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Atmospheric new-particle formation (NPF) affects climate by contributing to a large fraction of the cloud condensation nuclei (CCN). Highly oxygenated organic molecules (HOMs) drive the early particle growth and therefore substantially influence the survival of newly formed particles to CCN. Nitrogen oxide (NOₓ) is known to suppress the NPF driven by HOMs, but the underlying mechanism remains largely unclear. Here, we examine the response of particle growth to the changes of HOM formation caused by NOₓ. We show that NOₓ suppresses particle growth in general, but the suppression is rather nonuniform and size dependent, which can be quantitatively explained by the shifted HOM volatility after adding NOₓ. By illustrating how NOₓ affects the early growth of new particles, a critical step of CCN formation, our results help provide a refined assessment of the potential climatic effects caused by the diverse changes of NOₓ level in forest regions around the globe.

The formation of secondary particles in the atmosphere accounts for more than half of global cloud condensation nuclei. Experiments at the CERN CLOUD (Cosmics Leaving OUtdoor Droplets) chamber have underlined the importance of ions for new particle formation, but quantifying their effect in the atmosphere remains challenging. By using a novel instrument setup consisting of two nanoparticle counters, one of them equipped with an ion filter, we were able to further investigate the ion-related mechanisms of new particle formation. In autumn 2015, we carried out experiments at CLOUD on four systems of different chemical compositions involving monoterpenes, sulfuric acid, nitrogen oxides, and ammonia. We measured the influence of ions on the nucleation rates under precisely controlled and atmospherically relevant conditions. Our results indicate that ions enhance the nucleation process when the charge is necessary to stabilize newly formed clusters, i.e., in conditions in which neutral clusters are unstable. For charged clusters that were formed by ion-induced nucleation, we were able to measure, for the first time, their progressive neutralization due to recombination with oppositely charged ions. A large fraction of the clusters carried a charge at 1.5 nm diameter. However, depending on particle growth rates and ion concentrations, charged clusters were largely neutralized by ion–ion recombination before they grew to 2.5 nm. At this size, more than 90 % of particles were neutral. In other words, particles may originate from ion-induced nucleation, although they are neutral upon detection at diameters larger than 2.5 nm. Observations at Hyytiälä, Finland, showed lower ion concentrations and a lower contribution of ion-induced nucleation than measured at CLOUD under similar conditions. Although this can be partly explained by the observation that ion-induced fractions decrease towards lower ion concentrations, further investigations are needed to resolve the origin of the discrepancy., published version, peerReviewed

An instrument has been developed which allows an entire suite of oxidation products (H2SO4 and Extremely Low Volatile Organic Compounds, ELVOCs) to be measured along with the concentrations of the key radical species OH and HO2 +RO2. The system combines the techniques for chemical conversion of OH or HO2 +RO2 into H2SO4 together with nitrate ion (NO3-) Chemical Ionization (CI) and Atmospheric Pressure interface - Time of Flight Mass Spectrometer (NO3- CI-APi-ToF) which has been previously used for the detection of ELVOCs and a few other oxygenated organic species. The system exhibits the same sensitivity towards OH or HO2 +RO2 as previous quadrupole chemical ionization (CIMS) measurements with limits of detection of ~2 x 105 and ~2 x 106 molecule cm-3 for OH and HO2+RO2 respectively. Unlike previous CIMS measurements, the use of a NO3- CI-APi-ToF allows the acquisition of the entire mass spectrum at high resolution with each measurement, allowing one to see how the organic species behave when the sample flow is perturbed with reagent gasses (SO2 or NO). While the combination of these measurements into one instrument is of great practical value, it is the combination of these data within the spectra obtained in each mode that extends the information far beyond the measurements themselves.

A recent CLOUD (Cosmics Leaving OUtdoor Droplets) chamber study showed that sulfuric acid and dimethylamine produce new aerosols very efficiently, and yield particle formation rates that are compatible with boundary layer observations. These previously published new particle formation (NPF) rates are re-analyzed in the present study with an advanced method. The results show that the NPF rates at 1.7 nm are more than a factor of 10 faster than previously published due to earlier approximations in correcting particle measurements made at larger detection threshold. The revised NPF rates agree almost perfectly with calculated rates from a kinetic aerosol model at different sizes (1.7 nm and 4.3 nm mobility diameter). In addition, modeled and measured size distributions show good agreement over a wide range (up to ca. 30 nm). Furthermore, the aerosol model is modified such that evaporation rates for some clusters can be taken into account; these evaporation rates were previously published from a flow tube study. Using this model, the findings from the present study and the flow tube experiment can be brought into good agreement. This confirms that nucleation proceeds at rates that are compatible with collision-controlled (a.k.a. kinetically-controlled) new particle formation for the conditions during the CLOUD7 experiment (278 K, 38% RH, sulfuric acid concentration between 1×106 and 3×107 cm-3 and dimethylamine mixing ratio of ~40 pptv). Finally, the simulation of atmospheric new particle formation reveals that even tiny mixing ratios of dimethylamine (0.1 pptv) yield NPF rates that could explain significant boundary layer particle formation. This highlights the need for improved speciation and quantification techniques for atmospheric gas-phase amine measurements.

It has been postulated that secondary organic particulate matter plays a pivotal role in the early growth of newly formed particles in forest areas. The recently detected class of extremely low volatile organic compounds (ELVOC) provides the missing organic vapours and possibly contributes a~significant fraction to atmospheric SOA. ELVOC are highly oxidized multifunctional molecules (HOM), formed by sequential rearrangement of peroxy radicals and subsequent O2 addition. Key for efficiency in early particle growth is that formation of HOM is induced by one attack of the oxidant (here O3) and followed by an autoxidation process involving molecular oxygen. Similar mechanisms were recently observed and predicted by quantum mechanical calculations e.g. for isoprene. To assess the atmospheric importance and therewith the potential generality, it is crucial to understand the formation pathway of HOM.To elucidate the formation path of HOM as well as necessary and sufficient structural prerequisites of their formation we studied homologues series of cycloalkenes in comparison to two monoterpenes. We were able to directly observe highly oxidized multifunctional peroxy radicals with 8 or 10 O-atoms by an Atmospheric Pressure interface High Resolution Time of Flight Mass Spectrometer equipped with a NO3−-Chemical Ionization (CI) source. In case of O3 acting as oxidant the starting peroxy radical is formed on the so called vinylhydroperoxide path. HOM peroxy radicals and their termination reactions with other peroxy radicals, including dimerization, allowed for analysing the observed mass spectra and narrow down the likely formation path. As consequence we propose that HOM are multifunctional percarboxylic acids; with carbonyl-, hydroperoxy-, or hydroxy-groups arising from the termination steps. We figured that aldehyde groups facilitate the initial rearrangement steps. In simple molecules like cyloalkenes autoxidation was limited to both terminal C-atoms and two further C-atoms in the respective α-positions. In more complex molecules containing tertiary H-atoms or small constraint rings even higher oxidation degree were possible, either by simple H-shift of the tertiary H-atom or by initialisation of complex ring-opening reactions.

Item does not contain fulltext M. Rissanen English in Transition. Corpus-based studies in linguistic variation and genre styles Berlin-New York:Mouton de Gruyter ,1999 3110156326