Abstract
Abstract. We studied the atmospheric boundary layer (ABL) dynamics and the impact on atmospheric chemistry during the HUMPPA-COPEC-2010 campaign. We used vertical profiles of potential temperature and specific moisture, obtained from 132 radio soundings, to determine the main boundary layer characteristics during the campaign. We propose a classification according to several main ABL prototypes. Further, we performed a case study of a single day, focusing on the convective boundary layer, to analyse the influence of the dynamics on the chemical evolution of the ABL. We used a mixed layer model, initialized and constrained by observations. In particular, we investigated the role of large scale atmospheric dynamics (subsidence and advection) on the ABL development and the evolution of chemical species concentrations. We find that, if the large scale forcings are taken into account, the ABL dynamics are represented satisfactorily. Subsequently, we studied the impact of mixing with a residual layer aloft during the morning transition on atmospheric chemistry. The time evolution of NOx and O3 concentrations, including morning peaks, can be explained and accurately simulated by incorporating the transition of the ABL dynamics from night to day. We demonstrate the importance of the ABL height evolution for the representation of atmospheric chemistry. Our findings underscore the need to couple the dynamics and chemistry at different spatial scales (from turbulence to mesoscale) in chemistry-transport models and in the interpretation of observational data.
Highlights
The atmospheric boundary layer (ABL) dynamics and their impact on atmospheric chemistry are studied by combining field observations, taken during the HUMPPA-COPEC-2010 campaign (Williams et al, 2011), with a modelling study
It is relevant and timely to study the atmospheric processes over the boreal forest at a range of scales in order to understand the interactions between the dynamics and chemistry
Guided and constrained by this data, we focus on the influence of large scale forcings and transitions in the morning from nocturnal to daytime conditions on the boreal atmospheric boundary layer dynamics and the associated atmospheric chemistry
Summary
The atmospheric boundary layer (ABL) dynamics and their impact on atmospheric chemistry are studied by combining field observations, taken during the HUMPPA-COPEC-2010 campaign (Williams et al, 2011), with a modelling study. These prototypes correspond to stable, convectively mixed and conditionally unstable boundary layers This classification of the structure of the ABL enables the identification of important processes for atmospheric chemistry during HUMPPA-COPEC-2010, like the intensity of mixing, turbulent time scales, the atmospheric dilution capacity and the entrainment of free tropospheric air. The day is selected because important processes took place that can be overlooked when analysing the impact of the boundary layer dynamics on chemistry These processes, associated with temporal transitions and large-scale forcings, include subsidence, the advection of air masses and, in the morning, the connection with a residual boundary layer from the previous day. The strategy for obtaining meteorological data during field campaigns is discussed
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