A mask someone could wear for hours will never block all smells. Even in a N99 you still smell gases and other small things
N95 – Filters at least 95% of airborne particles. Not resistant to oil.
Surgical N95 – A NIOSH-approved N95 respirator that has also been cleared by the Food and Drug Administration (FDA) as a surgical mask.
N99 – Filters at least 99% of airborne particles. Not resistant to oil.
N100 – Filters at least 99.97% of airborne particles. Not resistant to oil.
R95 – Filters at least 95% of airborne particles. Somewhat resistant to oil.
P95 – Filters at least 95% of airborne particles. Strongly resistant to oil.
P99 – Filters at least 99% of airborne particles. Strongly resistant to oil.
P100 – Filters at least 99.97% of airborne particles. Strongly resistant to oil.
Additionally, see https://www.ecfr.gov/current/title-42/part-84