| 1. |
- Kiendler-Scharr, A., et al.
(author)
-
Ubiquity of organic nitrates from nighttime chemistry in the European submicron aerosol
- 2016
-
In: Geophysical Research Letters. - 0094-8276. ; 43:14, s. 7735-7744
-
Journal article (peer-reviewed)abstract
- In the atmosphere nighttime removal of volatile organic compounds is initiated to a large extent by reaction with the nitrate radical (NO3) forming organic nitrates which partition between gas and particulate phase. Here we show based on particle phase measurements performed at a suburban site in the Netherlands that organic nitrates contribute substantially to particulate nitrate and organic mass. Comparisons with a chemistry transport model indicate that most of the measured particulate organic nitrates are formed by NO3 oxidation. Using aerosol composition data from three intensive observation periods at numerous measurement sites across Europe, we conclude that organic nitrates are a considerable fraction of fine particulate matter (PM1) at the continental scale. Organic nitrates represent 34% to 44% of measured submicron aerosol nitrate and are found at all urban and rural sites, implying a substantial potential of PM reduction by NOx emission control.
|
|
| 2. |
- Novelli, A., et al.
(author)
-
Evaluation of OH and HO2 concentrations and their budgets during photooxidation of 2-methyl-3-butene-2-ol (MBO) in the atmospheric simulation chamber SAPHIR
- 2018
-
In: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 18:15, s. 11409-11422
-
Journal article (peer-reviewed)abstract
- Several previous field studies have reported unexpectedly large concentrations of hydroxyl and hydroperoxyl radicals (OH and HO2, respectively) in forested environments that could not be explained by the traditional oxidation mechanisms that largely underestimated the observations. These environments were characterized by large concentrations of biogenic volatile organic compounds (BVOC) and low nitrogen oxide concentration. In isoprene-dominated environments, models developed to simulate atmospheric photochemistry generally underestimated the observed OH radical concentrations. In contrast, HO2 radical concentration showed large discrepancies with model simulations mainly in non-isoprene-dominated forested environments. An abundant BVOC emitted by lodgepole and ponderosa pines is 2-methyl- 3-butene-2-ol (MBO), observed in large concentrations for studies where the HO2 concentration was poorly described by model simulations. In this work, the photooxidation of MBO by OH was investigated for NO concentrations lower than 200 pptv in the atmospheric simulation chamber SAPHIR at Forschungszentrum Julich. Measurements of OH and HO2 radicals, OH reactivity (kO(H)), MBO, OH precursors, and organic products (acetone and formaldehyde) were used to test our current understanding of the OH-oxidation mechanisms for MBO by comparing measurements with model calculations. All the measured trace gases agreed well with the model results (within 15 %) indicating a well understood mechanism for the MBO oxidation by OH. Therefore, the oxidation of MBO cannot contribute to reconciling the unexplained high OH and HO2 radical concentrations found in previous field studies.
|
|
| 3. |
- Rolletter, M., et al.
(author)
-
Investigation of the alpha-pinene photooxidation by OH in the atmospheric simulation chamber SAPHIR
- 2019
-
In: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 19:18, s. 11635-11649
-
Journal article (peer-reviewed)abstract
- The photooxidation of the most abundant monoterpene, alpha-pinene, by the hydroxyl radical (OH) was investigated at atmospheric concentrations in the atmospheric simulation chamber SAPHIR. Concentrations of nitric oxide (NO) were below 120 pptv. Yields of organic oxidation products are determined from measured time series giving values of 0.11 +/- 0.05, 0.19 +/- 0.06, and 0.05 +/- 0.03 for formaldehyde, acetone, and pinonaldehyde, respectively. The pinonaldehyde yield is at the low side of yields measured in previous laboratory studies, ranging from 0.06 to 0.87. These studies were mostly performed at reactant concentrations much higher than observed in the atmosphere. Time series of measured radical and trace-gas concentrations are compared to results from model calculations applying the Master Chemical Mechanism (MCM) 3.3.1. The model predicts pinonaldehyde mixing ratios that are at least a factor of 4 higher than measured values. At the same time, modeled hydroxyl and hydroperoxy (HO2) radical concentrations are approximately 25 % lower than measured values. Vereecken et al. (2007) suggested a shift of the initial organic peroxy radical (RO2) distribution towards RO2 species that do not yield pinonaldehyde but produce other organic products. Implementing these modifications reduces the model-measurement gap of pinonaldehyde by 20 % and also improves the agreement in modeled and measured radical concentrations by 10 %. However, the chemical oxidation mechanism needs further adjustment to explain observed radical and pinonaldehyde concentrations. This could be achieved by adjusting the initial RO2 distribution, but could also be done by implementing alternative reaction channels of RO2 species that currently lead to the formation of pinonaldehyde in the model.
