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

Abstract

Abstract. Mixing ratios and fluxes of six selected volatile organic compounds (VOCs) 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 mixing ratios, and fluxes were calculated from these using both the disjunct and the virtual disjunct eddy covariance techniques. The two flux systems, which operated in alternate half hours, showed good agreement, with R 2 values ranging between 0.74 and 0.9 for the individual analytes. On average, fluxes measured in the disjunct mode were approximately 20% lower than those measured in the virtual mode. This difference is due to both the dampening of the VOC signal by the disjunct flux sampler and carry over from one sample to the next. Correcting for these effects reduced the difference to less than 7%. 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 some of the VOCs present. Concentrations and fluxes of the oxygenated compounds were highest on average, ranging between 0.15 to 1 mg m −2 h −1 ; the fluxes of aromatic compounds were lower, between 0.12 to 0.28 mg m −2 h −1 . The observed fluxes were up-scaled to give city wide emission estimates for each compound and the results compared to estimates made by the National Atmospheric Emission Inventory (NAEI) for the same flux footprint. Fluxes of toluene and benzene compared most closely differing by approximately 50%, while in contrast the oxygenated fluxes were found to be between 3.6-6.3 times larger than the annual average predicted by the NAEI.

A new disjunct eddy-covariance system for BVOC flux measurements – validation on CO<sub>2</sub> and H<sub>2</sub>O fluxes

“…Sample carry over is an additional source of uncertainty and bias (Langford et al, 2009). It results from the air remaining in the reservoir because of the partial vacuum before the capture of the next sample, and from the air remaining in the "dead volume" between the reservoir and the online analyser.…”

Measurements of OVOC fluxes by eddy covariance using a proton-transfer-reaction mass spectrometer – method development at a coastal site

“…Other sources include plant decay (Warneke et al, 1999), industrial emissions (such as solvents, fuel additive, antifreeze, etc. ; Langford et al, 2009), and atmospheric reactions such as the oxidation of methane. In addition to consumption by the hydroxyl radical (OH), methanol is removed from the planetary boundary layer (PBL) via deposition to land and to the ocean surface (Heikes et al, 2002;Williams et al, 2004;Carpenter et al, 2004), resulting in an overall atmospheric lifetime of about 4.7 days globally (Millet et al, 2008).…”

DOAS measurements of formaldehyde and glyoxal above a south-east Asian tropical rainforest

“…OH measurements were made using the Fluorescence Assay by Gas Expansion (FAGE) technique (Whalley et al, 2011) and measurements of aerosol surface area were performed using a Differential Mobility Particle Sizer (DMPS) (Winklmayr et al, 1991). Measurements of isoprene were made using Gas Chromatography with Flame Ionisation Detection (GC-FID) at 5 m, on top of the FAGE container and with Proton Transfer Reaction Mass Spectrometry (PTRMS) at 75 m on the GAW tower (Langford et al, 2009;Hopkins et al, 2003). Figure 5 summarises the results from the LP-DOAS for both campaigns.…”