Elemental carbon deposition to urban tree canopies: magnitudes and spatial patterns
Alexandra G. Ponette-González1, Tate E. Barrett2, Jenna E. Rindy3 and Rebecca J. Sheesley4
Urban areas are a major source of atmospheric elemental carbon (EC), a component of fine particulate matter and a powerful climate-forcing agent. However, empirical measurements of EC removal from urban atmospheres by wet and dry deposition are few in number and virtually none explicitly quantify intra-urban variability in deposition rates. Tree canopies are likely important sinks for EC on the cityscape because of their propensity to scavenge suspended particulate matter, of which EC can be a significant component in urban settings. This research aims to quantify magnitudes and spatial patterns of total (wet + dry) EC deposition to urban tree canopies in the Dallas-Fort Worth Metroplex using the throughfall method (collection of water that falls from the canopy to the forest floor). In March 2017, we established 41 throughfall collectors across a 51 km2 area in the City of Denton, Texas. Collectors were deployed beneath 22 post oak (Quercus stellata) and 19 live oak (Quercus virginiana) trees in residential yards and urban greenspaces, both near (≤100 m) and far from roads (>100 m) with truck traffic. Additionally, 16 bulk rainfall samplers were established in grassy areas with no canopy cover. Throughfall and rainfall are currently being sampled on an event basis. Total EC deposition to urban tree canopies measured during a single rainfall event in May 2017 ranged widely, from 0.12 to 5.6 mg m-2. On average, EC deposition to post oak canopies was more than 2-fold higher (1.8 ± 2.0 (SD) mg m-2) compared to live oak canopies (0.67 ± 0.27 mg m-2) whereas bulk rainfall deposition was 0.077 ± 0.11 mg m-2. Our preliminary findings show that oak trees are effective urban air filters, removing up to 23 times more EC from the atmosphere than rainwater alone. Qualitative observations suggest that tree size and density of emissions sources within a 50-m radius buffer also contribute to spatial variability in EC deposition. Resolving surface controls on atmospheric EC removal is key to developing and assessing climate and air quality mitigation strategies.
1Department of Geography and the Environment, University of North Texas, firstname.lastname@example.org 2Department of Geography and the Environment, University of North Texas, Tate.Barrett@unt.edu 3Department of Geography and the Environment, University of North Texas, Jenna.Rindy@unt.edu 4Department of Environmental Science, Baylor University, Rebecca_Sheesley@baylor.edu