Carbon Dioxide (Urban CO2 Dome - Other U.S. Cities) – Summary
HYPERLINK "http://www.co2science.org/scripts/CO2ScienceB2C/subject/u/summaries/urbanco2otherus.jsp" http://www.co2science.org/scripts/CO2ScienceB2C/subject/u/summaries/urbanco2otherus.jsp
Following the discovery and characterization of the HYPERLINK "http://www.co2science.org/scripts/CO2ScienceB2C/subject/u/phxurbanco2dome.jsp" urban CO2 dome of Phoenix, Arizona, USA, studies of urban CO2 domes began to be conducted in many other parts of the world. In this summary, we describe the results of investigations of this phenomenon that have been conducted in other U.S. cities.
HYPERLINK "http://www.co2science.org/scripts/CO2ScienceB2C/articles/V7/N7/C3.jsp" Pataki et al. (2003) measured atmospheric CO2 concentrations continuously, and carbon and oxygen isotopic composition weekly, 18 meters above the ground in Salt Lake City, Utah, for a period of one year, after which the seasonal cycles of δ13C and δ18O were used to assess the proportional contributions of natural gas combustion, gasoline combustion, and biogenic respiration to the urban CO2 concentration in excess of the rural background concentration at different times of the year. This work revealed that urban CO2 concentrations were highest in the winter, with maximum nighttime values approaching 600 ppm. Nighttime average values, however, were considerably lower, ranging from approximately 390-480 ppm in the winter and from 375-400 ppm in the spring and summer. Afternoon values, on the other hand, were typically within 5 ppm of the rural background value of 372 ppm. As for the isotopic measurements, Pataki et al. indicate they revealed that approximately 60% of the winter urban-rural CO2 differential came from natural gas combustion, while 40% was derived from the burning of gasoline. This latter component also remained a large portion of the urban CO2 dome in the summer; but the natural gas component essentially vanished during that season of the year, and biogenic plant and soil respiration had their largest effect in the spring and late summer. Consequently, as has been demonstrated in most other urban CO2 dome studies, the vast majority of the CO2 in the boundary-layer air of Salt Lake City that is in excess of the rural background level owes its existence to the burning of fossil fuels.
In a subsequent study of Salt Lake City's urban CO2 dome, HYPERLINK "http://www.co2science.org/scripts/CO2ScienceB2C/articles/V9/N7/C2.jsp" Pataki et al. (2005) described what they learned from measurements of the air's CO2 concentration and its isotopic (δ13C) composition that were made at four locations in the Salt Lake Valley during a persistent "cold pool" event in the winter of 2004, when the air in the valley was trapped beneath an inversion that formed on 5 January and did not "mix out" until 20 days later. In this investigation they found that mean daily (24-hour) CO2 concentrations at the tops of four- and five-story buildings and at the tops of 4.5- and 9-meter-tall towers ranged from 382 to 527 ppm (a 40% increase above rural background values) during the close-to-three-week measurement period. In addition, the δ13C data indicated that the major source of the cold-pool CO2 was the local combustion of gasoline and natural gas; and Pataki et al. determined that the local air's CO2 concentration was generally well correlated with its particulate matter concentration. The six researchers thus concluded that atmospheric CO2 concentrations, "which are not commonly monitored in most urban areas at present, can provide useful information regarding atmospheric transport and mixing in complex terrain such as mountain basins."
