- Eliminating existing grandfathered-in wood burning fireplaces. Costs almost nothing as measured by dollars.
- Emission controls on restaurant exhaust. This is currently required only for restaurants that chat-grill more than a certain amount of beef. Restaurants that smoke up whole blocks grilling pork, lamb, veggies, etc are exempt. These emission controls are not that expensive.
- Outdated fuel-burning devices such as 2-stroke leaf blowers and old cars. Electric leaf blowers are cheap now. Old cars are fun, and banning or taxing them would be unpopular but would cost almost zero dollars.
https://ca-times.brightspotcdn.com/dims4/default/6c4535d/214...
I would imagine that the average restaurant grill emits very little NOx and a whole lot of PM2.5.
The cleanup for it started in 2006 and is ongoing today. It's only within the past decade that fish finally started swimming in the river. And now the neighborhoods that it runs through are seeing huge increases in property values and new development as this former toxic waste dump is now converted into water-front bike trails and parks.
We absolutely still see the benefits of the Clean Water Act today.