The bar was closed, and at a table in the back sat someone new: an engineering professor whose specialty is air quality.“If this is going to work right, the ventilation keeps up with the head count,” explained the expert, Mark Hernandez of the University of Colorado. Every 15 minutes, he would walk to the front desk to check how many people were now seated indoors. Then he would compare that number to the air’s current levels of carbon dioxide and particulate matter, to see how much exhaled breath lingered in the air and what expelled aerosols it could contain.Indoor dining remains risky,...…The bar was closed, and at a table in the back sat someone new: an engineering professor whose specialty is air quality.“If this is going to work right, the ventilation keeps up with the head count,” explained the expert, Mark Hernandez of the University of Colorado. Every 15 minutes, he would walk to the front desk to check how many people were now seated indoors. Then he would compare that number to the air’s current levels of carbon dioxide and particulate matter, to see how much exhaled breath lingered in the air and what expelled aerosols it could contain.Indoor dining remains risky,...WW…