A Predictive Model for Salt Nanoparticle Formation UsingHeterodimer Stability Calculations

Abstract. Acid–base clusters and stable salt formation are critical drivers of new particle formation events in the atmosphere. In this study, we explore the relationship between J1.5, the theoretically predicted formation rate of clusters larger than 4 acid and 4 base molecules, and acid–base heterodimer stability, a property that is relatively easy to calculate using computational methods. Heterodimer stability as a function of gas-phase acidity, aqueous-phase acidity, heterodimer proton transference, vapor pressure, dipole moment, and polarizability were explored for the salts comprised of sulfuric acid, methanesulfonic acid, and nitric acid with nine bases. The best predictor of heterodimer stability was found to be gas-phase acidity. The relationship between heterodimer stability and J1.5 was analyzed for sulfuric acid salts over a range of monomer concentrations from 105 to 109 molec cm−3 and temperatures from 248 to 348 K. Heterodimer concentration was calculated from heterodimer stability and yielded an expression for predicting J1.5 for any salt, given approximately equal acid and base monomer concentrations and knowledge of monomer concentration and temperature. This parameterization was tested for the sulfuric acid–ammonia system by comparing the predicted values to experimental data and was found to be accurate within 2 orders of magnitude. We show that one can create a simple parameterization that incorporates the dependence on temperature and monomer concentration on J1.5 by defining a new term that we call the normalized heterodimer concentration, Φ. A plot of J1.5 vs. Φ collapses to a single monotonic curve for all weak salts of sulfuric acid, and can be used to accurately estimate J1.5 in atmospheric models.

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A predictive model for salt nanoparticle formation using heterodimer stability calculations

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-11637-2021 ◽

2021 ◽

Vol 21 (15) ◽

pp. 11637-11654

Author(s):

Sabrina Chee ◽

Kelley Barsanti ◽

James N. Smith ◽

Nanna Myllys

Keyword(s):

Sulfuric Acid ◽

Gas Phase ◽

Formation Rate ◽

Methanesulfonic Acid ◽

Monomer Concentration ◽

Concentration Effects ◽

Gas Phase Acidity ◽

Acid And Base ◽

Aqueous Phase Acidity ◽

Sulfate Salts

Abstract. Acid–base clusters and stable salt formation are critical drivers of new particle formation events in the atmosphere. In this study, we explore salt heterodimer (a cluster of one acid and one base) stability as a function of gas-phase acidity, aqueous-phase acidity, heterodimer proton transference, vapor pressure, dipole moment and polarizability for salts comprised of sulfuric acid, methanesulfonic acid and nitric acid with nine bases. The best predictor of heterodimer stability was found to be gas-phase acidity. We then analyzed the relationship between heterodimer stability and J4×4, the theoretically predicted formation rate of a four-acid, four-base cluster, for sulfuric acid salts over a range of monomer concentrations from 105 to 109 molec cm−3 and temperatures from 248 to 348 K and found that heterodimer stability forms a lognormal relationship with J4×4. However, temperature and concentration effects made it difficult to form a predictive expression of J4×4. In order to reduce those effects, heterodimer concentration was calculated from heterodimer stability and yielded an expression for predicting J4×4 for any salt, given approximately equal acid and base monomer concentrations and knowledge of monomer concentration and temperature. This parameterization was tested for the sulfuric acid–ammonia system by comparing the predicted values to experimental data and was found to be accurate within 2 orders of magnitude. We show that one can create a simple parameterization that incorporates the dependence on temperature and monomer concentration on J4×4 by defining a new term that we call the normalized heterodimer concentration, Φ. A plot of J4×4 vs. Φ collapses to a single monotonic curve for weak sulfate salts (difference in gas-phase acidity >95 kcal mol−1) and can be used to accurately estimate J4×4 within 2 orders of magnitude in atmospheric models.

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Model for acid-base chemistry in nanoparticle growth (MABNAG)

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-7175-2013 ◽

2013 ◽

Vol 13 (3) ◽

pp. 7175-7222 ◽

Cited By ~ 1

Author(s):

T. Yli-Juuti ◽

K. Barsanti ◽

L. Hildebrandt Ruiz ◽

A.-J. Kieloaho ◽

U. Makkonen ◽

...

