Ozone pollution in China: Background and transboundary contributions to ozone concentration & related health effects across the country.

China experiences high ozone concentrations with highest annual 8-hour maximum concentration in eastern China of 78 μg/m3 and was followed by southern (73 μg/m3), north-western (69 μg/m3), northern (68 μg/m3), central (67 μg/m3), north eastern (65 μg/m3) and south-western China (59 μg/m3). Ozone concentration peaked in spring season in 4 (eastern, northern, north eastern & central) of 7 regions across China while lowest concentration in most regions across China was experienced in winter season with central and southern China being the only exceptions. Regions outside Asia contributed ozone to all regions across China with highest contributions in 4 (East, Central, North & Northeast) of the 7 regions. South-western China had the largest ozone contribution from outside (23%) and was followed by 16.39% outside ozone contribution in north-western China, 11.64% contribution in north eastern China, 11% contribution in northern China, 7.85% contribution in southern China, 5.28% contribution in central China while 4.56% contribution in eastern China. Policy relevant background (PRB) concentration was above 47 μg/m3 in all regions across China and contributed about 71-94% to total ozone concentration with highest PRB concentration of 65.25 μg/m3 recorded in north-west China. China recorded 93,351 (95%CI: 11001-169,898) ozone related premature mortality in 2015 with 42,673 (95%CI: 11001-69,586) respiratory mortality and 50,678 (95%CI: 0-100,312) cardiovascular mortality. Northern and eastern China recorded high ozone related mortality with 18,230 (95%CI: 4700-29,727) & 12,261 (95%CI: 3161-19,993) respiratory and 21,662 (95%CI: 0-42,877) & 14,528 (95%CI: 0-28,757) cardiovascular deaths respectively. In terms of foreign contributions, premature mortality due to ozone from outside Asia contributed the most to China with 1070 (95%CI: 276-1746) respiratory mortality and 1270 (95%CI: 0-2515) cardiovascular mortality. East Asia contributed to about 419 (95%CI: 109-679) respiratory deaths and 501 (95%CI: 0-989) cardiovascular deaths while North Asia contributed to 220 (95%CI: 56-358) respiratory mortality and 260 (95%CI, 0-515) cardiovascular mortality.