Comparing Urban-to-Rural Environmental Gradients in the Houston Metropolitan Area between a drought (2011) and a normal year (2012)

As climate continues to change and weather events trend toward the more extreme, questions are raised about how this affects urban environments and regional atmospheric chemistry. The largest contributors to organic chemistry in the atmosphere are plants that emit biogenic volatile organic compounds (BVOCs.) This project aims to use the urban-to-rural gradient north of Houston to study long term effects of different microclimates on oak trees growing under field conditions. To begin to do this, three weather station were placed along a gradient away from downtown Houston, at a participating high school, through a forested suburban community, at a junior high school in The Woodlands, to the ranger station in Sam Houston National Forest (SHNF), 90 km from downtown. We monitor weather, carbon dioxide, and ozone gradients. This data is supplemented by TCEQ and NCDC records. Temperature gradients from Houston to SHNF during the 2011 summer averaged 0.1°C during the day and 2.2°C at night; during the 2011-2012 winter they averaged 1.9°C during the day and 2.4°C at night; and during the 2012 summer gradients averaged 1.1°C during the day and 2.7°C at night. Additionally, field trips were made weekly throughout the spring, summer, and fall to take leaf level measurements using a CIRAS-II photosynthesis analyzer, which was augmented to sample emitted VOCs from the leaf using activated carbon packed tubes, later analyzed by gas chromatography. Differences between the sites and the ability of the trees at each site to acclimate are discussed using several case studies with respect to drought in 2011 and adequate rainfall in spring and summer 2012.