As to the question of rules regarding when and where peaceful protests may be held, that's highly dependent on the specific location of the protest.
The venturi mask, also known as an air-entrainment mask (and sometimes by the brand name VentimaskÂ®), is a medical device to deliver a known oxygen concentration to patients on controlled oxygen therapy.
Others recommend a dab of Vapo-rub under the nose to cover it. If you think of that option and realize that it actually opens up your nasal passages to even more of the odor molecules, I think not. Face masks help some, a gas mask-like respirator device works, but is cumbersome.