|
|
| 4. |
- Zhao, D. F., et al.
(author)
-
Size-dependent hygroscopicity parameter (κ) and chemical composition of secondary organic cloud condensation nuclei
- 2015
-
In: Geophysical Research Letters. - 1944-8007. ; 42:24
-
Journal article (peer-reviewed)abstract
- Secondary organic aerosol components (SOA) contribute significantly to the activation of cloud condensation nuclei (CCN) in the atmosphere. The CCN activity of internally mixed submicron SOA particles is often parameterized assuming a size-independent single-hygroscopicity parameter κ. In the experiments done in a large atmospheric reactor (SAPHIR, Simulation of Atmospheric PHotochemistry In a large Reaction chamber, Jülich), we consistently observed size-dependent κ and particle composition for SOA from different precursors in the size range of 50nm–200nm. Smaller particles had higher κ and a higher degree of oxidation, although all particles were formed from the same reaction mixture. Since decreasing volatility and increasing hygroscopicity often covary with the degree of oxidation, the size dependence of composition and hence of CCN activity can be understood by enrichment of higher oxygenated, low-volatility hygroscopic compounds in smaller particles. Neglecting the size dependence of κ can lead to significant bias in the prediction of the activated fraction of particles during cloud formation.
|
|
| 5. |
- Roldin, Pontus, et al.
(author)
-
Modelling the contribution of biogenic volatile organic compounds to new particle formation in the Julich plant atmosphere chamber
- 2015
-
In: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7324. ; 15:18, s. 10777-10798
-
Journal article (peer-reviewed)abstract
- We used the Aerosol Dynamics gas- and particle-phase chemistry model for laboratory CHAMber studies (ADCHAM) to simulate the contribution of BVOC plant emissions to the observed new particle formation during photooxidation experiments performed in the Julich Plant-Atmosphere Chamber and to evaluate how well smog chamber experiments can mimic the atmospheric conditions during new particle formation events. ADCHAM couples the detailed gas-phase chemistry from Master Chemical Mechanism with a novel aerosol dynamics and particle phase chemistry module. Our model simulations reveal that the observed particle growth may have either been controlled by the formation rate of semi- and low-volatility organic compounds in the gas phase or by acid catalysed heterogeneous reactions between semi-volatility organic compounds in the particle surface layer (e.g. peroxyhemiacetal dimer formation). The contribution of extremely low-volatility organic gas-phase compounds to the particle formation and growth was suppressed because of their rapid and irreversible wall losses, which decreased their contribution to the nano-CN formation and growth compared to the atmospheric situation. The best agreement between the modelled and measured total particle number concentration (R-2 > 0.95) was achieved if the nano-CN was formed by kinetic nucleation involving both sulphuric acid and organic compounds formed from OH oxidation of BVOCs.
|
|
| 6. |
- Wu, Cheng, 1985, et al.
