Reactions between ozone and terpenoids within a forest on Mt. Fuji

Abstract

Biogenic hydrocarbons react with ozone in forest ecosystems to produce oxygenated compounds, which are partially incorporated into secondary organic aerosols (SOAs). The hydrocarbons also react with OH radicals, controlling the levels of photochemical oxidants. These reactions occur simultaneously, and the concentrations of ozone and SOAs depend on the abundances of the relevant components, such as biogenic hydrocarbons. In this chapter, results of observations of these compounds in a Japanese larch forest (Larix kaempferi) in the foothills of Mt. Fuji are provided as a case study. Ozone concentrations increased with the height measured within the canopy, suggesting that ozone is decomposed within the forest and/or is absorbed by the forest canopy. The biogenic hydrocarbons isoprene and monoterpenes are emitted from the forest ecosystem and the monoterpene flux can be explained by the temperature and soil water content. The annual emission of monoterpenes plus isoprene was determined to be 0.93 % of the net ecosystem exchange. Oxygenated compounds, originating from isoprene and a-pinene, were found in the suspended particulate matter. The concentrations of these compounds and ozone were well correlated, suggesting that, along with terpenoid emissions, the anthropogenic inflow and subsequent oxidation of the terpenoids also promote biogenic SOA formation within the forest canopy.