You go out and breathe toxic air for 40 minutes, he said, and it does more harm than good.
Scores of Utahns like Farnsworth have been looking for refuge from the bad air quite a bit lately.
Today marks two weeks straight of poor air quality from Provo to Logan. And high pollution levels are expected to endure at least until Saturday, when a storm might come in and blow the muck away.
There are some solutions, both personal and community-minded. Many Utahns are already experts in coping.
Anytime an alert goes out, people in sensitive groups know to take extra care. They include children, older Utahns and hundreds of thousands of northern Utahns with heart and lung problems.
The problem is so-called PM 2.5 pollution, made up largely of soot particles about 1/40th the width of a human hair and smaller. Autos generate most of the PM 2.5 in Utah, followed by industry, and the pollution builds up during wintertime inversions when cold, dirty air in the valleys gets tamped down under warmer air.
And everyone is affected, since the particles bury themselves deep in the lungs and cause long-term damage that can lead to premature death. So, when levels get high, even healthy people are advised to avoid exertion outdoors.
Kathy Van Dame, director of the Wasatch Clean Air Coalition and a retired nurse, often fields calls from concerned northern Utah residents.
People ask me what they can do, she said.
Air cleaners or purifiers can help. The purifying systems can cost anywhere from $100 to $1,000 and were recently recommended by heart doctors at LDS Hospital who found that increases in PM 2.5 lead to more heart attacks and other acute heart problems.
Van Dame also suggested choosing one that meets "HEPA" standards and that does not produce ozone, another dangerous pollutant.
HEPA applies to filters that screen out all but the tiniest pollutants, bacteria, mold and allergens.
These super-screening filters are available for ordinary gas furnaces for about $15 apiece.
Van Dame said she knows of people who use paper face masks for pollution protection, but she has seen no scientific reviews showing they are effective.
Salt Lake City pediatrician Louis Borgenicht sees more children in his office when the polluted air settles in. There's no question that it's not healthy, he said.
Borgenicht advises patients to stay indoors, if possible, during the pollution. And when the air is cold and the pollution is high, children should be not allowed to exert themselves outdoors, he said.
The issue is larger than getting a HEPA filter, he said. It's social. It's political, and, to an extent, it's economic.
Cheryl Heying of the Utah Division of Air Quality says community measures can have a big impact if people use them to cut down pollution. Car-pooling and using public transit helps.
If you can, drive less, she added. If you can't, drive smarter.
Maureen Card, Farnsworth's sister, sometimes joins him on the mall walks. She and her husband prefer the outdoors, but she developed asthma as an adult, she said.
It's so important to have air quality so we can breathe, Card said. We don't have a chance if we are breathing poison. . . . Our governor and our leaders should do all they can to clean this up.