Emissions of volatile organic compounds inferred from airborne flux measurements over a megacity

Abstract

Abstract. Toluene and benzene are used for assessing the ability to measure disjunct eddy covariance (DEC) fluxes of Volatile Organic Compounds (VOC) using Proton Transfer Reaction Mass Spectrometry (PTR-MS) on aircraft. Statistically significant correlation between vertical wind speed and mixing ratios suggests that airborne VOC eddy covariance (EC) flux measurements using PTR-MS are feasible. City-average midday toluene and benzene fluxes are calculated to be on the order of 15.5±4.0 mg/m2/h and 4.7±2.3 mg/m2/h respectively. These values argue for an underestimation of toluene and benzene emissions in current inventories used for the Mexico City Metropolitan Area (MCMA). Wavelet analysis of instantaneous toluene and benzene measurements during city overpasses is tested as a tool to assess surface emission heterogeneity. High toluene to benzene flux ratios above an industrial district (e.g. 10–15) including the International airport (e.g. 3–5) and a mean flux (concentration) ratio of 3.2±0.5 (3.9±0.3) across Mexico City indicate that evaporative fuel and industrial emissions play an important role for the prevalence of aromatic compounds. Based on a tracer model, which was constrained by BTEX (Benzene/Toluene/Ethylbenzene/m,p,o-Xylenes) compound concentration ratios, the fuel marker methyl-tertiary-butyl-ether (MTBE) and the biomass burning marker acetonitrile (CH3CN), we show that a combination of industrial, evaporative fuel, and exhaust emissions account for >90% of all BTEX sources. Our observations suggest that biomass burning emissions play a minor role for the abundance of BTEX compounds (0–10%) in the MCMA.

Biogenic emission measurement and inventories determination of biogenic emissions in the eastern United States and Texas and comparison with biogenic emission inventories

“…Nevertheless, we expect that such improvements may only provide marginally better results. Better constraints on emission inventories on regional scales may ultimately come from airborne eddy covariance measurements as recently demonstrated by Karl et al [2009], who estimated uncertainties of 40% in the measured fluxes. Such uncertainties are slightly smaller than the uncertainties in the emission inventories themselves and will therefore be needed to provide useful constraints.…”

Source identification of VOCs at an urban site of western India: Effect of marathon events and anthropogenic emissions

“…Recent observations and model studies suggest large uncertainties of VOC emission inventories in major metropolitan areas of developing countries [e.g. Warneke et al, 2007;Karl et al, 2009;Ohara et al, 2007]. The development of VOC emission inventory is very complex not only because of the numerous sources but also because of the many number of species included.…”

Photochemical aging of volatile organic compounds in the Los Angeles basin: Weekday‐weekend effect

“…Furthermore, in Figure 3 the toluene plot shows more scatter for the fresher plumes than do the other two plots. Additional sources for toluene other than vehicle traffic are most likely the cause for the higher enhancement ratios; these additional sources of toluene have been identified as industrial and evaporative emissions in Mexico City [Karl et al, 2009].…”