H. Vuollekoski

Effect of ions on sulfuric acid-water binary particle formation: 2. Experimental data and comparison with QC-normalized classical nucleation theory

We report comprehensive, demonstrably contaminant-free measurements of binary particle formation rates by sulfuric acid and water for neutral and ion-induced pathways conducted in the European Organization for Nuclear Research Cosmics Leaving Outdoor Droplets chamber. The recently developed Atmospheric Pressure interface-time of flight-mass spectrometer was used to detect contaminants in charged clusters and to identify runs free of any contaminants. Four parameters were varied to cover ambient conditions: sulfuric acid concentration (10^5 to 10^9  mol cm^(−3)), relative humidity (11% to 58%), temperature (207 K to 299 K), and total ion concentration (0 to 6800 ions cm^(−3)). Formation rates were directly measured with novel instruments at sizes close to the critical cluster size (mobility size of 1.3 nm to 3.2 nm). We compare our results with predictions from Classical Nucleation Theory normalized by Quantum Chemical calculation (QC-normalized CNT), which is described in a companion paper. The formation rates predicted by the QC-normalized CNT were extended from critical cluster sizes to measured sizes using the UHMA2 sectional particle microphysics model. Our results show, for the first time, good agreement between predicted and measured particle formation rates for the binary (neutral and ion-induced) sulfuric acid-water system. Formation rates increase with RH, sulfuric acid, and ion concentrations and decrease with temperature at fixed RH and sulfuric acid concentration. Under atmospheric conditions, neutral particle formation dominates at low temperatures, while ion-induced particle formation dominates at higher temperatures. The good agreement between the theory and our comprehensive data set gives confidence in using the QC-normalized CNT as a powerful tool to study neutral and ion-induced binary particle formation in atmospheric modeling.

Sub-3 nm Particle Detection with Commercial TSI 3772 and Airmodus A20 Fine Condensation Particle Counters

In this work, we explored the possibility to detect sub-3 nm particles with commercially available TSI 3772 and Airmodus A20 Condensation Particle Counters (CPCs), when operated under modified temperature and inlet flow settings. We generated highly monodisperse sub-3 nm nanoparticles and characterized the CPCs with temperature differences between the saturator and the condenser varying from 36ºC (the 36/37 settings) to 40ºC (the 40/40 settings), while the factory settings were 17 and 24ºC. The 36/37 settings yielded no homogeneously nucleated background in dry conditions. With these settings, the detection efficiency was significantly improved from the factory settings, resulting in the detection of the smallest charged particles down to below 1.5 nm compared with the nominal cut-sizes of 10 and 7 nm. With the 40/40 settings and consequently higher supersaturation, homogeneous nucleation produced a background of around 0.5–2 cm−3, while the CPCs were sensitive to charged particles down to 1 nm in mobility diameter. The supersaturation field corresponding to the new operation conditions with the 36/37 settings was modeled by using COMSOL and OpenFOAM. The observations were reproduced very well by applying the heterogeneous nucleation theory to the obtained supersaturation field. Our work shows that the TSI 3772 and Airmodus A20 fine CPCs can have a comparable performance with a more expensive ultrafine CPC, such as TSI 3776, thus offering a widely available tool for the detection of sub-3 nm particles. Copyright 2015 American Association for Aerosol Research

Simulating Marine New Particle Formation and Growth Using the M7 Modal Aerosol Dynamics Modal

A modal atmospheric aerosol model (M7) is evaluated in terms of predicting marine new particle formation and growth. Simulations were carried out for three different nucleation schemes involving (1) kinetic self-nucleation of OIO (2) nucleation via OIO activation by H2SO4 and (3) nucleation via OIO activation by H2SO4 plus condensation of a low-volatility organic vapour. Peak OIO and H2SO4 vapour concentrations were both limited to molecules cm-3 at noontime while the peak organic vapour concentration was limited to molecules cm-3. All simulations produced significant concentrations of new particles in the Aitken mode. From a base case particle concentration of 222 cm-3 at radii >15 nm, increases in concentrations to 366 cm-3 were predicted from the OIO-OIO case, 722 cm-3 for the OIO-H2SO4 case, and 1584 cm-3 for the OIO-H2SO4 case with additional condensing organic vapours. The results indicate that open ocean new particle production is feasible for clean conditions; however, new particle production becomes most significant when an additional condensable organic vapour is available to grow the newly formed particles to larger sizes. Comparison to sectional model for a typical case study demonstrated good agreement and the validity of using the modal model.

Climatic implications of the Brazilian biofuel transition

A global climate model is being run to study the consequences of Brazil transitioning from fossil to biofuels over the next few decades. Assuming all other factors constant, preliminary results suggest little to no climatic relevance.

Air Ion Measurements at Mace Head on the West Coast of Ireland

Coastal nucleation events and behavior of cluster ions were characterized through the measurements of air ion mobility distributions at the Mace Head research station on the west coast of Ireland in 2006. We measured concentrations of cluster ions and charged aerosol particles in the size range of 0.4–40 nm. These measurements allow us to characterize freshly nucleated charged particles with diameter below 3 nm. The analysis shows that bursts of intermediate ions (1.6–7 nm) are a frequent phenomenon in marine coastal environment. Nucleation evens occurred during most of the measurement days. We classified the nucleation burst events. Particle formation and growth events mostly coincided with the presence of low tide. Small ions concentrations appear to be strongly dependent on the variations of meteorological parameters including wind speed and direction.

Simulations of Iodine Dioxide Nucleation

Aerosol dynamical simulations of coastal new particle formation have been performed in order to investigate the nucleation and growth mechanisms in this environment. In the simulations, it is assumed that the nucleating vapour is iodine dioxide. Both Eulerian and Lagrangian type simulations have been performed and compared to observations. We have found it difficult to achieve the observed, enormous growth rates, and simulations agree with the experiments only when OIO concentration is very high and growth time has been prolonged