Recent intensification of winter haze in China linked to foreign emissions and meteorology.

Averaged over the North China Plain, both the observed inverse visibility and modeled PM 2.5 concentration (sum of dry sulfate, BC (black carbon) and POM (primary organic matter) in this study, see Methods) show increasing trends over 1980–1990, followed by decreasing trends between 1990–1996 and an increasing trend in 1996–2014 (Fig. 1c,d ).

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Over 1990–1996, the contributions to DJF mean PM 2.5 concentration in the North China Plain from almost all the tagged source regions decrease, leading to an overall trend of −4.7 (±2.8) μg m −3 decade −1 , which can be decomposed to −3.3 (±3.0), −0.5 (±0.8) and −0.9 (±0.9) μg m −3 decade −1 from North China Plain, rest of China and foreign emissions, respectively.

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