News & Events

Grad student talk - What's causing morning nitric oxide 'pulse' above the canopy at a forested site?

Thursday, September 23, 2010, 4:30PM - 5:30PM


Brian Seok



RL-1 269

Full title: "What's causing morning nitric oxide 'pulse' above the canopy at a forested site in northern Michigan?"

Nitrogen oxides (NO + NO2 = NOx) and ozone (O3) concentrations below, in, and above the canopy were measured continuously during the summer and fall of 2008 from the Ameriflux tower at the University of Michigan Biological Station (UMBS). Temperature throughout the canopy and turbulent wind speed data above the canopy were also collected. The composite isopleths of the collected chemical vertical profile data show a rapid rate of increase in nitric oxide (NO) concentrations (Δ0.1 ppbv/hr) during sunrise (between 6 and 9 am EST) in the upper part of the canopy. There are several hypotheses to the source and cause of this observed morning NO concentration peak inside the canopy. One explanation could be upward transport of NO emitted by the soil to the crown-layer. An alternative hypothesis is that the source of the NO "pulse" in the morning is the result of photodissociation of nitrogen dioxide (NO2) accumulated overnight inside the canopy. In addition to interpreting the collected profile data, a single column canopy model is used to test these hypotheses and examine the combined effect of emissions, transport, chemistry, and deposition inside the forest canopy in modulating NOx and O3 atmosphere-biosphere exchange. Finally, I will reflect on how this research project is teaching me a valuable lesson in life and preparing myself for scientific career.