Keyword(s):

Particle Size ◽

Sulfuric Acid ◽

Gas Phase ◽

Organic Compounds ◽

Particle Growth ◽

Particle Phase ◽

Vapor Pressures ◽

Salt Formation ◽

Acid Base ◽

Nanoparticle Growth

Abstract. Climatic effects of newly-formed atmospheric secondary aerosol particles are to a large extent determined by their condensational growth rates. However, all the vapors condensing on atmospheric nanoparticles and growing them to climatically relevant sizes are not identified yet and the effects of particle phase processes on particle growth rates are poorly known. Besides sulfuric acid, organic compounds are known to contribute significantly to atmospheric nanoparticle growth. In this study a particle growth model MABNAG (Model for Acid-Base chemistry in NAnoparticle Growth) was developed to study the effect of salt formation on nanoparticle growth, which has been proposed as a potential mechanism lowering the equilibrium vapor pressures of organic compounds through dissociation in the particle phase and thus preventing their evaporation. MABNAG is a model for monodisperse aqueous particles and it couples dynamics of condensation to particle phase chemistry. Non-zero equilibrium vapor pressures, with both size and composition dependence, are considered for condensation. The model was applied for atmospherically relevant systems with sulfuric acid, one organic acid, ammonia, one amine and water in the gas phase allowed to condense on 3–20 nm particles. The effect of dissociation of the organic acid was found to be small under ambient conditions typical for a boreal forest site, but considerable for base-rich environments (gas phase concentrations of about 1010 cm−3 for the sum of the bases). The contribution of the bases to particle mass decreased as particle size increased, except at very high gas phase concentrations of the bases. The relative importance of amine versus ammonia did not change significantly as a function of particle size. While our results give a reasonable first estimate on the maximum contribution of salt formation to nanoparticle growth, further studies on, e.g. the thermodynamic properties of the atmospheric organics, concentrations of low-volatility organic acids and amines, along with studies investigating the applicability of thermodynamics for the smallest nanoparticles are needed to truly understand the acid-base chemistry of atmospheric nanoparticles.

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Interaction between Dicarboxylic Acid and Sulfuric Acid-Base Clusters Enhances New Particle Formation

10.5194/acp-2018-975 ◽

2018 ◽

Cited By ~ 1

Author(s):

Yun Lin ◽

Yuemeng Ji ◽

Yixin Li ◽

Jeremiah Secrest ◽

Wen Xu ◽

...

Keyword(s):

Sulfuric Acid ◽

Organic Acids ◽

Critical Nucleus ◽

Dicarboxylic Acids ◽

Particle Formation ◽

Water Molecules ◽

New Particle Formation ◽

Acid Base ◽

Covalent Bonds ◽

Acid And Base

Abstract. Dicarboxylic acids are believed to stabilize pre-nucleation clusters and facilitate new particle formation in the atmosphere, but the detailed mechanism leading to the formation of multi-component critical nucleus involving organic acids, sulfuric acid (SA), base species, and water remains unclear. In this study, theoretical caculations are performed to elucidate the interactions between succinic acid (SUA) and clusters consisting of SA-ammonia (AM)/dimethylamine (DMA) in the presence of hydration of up to six water molecules. Formation of the hydrated SUA·SA·base clusters by adding one SUA molecule to the SA·base hydrates is energetically favorable. The addition of SUA to the SA·base hydrates either triggers proton transfer from SA to the base molecule, resulting in formation of new covalent bonds, or strengthens the pre-existing covalent bonds. The presence of SUA promotes hydration of the SA·AM and SA·AM·DMA clusters but dehydration of the SA·DMA clusters. At equilibrium, the uptake of SUA competes with the uptake of the second SA molecule to stabilize the SA·base clusters at atmospherically relevant concentrations. The clusters containing both the base and organic acid are capable of further binding with acid molecules to promote their subsequent growth. Our results indicate that the multi-component nucleation involving organic acids, sulfuric acid, and base species promotes new particle formation in the atmosphere, particularly under polluted conditions.

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Model for acid-base chemistry in nanoparticle growth (MABNAG)

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-12507-2013 ◽

2013 ◽

Vol 13 (24) ◽

pp. 12507-12524 ◽

Cited By ~ 32

Author(s):

T. Yli-Juuti ◽

K. Barsanti ◽

L. Hildebrandt Ruiz ◽

A.-J. Kieloaho ◽

U. Makkonen ◽

...

