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A Corsi-Rosenthal air filter is easy to build. Buy four MERV 13 furnace filters, a box fan and some masking tape. Using the fan's cardboard packing, create a cube with a solid cardboard bottom, filters on the sides and a fan on top. Direct the fan blowing upward, so it pulls air through the filters on the side of the box. Seal the edges with masking tape and plug it in. You now have an air filter that's roughly equivalent to the HEPA filters they use in surgical operating suites.

These box filters first became popular during the early days of COVID, when air filtration of small droplets seemed like a good idea. I built a few then, for my classroom, lab and my wife's second-graders. I still have one downstairs in our house, as a device that filters COVID-bearing droplets is also remarkably effective at filtering out smoke when I load our wood stove wrong and it backdrafts.

What does this have to do with the future of Minnesota? Climate change is certainly here, and warmer, drier weather patterns are leading to more frequent forest fires in the parts of North America that are upwind of us ("Ashen gloom, record bad air," front page, June 15). Unlike the methylmercury in walleye from coal-burning power plants, there's no way to opt out of breathing, and everyone in Minnesota will need to either figure out how to mitigate this health risk or suffer the health consequences.

Is wood smoke really that bad? Yes. Richard and Elizabeth Muller wrote a short memo that compared deaths from smoking cigarettes to death from air pollution (in China). In brief, the worst sort of air pollution is particles 2.5 microns or smaller — small enough to move directly into your blood stream — which are linked to many cardiovascular and respiratory problems. Roughly speaking, every 22 μg/m^3 of PM2.5 concentration in the air is equivalent to smoking one cigarette. At 7 p.m. on June 14, the PM2.5 level was about 220 μg/m^3 in St. Paul. If you breathe that air for a day, it's equivalent to smoking about 10 cigarettes.

What kind of future are we going to have in Minnesota? One where we each must take responsibility for mitigating climate change in our literal backyards and living rooms? One where the Legislature (and the feds) do little to keep the situation from getting even worse?

Nathan Moore, Winona, Minn.

The writer is a physics professor.


When we who live in this beautiful city, Minneapolis, decided we wanted to live here, we took on certain responsibilities as good neighbors. One of our jobs is to maintain our wonderful sidewalks. Sidewalks define us as different from suburbs. While walking on a friendly, well-maintained sidewalk, we can admire flowering or snow-laden trees and gardens or freshly-fallen snow, greet our neighbors and witness the beauty of each season. As residents, we need to sweep away summertime tree debris such as scattered branches and seeds as well as litter. In wintertime, we must find a way to shovel snow and chop ice so we can safely walk.

To abandon these jobs and stress our city's strained budget, expecting government to pick up the tab, is unnecessary ("What not to do in Minneapolis: City-funded sidewalk plowing," Opinion Exchange, June 13). Let's consider other funding sources such as revenue from fines levied on noncompliant residents. Those of us who cannot manage sidewalk chores due to age or health could seek assistance from groups looking for volunteer opportunities or who must fulfill community service because they have committed crimes. National Night Out is a perfect opportunity to provide sign-up sheets for young and old to offer to help others with house maintenance chores such as these.

If the city of Minneapolis is looking for ways to help its residents shovel snow, a bobcat could follow our city's street snowplow to open up street corners, driveways and alleys where snow accumulates and accidents are likely to happen. When streets are plowed, heavy, packed snow shoveled up from the street currently lands back in our just-cleared driveways, corners and alleys. This is both a source of frustration and a setup for heart attack or fracture. The City Council has many important issues to handle, including crime. Perhaps those who are found guilty of crimes such as carjacking could be rehabilitated by learning to drive bobcats, shoveling snow for those who are unable or issuing fines to those who are noncompliant.

Working together does not mean finding new ways to avoid our traditional chores. It means remembering the old ways to take care of business.

Carolyn Light Bell, Minneapolis


Thank you, Steve Brandt ("What not to do in Minneapolis: City-funded sidewalk plowing"). It is impractical, expensive and perhaps futile for the city to shovel all the sidewalks in Minneapolis. Your suggestions for other solutions are on target, starting with neighborliness.

A compromise might solve most of the problems: Task the city with snow removal at intersections. Corners are where most kids try to get on the school bus without slipping under it. Metro Transit riders face the same problem. Some years the cross-plowed berms stand tall and freeze solid. Occasionally, after heavy snows, they get so high it's difficult to see cross traffic.

My wife and I like to walk in the winter. With spikes on our shoes, we do OK navigating the sidewalks. Shoveled is best, but uncleared is doable. Mountain-climbing at intersections is not OK. Instead, we look for a path to the street some conscientious neighbor has hacked through the snow dam left by the plows. But then we end up walking in the street. Not optimal for anyone, especially older folks. Clearing corners is scalable, too. Coordinate with schools and Metro Transit to identify where to start.

Keeping intersections free of snow and ice would be expensive, too. But the return on money spent might be worth it.

John Widen, Minneapolis


I work as a criminal prosecutor. Without commenting on any particular case, I believe that Joe Tamburino's June 2 commentary misses the mark ("Could Ellison's book create new appeal grounds for Chauvin?" Opinion Exchange). It's easy to make an assertion that any form of trial preparation has problems, but it's another matter to back up claims of impropriety in court. Prosecutors can conduct practice trials with employee stand-ins for real witnesses to the facts. This can be done in front of mock jurors without in any way generating new information that must be disclosed. The only caveat is that if a real witness in the case is answering questions, that person's statements must be disclosed, mock jury or no. The obligation to disclose all witness statements is well known to courts and prosecutors. Mock juror deliberations appear to be neither exculpatory "Brady" material nor subject to disclosure under criminal procedure rules. As laypeople, the jurors themselves do not offer expert opinions. In addition, mock jurors shouldn't fall under different data practices laws than anyone else doing work for a prosecutor's office because this work already can include volunteers or contractors. Contrary to the claim otherwise, the findings of mock juries would be as much work product as anything generated internally through a law firm's trial prep.

Finally, in the rare event a mock juror found themselves randomly selected to be a potential juror in the real trial of the same case, our justice system is specifically designed to weed out individuals with such a connection through jury selection.

Joe Glasrud, Breckenridge, Minn.

The writer is the Wilkin County attorney.

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