Alkyl nitrates in the boreal forest: formation via the NO.sub.3-, OH- and O.sub.3-induced oxidation of biogenic volatile organic compounds and ambient lifetimes

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 (ANs) 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 reactivity and the mixing ratio of total alkyl nitrates (ΣANs) in the Finnish boreal forest enabled assessment of the relative importance of NO.sub.3 -, O.sub.3 - and OH-initiated formation of alkyl nitrates from BVOCs in this environment. The high reactivity of the forest air towards NO.sub.3 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 accounted for 49 % of the local production rate of ANs, with contributions of 21 %, 18 % and 12 % for NO.sub.3, OH and O.sub.3 during the day. The lifetimes of the gas-phase ANs formed in this environment were on the order of 2 h due to efficient uptake to aerosol (and dry deposition), resulting in the transfer of reactive nitrogen from anthropogenic sources to the forest ecosystem.