Keyword(s):

Particle Size ◽

Sulfuric Acid ◽

Gas Phase ◽

Organic Compounds ◽

Growth Rates ◽

Particle Growth ◽

Particle Phase ◽

Salt Formation ◽

Acid Base ◽

Nanoparticle Growth

Abstract. Climatic effects of newly-formed atmospheric secondary aerosol particles are to a large extent determined by their condensational growth rates. However, all the vapours condensing on atmospheric nanoparticles and growing them to climatically relevant sizes are not identified yet and the effects of particle phase processes on particle growth rates are poorly known. Besides sulfuric acid, organic compounds are known to contribute significantly to atmospheric nanoparticle growth. In this study a particle growth model MABNAG (Model for Acid-Base chemistry in NAnoparticle Growth) was developed to study the effect of salt formation on nanoparticle growth, which has been proposed as a potential mechanism lowering the equilibrium vapour pressures of organic compounds through dissociation in the particle phase and thus preventing their evaporation. MABNAG is a model for monodisperse aqueous particles and it couples dynamics of condensation to particle phase chemistry. Non-zero equilibrium vapour pressures, with both size and composition dependence, are considered for condensation. The model was applied for atmospherically relevant systems with sulfuric acid, one organic acid, ammonia, one amine and water in the gas phase allowed to condense on 3–20 nm particles. The effect of dissociation of the organic acid was found to be small under ambient conditions typical for a boreal forest site, but considerable for base-rich environments (gas phase concentrations of about 1010 cm−3 for the sum of the bases). The contribution of the bases to particle mass decreased as particle size increased, except at very high gas phase concentrations of the bases. The relative importance of amine versus ammonia did not change significantly as a function of particle size. While our results give a reasonable first estimate on the maximum contribution of salt formation to nanoparticle growth, further studies on, e.g. the thermodynamic properties of the atmospheric organics, concentrations of low-volatility organics and amines, along with studies investigating the applicability of thermodynamics for the smallest nanoparticles are needed to truly understand the acid-base chemistry of atmospheric nanoparticles.

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Unexpectedly acidic nanoparticles formed in dimethylamine–ammonia–sulfuric-acid nucleation experiments at CLOUD

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-13601-2016 ◽

2016 ◽

Vol 16 (21) ◽

pp. 13601-13618 ◽

Cited By ~ 14

Author(s):

Michael J. Lawler ◽

Paul M. Winkler ◽

Jaeseok Kim ◽

Lars Ahlm ◽

Jasmin Tröstl ◽

...

Keyword(s):

Sulfuric Acid ◽

Gas Phase ◽

Composition Gradient ◽

Ionization Mass ◽

Acid Base ◽

Base Pairs ◽

Size Dependent ◽

Desorption Chemical Ionization ◽

Preferential Uptake ◽

Particulate Ammonium

Abstract. New particle formation driven by acid–base chemistry was initiated in the CLOUD chamber at CERN by introducing atmospherically relevant levels of gas-phase sulfuric acid and dimethylamine (DMA). Ammonia was also present in the chamber as a gas-phase contaminant from earlier experiments. The composition of particles with volume median diameters (VMDs) as small as 10 nm was measured by the Thermal Desorption Chemical Ionization Mass Spectrometer (TDCIMS). Particulate ammonium-to-dimethylaminium ratios were higher than the gas-phase ammonia-to-DMA ratios, suggesting preferential uptake of ammonia over DMA for the collected 10–30 nm VMD particles. This behavior is not consistent with present nanoparticle physicochemical models, which predict a higher dimethylaminium fraction when NH3 and DMA are present at similar gas-phase concentrations. Despite the presence in the gas phase of at least 100 times higher base concentrations than sulfuric acid, the recently formed particles always had measured base : acid ratios lower than 1 : 1. The lowest base fractions were found in particles below 15 nm VMD, with a strong size-dependent composition gradient. The reasons for the very acidic composition remain uncertain, but a plausible explanation is that the particles did not reach thermodynamic equilibrium with respect to the bases due to rapid heterogeneous conversion of SO2 to sulfate. These results indicate that sulfuric acid does not require stabilization by ammonium or dimethylaminium as acid–base pairs in particles as small as 10 nm.

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On the composition of ammonia-sulfuric acid clusters during aerosol particle formation

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-13413-2014 ◽

2014 ◽

Vol 14 (9) ◽

pp. 13413-13464 ◽

Cited By ~ 1

Author(s):

S. Schobesberger ◽

A. Franchin ◽

F. Bianchi ◽

L. Rondo ◽

J. Duplissy ◽

...

