Skip to main content
ARS Home » Research » Publications at this Location » Publication #127371
Title: SEASONAL AND DIURNAL VARIATIONS OF NEAR-SURFACE ATMOSPHERIC CO2 CONCENTRATION WITHIN A RESIDENTIAL SECTOR OF THE URBAN CO2 DOME OF PHOENIX,ARIZONA, USA

Author
item IDSO, SHERWOOD
item IDSO, CRAIG - ASU, TEMPE, AZ
item BALLING JR, ROBERT - ASU TEMPE AZ

Submitted to: Atmospheric Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: It recently has been demonstrated that near-surface atmospheric CO2 concentrations in large cities may be substantially higher than those of surrounding rural areas, and it has been suggested that this phenomenon may provide a natural laboratory for studying the effects of atmospheric CO2 enrichment on plant growth and development. To assess the potential of this concept, we measured atmospheric CO2 concentrations in a residential sector of the urban CO2 dome of Phoenix, Arizona, at one- minute intervals for most of an entire year, finding that mean daytime CO2 concentrations 21 km from the center of the city, but still within the metropolitan area and close to its two major freeways, were only 10% greater than values characteristic of rural air. We thus conclude that some of the experimental plots of a research program designed to capitalize upon the range of CO2 concentrations provided by a city's urban CO2 dome would have to be established close to the center of the metropolitan complex in order to provide meaningful experimental treatments, and that this requirement might introduce confounding effects due to higher levels of noxious air pollutants that may exist near the city center. This information should help scientists contemplating such studies to better design their experiments.

Technical Abstract: Over most of an entire year (315 days), we obtained 1-minute averages of near-surface (2-m height) atmospheric OC2 concentration, temperature, and wind speed in a residential area of a suburb of Phoenix, Arizona. Daily minimum CO2 concentrations, which occurred during the afternoon, were nearly invariant over the year, averaging 390.2 plus or minus 0.2 ppm. Daily maximum CO2 concentrations, however, which occurred at night, varied seasonally with the air temperature, exhibiting a mean peak of 490.6 ppm about two hours before midnight during the coldest part of the year (December-January) and 424.3 ppm just before sunrise during the warmest part of the year (July-August). Reevaluating prior assessments of the strength of the urban CO2 dome at the center of Phoenix, our results suggest a mean cold-season maximum there of 619.3 ppm, which is 67.4% greater than the rural background value. At our residential site, however, the mean cold-season maximum was only 32.6% greater than the surrounding rural mean. Averaged over the entire night, this enhancement dropped to 25.4% in the cold season and 10.9% in the warm season, while over the daylight period it averaged 10.5% and 10.1% in the cold and warm seasons, respectively. CO2 concentrations were greater on weekdays than on weekends from 0415 to 0830 in the warm season and from 0445 to 1045 in the cold season. During peak morning traffic, the maximum weekday-weekend CO2 differential was 35.9 ppm in the cold season and 22.0 in the warm season.