Secondary organic aerosol contributes to the atmospheric particle burden with implications for air quality and climate. Biogenic volatile organic compounds emitted from plants are important secondary organic aerosol precursors with isoprene emissions dominating globally. However, its yield of particle mass from oxidation is generally modest compared to that of other terpenoids. Here we show that isoprene, carbon monoxide and methane can suppress the instantaneous mass and the overall mass yield derived from monoterpenes in mixtures. We find that isoprene scavenges hydroxyl radicals preventing reaction with monoterpenes and the resulting isoprene peroxy radicals scavenge highly oxygenated monoterpene products. These effects reduced the yield of low-volatility products that would otherwise form secondary organic aerosol. Global model calculations indicate that oxidant and product scavenging can operate effectively in the real atmosphere. Highly reactive, modest aerosol yield compounds are not necessarily net producers and their oxidation can suppress both particle number and mass.

This work reports the synthesis and application of metal-organic framework (MOF)@microporous organic network (MON) hybrid materials. Coating a MOF, UiO-66-NH2, with MONs forms hybrid microporous materials with hydrophobic surfaces. The original UiO-66-NH2 shows good wettability in water. In comparison, the MOF@MON hybrid materials float on water and show excellent performance for adsorption of a model organic compound, toluene, in water. Chemical etching of the MOF results in the formation of hollow MON materials.

Abstract. Isoprene oxidation by nitrate radical (NO3) is a potentially important source of secondary organic aerosol (SOA). It is suggested that the second or later-generation products are the more substantial contributors to SOA. However, there are few studies investigating the multi-generation chemistry of isoprene-NO3 reaction, and information about the volatility of different isoprene nitrates, which is essential to evaluate their potential to form SOA and determine their atmospheric fate, is rare. In this work, we studied the reaction between isoprene and NO3 in the SAPHIR chamber (Jülich) under near-atmospheric conditions. Various oxidation products were measured by a high-resolution time-of-flight chemical ionization mass spectrometer using Br− as the reagent ion. Most of the products detected are organic nitrates, and they are grouped into monomers (C4 and C5 products) and dimers (C10 products) with 1–3 nitrate groups according to their chemical composition. Most of the observed products match expected termination products observed in previous studies, but some compounds such as monomers and dimers with three nitrogen atoms were rarely reported in the literature as gas-phase products from isoprene oxidation by NO3. Possible formation mechanisms for these compounds are proposed. The multi-generation chemistry of isoprene and NO3 is characterized by taking advantage of the time behavior of different products. In addition, the vapor pressures of diverse isoprene nitrates are calculated by different parametrization methods. An estimation of the vapor pressure is also derived from their condensation behavior. According to our results, isoprene monomers belong to intermediate-volatility or semi-volatile organic compounds and thus have little effect on SOA formation. In contrast, the dimers are expected to have low or extremely low volatility, indicating that they are potentially substantial contributors to SOA. However, the monomers constitute 80 % of the total explained signals on average, while the dimers contribute less than 2 %, suggesting that the contribution of isoprene NO3 oxidation to SOA by condensation should be low under atmospheric conditions. We expect a SOA mass yield of about 5 % from the wall-loss- and dilution-corrected mass concentrations, assuming that all of the isoprene dimers in the low- or extremely low-volatility organic compound (LVOC or ELVOC) range will condense completely.

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The reactions of biogenic volatile organic compounds (BVOC) with the nitrate radicals (NO 3 ) are major nighttime sources of organic nitrates and secondary organic aerosols (SOA) in regions influenced by BVOC and anthropogenic emissions. In this study, the formation of gas-phase highly oxygenated organic molecules-organic nitrates (HOM-ON) from NO 3 -initiated oxidation of a representative monoterpene, β-pinene, was investigated in the SAPHIR chamber (Simulation of Atmosphere PHotochemistry In a large Reaction chamber). Six monomer (C = 7−10, N = 1−2, O = 6−16) and five accretion product (C = 17−20, N = 2−4, O = 9−22) families were identified and further classified into firstor second-generation products based on their temporal behavior. The time lag observed in the peak concentrations between peroxy radicals containing odd and even number of oxygen atoms, as well as between radicals and their corresponding termination products, provided constraints on the HOM-ON formation mechanism. The HOM-ON formation can be explained by unimolecular or bimolecular reactions of peroxy radicals. A dominant portion of carbonylnitrates in HOM-ON was detected, highlighting the significance of unimolecular termination reactions by intramolecular H-shift for the formation of HOM-ON. A mean molar yield of HOM-ON was estimated to be 4.8% (−2.6%/+5.6%), suggesting significant HOM-ON contributions to the SOA formation.

