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Oxidation flow reactors (OFRs) allow the concentration of a given atmospheric oxidant to be increased beyond ambient levels in order to study secondary organic aerosol (SOA) formation and aging over varying periods of equivalent aging by that oxidant. Previous studies have used these reactors to determine the bulk OA mass and chemical evolution. To our knowledge, no OFR study has focused on the interpretation of the evolving aerosol size distributions. In this study, we use size-distribution measurements of the OFR and an aerosol microphysics model to learn about size-dependent processes in the OFR. Specifically, we use OFR exposures between 0.09 and 0.9 equivalent days of OH aging from the 2011 BEACHON-RoMBAS and GoAmazon2014/5 field campaigns. We use simulations in the TOMAS (TwO-Moment Aerosol Sectional) microphysics box model to constrain the following parameters in the OFR: (1) the rate constant of gas-phase functionalization reactions of organic compounds with OH, (2) the rate constant of gas-phase fragmentation reactions of organic compounds with OH, (3) the reactive uptake coefficient for heterogeneous fragmentation reactions with OH, (4) the nucleation rate constants for three different nucleation schemes, and (5) an effective accommodation coefficient that accounts for possible particle diffusion limitations of particles larger than 60nm in diameter. We find the best model-to-measurement agreement when the accommodation coefficient of the larger particles (Dp>60nm) was 0.1 or lower (with an accommodation coefficient of 1 for smaller particles), which suggests a diffusion limitation in the larger particles. When using these low accommodation-coefficient values, the model agrees with measurements when using a published H2SO4-organics nucleation mechanism and previously published values of rate constants for gas-phase oxidation reactions. Further, gas-phase fragmentation was found to have a significant impact upon the size distribution, and including fragm, United States. Department of Energy. Office of Biological and Environmental Research (grant no. DE-SC0011780), United States. National Oceanic and Atmospheric Administration. Office of Atmospheric Chemistry, Carbon Cycle, and Climate Program (cooperative agreement award no. NA17OAR430001), United States. National Oceanic and Atmospheric Administration. Office of Atmospheric Chemistry, Carbon Cycle, and Climate Program (cooperative agreement award no. NA17OAR4310002), National Science Foundation (U.S.). Atmospheric Chemistry program (grant no. AGS-1559607), National Science Foundation (U.S.). Atmospheric Chemistry program (grant no. AGS-1558966), Fundação de Amparo à Pesquisa do Estado do Amazonas, Fundação de Amparo à Pesquisa do Estado de São Paulo, Brazil Scientific Mobility Program, United States. National Oceanic and Atmospheric Administration (grant NA10OAR4310106 (MIT)), National Science Foundation (U.S.), Austrian Science Fund (project no. L518-N20)

The growth of freshly formed aerosol particles can be the bottleneck in their survival to cloud condensation nuclei. It is therefore crucial to understand how particles grow in the atmosphere. Insufficient experimental data has impeded a profound understanding of nano-particle growth under atmospheric conditions. Here we study nano-particle growth in the CLOUD (Cosmics Leaving OUtdoors Droplets) chamber, starting from the formation of molecular clusters. We present measured growth rates at sub-3 nm sizes with different atmospherically relevant concentrations of sulphuric acid, water, ammonia and dimethylamine. We find that atmospheric ions and small acid-base clusters, which are not generally accounted for in the measurement of sulphuric acid vapour, can participate in the growth process, leading to enhanced growth rates. The availability of compounds capable of stabilizing sulphuric acid clusters governs the magnitude of these effects and thus the exact growth mechanism. We bring these observations into a coherent framework and discuss their significance in the atmosphere.

An oxidation flow reactor (OFR) is a vessel inside which the concentration of a chosen oxidant can be increased for the purpose of studying SOA formation and aging by that oxidant. During the BEACHON-RoMBAS (Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H[subscript 2]O, Organics & Nitrogen–Rocky Mountain Biogenic Aerosol Study) field campaign, ambient pine forest air was oxidized by OH radicals in an OFR to measure the amount of SOA that could be formed from the real mix of ambient SOA precursor gases, and how that amount changed with time as precursors changed. High OH concentrations and short residence times allowed for semicontinuous cycling through a large range of OH exposures ranging from hours to weeks of equivalent (eq.) atmospheric aging. A simple model is derived and used to account for the relative timescales of condensation of low-volatility organic compounds (LVOCs) onto particles; condensational loss to the walls; and further reaction to produce volatile, non-condensing fragmentation products. More SOA production was observed in the OFR at nighttime (average 3 µg m[superscript −3] when LVOC fate corrected) compared to daytime (average 0.9 µg m[superscript −3] when LVOC fate corrected), with maximum formation observed at 0.4–1.5 eq. days of photochemical aging. SOA formation followed a similar diurnal pattern to monoterpenes, sesquiterpenes, and toluene+p-cymene concentrations, including a substantial increase just after sunrise at 07:00 local time. Higher photochemical aging (> 10 eq. days) led to a decrease in new SOA formation and a loss of preexisting OA due to heterogeneous oxidation followed by fragmentation and volatilization. When comparing two different commonly used methods of OH production in OFRs (OFR185 and OFR254-70), similar amounts of SOA formation were observed. We recommend the OFR185 mode for future forest studies. Concurrent gas-phase measurements of air after OH oxidation illustrate the decay of primary VOCs, produc, National Science Foundation (U.S.) (Grant AGS-1243354), National Science Foundation (U.S.) (Grant AGS-1360834), National Oceanic and Atmospheric Administration (Grant NA13OAR4310063), National Oceanic and Atmospheric Administration (Grant NA10OAR4310106), United States. Dept. of Energy. Atmospheric System Research Program (DE-SC0011105), Austrian Science Fund (Project L518-N20), United States. Environmental Protection Agency (STAR 83587701-0)

