A thick fog engulfed Athens yesterday, leading to flight disruptions and reviving pollution concerns. Several domestic flights were canceled and two incoming international flights were forced to land in Iraklion. Experts attributed the thickness of the fog to humidity and heavy pollution. «The great concentration of pollution particles in the Athens atmosphere collects moisture, thus forming a blanket of fog over the city,» Michalis Petrakis, director of the atmospheric environment institute of the National Observatory of Athens, told Kathimerini. Meanwhile, the World Health Organization said it would be reducing the precautionary level for air pollution particles in cities. The proposed level is 20 milligrams per cubic meter, as compared to the European Union average measurement of 40mg/cubic meter. «By keeping within these limits we can reduce pollution-related deaths by 15 percent,» said Maria Neira, director of WHO’s public health and environment department. The top count in Athens yesterday was 91 mg/cubic meter.