People cycle on street during Car-Free Sunday event in Brussels, Belgium, Sept. 22, 2019. Car Free Sunday was observed in the capital city of Brussels. In Brussels, the objective of this 2019 edition was to reduce the impact of mobility on air quality. (Xinhua/Pan Geping)

People enjoy outdoor time during Car-Free Sunday event in Brussels, Belgium, Sept. 22, 2019. Car Free Sunday was observed in the capital city of Brussels. In Brussels, the objective of this 2019 edition was to reduce the impact of mobility on air quality. (Xinhua/Pan Geping)

People look at a real-time air quality broadcast screen during Car-Free Sunday event in Brussels, Belgium, Sept. 22, 2019. Car Free Sunday was observed in the capital city of Brussels. In Brussels, the objective of this 2019 edition was to reduce the impact of mobility on air quality. (Xinhua/Pan Geping)