Most of the pollution comes from the coal power plants and the vehicle emissions (due to the exploding number of cars in China). Factory emission is relatively less or actually declined. However, as the no. power plant and vehicle emission (i.e. carbon monoxide) are on the increae and those catalylic converters in Mainland cars are either non-existent or malfunctioning, leading to incomplete combustion, the total volume of pollution is increasing.
As for the factory condition, it depends. My bro works at a multinational company with factories in the PRD. The larger firms tend to offer better working conditions then the smaller firms, as the big companies do not want to be critcized for sweat shop labour conditions. So most of the big firm's factories have fairly reasonable working conditions. Foxconn, the Taiwan firm responsible for making Apple's ipod and ipads, has 300,000+ employees, so an occassional suicide cannot be ruled out due to the sheer size of the company. However, the smaller local firms with tight budgets and profit margins are another story, they are willing to cut cost and corners in areas you don't want to know...
All in all, if it weren't for the pollution, Hong Kong is actually not a bad place to live, the public transportation is clean and efficient, crime rate is low and there is wide usage of English. The ever worsening pollution from the north however is a serious problem.