Modelling atmospheric OH-reactivity in a boreal forest ecosystem,

Abstract

We have modelled the total atmospheric OH- reactivity in a boreal forest and investigated the individ- ual contributions from gas phase inorganic species, iso- prene, monoterpenes, and methane along with other impor- tant VOCs. Daily and seasonal variation in OH-reactivity for the year 2008 was examined as well as the vertical OH- reactivity profile. We have used SOSA; a one dimensional vertical chemistry-transport model (Boy et al., 2011a) to- gether with measurements from Hyyti ̈ l ̈ , SMEAR II station, aa Southern Finland, conducted in August 2008. Model sim- ulations only account for ∼30–50 % of the total measured OH sink, and in our opinion, the reason for missing OH- reactivity is due to unmeasured unknown BVOCs, and limi- tations in our knowledge of atmospheric chemistry including uncertainties in rate constants. Furthermore, we found that the OH-reactivity correlates with both organic and inorganic compounds and increases during summer. The summertime canopy level OH-reactivity peaks during night and the verti- cal OH-reactivity decreases with height.