Eddy covariance flux measurements of pollutant gases in urban Mexico City

Abstract

Abstract. Eddy covariance (EC) flux measurements of the atmosphere/surface exchange of gases over an urban area are a direct way to improve and evaluate emissions inventories, and, in turn, to better understand urban atmospheric chemistry and the role that cities play in regional and global chemical cycles. As part of the MCMA-2003 study, we demonstrated the feasibility of using eddy covariance techniques to measure fluxes of selected volatile organic compounds (VOCs) and CO2 from a residential district of Mexico City (Velasco et al., 2005a, b). During the MILAGRO/MCMA-2006 field campaign, a second flux measurement study was conducted in a different district of Mexico City to corroborate the 2003 flux measurements, to expand the number of species measured, and to obtain additional data for evaluation of the local emissions inventory. Fluxes of CO2 and olefins were measured by the conventional EC technique using an open path CO2 sensor and a Fast Isoprene Sensor calibrated with a propylene standard. In addition, fluxes of toluene, benzene, methanol and C2-benzenes were measured using a virtual disjunct EC method with a Proton Transfer Reaction Mass Spectrometer. The flux measurements were analyzed in terms of diurnal patterns and vehicular activity and were compared with the most recent gridded emissions inventory. In both studies, the results showed that the urban surface of Mexico City is a net source of CO2 and VOCs with significant contributions from vehicular traffic. Evaporative emissions from commercial and other anthropogenic activities were significant sources of toluene and methanol. The data show that the emissions inventory is in reasonable agreement with measured olefin and CO2 fluxes, while C2-benzenes and toluene emissions from evaporative sources are overestimated in the inventory. It appears that methanol emissions from mobile sources occur, but are not present in the mobile emissions inventory.

Relative humidity-dependent viscosity of secondary organic material from toluene photo-oxidation and possible implications for organic particulate matter over megacities

“…First, organic particulate matter over megacities is most likely more complicated than toluene-derived SOM. Toluene and other aromatics can account for a large fraction of nonmethane hydrocarbon emission in urban environments (Singh et al, 1985;Na et al, 2005;Suthawaree et al, 2012), and toluene and aromatics are thought to be one of the main sources of SOM particles in urban environments (Odum et al, 1997;Schauer et al, 2002a, b;Vutukuru et al, 2006;Velasco et al, 2007Velasco et al, , 2009de Gouw et al, 2008;Gentner et al, 2012;Liu et al, 2012;Hayes et al, 2015). Nevertheless, large alkanes and unspeciated nonmethane organic gases also likely play a role in SOM formation in urban environments.…”

Diurnal Variation of CO₂ Flux in an Urban Area of Tokyo

“…These studies, however, focused on seasonal variations, not diurnal-scale variations. Revealing the controlling factors of diurnal scale variations is still limited (Velasco et al 2009;Ward et al 2013;Ward et al 2015;Lietzke et al 2015).…”

Progress and opportunities for monitoring greenhouse gases fluxes in Mexican ecosystems: the MexFlux network

“…For example, Figure 4 compares the average diurnal CO 2 flux measured using eddy covariance during a short study over the Escandón district in Mexico City with emission profiles extracted from the local emissions inventory (Velasco et al, 2009(Velasco et al, , 2011. It is noteworthy that the CO 2 emission sources in urban ecosystems can be much more diverse than in natural ecosystems and their analysis requires a detailed interpretation of the measured fluxes (Fig.…”

“…Among the research published in peer-reviewed literature are RS measurements in tropical forests (Davidson et al, 1993;Vargas and Allen, 2008;Vargas, 2012), NEE from subtropical and semiarid ecosystems (Hastings et al, 2005;Pérez-Ruiz et al, 2010) and in urban areas of Mexico City (Velasco et al, 2005(Velasco et al, , 2009(Velasco et al, , 2011, and ET in semiarid ecosystems (Watts et al, 2007;Vivoni et al, 2008). These measurements of energy, water vapor and CO 2 fluxes in Mexican ecosystems originated from individual efforts, and unfortunately there is a lack of a strategic governmental program to ensure long-term funds for the establishment and continuity of these types of studies.…”

“…MexFlux is the network of flux measurements of GHGs and energy fluxes from terrestrial, urban, (Velasco et al, 2009;Velasco et al, 2011). ** This tower measured fluxes from the ocean and was located at the Todos Santos island in front of Ensenada, Baja California (Reimer et al, in review).…”