re: What were the grinders grinding?
It's not the substance, but the volume and the quality. The Chicago Tribune points out that Blommer fails to meet standards on opacity. Particulates in that volume can in fact harm people with asthma and other respiratory ailments, as well as the very young and the very old, who are more vulnerable to a great many health issues than adults and older children are.
We have many small chocolate factories near us. It's a well-known phenomenon that when one can smell chocolate at the high school, it will rain. Prevailing winds and all. Yet we have no environmental problems or adverse health effects resulting from the chocolate aroma, but we have no billowing clouds of cocoa powder on Market Street either.