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

Abstract

Dry deposition is an important ozone sink in the planetary boundary layer (PBL), but how different PBL parameterization schemes affect the ozone dry deposition impacts has not been well quantified. Here we investigate the influences of PBL mixing parameterizations on surface ozone and dry deposition in eastern China using a regional air quality model (WRF-Chem) and further quantify the contributions of dry deposition to ozone tendencies both near the surface and in the PBL with integrated process rates (IPR) analysis. We analyze three PBL schemes coupled with their corresponding surface layer (SFL) schemes, including Yonsei University (YSU), Mellor–Yamada–Janjić (MYJ), and Asymmetric Convective Model v2 (ACM2). We find that using different PBL-SFL schemes in general produces similar monthly mean meteorological fields, leading to relatively small uncertainties, ranging from 6.5% to 18.5% in monthly mean surface ozone concentrations and 3.6% to 15.3% in total ozone dry deposition in eastern China. However, these uncertainties can frequently exceed 30% in summer at the daily scale. IPR analyses with YSU_MM5 show that ozone dry deposition accounts for 80–89% of surface ozone losses and 45–58% of PBL ozone losses. Model sensitivity simulations by suppressing ozone dry deposition would enhance surface ozone in eastern China by 24–30% (20.6–35.7 μg m−3) during the daytime and 61–82% (26.0–46.1 μg m−3) at night. Ozone dry deposition significantly promotes the downward vertical mixing of ozone to the surface layer, which contributes to smoothing the near-surface ozone gradients as caused by ozone dry deposition and titration, thus explaining the smaller contribution estimated by the sensitivity approach than IPR analyses. We further show that different meteorological conditions simulated by different PBL-SFL schemes affect daily ozone simulations not only through the chemistry process as previously recognized but also considerably by the dry deposition process.