Boreal Forest OH Reactivity - Project Description

Boreal forests cover about 10% of Earth's land surface and are globally
 significant sources of biogenic volatile organic compounds.
 This project involved deployment of newly developed instrumentation (Sinha et
 al., ACP,2008) within the canopy of the boreal forest in Hyytiäla, to directly
 measure the total atmospheric OH reactivity. In combination with existing
 measurements of reactive hydrocarbons and aerosol performed at this site by Dr.
 Taina Ruuskanen and co-workers of Prof. Kulmala from the University of
 Helsinki, this  enabled new insights regarding 1) the photochemical processing
 of reactive biogenic VOC emissions, 2) the OH radical budget and 3) improved
 representation of the OH sink term in photochemical models such as e.g. MALTE –
 see Boy et al.,ACP, 2006).

Scientific objectives of the project:

1) Ascertain whether there is missing sink of OH reactivity in the boreal forest
 air.

2) Apportion the relative importance and contribution of measured reactive VOCs
 such as monoterpenes and isoprene to the total OH reactivity of the boreal
 forest air.

3) Elucidate photochemical processing by the OH radical at canopy heights.

4) Explore the link between OH reactivity measurements and secondary organic
 aerosol which is formed when the OH radical oxidizes reactive hydrocarbons, by
 using the atmosphere aerosol model MALTE (Boy et al., 2006).

5) Test the representation schemes in photochemical models that predict ambient
 OH radical variations (Boy et al., 2005).

6) Improve our understanding of the hydroxyl radical (OH) budget by constraining
 the OH sink with direct measurements.

This project was accomplished with financial support from ACCENT, EUSAAR and the
 Max Planck Gesellschaft.