In yet another Salt Lake City urban CO2 dome study - this one conducted between 15 Dec 2004 and 20 Jan 2005 at a height of 18 meters above the ground on the campus of the University of Utah - HYPERLINK "http://www.co2science.org/scripts/CO2ScienceB2C/articles/V9/N39/C3.jsp" Pataki et al. (2006) measured atmospheric CO2 concentration and its stable carbon isotope composition (δ13C) by means of tunable diode laser absorption spectrometry, conventional isotope ratio mass spectrometry, and infrared gas analysis. In terms of maximum CO2 concentrations observed, this work revealed that toward the end of the measurement period, values as high as 600 ppm were recorded, coinciding with a major inversion event. On a diurnal basis, there was also a pattern of "relatively larger contributions of natural gas combustion in early morning, pre-dawn hours representing about 60-70% of total fossil fuel-derived CO2, and smaller contributions of about 30-40% during late afternoon and evening rush hour," which findings, according to Pataki et al., are "consistent with greater natural gas use during cold nighttime hours and increased gasoline combustion during evening rush hour." In addition, they report there was a pattern of "decreasing relative contributions of natural gas combustion over [a] week-long measurement period that corresponded to increasing ambient air temperature," which the researchers say was likely due to "reduced natural gas usage for residential heating during a warming period." This study thus demonstrated "for the first time," as they phrased it, that "atmospheric measurements may be used to infer patterns of energy and fuel usage on hourly to daily time scales," and that these measurements can provide "insight into urban energy use patterns and drivers." In addition, the data shed more light on the origin of the urban CO2 dome, highlighting the major roles played by the heating of homes and other buildings by the burning of natural gas and the powering of cars and other vehicles by the burning of gasoline.
Last of all, working within and around Baltimore, Maryland, HYPERLINK "http://www.co2science.org/scripts/CO2ScienceB2C/articles/V9/N6/B1.jsp" Ziska et al. (2004) characterized the gradual changes that occur in a number of environmental variables as one moves from a rural location (a farm approximately 50 km from the city center) to a suburban location (a park approximately 10 km from the city center) to an urban location (the Baltimore Science Center approximately 0.5 km from the city center). At each of these locations, four 2 x 2 m plots were excavated to a depth of about 1.1 m, after which they were filled with identical soils, the top layers of which contained seeds of naturally-occurring plants of the general area. These seeds sprouted in the spring of the year, and the plants they produced were allowed to grow until they senesced in the fall, after which all of them were cut at ground level, removed, dried and weighed.
The data from this study indicated that along the rural-to-suburban-to-urban transect, the only consistent differences in the measured environmental variables were a rural-to-urban increase of 21% in average daytime atmospheric CO2 concentration and increases of 1.6 and 3.3°C in maximum (daytime) and minimum (nighttime) daily temperatures, respectively, which changes, in the words of Ziska et al., "were consistent with most short-term (~50 year) global change scenarios regarding CO2 concentration and air temperature." In addition, they determined that "productivity, determined as final above-ground biomass, and maximum plant height were positively affected by daytime and soil temperatures as well as enhanced CO2, increasing 60 and 115% for the suburban and urban sites, respectively, relative to the rural site."
With respect to these observations, Ziska et al. say their results suggest that "urban environments may act as a reasonable surrogate for investigating future climatic change in vegetative communities." What is more, their results indicate that the twin evils of the radical environmentalist movement (rising air temperatures and CO2 concentrations) tend to produce dramatic increases in the productivity of the natural ecosystems typical of the greater Baltimore area and, by inference, would probably do the same for many other areas, both urban, where productivity increases are likely already appearing, and rural, where they can be expected to appear sometime in the future, as the HYPERLINK "http://www.co2science.org/scripts/CO2ScienceB2C/subject/g/greeningearth.jsp" greening of the earth continues.
References
Pataki, D.E., Bowling, D.R. and Ehleringer, J.R. 2003. Seasonal cycle of carbon dioxide and its isotopic composition in an urban atmosphere: Anthropogenic and biogenic effects. Journal of Geophysical Research 108: 10.1029/2003JD003865.
Pataki, D.E., Bowling, D.R., Ehleringer, J.R. and Zobitz, J.M. 2006. High resolution atmospheric monitoring of urban carbon dioxide sources. Geophysical Research Letters 33: 10.1029/2005GL024822.
Pataki, D.E., Tyler, B.J., Peterson, R.E., Nair, A.P., Steenburgh, W.J. and Pardyjak, E.R. 2005. Can carbon dioxide be used as a tracer of urban atmospheric transport? Journal of Geophysical Research 110: 10.1029/2004JD005723.
Ziska, L.H., Bunce, J.A. and Goins, E.W. 2004. Characterization of an urban-rural CO2/temperature gradient and associated changes in initial plant productivity during secondary succession. Oecologia 139: 454-458.
Last updated 22 November 2006