(author)
-
Impacts of soil moisture on de novo monoterpene emissions from European beech, Holm oak, Scots pine, and Norway spruce
- 2015
-
In: Biogeosciences. - 1726-4170 .- 1726-4189. ; 12, s. 177-191
-
Journal article (peer-reviewed)abstract
- Impacts of soil moisture on de novo monoterpene (MT) emissions from Holm oak, European beech, Scots pine, and Norway spruce were studied in laboratory experiments. The volumetric water content of the soil, Θ, was used as the reference quantity to parameterize the dependency of MT emissions on soil moisture and to characterize the severity of the drought. When θ dropped from 0.4m3 ×m-3 to ∼0.2m3 ×m-3 slight increases of de novo MT emissions were observed but with further progressing drought the emissions decreased to almost zero. In most cases the increases of MT emissions observed under conditions of mild drought were explainable by increases of leaf temperature due to lowered transpirational cooling. When Θ fell below certain thresholds, MT emissions decreased simultaneously with 2 and the relationship between Θ and MT emissions was approximately linear. The thresholds of θ (0.044-0.19m3 ×m-3) were determined, as well as other parameters required to describe the soil moisture dependence of de novo MT emissions for application in the Model of Emissions of Gases and Aerosols from Nature, MEGAN. A factorial approach was found appropriate to describe the impacts of 2, temperature, and light. Temperature and θ influenced the emissions largely independently from each other, and, in a similar manner, light intensity and θ acted independently on de novo MT emissions. The use of θ as the reference quantity in a factorial approach was tenable in predicting constitutive de novo MT emissions when θ changed on a time scale of days. Empirical parameterization with θ as a reference was only unsuccessful when soil moisture changed rapidly
|
|
| 7. |
- Zhao, D. F., et al.
(author)
-
Environmental conditions regulate the impact of plants on cloud formation
- 2017
-
In: Nature Communications. - 2041-1723. ; 8
-
Journal article (peer-reviewed)abstract
- The terrestrial vegetation emits large amounts of volatile organic compounds (VOC) into the atmosphere, which on oxidation produce secondary organic aerosol (SOA). By acting as cloud condensation nuclei (CCN), SOA influences cloud formation and climate. In a warming climate, changes in environmental factors can cause stresses to plants, inducing changes of the emitted VOC. These can modify particle size and composition. Here we report how induced emissions eventually affect CCN activity of SOA, a key parameter in cloud formation. For boreal forest tree species, insect infestation by aphids causes additional VOC emissions which modifies SOA composition thus hygroscopicity and CCN activity. Moderate heat increases the total amount of constitutive VOC, which has a minor effect on hygroscopicity, but affects CCN activity by increasing the particles' size. The coupling of plant stresses, VOC composition and CCN activity points to an important impact of induced plant emissions on cloud formation and climate.
|
|
| 8. |
- McFiggans, Gordon, et al.
(author)
-
Secondary organic aerosol reduced by mixture of atmospheric vapours
- 2019
-
In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 565:7741, s. 587-593
-
Journal article (peer-reviewed)abstract
- Secondary organic aerosol contributes to the atmospheric particle burden with implications for air quality and climate. Biogenic volatile organic compounds such as terpenoids emitted from plants are important secondary organic aerosol precursors with isoprene dominating the emissions of biogenic volatile organic compounds globally. However, the particle mass from isoprene oxidation is generally modest compared to that of other terpenoids. Here we show that isoprene, carbon monoxide and methane can each suppress the instantaneous mass and the overall mass yield derived from monoterpenes in mixtures of atmospheric vapours. We find that isoprene 'scavenges' hydroxyl radicals, preventing their reaction with monoterpenes, and the resulting isoprene peroxy radicals scavenge highly oxygenated monoterpene products. These effects reduce 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. Thus highly reactive compounds (such as isoprene) that produce a modest amount of aerosol are not necessarily net producers of secondary organic particle mass and their oxidation in mixtures of atmospheric vapours can suppress both particle number and mass of secondary organic aerosol. We suggest that formation mechanisms of secondary organic aerosol in the atmosphere need to be considered more realistically, accounting for mechanistic interactions between the products of oxidizing precursor molecules (as is recognized to be necessary when modelling ozone production).
|
|
