Dust levels in the air in Bulgaria have remained above the norm throughout January, because of fog that had covered the county several times over the month, the executive environmental agency said on January 22.

Between January 9 and 10, dust levels in the air in Sofia were four times the norm of 50 mg p cu m, AFP news agency said.

In Plovdiv, dust pollution reached levels six times the norm only a week ago, the highest levels in two years, AFP quoted data from the environmental agency.

The increased dust levels led to a two-fold increase in the number of patients treated for breathing illnesses over the past six weeks, 24 Chasa daily quoted Plovdiv hospital chief Georgy Blagoev as saying.

Authorities blamed the air pollution on thick fog that was said to trap dust emitted by the industry, coal-fired heating plants and traffic, AFP said.