Aerosols have a strong, yet poorly quantified, effect on climate. The growth of the smallest atmospheric particles from diameters in the nanometre range to sizes at which they may act as seeds for cloud droplets is a key step linking aerosols to clouds and climate. In many environments, atmospheric nanoparticles grow by taking up organic compounds that are derived from biogenic hydrocarbon emissions. Several mechanisms may control this uptake. Condensation of low-volatility vapours and formation of organic salts probably dominate the very first steps of growth in particles close to 1 nm in diameter. As the particles grow further, formation of organic polymers and effects related to the phase of the particle probably become increasingly important. We suggest that dependence of particle growth mechanisms on particle size needs to be investigated more systematically.
Comparison of Approaches for Measuring the Mass Accommodation Coefficient for the Condensation of Water and Sensitivities to Uncertainties in Thermophysical Properties
| JOURNAL OF PHYSICAL CHEMISTRY A
We compare and contrast measurements of the mass accommodation coefficient of water on a water surface made using ensemble and single particle techniques under conditions of supersaturation and subsaturation, respectively. In particular, we consider measurements made using an expansion chamber, a continuous flow streamwise thermal gradient cloud condensation nuclei chamber, the Leipzig Aerosol Cloud Interaction Simulator, aerosol optical tweezers, and electrodynamic balances. Although this assessment is not intended to be comprehensive, these five techniques are complementary in their approach and give values that span the range from near 0.1 to 1.0 for the mass accommodation coefficient. We use the same semianalytical treatment to assess the sensitivities of the measurements made by the various techniques to thermophysical quantities (diffusion constants, thermal conductivities, saturation pressure of water, latent heat, and solution density) and experimental parameters (saturation value and temperature). This represents the first effort to assess and compare measurements made by different techniques to attempt to reduce the uncertainty in the value of the mass accommodation coefficient. Broadly, we show that the measurements are consistent within the uncertainties inherent to the thermophysical and experimental parameters and that the value of the mass accommodation coefficient should be considered to be larger than 0.5. Accurate control and measurement of the saturation ratio is shown to be critical for a successful investigation of the surface transport kinetics during condensation/evaporation. This invariably requires accurate knowledge of the partial pressure of water, the system temperature, the droplet curvature and the saturation pressure of water. Further, the importance of including and quantifying the transport of heat in interpreting droplet measurements is highlighted; the particular issues associated with interpreting measurements of condensation/evaporation rates with varying pressure are discussed, measurements that are important for resolving the relative importance of gas diffusional transport and surface kinetics.
Measurement of the nucleation of atmospheric aerosol particles
Kulmala, M; Petaja, T; Nieminen, T; Sipila, M; Manninen, HE; Lehtipalo, K; Dal Maso, M; Aalto, PP; Junninen, H; Paasonen, P; Riipinen, I; Lehtinen, KEJ; Laaksonen, A; Kerminen, VM
| Nat Protoc
The formation of new atmospheric aerosol particles and their subsequent growth have been observed frequently at various locations all over the world. The atmospheric nucleation rate (or formation rate) and growth rate (GR) are key parameters to characterize the phenomenon. Recent progress in measurement techniques enables us to measure atmospheric nucleation at the size (mobility diameter) of 1.5 (+/- 0.4) nm. The detection limit has decreased from 3 to 1 nm within the past 10 years. In this protocol, we describe the procedures for identifying new-particle-formation (NPF) events, and for determining the nucleation, formation and growth rates during such events under atmospheric conditions. We describe the present instrumentation, best practices and other tools used to investigate atmospheric nucleation and NPF at a certain mobility diameter (1.5, 2.0 or 3.0 nm). The key instruments comprise devices capable of measuring the number concentration of the formed nanoparticles and their size, such as a suite of modern condensation particle counters (CPCs) and air ion spectrometers, and devices for characterizing the pre-existing particle number concentration distribution, such as a differential mobility particle sizer (DMPS). We also discuss the reliability of the methods used and requirements for proper measurements and data analysis. The time scale for realizing this procedure is 1 year.
Cloud condensation nuclei production associated with atmospheric nucleation: a synthesis based on existing literature and new results
Kerminen, VM; Paramonov, M; Anttila, T; Riipinen, I; Fountoukis, C; Korhonen, H; Asmi, E; Laakso, L; Lihavainen, H; Swietlicki, E; Svenningsson, B; Asmi, A; Pandis, SN; Kulmala, M; Petaja, T
| Atmos. Chem. Phys.
