<p>The formation of alkyl nitrates in various oxidation processes taking place throughout the diel cycle can represent an important sink of reactive nitrogen and mechanism for chain-termination in atmospheric photo-oxidation cycles. The low volatility alkyl nitrates formed from biogenic volatile organic compounds (BVOCs), especially terpenoids, enhance rates of production and growth of secondary organic aerosol. Measurements of the NO<sub>3</sub>-reactivity and the mixing ratio of total alkyl nitrates in the Finnish boreal forest enabled assessment of the relative importance of NO<sub>3</sub><sup>−</sup>, O<sub>3</sub><sup>−</sup> and OH-initiated formation of alkyl-nitrates from BVOCs in this environment. The high reactivity of the forest air towards NO<sub>3</sub> resulted in reactions of the nitrate radical with terpenes contributing substantially to formation of ANs not only during the night but also during daytime. Overall, night-time reactions of NO<sub>3</sub> accounted for 49 % of the local production rate of ANs, with contributions of 21 %, 18 % and 12 % for NO<sub>3</sub>, OH and O<sub>3</sub>, during the day. The lifetimes of the gas-phase ANs formed in this environment were of the order of 2 hours implying that the lifetime of NO<sub><i>x</i></sub> is strongly controlled by biogenic emissions from the forest. As the organic nitrates are lost to the particle phase and via dry-deposition to foliar surfaces, the overall result is transfer of reactive nitrogen from anthropogenic sources to the forest ecosystem.</p>