I live 2 miles from Napa County line. Napa itself is about 15 miles away. Air quality has been quite good. But that can change weekly. As Yogi Berra use to say, "Nobody goes there anymore. it's too crowded." Highway 29 can be a mess on the weekends. Either travel on Silverado Trail or head over to Highway 12 in Sonoma. Many of the wineries require reservations. I would select a few based on the types of wines you drink, Cabernet, Merlot, Chardonnay, sparkling wine, sweet/dry, etc. Grab a map and plan it out.
We like to drop in at Walmart in Napa or Genova Delicatessen, 1550 Trancas St., Napa and grab some baguettes, salami, cheese, raviolis, and artichoke frittatas and drive to Yountville. If it's not too crowded, which is rare, grab some pastries and baguettes from Bouchon Bakery, one of our favorites and have a picnic down the street. If you don't want to hassle with that, drop into V. Sattui, which has a full deli and you can picnic on their grounds under some shaded trees. They do not allow outside food though.
If you want fewer people, you can go over the hill to the parallel valley, Sonoma Valley and specifically, Valley of the Moon where there are just as many high quality wineries and a less frenetic pace. Stopping into Glen Ellen and checking out Jack London State Park is always nice. But whatever you do, plan it out and make reservations.
Have a great trip.