Keyword(s):

Boundary Layer ◽

Sulfuric Acid ◽

Gas Phase ◽

Particle Formation ◽

Atmospheric Conditions ◽

New Particle Formation ◽

Acid Base ◽

Wide Range ◽

Charged Clusters ◽

Positively Charged

Abstract. The formation of particles from precursor vapors is an important source of atmospheric aerosol. Research at the Cosmics Leaving OUtdoor Droplets (CLOUD) facility at CERN tries to elucidate which vapors are responsible for this new particle formation, and how in detail it proceeds. Initial measurement campaigns at the CLOUD stainless-steel aerosol chamber focused on investigating particle formation from ammonia (NH3) and sulfuric acid (H2SO4). Experiments were conducted in the presence of water, ozone and sulfur dioxide. Contaminant trace gases were suppressed at the technological limit. For this study, we mapped out the compositions of small NH3-H2SO4 clusters over a wide range of atmospherically relevant environmental conditions. We covered [NH3] in the range from <2 to 1400 pptv, [H2SO4] from 3.3 × 106 to 1.4 × 109 cm−3, and a temperature range from −25 to +20 °C. Negatively and positively charged clusters were directly measured by an atmospheric pressure interface time-of-flight (APi-TOF) mass spectrometer, as they initially formed from gas-phase NH3 and H2SO4, and then grew to larger clusters containing more than 50 molecules of NH3 and H2SO4, corresponding to mobility-equivalent diameters greater than 2 nm. Water molecules evaporate from these clusters during sampling and are not observed. We found that the composition of the NH3-H2SO4 clusters is primarily determined by the ratio of gas-phase concentrations [NH3] / [H2SO4], as well as by temperature. Pure binary H2O-H2SO4 clusters (observed as clusters of only H2SO4) only form at [NH3] / [H2SO4]<0.1 to 1. For larger values of [NH3] / [H2SO4], the composition of NH3-H2SO4 clusters was characterized by the number of NH3 molecules m added for each added H2SO4 molecule n (Δm / Δn), where n is in the range 4–18 (negatively charged clusters) or 1–17 (positively charged clusters). For negatively charged clusters, Δm / Δn saturated between 1 and 1.4 for [NH3] / [H2SO4]>10. Positively charged clusters grew on average by Δm / Δn = 1.05 and were only observed at sufficiently high [NH3] / [H2SO4]. The H2SO4 molecules of these clusters are partially neutralized by NH3, in close resemblance to the acid-base bindings of ammonium bisulfate. Supported by model simulations, we substantiate previous evidence for acid-base reactions being the essential mechanism behind the formation of these clusters under atmospheric conditions and up to sizes of at least 2 nm. Our results also suggest that yet unobservable electrically neutral NH3-H2SO4 clusters grow by generally the same mechanism as ionic clusters, particularly for [NH3] / [H2SO4]>10. We expect that NH3-H2SO4 clusters form and grow also mostly by Δm / Δn>1 in the atmosphere's boundary layer, as [NH3] / [H2SO4] is mostly larger than 10. We compared our results from CLOUD with APi-TOF measurements of NH3-H2SO4 anion clusters during new particle formation in the Finnish boreal forest. However, the exact role of NH3-H2SO4 clusters in boundary layer particle formation remains to be resolved.

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Unexpectedly acidic nanoparticles formed in dimethylamine-ammonia-sulfuric acid nucleation experiments at CLOUD

10.5194/acp-2016-361 ◽

2016 ◽

Cited By ~ 1

Author(s):

Michael J. Lawler ◽

Paul M. Winkler ◽

Jaeseok Kim ◽

Lars Ahlm ◽

Jasmin Tröstl ◽

...

Keyword(s):

