It is the objective of this research to improve the understanding of urban boundary layer dynamics through synergy analysis of advanced ABL observations from ground-based remote sensing.
Air quality and local climates in cities are strongly influenced by the urban environment both directly through alterations in surface morphology and the surface energy balance and also indirectly via atmospheric boundary layer dynamics as these affect the transport of air pollutants, heat, and moisture. Despite its importance for various applications, it remains challenging to describe the complex characteristics of the three-dimensional wind, temperature, aerosol, and moisture fields within the urban atmospheric boundary layer.
Urban atmosphere dynamics are driven by a combination of synoptic flow and heterogeneous surface characteristics, which can vary greatly along the rural-urban gradient but also at smaller scales between neighbourhoods. Given the city is comparatively rough and supplies additional heat from anthropogenic emissions and heat storage in the impervious building canopy, buoyancy is generally enhanced over urban areas. This can encourage the vertical dispersion and mixing of pollutants and other constituents and hence lead to greater mixed layer heights compared to the rural surroundings. Under certain synoptic conditions (weak wind, low cloud cover), thermal contrasts can induce local circulations at neighbourhood (e.g. park breeze) to regional scales (e.g. urban breeze). Effects of such circulations on near-surface air quality are complex as they can reduce pollution concentrations through dilution but can also entrain polluted air circulating aloft (e.g. aerosol plumes from long range transport, or accumulated pollution in the residual layer). Areas of reduced surface roughness (e.g. river) may act as ventilation corridors along which air from rural sources is advected into the city centre. Again, this can improve air quality, but may also bring along pollutants emitted by sources outside of the city (e.g. agriculture, industry). The displacement of warm air from the city centre towards surrounding areas can again result in a warming of downwind suburbs.