Wildfire Smoke Emergency Declaration Act of 2021 This bill authorizes the President to declare a smoke emergency and provide emergency assistance to affected communities under specified circumstances. Specifically, the President, upon determining that there is, or anticipating that there will be, a significant decrease in air quality due to wildland fire smoke in one or more states, may declare a smoke emergency. The governor or other agency of a state that is or will be affected may request such a declaration. If the President declares a smoke emergency, the Federal Emergency Management Agency (FEMA) and other federal agencies may provide emergency assistance to states and local communities that are or will be affected by the emergency, including grants, equipment, supplies, and personnel and resources for establishing smoke shelters, air purifiers, and additional air monitoring sites. The Small Business Administration may provide grants to any small business concern that loses a significant amount of revenue due to wildland fire smoke in an area in which the President has declared a smoke emergency.