Temporal and spatial patterns of air temperature and CO2 concentration in metropolitan Phoenix

Net productivity of urban vegetation is likely impacted by temporal and spatial variations in temperature and atmospheric CO₂ in and around urban environments. Data collected along multiple transects on surface streets within the urban and suburban Phoenix metropolitan area in June and December 1999 were evaluated for temporal and spatial patterns in temperature and atmospheric CO₂ concentration. All measurements were made over asphalt from a vehicle traveling at an average speed of 14.7 m/s around 0500 and 1500 HR under clear, calm, anticyclonic conditions. Temperature was measured using shielded copper constantan thermocouple wire 0.5, 2, and 5 m above ground. Atmospheric CO₂ was measured 2.5 m above ground using a LI-COR 6250 infrared gas analyzer in open system mode. Temperature data were normalized to data collected at Phoenix Sky Harbor Airport for the appropriate day and time. To elucidate spatial patterns, all data for each time period were pooled and categorized based on distance from the Phoenix urban core. Urban to rural gradients of high to low temperature were present and most apparent during early morning summer hours, with mean urban and rural temperature differences of 3.8^oC. Atmospheric CO₂ concentration varied most during winter mornings, with 27% higher concentrations in urban areas than at the desert fringe. In general, CO₂ concentration was highest in winter and during early morning hours for both seasons. These data suggest that heating of urban surfaces and elevated CO₂ levels in the inner city might benefit urban landscape plants, particularly those that are biologically active during winter.