全边界层选用相似理论对O_3、NO_x浓度及沉降的影响

Impacts of the PBL Similarity on Concentrations and Dry Deposition Velocities of O_3 and NO_x

将广泛应用于东亚地区的LLA(Lurmann Lloyd Atkinson)化学机制耦合到欧拉型区域空气质量模式(RAQM),并考虑区域污染物长期模拟研究中降水随时间变化的非均匀性,讨论了湍流参数化过程中相似理论在近地层和全边界层的应用对湍流垂直扩散系数(Kz)与干沉降速度(V),O3与NOx浓度的影响。结果表明,全边界层应用相似理论明显低估了Kz值,近地层50m处Kz值被低估20%以上,750m处其值被低估约70%;O3、NOx的干沉降速度在日本东部与南部海域被低估了10%以上,在朝鲜半岛东部和西部海域模拟值普遍偏高。Kz和干沉降速度的不同直接影响污染物的浓度和沉降量分布。Kz值的被低估对NOx浓度有明显影响,在近地层50m处NOx浓度最大可增加约30%,整个边界层中NOx平均浓度除台湾省东北海域外普遍增加5%~20%。O3浓度则受干沉降作用的影响较大。虽然近地层、全边界层分别应用相似理论都较好地模拟了O3与NOx峰值浓度出现的时间,但相似理论应用于全边界层会引起较大的误差。即使是大区域、长期空气质量模拟研究,也建议相似理论仅应用于近地层,且模式第一层高度应设置在常通量层内。

Spatial distributions of vertical eddy diffusivity(Kz),dry deposition velocity(V),and concentrations of O3 and NOx over East Asia are simulated using the surface-layer similarity and the whole PBL similarity in the turbulence parameterization,after coupling the widely applied LLA(Lurmann Lloyd Atkinson)chemical mechanism in East Asia into the Regional Air Quality Eulerian Model(RAQM)and considering the temporal heterogeneity in rainwater in long-term modeling studies of air pollutants over a large domain.Simulations indicate that Kz values are significantly underestimated by the whole PBL similarity,with above 20% at 50 m and around 70% at 750 m high above the ground,respectively.Dry deposition velocities of O3 and NOx are underestimated at least 10% in the sea area on the east and south of Japan,while in the sea area on the east and west of Korea Peninsula the values are generally higher.Large deviations in Kz and dry deposition velocity between the two schemes lead to different results of O3 and NOx.Underestimation of Kz values leads to large changes in NOx concentrations,with a maximum increase of 30% at 50 m high above the ground and approximately 5%-20% increases in mean NOx levels in the whole PBL except the sea area on the northeast of Taiwan.However,the concentrations of O3 are dependent significantly on the dry deposition process.The surface-layer similarity and the whole PBL similarity well depict the timing of O3 and NOx peaks while the surface-layer similarity follows observations in amplitude better than the whole PBL similarity.The surface-layer similarity is a better choice than the whole PBL similarity and the first vertical model layer should be set within the surface constant flux layer even in long-term regional simulations of air pollutants.