The boundary layer and its effects on canopy-level ozone and NOx mixing ratios.

Abstract

PROPHET held a measurement intensive during the summer of 2000 at a forested site in rural northern Michigan whose purpose was to better understand the transport and fate of bith anthropogenic and biogenic emissions on atmospheric chemistry. as part of PROPHET, measurements of both the convective and nocturnal boundary layers were taken to determine the influence of each on the observed ozone and NOx mixing ratios. Backward transport trajectories at heights based on the maximum height of the convective boundary layer (CBL) were compared with trajectories produced by the method of Cooper et al, [2000] to determine if a difference in transport source region between air within the CBL and air in the free troposphere existed. The two methods were compared to determine which could better explain the observed ozone and NOx mixing ratios for two case studies. An exercise bike was used to launch tethered balloons that measured the nocturnal boundary layer (NBL) and showed that observed morning peaks in NOx appear to be correlated with the entrainment of polluted layers into the growing CBL. Ozone was found to depend on transport, NOx, sunlight and boundary layer dynamics.