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Title: AN INTENSIVE TWO-WEEK STUDY OF AN URBAN CO2 DOME

Author
item IDSO, C - ARIZONA STATE UNIV
item IDSO, SHERWOOD
item BALLING JR, R - ARIZONA STATE UNIV

Submitted to: Atmospheric Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: It has recently been discovered that just as cities exhibit elevated air temperatures or urban heat islands, so too do they exhibit elevated atmospheric CO2 concentrations or urban CO2 domes. This fact is of great significance, because the combination of these two phenomena-- elevated air temperature and CO2 concentration--is being predicted to occur for the world as a whole as a consequence of the continued burning of fossil fuels. Hence, it is possible that cities may serve as models of the entire planet in efforts to determine certain effects of predicted global change. Before these natural laboratories can be used as such, however, it is necessary to quantitatively characterize the spatial and temporal characteristics of the urban CO2 dome. Our research achieves the first of these goals for the coldest part of the year in Phoenix, Arizona. It also establishes a protocol for others to follow in making similar measurements in other cities. Consequently, our study lays the groundwork for the future exploration of this important subject, which could prove a valuable tool in our efforts to better understand and anticipate the societal consequences of continued human-induced CO2 emissions.

Technical Abstract: Atmospheric CO2 concentrations were measured prior to dawn and in the middle of the afternoon at a height of two meters above the ground along four transects through the metropolitan area of Phoenix, Arizona, on 14 consecutive days in January 2000. The data revealed the existence of a strong urban CO2 dome, which exhibited a peak CO2 concentration at the center of the city that was 75% greater than that of the surrounding rural area. Mean city-center peak enhancements averaged 43% on weekdays and 38% on weekends. Averaged over the entire commercial sector of the city, they were 30% on weekdays and 23% on weekends. These results indicate that commercial work-week activities increase near-surface CO2 concentrations in the commercial sector of the city by 30% above those on non-workdays (30% / 23% = 1.30). Over the surrounding residential areas, on the other hand, there are no weekday-weekend differences. Furthermore, because of enhanced vertical mixing during the day, near- surface CO2 concentrations in the afternoon are typically reduced from those prior to sunrise. This situation is additionally perturbed by the prevailing southwest-to-northeast flow of air, which lowered afternoon CO2 concentrations on the southern and western edges of the city still more as a consequence of the importation of pristine rural air. The southwest-to-northeast flow of air also sometimes totally compensated for the afternoon vertical-mixing-induced loss of CO2 from areas on the northern and eastern sides of the city as a consequence of the northeastward advection of CO2 emanating from the central, southern, and western sectors of the city.