The ClearfLo project - understanding London's meteorology and composition

The ClearfLo project aims to understand the processes generating pollutants like ozone, NOx and particulate matter and their interaction with the urban atmospheric boundary layer. ClearfLo (www.clearflo.ac.uk) is a large multi-institution NERC-funded project that established integrated measurements of the meteorology, composition and particulate loading of London's urban atmosphere accompanied by modeling of urban meteorology and air pollution.

The project established a new long-term measurement infrastructure in London encompassing measurement capabilities at street level, in the urban background, at elevated levels and in the rural surrounding to determine the urban increment in meteorology and air pollution. These measurements were accompanied by high resolution modeling with the UK Met Office Unified model and WRF. This combined measuring/modelling approach enables us to identify the seasonal cycle in the meteorology and composition, together with the controlling processes. Two intensive observation periods in January/February 2012 and during the Olympics in summer 2012 measured London's atmosphere with higher level of detail. These IOPs will enable us (i) to determine the vertical structure and evolution of the urban atmosphere (ii) to determine the chemical controls on ozone production, particularly the role of biogenic emissions and (iii) to determine the processes controlling the evolution of the size, distribution and composition of particulate matter.

In this talk we present analysis of the long-term air pollution measurements over two years and the role the meteorology plays for air pollution concentrations. In particular we show measurements that indicate the dominant regimes of London's boundary layer, and model simulations that demonstrate the role of advection in setting the structure of the urban boundary layer and its mixing properties.