Trans-Regional Transport Of Haze Particles From The North China Plain To Yangtze River Delta During Winter

According to atmospheric modeling and satellite observations, cold fronts can cause trans-regional transport (TRT) of haze particles from the North China Plain (NCP) to Yangtze River Delta (YRD) in winter. However, compositions and aging of haze aerosols during the TRT have not been studied. We showed the TRT PM2.5 dominated by organic matter (OM) (30%) and secondary inorganic ions (36%) in the NCP and 29% and 60% in the YRD. Following the TRT, abundant spherical primary OM particles (i.e., tarballs) (71% by number) mainly from residential coal burning in rural areas of the NCP unexpectedly occurred in the YRD. The inert tarballs display similar sizes (similar to 300 nm) and O/C ratios (similar to 0.15), but the mixture of nitrate, sulfate, and secondary OM as the coatings completely convert the hydrophobic tarballs into hydrophilic ones in the TRT. The aging and transport of tarballs from the NCP to YRD further indicate that the TRT not only brought various trace gases (e.g., CO, SO2, NOx, and VOCs) but also carried large numbers of nanosized primary particles (e.g., tarball, metal, fly ash, and soot) with secondary coatings over 1,000 km. The findings suggest that these many nanosized tarballs containing brown carbon and highly toxic species in the NCP influence regional climate and human health in northern and eastern China, which needs more attention. Although the NCP and YRD have different energy consumption structures in winter and are two isolated administrative regions, we emphasize the need for a coordinated cross-regional emission reduction strategy for TRT haze control.Plain Language Summary The North China Plain (NCP) and Yangtze River Delta (YRD) are two isolated administrative regions in China with developed economies and serious regional haze pollution during winter. There are different particle sources in the NCP and YRD in winter, in particular for the abundant coal burning for heating and cooking in the NCP but not in the YRD. Recently, it has been found that cold air can cause trans-regional transport (TRT) of haze particles from the NCP to YRD in winter and further induces regional haze pollution in the YRD. However, there is no detailed information on the fine TRT haze particles. Here we raise several questions about the fine particles: What kinds of fine particles can be transported from the NCP to YRD? How are these particles changed during their TRT? The answers are important for evaluating the impacts of air pollution between the two large city-clusters on human health and climate. Therefore, we conducted field campaigns and analyzed compositions and aging of fine haze particles during their TRT. This study not only provides critical information about the TRT haze particles but also insights to the future coordination of air pollution control between the NCP and YRD in winter.Key PointsAbundant primary brown carbon in the North China Plain (NCP) can transport over 1,000 km to influence climate and human health in East ChinaThe aging of haze particles in the trans-regional transport significantly transformed their mixing structures and hygroscopic propertiesResidential coal burning in the rural areas of the NCP is the main source of these primary brown carbon aerosols