Im Laufe der letzten zwei Jahrhunderte nahm der Einfluss des Menschen auf die Zusammensetzung der Erdatmosphäre kontinuierlich zu. Intensive Landwirtschaft und der exzessive Gebrauch von fossilen Brennstoffen hat dazu geführt, dass sich die Konzentrationen bestimmter Spurengase in der Atmosphäre ständig erhöht haben. Wenngleich deren Anteile in der Atmosphäre immer noch sehr gering sind, haben sie entscheidenden Einfluss auf das Leben auf der Erde. Ansteigende Kohlendioxid (CO2)-, Methan (CH4)- und Lachgas (N2O)- Konzentrationen werden für die globale Erwärmung und den Klimawandel verantwortlich gemacht; zunehmende Konzentrationen von Stickoxiden (NOx=NO+NO2) tragen gleichzeitig zum Anstieg von phytotoxischem, bodennahem Ozon bei. Unter anderem wegen der genannten Gründe sind Pflanzen heutzutage zunehmend öfters abiotischem Stress, z.B. Hitze-, Trocken-, oxidativem Stress oder Kombinationen davon, ausgesetzt. Ziel dieser Arbeit ist es, zu einem besseren Verständnis der komplexen Wechselwirkungen zwischen Pflanzen und ihrer Umgebung während solcher Stresssituationen beizutragen. Unsere Untersuchungen fokussierten sich dabei hauptsächlich auf das Feedback von Pflanzen als Folge des Stresses, im Sinne von gesteigerten Emissionen von volatilen organischen Verbindungen (VOCs, vom englischen „volatile organic compounds“). Wie ich später zeigen werde, kann dieser etwas andere „Hilferuf“ von Pflanzen verschiedene Gründe und Funktionen haben. Unsere Experimente an hitze- und trockengestressten Pappeln veranschaulichten, wie sich diese Pflanzen an das zu erwartende, zukünftige Klima in Mitteleuropa anpassen werden. In diesen Messungen konnten wir zeigen, dass kurzzeitige Emissionen, sogenannte post illumination bursts (PIBs), von den Grünen Blattduftstoffen (GLVs, vom englischen „green leaf volatiles“) und Acetaldehyd infolge eines abrupten Licht-Dunkel-Wechsels, als nicht-invasive Stressmarker von hitze- und trockengestressten Pappeln benutzt werden können. Obwohl GLV-Emissi, Over the last two centuries, human activity was increasingly influencing the composition of the atmosphere. Intensive agriculture and combustion of fossil fuels has led to an atmospheric enrichment with several trace gases. Although the atmospheric concentration of these trace gases lies in the sub-percent range, their influence on life on earth is significant. Increasing carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) concentrations are thought to be responsible for global warming and associated climate change, while nitric oxides (NOx=NO+NO2) contribute to an enhanced production of phytotoxic ozone in the troposphere. Therefore, nowadays plants are more and more frequently exposed to related abiotic stresses, such as heat, drought and oxidative stress, or combinations thereof. This work aims to contribute to a better understanding of the complex interactions between plants and their environment during such stress events. Our experiments were focusing mainly on the stress feedback of plants in the sense of their enhanced emission of volatile organic compounds (VOCs). As I will illustrate further below, this unconventional “cry for help” of plants can have different reasons and purposes. Our investigations on heat and drought stressed poplar revealed how these plants will adapt to the climatic conditions expected for central Europe in the near future. In these experiments we could show that post illumination bursts (PIBs) of green leaf volatiles (GLVs) and acetaldehyde can be used as non-invasive markers of the heat and drought stress status of poplar plants. While in general GLVs emissions during stress situations are enhanced, in heat and drought stressed poplar the PIBs of GLVs and acetaldehyde were strongly suppressed. The same set of experiments revealed that in contrast to current theories, the suppression of isoprene synthesis in transgenic poplar does not adversely affect the stress mitigation capability of this plant species. This finding has im, by Werner Jud, Enth. u.a. 14 Veröff. d. Verf. aus den Jahren 2014 - 2015 . - Zsfassung in dt. Sprache, Innsbruck, Univ., Diss., 2015, OeBB, (VLID)866859