmentally better at that time. Notice how biting the sun in May and June is these days? You can get a good sunburn in 15 minutes at midday. I suspect the ozone layer is in worse shape than the authorities reveal.