Masked for the task: Two masked workers toil away at a production line for tiles at a workshop of the Monalisa Ceramics Company in Yuantan on Oct. 28. Since it and other ceramics factories have been relocated from Foshan, that city’s air quality has improved, with air quality in the first half of 2008 measuring better than air quality during the same period in 2007. Still, air pollution is a problem, particularly when it comes to respirable suspended particulates. Particulates registered at unsafe levels 20 to 29 percent of the time during the first half of 2008 in Foshan.