scholarly journals Hygroscopic behavior of atmospheric aerosols containing nitrates and water-soluble organic acids

2017 ◽  
Author(s):  
Bo Jing ◽  
Zhen Wang ◽  
Fang Tan ◽  
Yucong Guo ◽  
Shengrui Tong ◽  
...  
Keyword(s):  
Organic Acids ◽  
Organic Acid ◽  
Phase Behavior ◽  
Water Uptake ◽  
Sodium Nitrate ◽  
Atmospheric Aerosols ◽  
Water Soluble ◽  
Atmospheric Environment ◽  
Mass Transfer Limitation ◽  
Continuous Growth

Abstract. While nitrates have critical impacts on environmental effects of atmospheric aerosols, the effects of coexisting species on hygroscopicity of nitrates remain uncertain. The hygroscopic behaviors of nitrate aerosols (NH4NO3, NaNO3, Ca(NO3)2) and their internal mixtures with water soluble organic acids at varying mass ratios were determined using a hygroscopicity tandem differential mobility analyzer (HTDMA). The nitrate/organic acid mixed aerosols exhibit varying phase behavior and hygroscopic growth depending upon the type of components in the particles. Whereas pure nitrate particles show continuous water uptake with increasing RH, the deliquescence transition is still observed for ammonium nitrate particles internally mixed with organic acids such as oxalic acid and succinic acid with a high deliquescence point. The hygroscopicity of submicron aerosols containing sodium nitrate and an organic acid is also characterized by continuous growth, indicating that sodium nitrate tends to exist in a liquid-like state under dry conditions. It is observed that in contrast to the pure components the water uptake is hindered at low and moderate RH for calcium nitrate particles containing malonic acid or phthalic acid, suggesting the potential effects of mass transfer limitation in highly viscous mixed systems. Our findings improve fundamental understanding of the phase behavior and water uptake of nitrate-containing aerosols in the atmospheric environment.

scholarly journals Hygroscopic behavior of atmospheric aerosols containing nitrate salts and water-soluble organic acids

2018 ◽  
Vol 18 (7) ◽  
pp. 5115-5127 ◽  
Author(s):  
Bo Jing ◽  
Zhen Wang ◽  
Fang Tan ◽  
Yucong Guo ◽  
Shengrui Tong ◽  
...  
Keyword(s):  
Organic Acids ◽  
Phase Behavior ◽  
Water Uptake ◽  
Sodium Nitrate ◽  
Atmospheric Aerosols ◽  
Water Soluble ◽  
Atmospheric Environment ◽  
Nitrate Salt ◽  
Continuous Growth ◽  
Nitrate Salts

Abstract. While nitrate salts have critical impacts on environmental effects of atmospheric aerosols, the effects of coexisting species on hygroscopicity of nitrate salts remain uncertain. The hygroscopic behaviors of nitrate salt aerosols (NH4NO3, NaNO3, Ca(NO3)2) and their internal mixtures with water-soluble organic acids were determined using a hygroscopicity tandem differential mobility analyzer (HTDMA). The nitrate salt ∕ organic acid mixed aerosols exhibit varying phase behavior and hygroscopic growth depending upon the type of components in the particles. Whereas pure nitrate salt particles show continuous water uptake with increasing relative humidity (RH), the deliquescence transition is still observed for ammonium nitrate particles internally mixed with organic acids such as oxalic acid and succinic acid with a high deliquescence point. The hygroscopicity of submicron aerosols containing sodium nitrate and an organic acid is also characterized by continuous growth, indicating that sodium nitrate tends to exist in a liquid-like state under dry conditions. It is observed that in contrast to the pure components, the water uptake is hindered at low and moderate RH for calcium nitrate particles containing malonic acid or phthalic acid, suggesting the potential effects of mass transfer limitation in highly viscous mixed systems. Our findings improve fundamental understanding of the phase behavior and water uptake of nitrate-salt-containing aerosols in the atmospheric environment.

scholarly journals Characterization of Aerosol Composition, Aerosol Acidity and Organic Acid Partitioning at an Agriculture-Intensive Rural Southeastern U.S. Site

