Establishment of conceptual schemas of surface synoptic meteorological situations affecting fine particulate pollution across eastern China in the winter

In the present study, the characteristics of weather conditions and local meteorological
variables over the Beijing‐Tianjin‐Hebei (BTH) and the Yangtze River Delta (YRD) regions in the winter
are analyzed using the principal component analysis (PCA) method and daily PM2.5 accumulation rate.
Typical synoptic weather patterns over China in the winter can be classified into four types. During the Type
1 synoptic weather pattern, China is under the influence of the Siberian High, and northerly winds prevail;
this situation is beneficial to the transport of pollutants from north to south. However, when the Siberian
High is weak, southerly winds prevail which may result in the transport of pollutants from south to north.
The Type 2 weather pattern refers to a weak high pressure located in the BTH resulting in the accumulation
of pollutants. During the Type 3 weather pattern, an intense cold Siberian High moves to the south and
affects the northern areas of China. The associated front brings heavy precipitation in the YRD resulting in
the wet deposition of pollution. During the Type 4 weather condition, the weak Siberian High is blocked
by the northeast cold vortex and moves towards the south, causing the accumulation of pollution in the
YRD. The PCA model shows that there are two transport pathways for pollutants to the BTH (YRD) area:
one from the YRD (BTH) and Shandong during Types 1 and 2 (Types 1 and 3) situations and the other one
from the central provinces during Type 4 (Types 1 and 4).