Haze particles over a coal-burning region in the China Loess Plateau in winter: Three flight missions in December 2010

Heavy haze frequently occurs in winter over a coal-burning region, the Taiyuan Basin, in the eastern China Loess Plateau, which is the upstream area of the North China Plain. We participated in three research flights to collect aerosol particles and to monitor SO₂ concentration in hazes from the ground (780m asl) up to ∼4000m during 17-18 December, 2010. Meteorological records reveal that the whole haze column (ground to 4000m) was stable and could be further divided into three sub-layers depending on the sampling altitude, which are characterized by two shifts of the lapse rate of virtual potential temperature and water vapor mixing ratio: Layer-1, surface to 1500m; Layer-2, 1500∼3000m on 17 December, and 1500∼2500m on 18 December; Layer-3, above 3000m on 17 December and above 2500m on 18 December. SO₂ concentration was 16-116ppb with an average of 58ppb in the Layer-1, 2-45ppb with an average of 10ppb in the Layer-2, and 1-10ppb with an average of 4ppb in the Layer-3. The accumulation of SO₂ in the Layer-1 was due to the stable meteorological conditions and the strong anthropogenic emissions in addition to the possible valley topography. Analyses of the collected particles using a transmission electron microscope revealed the dominance of organic particles and fly ash in the Layer-1 and Layer-2 and sulfate particles in the Layer-3. The organic aerosols frequently contained certain amounts of Si and Cl. Fly ash particles consisted of O and Si with minor Fe, Mn, Zn, Ti, Pb, As, Co, and Cr. These two types of aerosol particles are typically emitted from coal burning. These results indicate that the haze particles were characterized in principle by aerosols from primary emissions of coal burning, which are different from those over the North China Plain where secondary sulfate particles are the dominant component.