Grantee Research Project Results
2018 Progress Report: The Effect of Ammonia on Organic Aerosols in a Changing Climate
EPA Grant Number: R835882Title: The Effect of Ammonia on Organic Aerosols in a Changing Climate
Investigators: Weber, Rodney J. , Ng, Nga Lee , Russell, Armistead G. , Huey, Greg
Current Investigators: Weber, Rodney J. , Russell, Armistead G. , Ng, Nga Lee , Huey, Greg
Institution: Georgia Institute of Technology
EPA Project Officer: Chung, Serena
Project Period: January 1, 2016 through December 31, 2018 (Extended to December 31, 2020)
Project Period Covered by this Report: January 1, 2018 through December 31,2018
Project Amount: $789,261
RFA: Particulate Matter and Related Pollutants in a Changing World (2014) RFA Text | Recipients Lists
Research Category: Air , Climate Change
Objective:
The overall objective of this research is to investigate how changes in emissions of key species that affect aerosol acidity (pH) influence the formation and chemical and physical properties of PM2.5, impacting air quality, human health and climate. A specific research focus is to assess secondary organic aerosol (SOA) formed under enhanced ammonia concentrations.
Progress Summary:
This project has three parts: (1) A field study, (2) an environmental chamber study and (3) an air quality modeling study. The first year of the project focused on the field study. Year 2 focused on analyzing the field study data and performing preliminary chamber studies. Modeling work focused on applying CMAQ to the observations and evaluating the simulated pollutant concentrations against observations taken as part of this project. In Year 3, two papers based on the field study results, were published. One focused on gas phase organic acids the other aerosol phase species and pH effects. Additional field data analysis and smog chamber experiments were conducted. Modeling focused on source of gas phase formic acid.
Field Study: To investigate the effects of ammonia (NH3) on organic aerosols, the SEARCH Yorkville (YRK) network site was selected as the main field study location for this project. A six-week intensive field study was undertaken in late summer when historical data showed highest NH3 concentrations would be expected.
Results from the study showed that for the study period NH3 concentrations were substantially higher than typical for the site, or the southeastern US. The study average NH3 concentration was 4 ppb, roughly double the more typical levels recorded at the site since 2011.
A highly sensitive technique for measuring gas-phase organic acids was developed and then deployed during the field study. These gas phase organic acid data, along with measurements of NH3 and HNO3, were combined with particle phase composition data and a thermodynamic model to predict the aerosol pH and gas-particle partitioning of
inorganic and organic species. PM1 aerosols were found to be highly acidic with pH values ranging from 0.9 to 3.8, with a study-average pH of 2.2 ± 0.6. While previous studies have shown that thermodynamic model predictions can accurately model the gas-particle partitioning of semi-volatile inorganic species (e.g., HNO3-NO3-, HCl-Cl- and NH3-NH4+) as a function of particle pH, predicting gas-particle partitioning behavior of organic species has not been established. Our results showed that the measured oxalic acid gas-particle partitioning ratios generally agreed with the analytical predictions. (Oxalic acid molar fraction in the particle phase ranged from 47 to 90 % at pH 1.2 to 3.4). Formic and acetic acids were the most abundant gas-phase organic acid, and oxalate was the most abundant particle phase organic acid, as has been found at many sites worldwide. Surprisingly, the measured organic acids were very highly correlated (r2=0.92) with the aged organic aerosol (i.e., AMS MO-OOA factor), which comprised roughly 45% of all the organic aerosol. Although the organic acids were correlated with MO-OOA, they made up only 12% of the MO-OOA. This remarkable correlation may provide a clue to how the organic aerosol ages in the atmosphere since the organic acid,
such as oxalate, are expected to be formed exclusively through a liquid phase oxidation route, which may suggest that much of the organic aerosol ages by a similar process. This has major implications and is contrary to current views, which are based on an aging process that depends mainly on gas phase oxidation and partitioning to the organic phase based on volatility, not aqueous phase oxidation and solubility and pH dependent gas/particle partitioning.
Field Study: To investigate the effects of ammonia (NH3) on organic aerosols, the SEARCH Yorkville (YRK) network site was selected as the main field study location for this project. A six-week intensive field study was undertaken in late summer when historical data showed highest NH3 concentrations would be expected.
Results from the study showed that for the study period NH3 concentrations were substantially higher than typical for the site, or the southeastern US. The study average NH3 concentration was 4 ppb, roughly double the more typical levels recorded at the site since 2011.
