Most people don't realize that because it's not true. The air quality of the combined statistical area of San Francisco is worse than that of the CSA containing Pittsburgh, but pollution in the expansive San Francisco-Oakland-San Jose CSA is centered elsewhere, whereas Pittsburgh is the pollution epicenter of its CSA. This is due chiefly to its geography, not some kind of moral failing. San Francisco has very favorable geography for air quality.
As for your linked article, that seems irrelevant. Nobody thinks Hanford, CA is an upcoming tech hub.
Moreover, after growing up in Pittsburgh and living in Seattle, I can tell you that Seattle definitely has less sunlight (it's not even close) than Pittsburgh. So much less that my doctor had to prescribe my Vitamin D to address a deficiency I had when I moved there (after living in Pittsburgh my whole life, no problems).
[1] "California is home to eight of the 10 cities in America where air pollution is worst" https://qz.com/963089/california-is-home-to-eight-of-the-10-...