An Observational Based Modeling of the Surface Layer Particulate Nitrate in the North China Plain During Summertime
Zhaofeng Tan, Haichao Wang, Keding Lu, Huabin Dong, Yuhan Liu, Limin Zeng, Min Hu, Yuanhang Zhang
Abstract
Abstract Particulate nitrate (pNO 3 − ) is an important component in atmospheric fine particulate matter. Here, we present a case study investigating the production and loss processes of pNO 3 − in surface‐layer based on the observation at a regional site Wangdu in North China Plain (NCP) during summer. The averaged diurnal of nitric acid (HNO 3 ) production reached a maximum of 1.5 μg m −3 h −1 determined from the observed OH and NO 2 , indicating a fast HNO 3 production in the surface layer during the daytime. The chemical processes affecting surface nitrate concentration and daily variation were simulated by a box model based on the Regional Atmospheric Chemical Mechanism version 2 and coupled with the ISORROPIA‐II thermodynamic equilibrium model. The chemical formation of total soluble nitrate (TNO 3 ) at the surface layer cannot explain the fast increase of pNO 3 − in the morning and overshoot pNO 3 − in the afternoon, suggesting missing processes in the model. The pNO 3 − budget analysis suggests the importance of entrainment from residual layer air into the surface layer as an important process for surface pNO 3 − concentration enhancement in the early morning. In the afternoon, the partition to pNO 3 − was limited due to the high temperature near the ground. Nevertheless, the observed fast nitrate production still significantly overshot pNO 3 − in the afternoon. This difference indicates HNO 3 production was less efficient throughout the boundary layer than what was observed in the surface layer. Our results highlight the importance of vertical measurements to understand the formation mechanism of nitrate pollution in summer.