A comparative analysis of isoprene depletion at canopy height and aloft.

Abstract

Rapid decrease of isoprene mixing ratios at night were observed over a forested region in northern Michigan as part of the PROPHET Summer 2000 research intensive. Measurements of isoprene were taken both near canopy height (34 m) and aloft (~150-600 m) on four separate dates to assess the influence of ozonolysis, vertical mixing, reaction with terpene produced OH radicals, and horizontal advection on isoprene depletion. Observed data were inconsistent with known ozone reaction rates. When compared to observed values, modeled isoprene decay due to OH chemistry suggests that this mechanism may play an important role in the process, but results also indicate terpene oxidation may not be a significant source of this OH. Flight data also provide evidence that vertical mixing alone is not responsible for isoprene decay, while horizontal advection of air from cleaner, isoprene-poor areas may play a large role in depletion of isoprene mixing ratios.