<p><strong>Abstract.</strong> The formation of organic nitrates (ON) in the gas phase and their impact on mass formation of Secondary Organic Aerosol (SOA) was investigated in a laboratory study for <i>α</i>-pinene and <i>β</i>-pinene photo-oxidation. Focus was the elucidation of those mechanisms that cause the often observed suppression of SOA mass formation by NO<sub>x</sub>, and therein the role of highly oxygenated multifunctional molecules (HOM). We observed that with increasing NO<sub>x</sub> (a) the portion of HOM organic nitrates (HOM-ON) increased, (b) the fraction of accretion products (HOM-ACC) decreased and (c) HOM-ACC contained on average smaller carbon numbers.</p> <p>Specifically, we investigated HOM organic nitrates (HOM-ON), arising from the termination reactions of HOM peroxy radicals with NO<sub>x</sub>, and HOM permutation products (HOM-PP), such as ketones, alcohols or hydroperoxides, formed by other termination reactions. Effective uptake coefficients γeff of HOM on particles were determined. HOM with more than 6 O-atoms efficiently condensed on particles (<i>γ</i></sub><sub>eff</sub> > 0.5 in average) and for HOM containing more than 8 O-atoms, every collision led to loss. There was no systematic difference in <i>γ</i></sub><sub>eff</sub> for HOM-ON and HOM-PP arising from the same HOM peroxy radicals. This similarity is attributed to the multifunctional character of the HOM: as functional groups in HOM arising from the same precursor HOM peroxy radical are identical, vapor pressures should not strongly depend on the character the final termination group. As a consequence, the suppressing effect of NO<sub>x</sub> on SOA formation cannot be simply explained by replacement of terminal functional groups by organic nitrate groups.</p> <p>The fraction of organic bound nitrate (OrgNO<sub>3</sub>) stored in gas-phase HOM-ON appeared to be substantially higher than the fraction of particulate OrgNO<sub>3</sub> observed by aerosol mass spectrometry. This result suggests losses of OrgNO<sub>3</sub> for organic nitrates in particles, probably due to hydrolysis of OrgNO<sub>3</sub> that releases HNO<sub>3</sub> into the gas phase but leaves behind the organic rest in the particulate phase. However, the loss of HNO<sub>3</sub> alone, could not explain the observed suppressing effect of NO<sub>x</sub> on particle mass formation from <i>α</i>-pinene and <i>β</i>-pinene.</p> <p>We therefore attributed most of the reduction in SOA mass yields with increasing NO<sub>x</sub> to the significant suppression of gas-phase HOM-ACC which have high molecular mass and are potentially important for SOA mass formation at low NO<sub>x</sub> conditions.</p>

Microporous organic networks (MONs) are a new class of porous materials. This work shows the application of MON chemistry for the preparation of magnetically separable catalytic systems. By the Sonogashira coupling of Fe III − tetrakis(4-ethynylphenyl)porphyrin and 1,4-diiodobenzene, Fe 3 O 4 nanoparticles were coated successfully with Fe−porphyrin networks. The average thickness of the homogeneous coating was ∼17 nm. According to the powder X-ray diffraction and N 2 isotherm analyses, the Fe−porphyrin network coating exhibited amorphous and microporous characteristics. The microporous Fe−porphyrin networks on the Fe 3 O 4 nanoparticles showed good catalytic performance for carbene insertion into the N−H bond of amines. The catalytic systems were easily recycled from the reaction mixture by magnetic separation. We believe that the synthetic strategy in this work can be extended to the various catalytic systems.

Abstract. Highly oxygenated organic molecules (HOM) are found to play an important role in the formation and growth of secondary organic aerosol (SOA). SOA is an important type of aerosol with significant impact on air quality and climate. Compared with the oxidation of volatile organic compounds by ozone (O3) and hydroxyl radical (OH), HOM formation in the oxidation by nitrate radical (NO3), an important oxidant at nighttime and dawn, has received less attention. In this study, HOM formation in the reaction of isoprene with NO3 was investigated in the SAPHIR chamber (Simulation of Atmospheric PHotochemistry In a large Reaction chamber). A large number of HOM, including monomers (C5), dimers (C10), and trimers (C15), both closed-shell compounds and open-shell peroxy radicals (RO2), were identified and were classified into various series according to their formula. Their formation pathways were proposed based on the peroxy radicals observed and known mechanisms in the literature, which were further constrained by the time profiles of HOM after sequential isoprene addition to differentiate first- and second-generation products. HOM monomers containing one to three N atoms (1–3N-monomers) were formed, starting with NO3 addition to carbon double bond, forming peroxy radicals, followed by autoxidation. 1N-monomers were formed by both the direct reaction of NO3 with isoprene and of NO3 with first-generation products. 2N-monomers (e.g., C5H8N2On(n=7–13), C5H10N2On(n=8–14)) were likely the termination products of C5H9N2On⚫, which was formed by the addition of NO3 to C5-hydroxynitrate (C5H9NO4), a first-generation product containing one carbon double bond. 2N-monomers, which were second-generation products, dominated in monomers and accounted for ∼34 % of all HOM, indicating the important role of second-generation oxidation in HOM formation in the isoprene + NO3 reaction under our experimental conditions. H shift of alkoxy radicals to form peroxy radicals and subsequent autoxidation (“alkoxy–peroxy” pathway) was found to be an important pathway of HOM formation. HOM dimers were mostly formed by the accretion reaction of various HOM monomer RO2 and via the termination reactions of dimer RO2 formed by further reaction of closed-shell dimers with NO3 and possibly by the reaction of C5–RO2 with isoprene. HOM trimers were likely formed by the accretion reaction of dimer RO2 with monomer RO2. The concentrations of different HOM showed distinct time profiles during the reaction, which was linked to their formation pathway. HOM concentrations either showed a typical time profile of first-generation products, second-generation products, or a combination of both, indicating multiple formation pathways and/or multiple isomers. Total HOM molar yield was estimated to be 1.2 %-0.7%+1.3%, which corresponded to a SOA yield of ∼3.6 % assuming the molecular weight of C5H9NO6 as the lower limit. This yield suggests that HOM may contribute a significant fraction to SOA yield in the reaction of isoprene with NO3.