A highly sensitive technique for measuring gas-phase organic acids was developed and then deployed during the field study. These gas phase organic acid data, along with measurements of NH3 and HNO3, were combined with particle phase composition data and a thermodynamic model to predict the aerosol pH and gas-particle partitioning of inorganic and organic species. PM1 aerosols were found to be highly acidic with pH values ranging from 0.9 to 3.8, with a study-average pH of 2.2 ± 0.6. While previous studies have shown that thermodynamic model predictions can accurately model the gas-particle partitioning of semi-volatile inorganic species (e.g., HNO3-NO3-, HCl-Cl- and NH3-NH4+) as a function of particle pH, predicting gas-particle partitioning behavior of organic species has not been established. Our results showed that the measured oxalic acid gas-particle partitioning ratios generally agreed with the analytical predictions. (Oxalic acid molar fraction in the particle phase ranged from 47 to 90 % at pH 1.2 to 3.4). Formic and acetic acids were the most abundant gas-phase organic acid, and oxalate was the most abundant particle phase organic acid, as has been found at many sites worldwide. Surprisingly, the measured organic acids were very highly correlated (r2=0.92) with the aged organic aerosol (i.e., AMS MO-OOA factor), which comprised roughly 45% of all the organic aerosol. Although the organic acids were correlated with MO-OOA, they made up only 12% of the MO-OOA. This remarkable correlation may provide a clue to how the organic aerosol ages in the atmosphere since the organic acid,
such as oxalate, are expected to be formed exclusively through a liquid phase oxidation route, which may suggest that much of the organic aerosol ages by a similar process. This has major implications and is contrary to current views, which are based on an aging process that depends mainly on gas phase oxidation and partitioning to the organic phase based on volatility, not aqueous phase oxidation and solubility and pH dependent gas/particle partitioning.
Chamber Study: A series of preliminary laboratory experiments were conducted at the Georgia Tech Environmental Chamber (GTEC) facility to investigate the formation and evolution of gas-phase organic acids, focusing on formic acid. The full suite of instruments was not available for the experiments until the end of 2018. This included comprehensive measurements of particle- and gas-phase composition using an AMS, FIGAERO and a Particle-Into-Liquid Sampler coupled to an anion IC (PILS-IC). Aerosol size distributions were measured using a Scanning Mobility Particle Sizer (SMPS). VOC were monitored by a Gas Chromatography Flame Ionization Detector (GC-FID) and specific gas phase organic acids with a CIMS. The suite of instruments is similar to what had been deployed at the YRK field site. Extensive chamber experiments began in the winter of 2018, however, not all instrument were operational due to various malfunctions. It was not until Jan. through Feb. 2019 that the full suite of the experiments could be performed. Preliminary results show that formic acid is a ubiquitous product of biogenic VOC oxidation.
Future Activities:
In year 4 of this project field study date analysis will continue. We anticipate two papers will be submitted based on the AMS and FIGERO data; one paper on the overall field study results and new findings possible from the combined AMS/FIGAERO data sets, and a second paper on the sources of MO-OOA. Analysis and interpreting the chamber experiments will be a major task in year 4. Models will be refined by combing both the field and new chamber data.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 19 publications | 11 publications in selected types | All 11 journal articles |
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Type | Citation | ||
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Nah T, Ji Y, Tanner DJ, Guo H, Sullivan AP, Ng NL, Weber RJ, Huey LG. Real-time measurements of gas-phase organic acids using SF6− chemical ionization mass spectrometry. Atmospheric Measurement Techniques 2018;11: 5087-5104. |
R835882 (2017) R835882 (2018) R835882 (2019) R835882 (Final) |
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Nah T, Guo H, Sullivan AP, Chen Y, Tanner DJ, Nenes A, Russell A, Ng NL, Huey LG, Weber RJ. Characterization of aerosol composition, aerosol acidity and water-soluble organic acids at an agriculture intensive rural southeastern US site. Atmospheric Chemistry and Physics 2018;18:11471-11491. |
R835882 (2018) R835882 (2019) R835882 (Final) |
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Supplemental Keywords:
fine particulates, measurement methods, environmental chemistry, source characterization, Georgia, Southeast, organics, biogenic, biosphere, health effects, human health, air quality modeling, air quality analysis, organic acids, pH, particle acidity, SOA, PM2.5, brown carbon, reactive oxygen species, oxidative potential.Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.