Real science is never settled, and anyone who has certainty on such things is not qualified to discuss it.
The COVID terrorists have made it darn hard to buy N95 or N100 particulate respirators.
An N100/P100 particulate respirator blocks 20X more than an N95. Both types must be fitted snugly to prevent leakage, and an N100 makes this much easier (at least the 3M ones I use). Valved masks are terrific for forest fire smoke.
N95 respirators offer the best protection against wildfire smoke and other types of air pollution, performing better than synthetic, cotton and surgical masks.
Researchers performed lab experiments to investigate the ability of different face masks and respirators to filter out particles in a range of sizes found in smoke and air pollution. They placed the different mask materials over a pipe that "breathes" in air and particles inside a plastic box.
N95s were so effective in the lab experiments that the researchers estimate their widespread use could reduce hospital visits attributable to wildfire smoke by 22% to 39%. The study's findings can provide evidence-based recommendations to help people protect themselves during wildfire season.
They found that N95s offer the best protection against wildfire smoke, reducing a person's exposure by a factor of 16. Synthetic and cotton masks do a poor job of filtering out the particle sizes found in wildfire smoke, and only reduced exposure by a factor of 2.2 and 1.4, respectively. Surgical masks filter more than 90% of the particles but previous research has shown they let about 50% of the air leak around the mask, making them only about as effective as the synthetic and cotton options.
N95s also worked best against larger dust particles and urban air pollution, which contains particles from car exhaust that are even smaller than particles from wildfire smoke.
Kodros emphasizes that these mask recommendations are specific to air pollution and do not apply to the coronavirus. "For COVID-19, you're wearing a mask to protect yourself and also to reduce your own emitted droplets," he said. Fabric masks have been shown to be effective for public health during the current crisis and the Centers for Disease Control and Prevention (CDC) recommends the use of masks with two or more layers of fabric that fit snugly over the nose and mouth.
WIND: if they work this well, and surgical masks and cotton masks work so poorly, then I’d bet this explains why masks for COVID as commonly worn do absolutely nothing to stop community spread (zero credible studies showing so).
The last paragraph is about avoiding criticism (up is down and down is up when it comes to COVID), and cites non-credible bullshit positions taken by the CDC based on non-science that repudiates decades of scientific literature.