Pollution plumes observed by aircraft over North China during the IPAC-NC field campaign

Strong pollution emissions from large urban and industrial centres in eastern China are thought to greatly impact regional air quality and global atmospheric chemistry. In this study, we investigate extensive pollution plumes over North China, observed by aircraft during the IPAC-NC (Influence of Pollution on Aerosols and Cloud Microphysics in North China) field campaign in spring 2006. Several pollution plumes were encountered, characterized by sharp and strong increases of SO2 and NOx (NO plus NO2) as well as remarkable O-3 variability. During a flight performed downwind of the megacity Tianjin on 9 April, O-3 was found to be depleted at NOx>15 ppbv and enhanced at NOx mixing ratios of 6-7 ppbv. Our analysis indicates that the plumes had recently been released by industrial plants, and partly mixed with urban emissions, giving rise to the large-scale transport of air pollution and substantial degradation of air quality.