2018 ◽  
Author(s):  
Theodora Nah ◽  
Hongyu Guo ◽  
Amy P. Sullivan ◽  
Yunle Chen ◽  
David J. Tanner ◽  
...  
Keyword(s):  
Oxalic Acid ◽  
Organic Acids ◽  
Organic Acid ◽  
Organic Aerosol ◽  
Water Soluble ◽  
Molar Concentration ◽  
Particle Phase ◽  
Aerosol Composition ◽  
Phase Water ◽  
Acetic Acids

Abstract. The implementation of stringent emission regulations has resulted in the decline of anthropogenic pollutants including sulfur dioxide (SO2), nitrogen oxides (NOx) and carbon monoxide (CO). In contrast, ammonia (NH3) emissions are largely unregulated, with emissions projected to increase in the future. We present real-time aerosol and gas measurements from a field study conducted in an agricultural-intensive region in the southeastern U.S. during the fall of 2016 to investigate how NH3 affects particle acidity and SOA formation via the gas-particle partitioning of semi-volatile organic acids. Particle water and pH were determined using the ISORROPIA-II thermodynamic model and validated by comparing predicted inorganic HNO3-NO3− and NH3-NH4+ gas-particle partitioning ratios with measured values. Our results showed that despite the high NH3 concentrations (study average 8.1 ± 5.2 ppb), PM1 were highly acidic with pH values ranging from 0.9 to 3.8, and a study-averaged pH of 2.2 ± 0.6. PM1 pH varied by approximately 1.4 units diurnally. Formic and acetic acids were the most abundant gas-phase organic acids, and oxalate was the most abundant particle-phase water-soluble organic acid anion. Measured particle-phase water-soluble organic acids were on average 6 % of the total non-refractory PM1 organic aerosol mass. The measured molar fraction of oxalic acid in the particle phase (i.e., particle-phase oxalic acid molar concentration divided by the total oxalic acid molar concentration) ranged between 47 and 90 % for PM1 pH 1.2 to 3.4. The measured oxalic acid gas-particle partitioning ratios were in good agreement with their corresponding thermodynamic predictions, calculated based on oxalic acid’s physicochemical properties, ambient temperature, particle water and pH. In contrast, gas-particle partitioning of formic and acetic acids were not well predicted for reasons currently unknown. For this study, higher NH3 concentrations relative to what has been measured in the region in previous studies had minor effects on PM1 organic acids and their influence on the overall organic aerosol and PM1 mass concentrations.

scholarly journals Effects of water-soluble organic carbon on aerosol pH

2019 ◽  
Vol 19 (23) ◽  
pp. 14607-14620 ◽  
Author(s):  
Michael A. Battaglia Jr. ◽  
Rodney J. Weber ◽  
Athanasios Nenes ◽  
Christopher J. Hennigan
Keyword(s):  
Organic Carbon ◽  
Activity Coefficient ◽  
Organic Acids ◽  
Organic Acid ◽  
Fine Particulate Matter ◽  
Water Soluble ◽  
Ph Changes ◽  
Water Soluble Organic Carbon ◽  
Soluble Organic Carbon ◽  
Acidic Conditions

Abstract. Water-soluble organic carbon (WSOC) is a ubiquitous and significant fraction of fine particulate matter. Despite advances in aerosol thermodynamic equilibrium models, there is limited understanding on the comprehensive impacts of WSOC on aerosol acidity (pH). We address this limitation by studying submicron aerosols that represent the two extremes in acidity levels found in the atmosphere: strongly acidic aerosol from Baltimore, MD, and weakly acidic conditions characteristic of Beijing, China. These cases are then used to construct mixed inorganic–organic single-phase aqueous particles and thermodynamically analyzed by the Extended Aerosol Inorganics Model (E-AIM) and ISORROPIA models in combination with activity coefficient model AIOMFAC (Aerosol Inorganic–Organic Mixtures Functional groups Activity Coefficient) to evaluate the effects of WSOC on the H+ ion activity coefficients (γH+) and activity (pH). We find that addition of organic acids and nonacid organic species concurrently increases γH+ and aerosol liquid water. Under the highly acidic conditions typical of the eastern US (inorganic-only pH ∼1), these effects mostly offset each other, giving pH changes of < 0.5 pH units even at organic aerosol dry mass fractions in excess of 60 %. Under conditions with weaker acidity typical of Beijing (inorganic-only pH ∼4.5), the nonacidic WSOC compounds had similarly minor effects on aerosol pH, but organic acids imparted the largest changes in pH compared to the inorganic-only simulations. Organic acids affect pH in the order of their pKa values (oxalic acid > malonic acid > glutaric acid). Although the inorganic-only pH was above the pKa value of all three organic acids investigated, pH changes in excess of 1 pH unit were only observed at unrealistic organic acid levels (aerosol organic acid concentrations > 35 µg m−3) in Beijing. The model simulations were run at 70 %, 80 %, and 90 % relative humidity (RH) levels and the effect of WSOC was inversely related to RH. At 90 % RH, WSOC altered aerosol pH by up to ∼0.2 pH units, though the effect was up to ∼0.6 pH units at 70 % RH. The somewhat offsetting nature of these effects suggests that aerosol pH is sufficiently constrained by the inorganic constituents alone under conditions where liquid–liquid phase separation is not anticipated to occur.