This paper synthesizes the available scientific information connecting atmospheric nucleation with subsequent cloud condensation nuclei (CCN) formation. We review both observations and model studies related to this topic, and discuss the potential climatic implications. We conclude that CCN production associated with atmospheric nucleation is both frequent and widespread phenomenon in many types of continental boundary layers, and probably also over a large fraction of the free troposphere. The contribution of nucleation to the global CCN budget spans a relatively large uncertainty range, which, together with our poor understanding of aerosol-cloud interactions, results in major uncertainties in the radiative forcing by atmospheric aerosols. In order to better quantify the role of atmospheric nucleation in CCN formation and Earth System behavior, more information is needed on (i) the factors controlling atmospheric CCN production and (ii) the properties of both primary and secondary CCN and their interconnections. In future investigations, more emphasis should be put on combining field measurements with regional and large-scale model studies.
Long-term volatility measurements of submicron atmospheric aerosol in Hyytiala, Finland
Hakkinen, SAK; Aijala, M; Lehtipalo, K; Junninen, H; Backman, J; Virkkula, A; Nieminen, T; Vestenius, M; Hakola, H; Ehn, M; Worsnop, DR; Kulmala, M; Petaja, T; Riipinen, I
| Atmos. Chem. Phys.
The volatility of submicron atmospheric aerosol particles was investigated at a boreal forest site in Hyytiala, Finland from January 2008 to May 2010. These long-term observations allowed for studying the seasonal behavior of aerosol evaporation with a special focus on compounds that remained in the aerosol phase at 280 degrees C. The temperature-response of evaporation was also studied by heating the aerosol sample step-wise to six temperatures ranging from 80 degrees C to 280 degrees C. The mass fraction remaining after heating (MFR) was determined from the measured particle number size distributions before and after heating assuming a constant particle density (1.6 g cm(-3)). On average 19% of the total aerosol mass remained in the particulate phase at 280 degrees C. The particles evaporated less at low ambient temperatures during winter as compared with the warmer months. Black carbon (BC) fraction of aerosol mass correlated positively with the MFR at 280 degrees C, but could not explain it completely: most of the time a notable fraction of this nonvolatile residual was something other than BC. Using additional information on ambient meteorological conditions and results from an Aerodyne aerosol mass spectrometer (AMS), the chemical composition of MFR at 280 degrees C and its seasonal behavior was further examined. Correlation analysis with ambient temperature and mass fractions of polycyclic aromatic hydrocarbons (PAHs) indicated that MFR at 280 degrees C is probably affected by anthropogenic emissions. On the other hand, results from the AMS analysis suggested that there may be very low-volatile organics, possibly organonitrates, in the non-volatile (at 280 degrees C) fraction of aerosol mass.
New particle formation at a remote site in the eastern Mediterranean
Pikridas, M; Riipinen, I; Hildebrandt, L; Kostenidou, E; Manninen, H; Mihalopoulos, N; Kalivitis, N; Burkhart, JF; Stohl, A; Kulmala, M; Pandis, SN
| J. Geophys. Res.-Atmos.
A year (6-April-2008 to 14-April-2009) of particulate monitoring was conducted at a remote coastal station on the island of Crete, Greece in the eastern Mediterranean. Fifty-eight regional new particle formation events were observed with an Air Ion Spectrometer (AIS), half of which occurred during the coldest months of the year (December-March). Particle formation was favored by air masses arriving from the west that crossed Crete or southern Greece prior to reaching the site and also by lower-than-average condensational sinks (CS). Aerosol composition data, which were acquired during month-long campaigns in the summer and winter, suggest that nucleation events occurred only when particles were neutral. This is consistent with the hypothesis that a lack of NH3, during periods when particles are acidic, may limit nucleation in sulfate-rich environments. Nucleation was not limited by the availability of SO2 alone, as nucleation events often did not take place during periods with high SO2 or H2SO4 concentrations. The above results support the hypothesis that an additional reactant (other than H2SO4) plays an important role in the formation and/or growth of new particles. Our results are consistent with NH3 being this missing reactant.
