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Title: Elevated atmospheric C02 concentration and temperature across an urban-rural transect

Author
item GEORGE, KATE - UNIV OF MARYLAND
item ZISKA, LEWIS
item Bunce, James
item QUEBEDEAUX, BRUNO - UNIV OF MARYLAND

Submitted to: Atmospheric Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2007
Publication Date: 11/1/2007
Citation: George, K., Ziska, L.H., Bunce, J.A., Quebedeaux, B. 2007. Elevated atmospheric C02 concentration and temperature across an urban-rural transect. Atmospheric Environment. 41:7654-7665.

Interpretive Summary: We studied atmospheric carbon dioxide levels, air temperature and other environmental factors to determine how they varied between urban, suburban, and rural areas and between years. The study took place at three locations in Maryland which represented a decrease in urbanization from a major metropolitan city to a rural agricultural area. We found that atmospheric carbon dioxide was increased by 16 % and air temperature by 2.1 degrees centigrade from the rural location to the city center. Ozone and nitrogen pollution from vehicular emissions and other sources was not increased at the urban compared to the rural site. Light in urban environments can be scattered by air borne pollution reducing the amount of direct light and increasing diffuse light. We found that although total light was lower at the urban site, possibly from shading of buildings during parts of the day, diffuse light was also lower compared to the rural site. The increase in carbon dioxide and air temperature are consistent with increases predicted globally in the short term with climate change. Urban environments are consequently suitable locations for investigating the effects of climate change on biological systems. This study contributes to our understanding of how our climate is influenced by humans and will be of interest to plant ecologists studying the effects of climate change on plant communities.

Technical Abstract: The heat island effect and the high use of fossil fuels in large city centers are well documented, but by how much fossil fuel consumption is elevating atmospheric CO2 concentrations and whether elevations in both atmospheric CO2 and air temperature are consistent from year to year are less well known. Our aim was to record atmospheric CO2 concentrations, air temperature and other environmental variables in an urban area and compare it to suburban and rural sites to see if urban sites are experiencing climates expected globally in the future with climate change. A transect was established from Baltimore city center (Urban site), to the outer suburbs of Baltimore (suburban site) and out to an organic farm (rural site). At each site a weather station was set-up to monitor environmental variables for five years. Atmospheric CO2 was consistently and significantly increased on average by 66 ppm from the rural to the urban site over the five years of the study. Air temperature was also consistently and significantly higher at the urban site (14.8 oC) compared to the suburban (13.6 oC) and rural (12.7 oC) sites. Relative humidity was not different between sites whereas the vapor pressure deficit (VPD) was significantly higher at the urban site compared to the suburban and rural sites. Increased nitrogen deposition at the rural site (2.3 % compared to 1.7 and 1.3 % at the suburban and urban sites) was small enough not to affect soil nitrogen content. Dense urban areas with large populations and high vehicular traffic have significantly different microclimates compared to outlying suburban and rural areas. The increases in atmospheric CO2 and air temperature are similar to changes predicted in the short term with global climate change, therefore providing an environment suitable for studying future effects of climate change on terrestrial ecosystems.