Spatial Patterns and Determinants of Winter Atmospheric Carbon Dioxide Concentrations in an Urban Environment

Abstract

The purpose of this article is to describe determinants and spatial patterns of atmospheric carbon dioxide (CO 2 ) in Phoenix, Arizona. Specifically, we use geographic information systems (GIS) and regression-based analyses to identify the human and biological factors that contribute to spatial and temporal variations in near-surface (2-meter height) atmospheric CO 2 levels. We use these factors to create estimated surfaces of CO 2 concentrations for the area. We evaluate the surfaces using records of CO 2 from independent monitoring stations and transects. To investigate the temporal patterns and variations in CO 2 concentrations, we estimate CO 2 surfaces for the early mornings and the afternoons, on weekdays when traffic is heavy and spatially focused and on weekends when it is lighter and more spatially dispersed. Findings suggest there is a distinct relationship between the structure of Phoenix CO 2 levels and spatial patterns of human activities and vegetation densities. Morning CO 2 levels are higher than afternoon levels and correspond closely to the density of traffic, population, and employment. The spatial structure of human activity explains the pattern of CO 2 better on weekdays than on weekends. CO 2 surfaces reflect declining densities of human activity with distance from the city center, the pattern of irrigated agriculture in the Phoenix area, and riparian habitats on the urban fringe. Spatial and temporal patterns of CO 2 concentrations are useful in understanding urban climate and ecosystem processes. Key Words: carbon dioxide, geographic information systems (GIS), regression-based mapping, urban climatology.nterest in interactions among carbon dioxide (CO 2 ), human activity, climate change, and ecosystem processes has been largely at global, hemispheric, and regional scales. To aid in understanding global changes to CO 2 , FLUXNET (along with EuroFlux, AmeriFlux, and MedeFlu) was devised as a world-wide coordinated initiative to disseminate data for long-term monitoring of CO 2 (FLUXNET 2001). Climatologists have examined how human-induced increases in atmospheric CO 2 levels affect climatic patterns , while biologists have concentrated on the impact of higher CO 2 levels on ecosystems and the "missing sink" problem-why atmospheric CO 2 concentrations are less than expected on the basis of estimated rates of anthropogenic emissions and simulated oceanic and terrestrial carbon uptake levels (Lloyd 1999). Scientists have paid less attention to urban-scale CO 2 processes, despite the fact that increases in atmospheric CO 2 are largely anthropogenic in origin and therefore heavily concentrated in urban areas.Recently, enhanced CO 2 levels in and around urban regions have been documented. Idso and colleagues found near-surface (2 meters) concentrations of CO 2 in January in Phoenix, Arizona in the near-dawn hours as high as 555 parts per million by volume (ppmv). This is 185 ppmv higher than the background readings of 370 ppmv in surrounding open desert and agricultural fields. Urban-rural differ...

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