The influences of dry deposition process on surface ozone simulations under different planetary boundary layer parameterization schemes over eastern China

Abstract

Dry deposition is a major sink of ozone in the planetary boundary layer (PBL). In this study, we investigate how different PBL parameterizations influence the simulations of surface ozone and its dry deposition fluxes over eastern China using the Weather Research and Forecasting Model coupled to Chemistry (WRF-Chem), and quantify the contributions of dry deposition to ozone change rates in the PBL with an integrated process rates (IPR) analysis method. As the exacerbated ozone pollution in urban areas of China has aroused extensive concern, we limit our discussion to the model results for three main city agglomerations: Beijing-Tianjin-Hebei (BTH) region, Yangtze River Delta (YRD) and Pearl River Delta (PRD). Firstly, three PBL schemes applying distinct turbulence closures are employed to examine the model sensitivities, including nonlocal closed Yonsei University (YSU), local closed Mellor–Yamada–Janjić (MYJ) and hybrid local-nonlocal scheme Asymmetric Convective Model v2 (ACM2), each coupling with one or two specific surface layer schemes. The results show that using different PBL schemes leads to the uncertainty of 6.5~18.5% for surface ozone concentration simulations, and of 3.6~15.3% for accumulated ozone dry deposition fluxes, while scarcely impacts the simulated surface ozone diurnal cycles. Among all schemes, MYJ generally calculates the lowest surface ozone concentration and dry deposition flux, especially during nighttime. According to the multiple linear regression analysis, the differences in dry deposition fluxes are dominated by the differences in surface ozone levels, and the contributions of differences in dry deposition velocities are more substantial at nighttime than at daytime. Secondly, by switching ozone dry deposition on-off based on simulation with YSU scheme, we find the absence of ozone dry deposition enhances surface ozone levels by 24~30% during daytime and by 61~82% during nighttime over the three regions. The IPR analyses indicate that when adding dry deposition process, the positive contributions of vertical mixing are elevated by 1~4 μg m-3 hr-1, partially compensating the accessorial negative contributions from dry deposition itself (by up to -8 μg m-3 hr-1) to the change rates of ozone within the PBL. Furthermore, IPR analysis is also conducted for the model results in July 20 to 23 over BTH, during which period YSU_MM5 simulates contrary ozone trend against MYJ_Eta scheme. In this episode, the choice of PBL schemes influences significantly on dry deposition, gas chemistry and advective transport processes, and the absolute contribution by simulation deviations of dry deposition process account 13% for the difference in gross ozone trend. Our study quantifies the influence of different PBL parameterization schemes on ozone simulations, emphasizing the importance of dry deposition process on governing the ozone change near surface and in the PBL.