Most Chinese working in the cities return to work today after a seven-day public holiday, Spring Festival. The annual Spring Festival, which also marks the start of Chinese New Year, traditionally begins with the second new moon following the winter solstice, usually in January or February. Like westerners on Thanksgiving and Christmas, people across China return to their hometown to reunite with family and friends. However, the sudden outbreak of COVID-19 last year halted the largest holiday mobilization in the world. In response to the crisis, in late 2019, local governments launched lockdowns and behavior restrictions that reduced short-term economic and social activity. Despite the negative aspects of the pandemic, reduced human activity provided a unique opportunity for atmospheric scientists to study the impact of an unprecedented intervention on air quality.