Hello, I have 2 transits in Beijing in the same month. Do I need a visa for each transit? Thanks!

June 28, June 28: Ottawa, Canada -> Chicago, USA
June 28, June 29: Chicago, USA -> Beijing, China (PEK: 3h:30min layoff).
June 29, June 29: Beijing (PEK) -> Pusan (KR)

July 08 - July 08: Seoul (KR) -> Beijing (PEK)
July 12 - July 12: Beijing (PEK) -> New York, USA
July 12 - July 12: New York, USA -> Ottawa, Canada