Elucidating a Biogenic HCHO Source from 1,2-ISOPOOH Decomposition on Red Oak Leaves

Abstract:

Isoprene hydroxyhydroperoxides (ISOPOOHs) are prominent isoprene-OH oxidation products in low NO_x environments that contribute significantly to the oxidizing capacity of the atmosphere and secondary organic aerosol formation. It has been observed in forests that ISOPOOH deposits strongly to forest canopy surfaces. However, the fate of this reactive carbon after depositing to leaf surfaces is poorly understood. Further, it has been shown that surfaces in atmospheric instrumentation can convert 1,2-ISOPOOH, the dominant ISOPOOH isomer, to formaldehyde (HCHO). Therefore, we hypothesize that deposition of ISOPOOH to leaves can act as a source of HCHO in forest canopies.

We present laboratory measurements of 1,2-ISOPOOH deposition to red oak (Quercus rubra) saplings in a glass leaf cuvette system capable of maintaining constant temperature, humidity, and photosynthetically active radiation. We show that exposing leaves to a few ppbv of ISOPOOH results in upwards of 50% conversion to HCHO at 50% RH and 30 °C with the lights on. However, we see no ISOPOOH uptake and no conversion to HCHO under dark conditions. This suggests that the deposition of 1,2-ISOPOOH is primarily controlled by the stomata and/or heterogeneous photochemistry. We will also present the effect of humidity, lights, and stomatal opening on the yield and mechanism of HCHO production from 1,2-ISOPOOH decomposition on leaves. Additionally, results will be placed into FORCAsT, a 1-D biosphere-atmosphere box model, to simulate ISOPOOH and HCHO and compare to measurements taken during the 2016 PROPHET-AMOS campaign.