Sulfuric Acid ◽

Gas Phase ◽

Composition Gradient ◽

Ionization Mass ◽

Acid Base ◽

Base Pairs ◽

Chemical Models ◽

Desorption Chemical Ionization ◽

Physico Chemical ◽

Preferential Uptake

Abstract. New particle formation driven by acid-base chemistry was initiated in the CLOUD chamber at CERN by introducing atmospherically relevant levels of gas phase sulfuric acid and dimethylamine (DMA). Ammonia was also present in the chamber as a gas-phase contaminant from earlier experiments. The composition of particles with volume median diameters (VMDs) as small as 10 nm was measured by the Thermal Desorption Chemical Ionization Mass Spectrometer (TDCIMS). Particulate ammonium-to-dimethylaminium ratios were higher than the gas phase ammonia-to-DMA ratios, suggesting preferential uptake of ammonia over DMA for the collected 10–30 nm VMD particles. This behavior is not consistent with present nanoparticle physico-chemical models, which predict a higher dimethylaminium fraction when NH3 and DMA are present at similar gas phase concentrations. Despite the presence in the gas phase of at least 100 times higher base concentrations than sulfuric acid, the recently formed particles always had measured base:acid ratios lower than 1 : 1. The lowest base fractions were found in particles below 15 nm VMD, with a strong size-dependent composition gradient that suggests a change to a mixed-phase state as the particles grew beyond this size. The reasons for the very acidic composition remain uncertain, but a possible explanation is that the particles did not reach thermodynamic equilibrium with respect to the bases due to rapid heterogeneous conversion of SO2 to sulfate. These results indicate that sulfuric acid does not require stabilization by ammonium or dimethylaminium as acid-base pairs in particles as small as 10 nm.

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On the composition of ammonia–sulfuric-acid ion clusters during aerosol particle formation

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-55-2015 ◽

2015 ◽

Vol 15 (1) ◽

pp. 55-78 ◽

Cited By ~ 54

Author(s):

S. Schobesberger ◽

A. Franchin ◽

F. Bianchi ◽

L. Rondo ◽

J. Duplissy ◽

...

Keyword(s):

Boundary Layer ◽

Sulfuric Acid ◽

Gas Phase ◽

Particle Formation ◽

Atmospheric Conditions ◽

New Particle Formation ◽

Acid Base ◽

Wide Range ◽

Charged Clusters ◽

Positively Charged

Abstract. The formation of particles from precursor vapors is an important source of atmospheric aerosol. Research at the Cosmics Leaving OUtdoor Droplets (CLOUD) facility at CERN tries to elucidate which vapors are responsible for this new-particle formation, and how in detail it proceeds. Initial measurement campaigns at the CLOUD stainless-steel aerosol chamber focused on investigating particle formation from ammonia (NH3) and sulfuric acid (H2SO4). Experiments were conducted in the presence of water, ozone and sulfur dioxide. Contaminant trace gases were suppressed at the technological limit. For this study, we mapped out the compositions of small NH3–H2SO4 clusters over a wide range of atmospherically relevant environmental conditions. We covered [NH3] in the range from < 2 to 1400 pptv, [H2SO4] from 3.3 × 106 to 1.4 × 109 cm−3 (0.1 to 56 pptv), and a temperature range from −25 to +20 °C. Negatively and positively charged clusters were directly measured by an atmospheric pressure interface time-of-flight (APi-TOF) mass spectrometer, as they initially formed from gas-phase NH3 and H2SO4, and then grew to larger clusters containing more than 50 molecules of NH3 and H2SO4, corresponding to mobility-equivalent diameters greater than 2 nm. Water molecules evaporate from these clusters during sampling and are not observed. We found that the composition of the NH3–H2SO4 clusters is primarily determined by the ratio of gas-phase concentrations [NH3] / [H2SO4], as well as by temperature. Pure binary H2O–H2SO4 clusters (observed as clusters of only H2SO4) only form at [NH3] / [H2SO4] < 0.1 to 1. For larger values of [NH3] / [H2SO4], the composition of NH3–H2SO4 clusters was characterized by the number of NH3 molecules m added for each added H2SO4 molecule n (Δm/Δ n), where n is in the range 4–18 (negatively charged clusters) or 1–17 (positively charged clusters). For negatively charged clusters, Δ m/Δn saturated between 1 and 1.4 for [NH3] / [H2SO4] > 10. Positively charged clusters grew on average by Δm/Δn = 1.05 and were only observed at sufficiently high [NH3] / [H2SO4]. The H2SO4 molecules of these clusters are partially neutralized by NH3, in close resemblance to the acid–base bindings of ammonium bisulfate. Supported by model simulations, we substantiate previous evidence for acid–base reactions being the essential mechanism behind the formation of these clusters under atmospheric conditions and up to sizes of at least 2 nm. Our results also suggest that electrically neutral NH3–H2SO4 clusters, unobservable in this study, have generally the same composition as ionic clusters for [NH3] / [H2SO4] > 10. We expect that NH3–H2SO4 clusters form and grow also mostly by Δm/Δn > 1 in the atmosphere's boundary layer, as [NH3] / [H2SO4] is mostly larger than 10. We compared our results from CLOUD with APi-TOF measurements of NH3–H2SO4 anion clusters during new-particle formation in the Finnish boreal forest. However, the exact role of NH3–H2SO4 clusters in boundary layer particle formation remains to be resolved.

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