A critical evaluation of proxy methods used to estimate the acidity of atmospheric particles

Abstract. Given significant challenges with available measurements of aerosol acidity, proxy methods are frequently used to estimate the acidity of atmospheric particles. In this study, four of the most common aerosol acidity proxies are evaluated and compared: (1) the ion balance method, (2) the molar ratio method, (3) thermodynamic equilibrium models, and (4) the phase partitioning of ammonia. All methods are evaluated against predictions of thermodynamic models and against direct observations of aerosol-gas equilibrium partitioning acquired in Mexico City during the MILAGRO study. The ion balance and molar ratio methods assume that any deficit in inorganic cations relative to anions is due to the presence of H+; and that a higher H+ loading and lower cation/anion ratio both correspond to increasingly acidic particles (i.e., lower pH). Based on the MILAGRO measurements, no correlation is observed between H+ levels inferred with the ion balance and aerosol pH predicted by the thermodynamic models and ammonia–ammonium (NH3–NH4+) partitioning. Similarly, no relationship is observed between the cation / anion molar ratio and predicted aerosol pH. Using only measured aerosol chemical composition as inputs without any constraint for the gas phase, the Extended Aerosol Inorganics Model (E-AIM) and ISORROPIA-II thermodynamic equilibrium models tend to predict aerosol pH levels that are inconsistent with the observed NH3–NH4+ partitioning. The modeled pH values from both models run with gas + aerosol inputs agreed well with the aerosol pH predicted by the phase partitioning of ammonia. It appears that (1) thermodynamic models constrained by gas + aerosol measurements, and (2) the phase partitioning of ammonia provide the best available predictions of aerosol pH. Furthermore, neither the ion balance nor the molar ratio can be used as surrogates for aerosol pH, and published studies to date with conclusions based on such acidity proxies may need to be reevaluated. Given the significance of acidity for chemical processes in the atmosphere, the implications of this study are important and far reaching.

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A critical evaluation of proxy methods used to estimate the acidity of atmospheric particles

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-2775-2015 ◽

2015 ◽

Vol 15 (5) ◽

pp. 2775-2790 ◽

Cited By ~ 146

Author(s):

C. J. Hennigan ◽

J. Izumi ◽

A. P. Sullivan ◽

R. J. Weber ◽

A. Nenes

Keyword(s):

Thermodynamic Equilibrium ◽

Critical Evaluation ◽

Atmospheric Particles ◽

Molar Ratio ◽

Ratio Method ◽

Thermodynamic Models ◽

Equilibrium Models ◽

Ion Balance ◽

Phase Partitioning ◽

Aerosol Acidity

Abstract. Given significant challenges with available measurements of aerosol acidity, proxy methods are frequently used to estimate the acidity of atmospheric particles. In this study, four of the most common aerosol acidity proxies are evaluated and compared: (1) the ion balance method, (2) the molar ratio method, (3) thermodynamic equilibrium models, and (4) the phase partitioning of ammonia. All methods are evaluated against predictions of thermodynamic models and against direct observations of aerosol–gas equilibrium partitioning acquired in Mexico City during the Megacity Initiative: Local and Global Research Objectives (MILAGRO) study. The ion balance and molar ratio methods assume that any deficit in inorganic cations relative to anions is due to the presence of H+ and that a higher H+ loading and lower cation / anion ratio both correspond to increasingly acidic particles (i.e., lower pH). Based on the MILAGRO measurements, no correlation is observed between H+ levels inferred with the ion balance and aerosol pH predicted by the thermodynamic models and NH3–NH4+ partitioning. Similarly, no relationship is observed between the cation / anion molar ratio and predicted aerosol pH. Using only measured aerosol chemical composition as inputs without any constraint for the gas phase, the E-AIM (Extended Aerosol Inorganics Model) and ISORROPIA-II thermodynamic equilibrium models tend to predict aerosol pH levels that are inconsistent with the observed NH3–NH4+ partitioning. The modeled pH values from both E-AIM and ISORROPIA-II run with gas &plus; aerosol inputs agreed well with the aerosol pH predicted by the phase partitioning of ammonia. It appears that (1) thermodynamic models constrained by gas &plus; aerosol measurements and (2) the phase partitioning of ammonia provide the best available predictions of aerosol pH. Furthermore, neither the ion balance nor the molar ratio can be used as surrogates for aerosol pH, and previously published studies with conclusions based on such acidity proxies may need to be reevaluated. Given the significance of acidity for chemical processes in the atmosphere, the implications of this study are important and far reaching.