Formation and Growth of Atmospheric Aerosol Particles
Petaja, T; Dal Maso, M; Sipila, M; Riipinen, I; Kerminen, VM; Kulmala, M
| NATURE'S NANOSTRUCTURES
New particle formation and growth in biomass burning plumes: An important source of cloud condensation nuclei
Experiments were performed in an environmental chamber to characterize the effects of photo-chemical aging on biomass burning emissions. Photo-oxidation of dilute exhaust from combustion of 12 different North American fuels induced significant new particle formation that increased the particle number concentration by a factor of four (median value). The production of secondary organic aerosol caused these new particles to grow rapidly, significantly enhancing cloud condensation nuclei (CCN) concentrations. Using inputs derived from these new data, global model simulations predict that nucleation in photo-chemically aging fire plumes produces dramatically higher CCN concentrations over widespread areas of the southern hemisphere during the dry, burning season (Sept.-Oct.), improving model predictions of surface CCN concentrations. The annual indirect forcing from CCN resulting from nucleation and growth in biomass burning plumes is predicted to be -0.2 W m(-2), demonstrating that this effect has a significant impact on climate that has not been previously considered. Citation: Hennigan, C. J., D. M. Westervelt, I. Riipinen, G. J. Engelhart, T. Lee, J. L. Collett Jr., S. N. Pandis, P. J. Adams, and A. L. Robinson (2012), New particle formation and growth in biomass burning plumes: An important source of cloud condensation nuclei, Geophys. Res. Lett., 39, L09805, doi: 10.1029/2012GL050930.
Simulating ultrafine particle formation in Europe using a regional CTM: contribution of primary emissions versus secondary formation to aerosol number concentrations
Fountoukis, C; Riipinen, I; van der Gon, HACD; Charalampidis, PE; Pilinis, C; Wiedensohler, A; O'Dowd, C; Putaud, JP; Moerman, M; Pandis, SN
| Atmos. Chem. Phys.
A three-dimensional regional chemical transport model (CTM) with detailed aerosol microphysics, PMCAMx-UF, was applied to the European domain to simulate the contribution of direct emissions and secondary formation to total particle number concentrations during May 2008. PMCAMx-UF uses the Dynamic Model for Aerosol Nucleation and the Two-Moment Aerosol Sectional (TOMAS) algorithm to track both aerosol number and mass concentration using a sectional approach. The model predicts nucleation events that occur over scales of hundreds up to thousands of kilometers especially over the Balkans and Southeast Europe. The model predictions were compared against measurements from 7 sites across Europe. The model reproduces more than 70% of the hourly concentrations of particles larger than 10 nm (N-10) within a factor of 2. About half of these particles are predicted to originate from nucleation in the lower troposphere. Regional nucleation is predicted to increase the total particle number concentration by approximately a factor of 3. For particles larger than 100 nm the effect varies from an increase of 20% in the eastern Mediterranean to a decrease of 20% in southern Spain and Portugal resulting in a small average increase of around 1% over the whole domain. Nucleation has a significant effect in the predicted N-50 levels (up to a factor of 2 increase) mainly in areas where there are condensable vapors to grow the particles to larger sizes. A semi-empirical ternary sulfuric acid-ammonia-water parameterization performs better than the activation or the kinetic parameterizations in reproducing the observations. Reducing emissions of ammonia and sulfur dioxide affects certain parts of the number size distribution.
Is it all vapors? Constraining the role of gas-phase organic oxidation to condensed-phase particle growth
Atmospheric aerosol particles influence global climate as well as impair air quality through their effects on atmospheric visibility and human health. Ultrafine (< 100 nm) particles often dominate aerosol numbers, and nucleation of atmospheric vapors is an important source of these particles. To have climatic relevance, however, the freshly nucleated particles need to grow in size. We combine observations from two continental sites (Egbert, Canada and Hyytiala, Finland) to show that condensation of organic vapors is a crucial factor governing the lifetimes and climatic importance of the smallest atmospheric particles. We model the observed ultrafine aerosol growth with a simplified scheme approximating the condensing species as a mixture of effectively non-volatile and semi-volatile species, demonstrate that state-of-the-art organic gas-particle partitioning models fail to reproduce the observations, and propose a modeling approach that is consistent with the measurements. We find that roughly half of the mass of the condensing mass needs to be distributed proportional to the aerosol surface area (thus implying that the condensation is governed by gas-phase concentration rather than the equilibrium vapour pressure) to explain the observed aerosol growth. We demonstrate the large sensitivity of predicted number concentrations of cloud condensation nuclei (CCN) to these interactions between organic vapors and the smallest atmospheric nanoparticles highlighting the need for representing this process in global climate models.