Jonathan Duplissy

Evolution of Organic Aerosols in the Atmosphere

Framework for Change Organic aerosols make up 20 to 90% of the particulate mass of the troposphere and are important factors in both climate and human heath. However, their sources and removal pathways are very uncertain, and their atmospheric evolution is poorly characterized. Jimenez et al. (p. 1525; see the Perspective by Andreae) present an integrated framework of organic aerosol compositional evolution in the atmosphere, based on model results and field and laboratory data that simulate the dynamic aging behavior of organic aerosols. Particles become more oxidized, more hygroscopic, and less volatile with age, as they become oxygenated organic aerosols. These results should lead to better predictions of climate and air quality. Organic aerosols are not compositionally static, but they evolve dramatically within hours to days of their formation. Organic aerosol (OA) particles affect climate forcing and human health, but their sources and evolution remain poorly characterized. We present a unifying model framework describing the atmospheric evolution of OA that is constrained by high–time-resolution measurements of its composition, volatility, and oxidation state. OA and OA precursor gases evolve by becoming increasingly oxidized, less volatile, and more hygroscopic, leading to the formation of oxygenated organic aerosol (OOA), with concentrations comparable to those of sulfate aerosol throughout the Northern Hemisphere. Our model framework captures the dynamic aging behavior observed in both the atmosphere and laboratory: It can serve as a basis for improving parameterizations in regional and global models.

Cluster Measurements at CLOUD using a High Resolution Ion Mobility Spectrometer - Mass Spectrometer Combination

Mass spectrometry is powerful tool for environmental and atmospheric chemistry analysis. Modern mass spectrometers demonstrate low detection limits, high sensitivity, and high resolving power. However, such high performance is not always enough to identify ambient ion clusters due to the clusters braking at the atmospheric pressure-to-vacuum interface of mass spectrometer. This study presents a high resolution ion mobility spectrometer-time-of-flight mass spectrometer (IMS-TOF) in the CLOUD experiment. This combination of orthogonal analytical techniques allows obtaining structural information in addition to mass-to-charge separation.

Molecular steps of neutral sulfuric acid and dimethylamine nucleation in CLOUD

We have run a set of experiments in the CLOUD chamber at CERN, Switzerland, studying the effect of dimethylamine (DMA) on sulfuric acid (SA)-water nucleation using a nitrate based Chemical Ionization Atmospheric Pressure ionization Time-Of-Flight Mass Spectrometer (CI-APi-TOF). Experiment was designed to produce neutral high m/z SA-DMA clusters in close to atmospherically relevant conditions to be detected and characterized by the CI-APi-TOF. We aimed in filling up the gap in measurement techniques from molecular level up to climatically relevant aerosol particles and thus improve our understanding of the role of sulfuric acid and DMA in atmospheric nucleation.

Hygroscopic and Volatile Properties of Ultrafine Particles in the Eucalypt Forests: Comparison with Chamber Experiments and the Role of Sulphates in New Particle Formation

Simultaneous measurements of the volatile and hygroscopic properties of ultrafine particles were conducted in a Eucalypt forest in Tumbarumba, South-East Australia, in November 2006. These measurements were part of an intensive field campaign EUCAP 2006 (Eucalypt Forest Aerosols and Precursors). The particles exhibited a 2 step volatilisation with the first component starting to evaporate at temperatures above 50 degrees Celsius. With the onset of evaporation of the first component the hygroscopic growth factor increased. This indicated that the particle was composed of a less volatile, but more hygroscopic core, which was coated with a more volatile, but less hygroscopic, coating. The fraction of the more hygroscopic component was proportional to the measured maximum SO2 concentration indicating the role of gaseous H2SO4 in new particle formation. As the volatilisation temperature of the second more hygroscopic component was above that for H2SO4 it is likely that this component is partially or fully neutralised H2SO4. Comparison with pinene smog chamber experiments shows an excellent agreement with the first step volatilisation indicating its origin in the photooxidation of a monoterpene precursor.