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AEROSOL pH IN HO CHI MINH CITY, VIET NAM

Vietnam Journal of Science and Technology ◽

10.15625/2525-2518/55/4c/12132 ◽

2018 ◽

Vol 55 (4C) ◽

pp. 72

Author(s):

Duong Huu Huy

Keyword(s):

Particulate Matter ◽

Air Quality ◽

Thermodynamic Equilibrium ◽

Fine Particulate Matter ◽

Terrestrial Ecosystems ◽

Ho Chi Minh City ◽

Viet Nam ◽

Equilibrium Models ◽

Phase Partitioning ◽

Fine Particulate

Aerosol pH is an important parameter that affects air quality, and the health of aquatic and terrestrial ecosystems. However, the lack of such data was reported in Ho Chi Minh City (HCMC), Vietnam. In this study, we estimated the aerosol pH in fine particulate matter (PM2.5) collected in HCMC, Vietnam using the thermodynamic equilibrium models (E-AIM Extended Aerosol Inorganics Model and ISORROPIA-II), and the phase partitioning of ammonia. Aerosol pHs estimated by different methods were 1.7 – 2.9. Good correlations between the phase-partitioning approach and models in predicting the aerosol pH were observed with R2 from 0.77 to 0.89, suggesting that the assumption of equilibrium is valid at the HCMC site.

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Thermodynamic characterization of Mexico City aerosol during MILAGRO 2006

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-7-9203-2007 ◽

2007 ◽

Vol 7 (3) ◽

pp. 9203-9233 ◽

Cited By ~ 17

Author(s):

C. Fountoukis ◽

A. Nenes ◽

A. Sullivan ◽

R. Weber ◽

T. VanReken ◽

...

Keyword(s):

Gas Phase ◽

Mexico City ◽

Thermodynamic Equilibrium ◽

Phase State ◽

Molar Ratio ◽

Inorganic Species ◽

Equilibrium Calculations ◽

Thermodynamic Equilibrium Model ◽

Thermodynamic Equilibrium Calculations

Abstract. Fast measurements of aerosol and gas-phase constituents coupled with the ISORROPIA-II thermodynamic equilibrium model are used to study the partitioning of semivolatile inorganic species and phase state of Mexico City aerosol sampled at the T1 site during the MILAGRO 2006 campaign. Overall, predicted semivolatile partitioning agrees well with measurements. PM2.5 is insensitive to changes in ammonia but is to acidic semivolatile species. Semi-volatile partitioning equilibrates on a timescale between 6 and 20 min. When the aerosol sulfate-to-nitrate molar ratio is less than 1, predictions improve substantially if the aerosol is assumed to follow the deliquescent phase diagram. Treating crustal species as "equivalent sodium" (rather than explicitly) in the thermodynamic equilibrium calculations introduces important biases in predicted aerosol water uptake, nitrate and ammonium; neglecting crustals further increases errors dramatically. This suggests that explicitly considering crustals in the thermodynamic calculations are required to accurately predict the partitioning and phase state of aerosols.

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Biological Study of Transition Metal Complexes with Adenine Ligand

Proceedings ◽

10.3390/ecsoc-23-06601 ◽

2019 ◽

Vol 41 (1) ◽

pp. 77 ◽

Cited By ~ 1

Author(s):

Hamad M. I. Hasan ◽

Aaza I. Yahiya ◽

Safaa S. Hassan ◽

Mabrouk M. Salama

Keyword(s):

Metal Complexes ◽

Molar Conductance ◽

Molar Ratio ◽

Biological Study ◽

Ratio Method ◽

Spectroscopic Techniques ◽

Stoichiometric Ratio ◽

Metal Contents ◽

Molar Ratio Method

Adenine complexes were prepared with some of the first series transition metals in a stoichiometric ratio of 1: 2 (Mn+: L), where Mn+ = Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, and Cd2+ ions. The Complexes were characterized by the physicochemical and spectroscopic techniques as electric conductivity, metal contents, IR, UV–Visible, and molar conductance techniques. The stoichiometric ratios of the synthesized complexes were confirmed by using molar ratio method. The dissociation constant of adenine ligand was determined spectrophotometrically. Solvent effect on the electronic spectra of the adenine ligand was examined using solvents with different polarities. The biological activity of adenine ligand and its metal complexes were tested in vitro against some selected species of fungi and bacteria. The results showed a satisfactory spectrum against the tested organisms.

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Electrochemical studies on anion coordination chemistry. Application of the molar-ratio method to competitive cyclic voltammetry

Analytical Chemistry ◽

10.1021/ac00069a031 ◽

1993 ◽

Vol 65 (21) ◽

pp. 3137-3142 ◽

Cited By ~ 22

Author(s):

Antonio. Bianchi ◽

Antonio. Domenech ◽

Enrique. Garcia-Espana ◽

Santiago V. Luis

Keyword(s):

Cyclic Voltammetry ◽

Coordination Chemistry ◽

Molar Ratio ◽

Ratio Method ◽

Electrochemical Studies ◽

Anion Coordination ◽

Molar Ratio Method ◽

Anion Coordination Chemistry

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Determination of Stability Constants and Thermodynamic parameters of Cefotaxime –Fe(III) Complex at Different Temperatures

Journal of Chemical Society of Nigeria ◽

10.46602/jcsn.v45i4.505 ◽

2020 ◽

Vol 45 (4) ◽

Author(s):

O. V. Ikpeazu ◽

I. E. Otuokere ◽

K. K. Igwe

Keyword(s):

