Lima suffers most from air pollution. The sedimentary dust has solid particles that settle as dust on different surfaces or float through the air. The fine particles are the most dangerous given that they are able to damage human respiratory systems. The recommended limit of these particles by the World Health Organization is 5 tons/km2/month. In February 2014, Lima recorded an average of 15.2 tons/km2. The two districts with the highest concentration of sedimentary dust are El Agustino (46.1 tons/km2) and Independencia (25.5 tons/km2) in February 2014.