Analysis of causes and transport characteristic of a continuous heavy pollution weather event in Luohe

Using conventional meteorological observations, particulate matter observation data, NCEP reanalysis with 1°×1° resolution, GDAS data with 1°×1° resolution, lidar measurements and other data, we have investigated the cause and transport characteristics related to a continuous heavy pollution weather event occurred in Luohe of Henan Province in late November 2018. The main results are as follow. (1) This pollution event is closely related to synoptic situation. In its early stage it was influenced by the stable zonal circulation and surface uniform pressure field, which was beneficial to the accumulation of pollutant. In its middle stage, the weak cold air moved eastward and southward under the control of the upper-level trough and surface transported high, causing the fast increase of pollutants because of detention effect. In its late stage, with the diffusion of low-level easterly cold air and the restore of stable situation, the pollutants continued to accumulate, which led to the continuous heavy pollution. (2) During the heavy pollution caused by PM_2.5, the pollution was exacerbated due to the stability and continuance of radiation inversion. During the heavy pollution caused by PM₁₀, the inversion layer disappeared, which was conducive to the transport and deposition of pollutants. During the heavy pollution caused by PM_2.5 and PM₁₀, the turbulence near the ground strengthened and formed inversion, resulting in the continuance pollution. (3) There are 5 major transport paths in this event. The pollution from the southwest and easterly paths has a high proportion, whose length is short and height is below 900 hPa. Both the two paths play a significant role in the short distance transport of PM_2.5. The pollution from the northwest and northerly paths has a great length, whose initial altitude is between 700 hPa and 600 hPa, showing that the long distance transportation in the upper-level is mainly PM₁₀. (4) Affected by stable conditions and high humidity in the surface layer, the high extinction zones maintain below 600 m, and the shallow boundary layer inhibits vertical diffusion, leading to the accumulation and long time coexisting of fine aerosol particles and dust. (5) This heavy pollution event is the result of the combined influence of local pollution accumulation and upper-level transport. Besides the high contribution of local pollution in Luohe, the high potential source areas are mainly concentrated in the southwest and northeast parts of Henan and the junction of Henan and Shandong, which is an important reason for the development of continuous pollution. During the heavy pollution, the surface northerly winds dominate, while the wind speed of other wind directions is small, which is conducive to the convergence and secondary conversion of pollutants and the pollution aggravating.