Diurnal, weekly, seasonal and spatial variabilities in carbon dioxide flux in different urban landscapes in Sakai, Japan

Abstract

<p><strong>Abstract.</strong> To evaluate CO<sub>2</sub> emissions in urban areas and their temporal and spatial variabilities, continuous measurements of CO<sub>2</sub> fluxes were conducted using the eddy covariance method at three locations in Sakai, Osaka, Japan. Based on the flux footprint at the measurement sites, CO<sub>2</sub> fluxes from the three sites were partitioned into five datasets representing a dense urban center, a moderately urban area, a suburb, an urban park, and a rural area. Distinct biological uptake of CO<sub>2</sub> was observed in the suburb, urban park, and rural areas in the daytime, whereas high emissions were observed at dense and moderate urban areas in daytime. Weekday CO<sub>2</sub> emissions in the dense urban center and suburban area were approximately 50 % greater than during weekend and holidays, but the other landscapes did not exhibit a clear weekly cycle. Seasonal variations in the urban park, rural area, and suburban area were influenced by vegetation activities, exhibiting the lowest daily emissions or even uptakes during summer months. In contrast, the dense and moderately urban areas exhibited higher emissions in winter and summer months, when emissions significantly increased as air temperature increased in summer and air temperature decreased in winter. Irrespective of the landcover type, all urban landscapes measured in this study acted as net annual CO<sub>2</sub> sources, with emissions ranging from 0.5 to 4.9 kg C m<sup>−2</sup> yr<sup>−1</sup>. The magnitude of the annual CO<sub>2</sub> emissions was negatively correlated with green fraction; areas with a smaller green fraction had higher annual CO<sub>2</sub> emissions. Upscaled flux estimates based on the green fraction indicated that the emissions for the entire city were 3.3 kg C m<sup>−2</sup> yr<sup>−1</sup>, which is equivalent to 0.5 Tg C yr<sup>−1</sup> or 1.8 Mt CO<sub>2</sub> yr<sup>−1</sup> based on the area of the city (149.81 km<sup>2</sup>). A network of eddy covariance measurements is a powerful tool to evaluate CO<sub>2</sub> emissions from urban areas.</p>

Urban land cover type determines the sensitivity of carbon dioxide fluxes to precipitation in Phoenix, Arizona

“…emissions from anthropogenic sources [6,[10][11][12][13][14][15][16]. In arid and semiarid regions, the trend in urbanization is even more pronounced than in other climate settings, which is crucial since about 30% of the global population is currently residing in cities in arid and semiarid climates [17][18][19].…”

“…Most CO 2 fluxes in cities are controlled by fuel combustion from vehicles, industries and buildings, rather than by biological processes [6,10,[22][23][24][25][26][27]. As a result, urban areas are net sources of CO 2 to the atmosphere [6,[28][29][30], though a high degree of spatiotemporal heterogeneity is present [6,15,[31][32][33]. Furthermore, the influence of point sources of CO 2 can play a disproportionate role as compared to natural ecosystems [6,34].…”

“…Indirect methods such as these are often associated with large uncertainties and a lack of spatial and temporal detail [6]. As an alternative applied in this study, the eddy covariance (EC) method [45] can be used to measure CO 2 fluxes (FC) in urban areas [6,11,12,15,16,30,39,46]. However, urban EC observations have been generally limited, as compared to those efforts in natural ecosystems, with most studies undertaken in very dense urban settings or in open low-density areas of northern latitudes [6,[47][48][49][50][51][52][53].…”

“…Ward et al [55] similarly studied three areas (woodland, suburban, and urban sites) in England, while Buckley et al [13] compared FC measurements in suburban and urban sites in Syracuse, USA. Ueyama and Ando [15] is one of the few studies to perform a direct comparison of multiple urban patches in Japan. In Indianapolis, as part of the INFLUX experiment, an important effort to measure FC over several urban landscapes was also carried out [56,57].…”

The Wintertime Covariation of CO2 and Criteria Pollutants in an Urban Valley of the Western United States

“…There has been growing interest in measuring CO 2 in urban areas to understand the processes controlling carbon emissions, since cities are responsible for~70% of anthropogenic CO 2 emissions globally (IEA, 2015). Cities around the world where intensive CO 2 observations and associated research efforts are taking place are Salt Lake City (McKain et al, 2012;Mitchell et al, 2018;Pataki et al, 2005), Paris (Dolman et al, 2006;Sarrat et al, 2007;Staufer et al, 2016), Osaka (Ueyama & Ando, 2016), Indianapolis (Lauvaux et al, 2016;Turnbull et al, 2015), Los Angeles (Newman et al, 2008;Newman et al, 2016), Rotterdam (Super et al, 2017), among others (Duren & Miller, 2012). If relationships between CO 2 concentrations and air pollutants in cities can be better understood, synergies between the growing effort to observe urban CO 2 and air quality can be realized.…”