Charged and neutral binary nucleation of sulfuric acid in free troposphere conditions

We present a data set of binary nucleation of sulfuric acid and water, measured in the CLOUD chamber at CERN during the CLOUD3 and CLOUD5 campaigns. Four parameters have been varied to cover neutral and ion-induced binary nucleation processes: Sulfuric acid concentration (1e5 to 1e8 molecules per cm^(−3)), relative humidity (10% to 80%), temperature (208-293K) and ion concentration (0-4000 ions per cm^(−3)). In addition, classical nucleation theory implemented with hydrates and ion induced nucleation is compared with the data set. Our model and data are also compared with nucleation rates measured at Puy de Dome in the tropopause.

Nucleation of H_2SO_4 and oxidized organics in CLOUD experiment

The research of atmospheric new particle formation has proceeded lately as the role of sulphuric acid has been established. Still, the roles of other atmospheric compounds in nucleation remain largely unclear. To clarify the first steps of atmospheric new particle formation extensive nucleation experiments were performed in CLOUD chamber in 2012. Especially the role of oxidations products of α-pinene was studied in detail. The experiments provided new information about the part of oxidized organics in nucleation.

Measuring composition and growth of ion clusters of sulfuric acid, ammonia, amines and oxidized organics as first steps of nucleation in the CLOUD experiment

The mechanisms behind the nucleation of vapors forming new particles in the atmosphere had been proven difficult to establish. One main aim of the CLOUD experiment was to explore in detail these first steps of atmospheric new particle formation by performing extremely well controlled laboratory experiments. We examined nucleation and growth in the presence of different mixtures of vapors, including sulfuric acid, ammonia, dimethylamine, and oxidation products of pinanediol or α-pinene. Among the employed state-of-the-art instrumentation, a high-resolution mass spectrometer that directly sampled negatively charged ions and clusters proved particularly useful. We were able to resolve most of the chemical compositions found for charged sub-2nm clusters and to observe their growth in time. These compositions reflected the mixture of condensable vapors in the chamber and the role of each individual vapor in forming sub-2nm clusters could be explored. By inter-comparing between individual experiments and ambient observations, we try to establish which vapors participate in nucleation in the actual atmosphere, and how.

Ternary H_2SO_4-H_2O-NH_3 Neutral and Charged Nucleation Rates for a Wide Range of Atmospheric Conditions

The formation of new particles for the ternary system involving sulfuric acid, water vapor and ammonia has been studied in detail. The nucleation rates were obtained from experiments at the CERN CLOUD chamber which allows the measurement of new particle formation under very well defined conditions. Some of its key features are the suppression of contaminants at the technological limit and a very precise control of a wide range of temperatures, trace gas concentrations and nucleation rates. The effect of ionizing radiation on the ternary nucleation rates was investigated by using the CERN proton synchrotron beam (beam conditions), natural galactic cosmic rays (gcr conditions) as well as the high voltage clearing field inside the chamber to suppress the effect of charges (neutral conditions). The dependence of the nucleation rate on ion concentration, sulfuric acid and ammonia concentration as well as temperature was studied extensively. This way, an unprecedented set of data was collected giving insight into the role of neutral and charged ternary NH_3 nucleation and the relative importance of the different parameters.

Evolution of α-pinene oxidation products in the presence of varying oxidizers: Negative APi-TOF point of view

Laboratory experiments conducted in the frame of the CLOUD project at CERN investigated the oxidation of α-pinene oxidation products in a carefully controlled environment and with different oxidation conditions: 1) pure ozonolysis (with the use of an hydroxyl radical (⋅OH) scavenger), 2) ozonolysis without use of a scavenger, and 3) pure ⋅OH oxidation using nitrous acid (HONO) to produce ⋅OH. The anions and negatively charged clusters present in the chamber were analyzed and their chemical composition compared for the different oxidation pathways.