; and (2) any recommendations for the reduction of rotorcraft noise in the District of Columbia. (d) Relevant operators and entities defined In this section, the term relevant operators and entities means— (1) the Chief of Police of the Metropolitan Police Department of the District of Columbia; (2) any medical rotorcraft operator that routinely flies a rotorcraft over the District of Columbia; and (3) any other operator that routinely flies a rotorcraft over the District of Columbia. 791. UFP study (a) In general Not later than 180 days after the date of enactment of this Act, the Administrator shall seek to enter into an agreement with the National Academies under which the National Research Council shall carry out a study examining airborne ultrafine particles and the effect of such particles on airport-adjacent communities. (b) Scope of study In carrying out the study under subsection (a), the National Research Council shall— (1) summarize the relevant literature and studies done on airborne UFPs worldwide; (2) focus on large hub airports; (3) examine airborne UFPs and the potential effect of such UFPs on airport-adjacent communities, including— (A) characteristics of UFPs present in the air; (B) spatial and temporal distributions of UFP concentrations; (C) primary sources of UFPs; (D) the contribution of aircraft and airport operations to the distribution of UFP concentrations compared to other sources; (E) potential health effects associated with elevated UFP exposures, including outcomes related to cardiovascular disease, respiratory infection and disease, degradation of neurocognitive functions, and other health effects; and (F) potential UFP exposures, especially to susceptible groups; (4) consider the concentration of UFPs resulting from various aviation fuel sources including aviation gasoline, sustainable aviation fuel, and hydrogen, to the extent practicable; (5) identify measures intended to reduce the release of UFPs