The mask shown in the picture is an anti-pollution mask (See Amazon).
Furthermore, the city with the worst air pollution in Spain is La Linea de la Concepción as of 2014 (Respro Bulletin Board, and also confirmed on the WHO website (downloadable Excel document)).
La Linea de la Conepción is the city on the Spanish side of the Spanish-Gibraltarian border.
Therefore, I think it is safe to assume that the police officers were wearing the masks for personal protection against the bad air-pollution in the area.
Credit:stackoverflow.com‘
4 Mar, 2024
5 Mar, 2024
4 Mar, 2024