In 1990, Tom Ottney wrote opinion articles about the air filter industry that were critical of the status quo. A need for a less confusing way to rate filters was apparent. To rank the National Air Filtration Association (NAFA) class group by dust diameter (size), a synthetic dust had to be invented to produce artificial discrete sizes of particulate matter for use as “test” dust. Decades later, Ottney reflects on the creation of ASHRAE Standard 52.2-1999.