What are they spraying all over the sidewalks and roads in China?

Here is something I googled. Keep in mind that my entire expertise is from reading the article, but the short answer is “It’s bleach, it can be harmful to people and the environment, and it isn’t really effective.”

Science Magazine – Mar. 12, 2020 - Does disinfecting surfaces really prevent the spread of coronavirus?
“According to a variety of local news reports from cities including Shanghai and Gwangju, South Korea, the disinfectant most commonly used outdoors is a diluted solution of sodium hypochlorite, or household bleach. But it’s unclear whether bleach destroys coronaviruses outside, and if it does kill them on surfaces it’s unclear whether it would kill viruses in the air. Bleach itself breaks down under ultraviolet (UV) light. Then again, Leon says, UV light seems to destroy coronaviruses as well. And coronavirus exposure from outdoor surfaces may be limited already…

”...There may even be downsides to widespread overzealous disinfection with bleach, notes Julia Silva Sobolik, a graduate student in Leon’s lab. “Bleach is highly irritating to mucous membranes,” Sobolik says. That means people exposed to sprayed disinfectants—especially the workers who spray them—are at risk of respiratory troubles, among other ailments…

”... In a recent television broadcast by state CCTV in China, Zhang Liubo, a researcher with China’s Center for Disease Control and Prevention, warned the public that, “Outdoor surfaces, such as roads, squares, lawns, should not be sprayed with disinfectants repeatedly. … Spraying disinfectants over a large area and repeatedly may cause environmental pollution and should be avoided.”

In China, people don’t spray any disinfectant over the sidewalks and roads. They usually spray disinfectant in some places where there are many people. Such as the train station, airport, and so on. While in quarantine, what people should do is stay at home. Do avoid interacting with other people. If you must go out because of something urgent, you must wear a mask.

True, but a mask won’t protect anyone from the fumes of chlorine bleach sprayed everywhere.