Biogenic Organics Coupling of the Land Ecosystem-Atmosphere-Climate System: From Concept to Quantitative Model
Secondary organic aerosol (SOA) and ozone are important contributors to the radiative forcing that drives climate change. These two atmospheric constituents are formed in the atmosphere from chemical reactions involving volatile organic compounds (VOC) emitted primarily from terrestrial ecosystems. Both ozone and SOA can directly influence solar radiation and thus change light and temperature at the Earth’s surface. SOA can have an additional indirect effect through impacts on cloud properties. Since VOC emissions from terrestrial ecosystems are extremely temperature and light sensitive, this can lead to a feedback between temperature/light and VOC emissions. Another feedback is associated with the water cycle since SOA can influence clouds and precipitation and because VOC emissions are sensitive to water availability. Human activities, primarily fossil fuel combustion, add to the complexity of this coupled system by amplifying the production of ozone and SOA from biogenic VOC. There is limited or even no production of SOA and ozone when biogenic VOC are emitted into a pristine atmosphere. It is only when biogenic VOC emissions mix with polluted air that SOA and ozone are produced at levels that have a significant impact on air quality and climate. The role of biogenic VOC in the land-atmosphere-climate system and potential feedback couplings is conceptually clear but developing an accurate quantitative representation is challenging. Progress towards this goal will be presented including leaf, branch, canopy and airborne observations from the recent Southeast Atmospheric Study (SAS). Priorities for future advances will also be discussed, including the need for more observational constraints and the development of a community model testbed.