Stability Constants ◽

Chelating Agent ◽

Continuous Variation ◽

Molar Ratio ◽

Variation Method ◽

Ratio Method ◽

Lactam Antibiotic ◽

Different Temperatures ◽

Mole Ratio Method ◽

Continuous Variation Method

Cefotaxime, a β-lactam antibiotic, has a structure which enables it to act as a chelating agent. The formation of Fe(III) complex with cefotaxime has been studied colorimetrically at an absorption maximum of 480 nm at different temperatures. The data showed that Fe(III) and cefotaxime combine in the molar ratio of 1:1 at pH 7.4 with ionic strength maintained using 0.1M KNO3. The stability constants of the complex were calculated to be 1.56 - 1.90 x 104 by continuous variation method and 1.34 - 1.71 x 104 by mole ratio method at 25 and 40 oC respectively. ∆HƟ values for the complex were calculated to be -1.02 x 104 and -1.05 x 104 J by continuous variation method and mole ratio method respectively. ∆GƟ of the complex were calculated to be -2.44 – (-2.51) x 104 J by continuous variation method and -2.41- (- 2.48) x 104 J by mole ratio method at 25 and 40 oC. ∆SƟ of the complex were calculated to be 2.44 - 2.51 x 104 J/K by continuous variation method and -2.41 -2.48) x 104 J/K by mole ratio method at 25 and 40 oC respectively. Cefotaxime is a good chelating agent and can be an efficient antidote in the therapy of copper overload or poisoning.

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Spectrophotometric Determination of Copper (II) with 5-Hydroxy-6-Mercapto-Benzo [a] Phenazine

Revista de Chimie ◽

10.37358/rc.08.1.1695 ◽

2008 ◽

Vol 59 (1) ◽

pp. 3-7

Author(s):

Aurora Reiss ◽

Mihaela Mureseanu ◽

Nicolae Muresan

Keyword(s):

Spectrophotometric Determination ◽

Molar Absorptivity ◽

Molar Ratio ◽

Variation Method ◽

Ratio Method ◽

Relative Standard ◽

Analytical Reagent ◽

Experimental Values ◽

Determination Of Copper

5-Hydroxy-6-mercapto-benzo [a] phenazine (HMBP) is proposed as a sensitive and selective analytical reagent for the extractive spectrophotometric determination of copper (II). Copper reacts with HMBP to give a dark red complex which is soluble in chloroform. The composition of the CuII � HMBP complex is established as 1:2 by Job�s continuous variation method and molar ratio method. The instability constant of the complex calculated by Job�s relation for nonisomolar series is 4.65 . 10-9, at room temperature. The CuII-HMBP complex in chlorophorm shows a maximum absorbance at 495 nm, with molar absorptivity and Sandell�s sensitivity values of 7.39 . 103dm3 mol-1 cm-1 and 0.012 mg cm-2, respectively. Beer�s law is obeyed in the concentration range 0.67 - 26.90 mg mL-1 and the detection limit is 0.59 mg mL-1. A repetition of the method is checked by finding the relative standard deviation (RSD) at 1.00 mg mL-1 CuII of 0.6%. The method is successfully employed for the determination of copper (II) in environmental samples. The reliability of the method is assured by analysing the standard alloys and by inter-comparison of experimental values, using an atomic absorption spectrometer.

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Thermodynamic characterization of Mexico City aerosol during MILAGRO 2006

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-2141-2009 ◽

2009 ◽

Vol 9 (6) ◽

pp. 2141-2156 ◽

Cited By ~ 79

Author(s):

C. Fountoukis ◽

A. Nenes ◽

A. Sullivan ◽

R. Weber ◽

T. Van Reken ◽

...

Keyword(s):

Gas Phase ◽

Mexico City ◽

Thermodynamic Equilibrium ◽

Phase State ◽

Early Morning ◽

Molar Ratio ◽

Aerosol Composition ◽

Inorganic Species ◽

Thermodynamic Equilibrium Model

Abstract. Fast measurements of aerosol and gas-phase constituents coupled with the ISORROPIA-II thermodynamic equilibrium model are used to study the partitioning of semivolatile inorganic species and phase state of Mexico City aerosol sampled at the T1 site during the MILAGRO 2006 campaign. Overall, predicted semivolatile partitioning agrees well with measurements. PM2.5 is insensitive to changes in ammonia but is to acidic semivolatile species. For particle sizes up to 1μm diameter, semi-volatile partitioning requires 15–30 min to equilibrate; longer time is typically required during the night and early morning hours. Aerosol and gas-phase speciation always exhibits substantial temporal variability, so that aerosol composition measurements (bulk or size-resolved) obtained over large integration periods are not reflective of its true state. When the aerosol sulfate-to-nitrate molar ratio is less than unity, predictions improve substantially if the aerosol is assumed to follow the deliquescent phase diagram. Treating crustal species as "equivalent sodium" (rather than explicitly) in the thermodynamic equilibrium calculations introduces important biases in predicted aerosol water uptake, nitrate and ammonium; neglecting crustals further increases errors dramatically. This suggests that explicitly considering crustals in the thermodynamic calculations is required to accurately predict the partitioning and phase state of aerosols.

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