63,010
edits
Changes
no edit summary
{| class="wikitable"
! Time period !! Development summary !! More details |-| 1990s || Air pollution in Beijing becomes very severe.<ref name="Improving Urban Air Quality in China: Beijing Case Study">{{cite web |title=Improving Urban Air Quality in China: Beijing Case Study |url=https://www.tandfonline.com/doi/pdf/10.1080/10473289.2005.10464726 |website=tandfonline.com |accessdate=13 May 2019}}</ref>
|-
|}
