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Abstract. Isoprene oxidation by nitrate radical (NO3) is a potentially importantsource of secondary organic aerosol (SOA). It is suggested that the secondor later-generation products are the more substantial contributors to SOA.However, there are few studies investigating the multi-generation chemistryof isoprene-NO3 reaction, and information about the volatility ofdifferent isoprene nitrates, which is essential to evaluate their potentialto form SOA and determine their atmospheric fate, is rare. In this work, westudied the reaction between isoprene and NO3 in the SAPHIR chamber(Jülich) under near-atmospheric conditions. Various oxidation productswere measured by a high-resolution time-of-flight chemical ionization massspectrometer using Br− as the reagent ion. Most of the productsdetected are organic nitrates, and they are grouped into monomers (C4and C5 products) and dimers (C10 products) with 1–3 nitrategroups according to their chemical composition. Most of the observedproducts match expected termination products observed in previous studies,but some compounds such as monomers and dimers with three nitrogen atomswere rarely reported in the literature as gas-phase products from isopreneoxidation by NO3. Possible formation mechanisms for these compounds areproposed. The multi-generation chemistry of isoprene and NO3 ischaracterized by taking advantage of the time behavior of differentproducts. In addition, the vapor pressures of diverse isoprene nitrates arecalculated by different parametrization methods. An estimation of the vaporpressure is also derived from their condensation behavior. According to ourresults, isoprene monomers belong to intermediate-volatility orsemi-volatile organic compounds and thus have little effect on SOAformation. In contrast, the dimers are expected to have low or extremely lowvolatility, indicating that they are potentially substantial contributors toSOA. However, the monomers constitute 80 % of the total explained signalson average, while the dimers contribute less than 2 %, suggesting that thecontribution of isoprene NO3 oxidation to SOA by condensation should below under atmospheric conditions. We expect a SOA mass yield of about 5 %from the wall-loss- and dilution-corrected mass concentrations, assuming thatall of the isoprene dimers in the low- or extremely low-volatility organiccompound (LVOC or ELVOC) range will condense completely.

Molecular composition and volatility of multi-generation products formed from isoprene oxidation by nitrate radical