Boundary layer dynamics and meteorology during morning elevated NOx mixing ratios.

Abstract

Measurements made at a rural forested site in Northern Michigan (Pellston) by the Program for Research on Oxidants: PHotochemistry, Emissions, and Transport (PROPHET) revealed elevated morning levels of nitrogen oxides (NOx) during summer intensives in 1997, 1998, 2000, and 2001. To determine boundary layer dynamics during the measurements of the ozone producing trace gas NOx, a boundary layer profiler, as well as balloon-borne sonde instrumentation, provided by the National Center for Atmospheric Research, was utilized to determine the possibility of entrainment of residual layer air as the cause for the elevated NOx levels. These boundary layer measurements were made during the 2001 PROPHET intensive, simultaneously with NOx measurements, revealing in one of two case study days, that entrainment likely occurred just prior to the morning NOx peak. In addition, other meteorological parameters measured on these two days, as well as two days from the 2000 intensive revealed that net solar radiation intensity correlated with observed higher morning NOx concentrations.