Whether it be at the national or state level, it's quite a gamut that a bill must run to become a law. One congressman's chief of staff told me several years ago that only 3% of the bills proposed in Congress eventually become law, and most of those that pass are for trivial things like declaring broccoli the vegetable of the month. I'm not sure if that 3% number is accurate (it might be high, especially in the current Congress), but his point was simply to illustrate, as is also done in the great Schoolhouse Rock video above, that it is very difficult to pass legislation.
Air Quality related bills still in play this legislative session include one to phase out wood-burning stoves (see this Salt Lake Tribune article) for home heating. It would be nice if we could ban wood burning altogether in winter, but this is a start. I had hoped that we might see a push to adopt cleaner Tier 3 gasoline sooner rather than later, which Gov. Herbert has advocated for, but as things stand now, only a house resolution that that urges (rather than binds) the powers that be to speed up the process has moved out of committee. Several bills incentivizing mass transit remain in play and it would be great if we saw something significant pass in this area.
Much can happen in the final days of the legislative session and sometimes there are surprises (good or bad). We'll see what arrives on the governor's desk in a couple of weeks.