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Extensive measurements were made using an Aerodyne quantum cascade laser absorption spectrometer (QCLAS) to study the diurnal and seasonal cycles of NH3 concentrations in Manchester city centre. Measurements made at rooftop levels showed traffic to be a significant source of NH3 concentrations in the winter. This was illustrated by a bimodal diurnal cycle of NH3 concentrations that was synchronized with traffic, and also by a correlation with NOx, a traffic related pollutant. These patterns were not observed during the summer, suggesting other sources become more important. Measurements were also made at street level during winter and summer, close to the traffic source. This time the contribution from traffic was also observed in the summer, albeit weaker. Enhanced NH3 concentrations were often seen in winds from the southwest that could not be related to local sources, suggesting that ambient concentrations in the city are strongly influenced by sources outside the city. It is estimated that the total NH3 emission from the city centre is between 0.7 and 2.3 t km−2 year−1. [ABSTRACT FROM AUTHOR]

The possibility of obtaining urban roughness length from satellite-derived maps of land cover is explored, using turbulence measurements taken above the urban canopy. The upwind land cover is identified using a source-area model. Firstly, from four sets of measurements taken in Birmingham (U.K.), it is shown that in an area mainly split between the land-cover types ‘urban’ and ‘suburban’, suburban cover in the upwind source area is the more important contributor to increasing measured roughness length. A smaller dataset obtained in a second U.K. city (Salford, Greater Manchester) shows a similar result. A roughness-length aggregation model is also applied to the data from both sites. This assigns values of roughness length to each of the land-cover classifications and uses the source-area model to predict the resultant roughness length based on the wind properties. The results from this are shown to agree with the earlier findings. [ABSTRACT FROM AUTHOR]