Abstract
Methacrolein (MACR) and methyl vinyl ketone (MVK) are key intermediate compounds in isoprene-initiated reactions, and they cause the formation of secondary organic aerosols and photochemical ozone. The importance of higher plants as a sink of these compounds and as a source of volatiles converted from these compounds was addressed in the present study. We exposed four non-isoprene-emitting plant species to MACR and MVK at concentrations of several to several hundred ppb, measured their uptake rates, and analyzed the volatiles converted from MACR and MVK by these plants. We used a flow-through chamber method to determine the exchange rates. Both MACR and MVK were absorbed by all plants via stomata. Two metabolites, methyl ethyl ketone (MEK) and 2-butanol, were detected when MVK was fumigated. The conversion ratio was 26–39% for MEK and 33–44% for all volatiles. Combined with the results of two previous relevant reports, our results suggest that MEK conversion from MVK normally occurs in a wide range of plant species, but the conversion ratio may depend on plant type, i.e., if plant species are isoprene-emitting or non-emitting, as well as on the fumigation concentrations. This finding also emphasizes the importance of bilateral exchange measurements of these compounds at lower concentrations close to ambient levels.
Highlights
Volatile organic compounds (VOC) and NOx are involved in the formation of photochemical ozone and degradation of air quality in urban and sub-urban areas [1]
We used PTR-TOF-MS and gas chromatograph mass spectrometer (GC-MS) to analyze VOC, and we showed that isoprene were the highest, followed by the reaction with OH radicals and reaction with ozone, suggesting that oxygenates MACR and methyl vinyl ketone (MVK) were absorbed by the four investigated species (Figure 1)
Isoprene-emitting trees may have more active enzymes for converting MVK to volatiles than non-emitting plants, because cells of the isoprene-emitting plants are always exposed to high concentrations of isoprene and its oxygenates, including MVK, during daytime
Summary
Volatile organic compounds (VOC) and NOx are involved in the formation of photochemical ozone and degradation of air quality in urban and sub-urban areas [1]. VOC reactions cause the formation of secondary organic aerosol (SOA), which affects human health and climate [2]. VOCs are degraded in the atmosphere by a number of reactions with OH, ozone, NO3 , and HO2 [3]. These oxidized products undergo gas-particle conversion processes such as nucleation, condensation, and heterogeneous and multiphase chemical reactions. The formation and growth of SOA depends on the original oxidized products. Goldstein and Galbally [4] estimated that 510–910 Tg C yr−1 of SOA was formed from globally emitted VOCs, with an annual emission of 1300 Tg C yr−1
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