scholarly journals Real-time measurements of gas-phase organic acids using SF<sub>6</sub><sup>−</sup> chemical ionization mass spectrometry

2018 ◽  
Author(s):  
Theodora Nah ◽  
Yi Ji ◽  
David J. Tanner ◽  
Hongyu Guo ◽  
Amy P. Sullivan ◽  
...  
Keyword(s):  
Organic Acids ◽  
Organic Acid ◽  
Real Time ◽  
Gas Phase ◽  
Atmospheric Chemistry ◽  
Chemical Ionization ◽  
Measurement Techniques ◽  
Water Soluble ◽  
Rural Site ◽  
Ionization Mass

Abstract. The sources and atmospheric chemistry of gas-phase organic acids are currently poorly understood due in part to the limited range of measurement techniques available. In this work, we evaluated the use of SF6− as a sensitive and selective chemical ionization reagent ion for real-time measurements of gas-phase organic acids. Field measurements are made using a chemical ionization mass spectrometer (CIMS) at a rural site in Yorkville, Georgia from September to October 2016 to investigate the capability of this measurement technique. Our measurements demonstrate that SF6− can be used to measure a range of organic acids in the atmosphere. Ambient concentrations of organic acids ranged from a few parts per trillion by volume (ppt) to several parts per billion by volume (ppb). Assuming that these organic acids are completely water-soluble, the carbon mass fraction of gas-phase water-soluble organic carbon (WSOCg) comprised of these organic acids ranged from 7 to 100 % with a study average of 30 %. All the organic acids displayed similar strong diurnal behaviors, reaching maximum concentrations between 5 and 7 pm local time. The organic acid concentrations are dependent on ambient temperature, with higher organic acid concentrations being measured during warmer periods.

scholarly journals Effects of Water-soluble Organic Carbon on Aerosol pH

2020 ◽  
Author(s):  
Christopher Hennigan ◽  
Michael Battaglia, Jr. ◽  
Rodney Weber ◽  
Athanasios Nenes
Keyword(s):  
Organic Carbon ◽  
Organic Acids ◽  
Organic Acid ◽  
Fine Particulate Matter ◽  
Dry Mass ◽  
Water Soluble ◽  
Ph Changes ◽  
Water Soluble Organic Carbon ◽  
Soluble Organic Carbon ◽  
Acidic Conditions

