If you live in or around Bakersfield, Calif., and you don’t already own a high quality HEPA air purifier, here’s another incentive: Your hometown has just been named the dirtiest city in America by Forbes.com. By averaging data from the American Lung Association’s State of the Air Report released earlier this year, Forbes was able to compile a single list of the cities with the dirtiest air, based on three criteria: year-round particle pollution, 24-hour particle pollution and ozone pollution.

One is tempted to interpret the Forbes list in another way: These are the places in the United States where you most need an air purifier to help rid your indoors air of the bad air outdoors. But that interpretation would be true only in reference to particle pollution. The list of worst cities for allergies, for example, reads differently from the list of most polluted cities.

Why Bakersfield? Fertilizers, pesticides, dust from tractors and other vehicles all contribute to the problem. And because the city is surrounded by mountains on three sides, there is nowhere for particulate pollution and ozone to go. Two major freeways also bring a steady stream of vehicle exhaust to the region as cars and trucks pass constantly through the San Joaquin Valley, in which Bakersfield and many other top dirtiest cities lie, in transit between the mega-population centers of Northern and Southern California.

But if they need air purifiers in Bakersfield, there are plenty of other California locales that don’t fare much better, according to Forbes. Next on the list is Los Angeles (with the worst ozone in the U.S., and among the worst particle pollution), followed by Visalia (#3) and Fresno (#4). The fifth dirtiest city is the first on the list not in the Golden State: It’s the steel-producing center of Pittsburgh, whose ozone levels only rank #24 but whose particle pollution levels are an ongoing public health concern. Some schools downwind from Pittsburgh have recently made headlines hoping to install air purifiers in classrooms to help kids breathe better, at least for a few hours a day.

Two other non-California cities are included in the top ten dirtiest cities list, including Birmingham, Ala. (#7), and Phoenix, Ariz. (#8). Other California cities making the list: Modesto (#6), San Diego (#9) and Sacramento (#10).