Mixing ratios and eddy covariance flux measurements of volatile organic compounds from an urban canopy (Manchester, UK)

B. Langford (1) , B. Davison (1) , E. Nemitz (2) , C. N. Hewitt (1)

1 Lancaster Environment Centre
2 Centre for Ecology & Hydrology (CEH) Edinburgh

Concentrations and fluxes of six volatile organic compounds (VOC) were measured above the city of Manchester (UK) during the summer of 2006. A proton transfer reaction-mass spectrometer was used for the measurement of concentrations, and fluxes were calculated using both the disjunct and the virtual disjunct eddy covariance techniques. The two flux systems, which operated in alternate half hours, showed reasonable agreement, with R² values ranging between 0.2 and 0.8 for the individual analytes. On average, fluxes measured in the disjunct mode were lower than those measured in the virtual mode by approximately 19%, of which at least 8% can be attributed to the differing measurement frequencies of the two systems and the subsequent attenuation of high frequency flux contributions. Observed fluxes are thought to be largely controlled by anthropogenic sources, with vehicle emissions the major contributor. However both evaporative and biogenic emissions may account for a fraction of the isoprene present. Fluxes of the oxygenated compounds were highest on average, ranging between 60?89 ?g m^?2 h^?1, whereas the fluxes of aromatic compounds were lower, between 19?42 ?g m^?2 h^?1. The observed fluxes of benzene were up-scaled to give a city wide emission estimate which was found to be significantly lower than that of the National Atmospheric Emissions Inventory (NAEI).

Domaines: Océan, Atmosphère

B. Langford, B. Davison, E. Nemitz, C. N. Hewitt. Mixing ratios and eddy covariance flux measurements of volatile organic compounds from an urban canopy (Manchester, UK). Atmospheric Chemistry and Physics Discussions, 2008, 8 (1), pp.245-284. ⟨hal-00303238⟩