1,2-ISOPOOH Deposition on Leaf Surfaces as a Source of HCHO and MVK in Pristine Conditions
Abstract
Isoprene hydroxyhydroperoxides (ISOPOOHs) are prominent isoprene-OH oxidation products in low NOx environments that contribute significantly to the oxidizing capacity of the atmosphere and secondary organic aerosol formation. Therefore, understanding ISOPOOH's sources and sinks is critical for atmospheric chemistry models to predict oxidation chemistry and secondary pollutant formation. It has been observed in forests that ISOPOOH has a large dry deposition velocity to forest canopy surfaces that act as a sink of reactive carbon. However, the fate of this reactive carbon after depositing to leaf surfaces is poorly understood. Additionally, it has been shown that forest canopies have upwards of 0.5 ppbv HCHO enhancement relative to above and below the canopy, which cannot be explained by current gas phase chemistry and meteorology. Further, it has been shown that surfaces in atmospheric instrumentation can convert 1,2-ISOPOOH, the dominant ISOPOOH isomer, to formaldehyde (HCHO) and methyl vinyl ketone (MVK). Therefore, we hypothesize that deposition of ISOPOOH to leaf surfaces can act as sources of HCHO and MVK in forest canopies.
We present 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. 1,2-ISOPOOH and MVK were quantified in the gas phase via a NH4+-chemical ionization mass spectrometer. HCHO was measured via a laser induced fluorescence instrument. Under both light and dark conditions, we show that 1 ppbv of 1,2-ISOPOOH produces 0.2 ppbv of HCHO and MVK. This suggests that, for the conditions of our study, the deposition of 1,2-ISOPOOH is primarily controlled by leaf surfaces and that this can explain part of the HCHO enhancement in forest canopies. Future studies will look at the effect of temperature and humidity on the yield of HCHO and MVK from 1,2-ISOPOOH decomposition on leaf surfaces.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A33J3076C
- Keywords:
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- 0315 Biosphere/atmosphere interactions;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0322 Constituent sources and sinks;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0365 Troposphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES