Revising the hygroscopicity of inorganic sea salt particles

Zieger, P.; Väisänen, O.; Corbin, J.; Partridge, D. G.; Bastelberger, S.; Mousavi-Fard, M.; Rosati, B.; Gysel, M.; Krieger, U.; Leck, C.; Nenes, A.; Riipinen, I.; Virtanen, A.; Salter, M.
2017 | Nat. Commun. | 8 (15883)

Sea spray is one of the largest natural aerosol sources and plays an important role in the Earth’s radiative budget. These particles are inherently hygroscopic, that is, they take-up moisture from the air, which affects the extent to which they interact with solar radiation. We demonstrate that the hygroscopic growth of inorganic sea salt is 8–15% lower than pure sodium chloride, most likely due to the presence of hydrates. We observe an increase in hygroscopic growth with decreasing particle size (for particle diameters <150 nm) that is independent of the particle generation method. We vary the hygroscopic growth of the inorganic sea salt within a general circulation model and show that a reduced hygroscopicity leads to a reduction in aerosol-radiation interactions, manifested by a latitudinal-dependent reduction of the aerosol optical depth by up to 15%, while cloud-related parameters are unaffected. We propose that a value of κs=1.1 (at RH=90%) is used to represent the hygroscopicity of inorganic sea salt particles in numerical models.

Measured Saturation Vapor Pressures of Phenolic and Nitro-aromatic Compounds

Bannan, TJ; Booth, AM; Jones, BT; O'Meara, S; Barley, MH; Riipinen, I; Percival, CJ; Topping, D
2017 | Environ. Sci. Technol. | 51 (7) (3922-3928)
aerosol formation , benzoic-acids , dicarboxylic-acids , enthalpies , mass spectrometry , nonelectrolyte organic-compounds , particulate matter , pure component properties , soa formation , solid-state

Phenolic and nitro-aromatic compounds are extremely toxic components of atmospheric aerosol that are currently not well understood. In this Article, solid and subcooled-liquid-state saturation vapor pressures of phenolic and nitro-aromatic compounds are measured using Knudsen Effusion Mass Spectrometry (KEMS) over a range of temperatures (298-318 K). Vapor pressure estimation methods, assessed in this study, do not replicate the observed dependency on the relative positions of functional groups. With a few exceptions, the estimates are biased toward predicting saturation vapor pressures that are too high, by 5-6 orders of magnitude in some cases. Basic partitioning theory comparisons indicate that overestimation of vapor pressures in such cases would cause us to expect these compounds to be present in the gas state, whereas measurements in this study suggest these phenolic and nitro-aromatic will partition into the condensed state for a wide range of ambient conditions if absorptive partitioning plays a dominant role. While these techniques might have both structural and parametric uncertainties, the new data presented here should support studies trying to ascertain the role of nitrogen containing organics on aerosol growth and human health impacts.

Response to Comment on “Measured Saturation Vapor Pressures of Phenolic and Nitro-Aromatic Compounds”

Topping, D; Riipinen, I; Percival, C; Bannan, T
2017 | Environ. Sci. Technol. | 51 (13) (7744-7745)

Estimates of the organic aerosol volatility in a boreal forest using two independent methods

Hong, J; Aijala, M; Hame, SAK; Hao, LQ; Duplissy, J; Heikkinen, LM; Nie, W; Mikkila, J; Kulmala, M; Prisle, NL; Virtanen, A; Ehn, M; Paasonen, P; Worsnop, DR; Riipinen, I; Petaja, T; Kerminen, VM
2017 | Atmos. Chem. Phys. | 17 (6) (4387-4399)
atmosphere , components , gaseous ammonium-nitrate , high-resolution , mass-spectrometer , particles , secondary , source apportionment , thermochemistry , time scales

The volatility distribution of secondary organic aerosols that formed and had undergone aging - i. e., the particle mass fractions of semi-volatile, low-volatility and extremely low volatility organic compounds in the particle phase - was characterized in a boreal forest environment of Hyytiala, southern Finland. This was done by interpreting field measurements using a volatility tandem differential mobility analyzer (VTDMA) with a kinetic evaporation model. The field measurements were performed during April and May 2014. On average, 40% of the organics in particles were semi-volatile, 34% were low-volatility organics and 26% were extremely low volatility organics. The model was, however, very sensitive to the vaporization enthalpies assumed for the organics (Delta H-VAP). The best agreement between the observed and modeled temperature dependence of the evaporation was obtained when effective vaporization enthalpy values of 80 kJ mol(-1) were assumed. There are several potential reasons for the low effective enthalpy value, including molecular decomposition or dissociation that might occur in the particle phase upon heating, mixture effects and compound-dependent uncertainties in the mass accommodation coefficient. In addition to the VTDMA-based analysis, semi-volatile and low-volatility organic mass fractions were independently determined by applying positive matrix factorization (PMF) to high-resolution aerosol mass spectrometer (HR-AMS) data. The factor separation was based on the oxygenation levels of organics, specifically the relative abundance of mass ions at m/z 43 (f43) and m/z 44 (f44). The mass fractions of these two organic groups were compared against the VTDMA-based results. In general, the best agreement between the VTDMA results and the PMF-derived mass fractions of organics was obtained when Delta H-VAP D 80 kJ mol(-1) was set for all organic groups in the model, with a linear correlation coefficient of around 0.4. However, this still indicates that only about 16% (R-2)of the variation can be explained by the linear regression between the results from these two methods. The prospect of determining of extremely low volatility organic aerosols (ELVOAs) from AMS data using the PMF analysis should be assessed in future studies.

Future Response of Temperature and Precipitation to Reduced Aerosol Emissions as Compared with Increased Greenhouse Gas Concentrations

Navarro, JCA; Ekman, AML; Pausata, FSR; Lewinschal, A; Varma, V; Seland, O; Gauss, M; Iversen, T; Kirkevag, A; Riipinen, I; Hansson, HC
2017 | J Clim | 30 (3) (939-954)
air quality , circulation , climate response , earth system model , global climate , intertropical convergence zone , late 20th-century , noresm1-m , pollutants , sensitivity

Experiments with a climate model (NorESM1) were performed to isolate the effects of aerosol particles and greenhouse gases on surface temperature and precipitation in simulations of future climate. The simulations show that by 2025-49 a reduction of aerosol emissions from fossil fuels following a maximum technically feasible reduction (MFR) scenario could lead to a global and Arctic warming of 0.26 and 0.84 K, respectively, as compared with a simulation with fixed aerosol emissions at the level of 2005. If fossil fuel emissions of aerosols follow a current legislation emissions (CLE) scenario, the NorESM1 model simulations yield a nonsignificant change in global and Arctic average surface temperature as compared with aerosol emissions fixed at year 2005. The corresponding greenhouse gas effect following the representative concentration pathway 4.5 (RCP4.5) emission scenario leads to a global and Arctic warming of 0.35 and 0.94 K, respectively. The model yields a marked annual average northward shift in the intertropical convergence zone with decreasing aerosol emissions and subsequent warming of the Northern Hemisphere. The shift is most pronounced in the MFR scenario but also visible in the CLE scenario. The modeled temperature response to a change in greenhouse gas concentrations is relatively symmetric between the hemispheres, and there is no marked shift in the annual average position of the intertropical convergence zone. The strong reduction in aerosol emissions in the MFR scenario also leads to a net southward cross-hemispheric energy transport anomaly both in the atmosphere and ocean, and enhanced monsoon circulation in Southeast Asia and East Asia causing an increase in precipitation over a large part of this region.

Molecular-resolution simulations of new particle formation: Evaluation of common assumptions made in describing nucleation in aerosol dynamics models

Olenius, T; Riipinen, I
2017 | Aerosol Sci Technol | 51 (4) (397-408)
atmospheric nano-particles , coagulation , condensation , events , growth , ions , number concentrations , size , sulfuric acid , supersaturated vapor

Aerosol dynamics models that describe the evolution of a particle distribution incorporate nucleation as a particle formation rate at a small size around a few nanometers in diameter. This rate is commonly obtained from molecular models that cover the distribution below the given formation size - although in reality the distribution of nanometer-sized particles cannot be unambiguously divided into separate sections of particle formation and growth. When incorporating nucleation, the distribution below the formation size is omitted, and the formation rate is assumed to be in a steady state. In addition, to reduce the modeled size range, the formation rate is often scaled to a larger size based on estimated growth and scavenging rates and the assumption that also the larger size is in a steady state. This work evaluates these assumptions by simulating sub-10 nm particle distributions in typical atmospheric conditions with an explicit molecular-resolution model. Particle formation is included either (1) dynamically, that is, the whole size range starting from single vapor molecules is modeled explicitly or (2) implicitly by using an input formation rate as is done in aerosol models. The results suggest that while each assumption can affect the outcome of new particle formation modeling, the most significant source of uncertainty affecting the formation rates and resulting nanoparticle concentrations is the steady-state assumption, which may lead to an overprediction of the concentrations by factors of approximately from two to even orders of magnitude. This can have implications for modeling and predicting atmospheric particle formation.

Microphysical explanation of the RH-dependent water affinity of biogenic organic aerosol and its importance for climate

Rastak, N; Pajunoja, A; Navarro, JCA; Ma, J; Song, M; Partridge, DG; Kirkevag, A; Leong, Y; Hu, WW; Taylor, NF; Lambe, A; Cerully, K; Bougiatioti, A; Liu, P; Krejci, R; Petaja, T; Percival, C; Davidovits, P; Worsnop, DR; Ekman, AML; Nenes, A; Martin, S; Jimenez, JL; Collins, DR; Topping, DO; Bertram, AK; Zuend, A; Virtanen, A; Riipinen, I
2017 | Geophys Res Lett | 44 (10) (5167-5177)
atmospheric aerosols , boreal forest , condensation nuclei activity , droplet activation kinetics , earth system model , hygroscopic growth , liquid phase-separation , mass-spectrometer , regional dust samples , southeastern united-states
A large fraction of atmospheric organic aerosol (OA) originates from natural emissions that are oxidized in the atmosphere to form secondary organic aerosol (SOA). Isoprene (IP) and monoterpenes (MT) are the most important precursors of SOA originating from forests. The climate impacts from OA are currently estimated through parameterizations of water uptake that drastically simplify the complexity of OA. We combine laboratory experiments, thermodynamic modeling, field observations, and climate modeling to (1) explain the molecular mechanisms behind RH-dependent SOA water-uptake with solubility and phase separation; (2) show that laboratory data on IP- and MT-SOA hygroscopicity are representative of ambient data with corresponding OA source profiles; and (3) demonstrate the sensitivity of the modeled aerosol climate effect to assumed OA water affinity. We conclude that the commonly used single-parameter hygroscopicity framework can introduce significant error when quantifying the climate effects of organic aerosol. The results highlight the need for better constraints on the overall global OA mass loadings and its molecular composition, including currently underexplored anthropogenic and marine OA sources. Plain Language Summary The interaction of airborne particulate matter ("aerosols") with water is of critical importance for processes governing climate, precipitation, and public health. It also modulates the delivery and bioavailability of nutrients to terrestrial and oceanic ecosystems. We present a microphysical explanation to the humidity-dependent water uptake behavior of organic aerosol, which challenges the highly simplified theoretical descriptions used in, e.g., present climate models. With the comprehensive analysis of laboratory data using molecular models, we explain the microphysical behavior of the aerosol over the range of humidity observed in the atmosphere, in a way that has never been done before. We also demonstrate the presence of these phenomena in the ambient atmosphere from data collected in the field. We further show, using two state-of-the-art climate models, that misrepresenting the water affinity of atmospheric organic aerosol can lead to significant biases in the estimates of the anthropogenic influence on climate.

Calcium enrichment in sea spray aerosol particles

Salter, M.; Hamacher-Barth, E.; Leck, C.; Werner, J.; Johnson, C.; Riipinen, I.; Nilsson, D.; Zieger, P.
2016 | Geophys Res Lett

Sea spray aerosol particles are an integral part of the Earth's radiation budget. To date, the inorganic composition of nascent sea spray aerosol particles have widely been assumed to be equivalent to the inorganic composition of seawater. Here we challenge this assumption using a laboratory sea spray chamber containing both natural and artificial seawater, as well as with ambient aerosol samples collected over the central Arctic Ocean during summer. We observe significant enrichment of calcium in submicrometer (<1μm in diameter) sea spray aerosol particles when particles are generated from both seawater sources in the laboratory as well as in the ambient aerosols samples. We also observe a tendency for increasing calcium enrichment with decreasing particle size. Our results suggest that calcium enrichment in sea spray aerosol particles may be environmentally significant with implications for our understanding of sea spray aerosol, its impact on Earth's climate, as well as the chemistry of the marine atmosphere.

Surface partitioning in organic–inorganic mixtures contributes to the size-dependence of the phase-state of atmospheric nanoparticles

Werner, J.; Dalirian, M.; Walz, M.-M.; Ekholm, V.; Wideqvist, U.; Lowe, S. J.; Öhrwall, G.; Persson, I.; Riipinen, I.; Björneholm, O.
2016 | Environ. Sci. Technol.

The effect of acid-base clustering and ions on the growth of atmospheric nano-particles

Lehtipalo, K.; Rondo, L.; Kontkanen, J.; Schobesberger, S.; Jokinen, T.; Sarnela, N.; Kurten, A.; Ehrhart, S.; Franchin, A.; Nieminen, T.; Riccobono, F.; Sipila, M.; Yli-Juuti, T.; Duplissy, J.; Adamov, A.; Ahlm, L.; Almeida, J.; Amorim, A.; Bianchi, F.; Breitenlechner, M.; Dommen, J.; Downard, AJ.; Dunne, E. M.; Flagan, R. C.; Guida, R.; Hakala, J.; Hansel, A.; Jud, W.; Kangasluoma, J.; Kerminen, V. M.; Keskinen, H.; Kim, J.; Kirkby, J.; Kupc, A.; Kupiainen-Maatta, O.; Laaksonen, A.; Lawler, M. J.; Leiminger, M.; Mathot, S.; Olenius, T.; Ortega, I. K.; Onnela, A.; Petaja, T.; Praplan, A.; Rissanen, M. P.; Ruuskanen, T.; Santos, F. D.; Schallhart, S.; Schnitzhofer, R.; Simon, M.; Smith, J. N.; Trostl, J.; Tsagkogeorgas, G.; Tome, A.; Vaattovaara, P.; Vehkamaki, H.; Vrtala, A. E.; Wagner, P. E.; Williamson, C.; Wimmer, D.; Winkler, P. M.; Virtanen, A.; Donahue, N. M.; Carslaw, K. S.; Baltensperger, U.; Riipinen, I.; Curtius, J.; Worsnop, D. R.; Kulmala, M.
2016 | Nat. Commun. | 7

Ion-induced nucleation of pure biogenic particles

Kirkby, J.; Duplissy, J.; Sengupta, K.; Frege, C.; Gordon, H.; Williamson, C.; Heinritzi, M.; Simon, M.; Yan, C.; Almeida, J.; Tröstl, J.; Nieminen, T.; Ortega, I. K.; Wagner, R.; Adamov, A.; Amorim, A.; Bernhammer, A.-K.; Bianchi, F.; Breitenlechner, M.; Brilke, S.; Chen, X.; Craven, J.; Dias, A.; Ehrhart, S.; Flagan, R. C.; Franchin, A.; Fuchs, C.; Guida, R.; Hakala, J.; Hoyle, C. R.; Jokinen, T.; Junninen, H.; Kangasluoma, J.; Kim, J.; Krapf, M.; Kürten, A.; Laaksonen, A.; Lehtipalo, K.; Makhmutov, V.; Mathot, S.; Molteni, U.; Onnela, A.; Peräkylä, O.; Piel, F.; Petäjä, T.; Praplan, A. P.; Pringle, K.; Rap, A.; Richards, N. A. D.; Riipinen, I.; Rissanen, M. P.; Rondo, L.; Sarnela, N.; Schobesberger, S.; Scott, C. E.; Seinfeld, J. H.; Sipilä, M.; Steiner, G.; Stozhkov, Y.; Stratmann, F.; Tomé, A.; Virtanen, A.; Vogel, A. L.; Wagner, A. C.; Wagner, P. E.; Weingartner, E.; Wimmer, D.; Winkler, P. M.; Ye, P.; Zhang, X.; Hansel, A.; Dommen, J.; Donahue, N. M.; Worsnop, D. R.; Baltensperger, U.; Kulmala, M.; Carslaw, K. S.; Curtius, J.
2016 | Nature | 533

The role of low volatility organic compounds in initial particle growth in the atmosphere

Tröstl, J.; Chuang, W. K.; Gordon, H.; Heinritzi, M.; Yan, C.; Molteni, U.; Ahlm, L.; Frege, C.; Bianchi, F.; Wagner, R.; Simon, M.; Lehtipalo, K.; Williamson, C.; Craven, J. S.; Duplissy, J.; Adamov, A.; Almeida, J.; Bernhammer, A.-K.; Breitenlechner, M.; Brilke, S.; Dias, A.; Ehrhart, S.; Flagan, R. C.; Franchin, A.; Fuchs, C.; Guida, R.M.; Gysel, M.; Hansel, A.; Hoyle, C. R.; Jokinen, T.; Junninen, H.; Kangasluoma, J.; Keskinen, H.; Kim, J.; Krapf, M.; Kürten, A.; Laaksonen, A.; Lawler, M.; Leiminger, M.; Mathot, S.; Möhler, O.; Nieminen, T.; Onnela, A.; Petäjä, T.; Piel, F. M.; Miettinen, P.; Rissanen, M. P.; Rondo, L.; Sarnela, N.; Schobesberger, S.; Sengupta, K.; Sipilä, M.; Smith, J. N.; Steiner, G.; Tomè, A.; Virtanen, A.; Wagner, A. C.; Weingartner, E.; Wimmer, D.; Winkler, P. M.; Ye, P.; Carslaw, K. S.; Curtius, J.; Dommen, J.; Kirkby, J.; Kulmala, M.; Riipinen, I.; Worsnop, D. R.; Donahue, N. M.; Baltensperger, U.
2016 | Nature | 533

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