&lt;p&gt;Water soluble organic carbon (WSOC) is a ubiquitous and significant fraction of fine particulate matter.&amp;#160; Despite advances in aerosol thermodynamic equilibrium models, there is limited understanding on the comprehensive impacts of WSOC on aerosol acidity (pH).&amp;#160; We address this limitation by studying submicron aerosol that represent the two extremes in acidity levels found in the atmosphere: strongly acidic aerosol from Baltimore, MD, and weakly acidic conditions characteristic of Beijing, China. These cases are then used to construct mixed inorganic/organic single-phase aqueous particles, and thermodynamically analyzed by the E-AIM and ISORROPIA models in combination with activity coefficient model AIOMFAC to evaluate the effects of WSOC on the H&lt;sup&gt;+&lt;/sup&gt; ion activity coefficients (&amp;#947;&lt;sub&gt;H+&lt;/sub&gt;) and activity (pH).&amp;#160; We find that addition of organic acids and non-acid organic species concurrently increases &amp;#947;&lt;sub&gt;H+&lt;/sub&gt; and aerosol liquid water.&amp;#160; Under the highly acidic conditions typical of the eastern U.S. (inorganic-only pH ~1), these effects mostly offset each other, giving pH changes of &lt; 0.5 pH units even at organic aerosol dry mass fractions in excess of 60%.&amp;#160; Under conditions with weaker acidity typical of Beijing (inorganic-only pH ~4.5), the non-acidic WSOC compounds had similarly minor effects on aerosol pH, but organic acids imparted the largest changes in pH compared to the inorganic-only simulations.&amp;#160; Organic acids affect pH in the order of their pKa values (oxalic acid &gt; malonic acid &gt; glutaric acid).&amp;#160; Although the inorganic-only pH was above the pK&lt;sub&gt;a&lt;/sub&gt; value of all three organic acids investigated, pH changes in excess of 1 pH unit were only observed at unrealistic organic acid levels (aerosol organic acid concentrations &gt; 35 &amp;#181;g m&lt;sup&gt;-3&lt;/sup&gt;) in Beijing.&amp;#160; The model simulations were run at 70%, 80%, and 90% relative humidity (RH) levels and the effect of WSOC was inversely related to RH.&amp;#160; At 90% RH, WSOC altered aerosol pH by up to ~0.2 pH units, though the effect was up to ~0.6 pH units at 70% RH.&amp;#160; The somewhat offsetting nature of these effects suggests that aerosol pH is sufficiently constrained by the inorganic constituents alone under conditions where liquid-liquid phase separation is not anticipated to occur.&lt;/p&gt;

scholarly journals Characterization of aerosol composition, aerosol acidity, and organic acid partitioning at an agriculturally intensive rural southeastern US site

2018 ◽  
Vol 18 (15) ◽  
pp. 11471-11491 ◽  
Author(s):  
Theodora Nah ◽  
Hongyu Guo ◽  
Amy P. Sullivan ◽  
Yunle Chen ◽  
David J. Tanner ◽  
...  
Keyword(s):  
Oxalic Acid ◽  
Organic Acids ◽  
Organic Acid ◽  
Organic Aerosol ◽  
Water Soluble ◽  
Molar Concentration ◽  
Particle Phase ◽  
Southeastern Us ◽  
Phase Water ◽  
Acetic Acids

Abstract. The implementation of stringent emission regulations has resulted in the decline of anthropogenic pollutants including sulfur dioxide (SO2), nitrogen oxides (NOx), and carbon monoxide (CO). In contrast, ammonia (NH3) emissions are largely unregulated, with emissions projected to increase in the future. We present real-time aerosol and gas measurements from a field study conducted in an agriculturally intensive region in the southeastern US during the fall of 2016 to investigate how NH3 affects particle acidity and secondary organic aerosol (SOA) formation via the gas–particle partitioning of semi-volatile organic acids. Particle water and pH were determined using the ISORROPIA II thermodynamic model and validated by comparing predicted inorganic HNO3-NO3- and NH3-NH4+ gas–particle partitioning ratios with measured values. Our results showed that despite the high NH3 concentrations (average 8.1±5.2 ppb), PM1 was highly acidic with pH values ranging from 0.9 to 3.8, and an average pH of 2.2±0.6. PM1 pH varied by approximately 1.4 units diurnally. Formic and acetic acids were the most abundant gas-phase organic acids, and oxalate was the most abundant particle-phase water-soluble organic acid anion. Measured particle-phase water-soluble organic acids were on average 6 % of the total non-refractory PM1 organic aerosol mass. The measured molar fraction of oxalic acid in the particle phase (i.e., particle-phase oxalic acid molar concentration divided by the total oxalic acid molar concentration) ranged between 47 % and 90 % for a PM1 pH of 1.2 to 3.4. The measured oxalic acid gas–particle partitioning ratios were in good agreement with their corresponding thermodynamic predictions, calculated based on oxalic acid's physicochemical properties, ambient temperature, particle water, and pH. In contrast, gas–particle partitioning ratios of formic and acetic acids were not well predicted for reasons currently unknown. For this study, higher NH3 concentrations relative to what has been measured in the region in previous studies had minor effects on PM1 organic acids and their influence on the overall organic aerosol and PM1 mass concentrations.

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