There is an ever-present coating of dust over the City of Beijing and in the spring there are dust storms that coat the entire city with red dust, much of it blown in from the Gobi Desert. People in Beijing do not leave their windows open when they go out. That type of foolhardiness is rewarded with a layer of dust over everything in your home upon your return.
Yesterday I was walking around the Chaoyang District, exploring, when I walked past a new shopping mall, most windows covered but some already displaying the wares inside. A Staples store posted a UPS logo in its window. On the sidewalk were two men, squatting in their uniform of black pants and white jackets while taking stones out of the street tree pits, putting them in buckets of water to soak, scrubbing them by hand, laying them to the side to dry, and then putting them back into the pit.
Labor is cheap in China. The minimum monthly wage in Beijing was recently raised to 730 RMB (~$100). There are always new arrivals from distant villages and that amount is more than many of them could make at home.
Those stones, cleaned by hand, will be coated in dust again in a few hours.