Anthropogenic and natural CO 2 emission sources in an arid urban environment

Abstract

Recent research has shown the Phoenix, AZ metropolitan region to be characterized by a CO 2 dome that peaks near the urban center. The CO 2 levels, 50% greater than the surrounding non-urban areas, have been attributed to anthropogenic sources and the physical geography of the area. We quantified sources of CO 2 emissions across the metropolitan region. Anthropogenic CO 2 emission data were obtained from a variety of government and NGO sources. Soil CO 2 efflux from the dominant land-use types was measured over the year. Humans and automobile activity produced more than 80% input of CO 2 into the urban environment. Soil CO 2 efflux from the natural desert ecosystems showed minimal emissions during hot and dry periods, but responded rapidly to moisture. Conversely, human maintained vegetation types (e.g. golf courses, lawns, irrigated agriculture) have greater efflux and are both temperature and soil moisture dependent. Landfills exhibited the most consistent rates, but were temperature and moisture independent. We estimate the annual CO 2 released from the predominant land-use types in the Phoenix region and present a graphical portrayal of soil CO 2 emissions and the total natural and anthropogenic CO 2 emissions in the metropolitan region using a GIS-based approach. The results presented here do not mimic the spatial pattern shown in previous studies. Only, with sophisticated mixing models will we be able to address the total effect of urbanization on CO 2 levels and the contribution to regional patterns.