Grantee Research Project Results
Final 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. , 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 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 was to investigate how changes in emissions of key species that affect aerosol acidity (pH), such as sulfate and ammonia, influence the formation (mass) and the chemical and physical properties of PM2.5. A specific research focus was to assess secondary organic aerosol (SOA) formed under enhanced ammonia concentrations. To meet these objectives, the project supported reseach focsing on chacterizing gas and particle phase organic acids based on an intensive field study at a rural site. Tangential projects also evolved from this research, including investigating the effects of changes in sulfate on aerosol composition in the southeastern US on aerosol toxicity, modeling pH throughout the continental USA, understanding the role of water-soluble organic species to fine particle pH, and the further development of Chemical Ionization Mass Spectroscopy (CIMS) technology.
Summary/Accomplishments (Outputs/Outcomes):
The research effort for this project had two major parts: a field study and data analysis/air quality modeling. The first year of the project focused on the field study. Analysis of the data generated from the field study then occurred over the remaining years. The result of this effort is the publication of eight papers, an additional one currently in review and one still in progress (see publication list below). Our findings are summarized as follows:
To investigate the effects of ammonia (NH3) on organic aerosols, the SEARCH Yorkville (YRK) network site was selected as the field study location due to anticipated high and varying ammonia concentrations. A six-week field study was conducted from Aug. 15, 2016 to Sept. 30, 2016. The site and study period were chosen based on an analysis of YRK historical NH3 data that showed periodic high NH3 concentrations due to air mass advection from nearby confined animal feeding operation (CAFO). The period of late summer was also chosen since it included anticipated periods of high temperature-driven biogenic volatile organic compound (VOC) emissions and also a transition period toward lower emissions moving into the cooler season in September.
Two relatively new instruments were deployed at Yorkville for the field intensive study, a chemical ionization mass spectrometer utilizing SF-6 ion chemistry (SF-6 CIMS) for online measurements of gas- phase organic acids and a Filter Inlet for Gases and AEROsols coupled to a high-resolution time-of-flight iodide-adduct chemical ionization mass spectrometer (FIGAERO-CIMS) for online measurements of particle and gas phase organic acids. For each instrument, a description and the instruments, data inversion, and example results from Yorkville are discussed in two separate papers (Nah et al, 2018a and Chen et al., 2020). The SF-6 CIMS provided one of the most comprehensive measurements of a suite of gas phase organic acids in any field study to date. This work demonstrated that SF−6 could be used to measure a range of organic acids in the relatively remote continental atmosphere. One-hour averaged ambient concentrations of organic acids at the site ranged from a few parts per trillion by volume (ppt) to several parts per billion by volume (ppb), with formic and acetic acid being the most abundant. All measured organic acids displayed similar strong diurnal behaviors, reaching maximum concentrations between 17:00 and 19:00 local time (eastern daylight time). The organic acid concentrations were found to be dependent on ambient temperature, with higher organic acid concentrations measured during warmer periods. Our results suggested that the primary sources of organic acids at Yorkville were biogenic in nature. Direct biogenic emissions of organic acids and/or their BVOC precursors were likely enhanced at high ambient temperatures, resulting in the observed variability of organic acid concentrations.
These gas phase concentrations were then combined with simultaneous measurements of the same organic acids in the aeosol particle phase to investigated how NH3 affected particle acidity and secondary organic aerosol (SOA) formation via the gas–particle partitioning of semi-volatile organic acids (Nah et al., 2018b). Particle water and pH were determined using the suite of measured gas and aeorsol ionic species and the ISORROPIA II thermodynamic model and validated by comparing predicted inorganic HNO3-NO3- and NH3-NH4+ gas–particle partitioning ratios with measured values. We found 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. Although formic and acetic acids were the most abundant gas-phase acids, 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 physico-chemical 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.
To further understand the formation of organic acid aerosols, and to place their concentrations in the larger context of the overall secondary organic aerosol (SOA) at the Yorkville site, data from two on-line mass spectrometry instruments, the high-resolution time-of-flight aerosol mass spectrometer (AMS) and FIGAERO-CIMS, were analyzed together (Chen et al., 2020). Through analysis of speciated organics data from FIGAERO-CIMS and factorization analysis of data obtained from both instruments, we observed notable SOA formation from isoprene and monoterpenes during both day and night. Specifically, in addition to isoprene epoxydiols (IEPOX) uptake, we identified isoprene SOA formation via hydroxyl hydroperoxide oxidation (ISOPOOH oxidation via non-IEPOX pathways) and isoprene organic nitrate formation via photooxidation in the presence of NOx and nitrate radical oxidation. Monoterpenes were found to be the most important SOA precursors at night. We observed significant contributions from highly-oxidized acid-like compounds to the aged OA factor from FIGAERO-CIMS. Taken together, our results showed that FIGAERO-CIMS measurements are highly complementary to the extensively used AMS factorization analysis, and together they provide more comprehensive insights into OA sources and composition.
We then investigated the sources of the low molecular weight carboxylic acids in fine aerosol particles through comparison with secondary organic aerosol (SOA) tracers. We found that isoprene was the most important local precursor for all five low molecular weight carboxylic acids, but via different pathways. We propose that monocarboxylic acids (formic and acetic acids) were mainly formed through gas-phase photochemical reactions, while dicarboxylic acids (oxalic, malonic, and succinic acids) were predominantly from aqueous processing. Unexpectedly high concentrations of particle-phase formic and acetic acids (in the form of formate and acetate, respectively) were observed and likely the components of long-range transport of OA, decoupled from their gas-phase counterparts. In addition, an extraordinarily strong correlation (R2 = 0.90) was observed between particulate the low molecular weight carboxylic acids and aged SOA, which we tentatively attribute to boundary layer dynamics. This work is currently in review (Chen et al., 2021)
As noted, our findings show that isoprene oxidation is likely a major source of formic acid, in agreement with some earlier studies. However, model simulations currently are biased low when predicting formic acid, suggesting some unknown process or source is not well represented in the models. Through our ongoing modeling study (Gao et al, 2021, paper still in progress) we have evaluated the effect of model sinks and sources on acid concentration by running a variety of scenarios with the purpose of determining if emissions or reactions are the main sources of organic acids. First, photolytic reactions between isoprene and monoterpenes were added to the model, leading to a negligible increase in acid concentrations. Proof-of-concept heterogeneous reactions between OH and isoprene epoxydiols (IEPOX) were incorporated into the model, which increased the simulated formic acid by 150%, though the diurnal profile was not similar to what we observed at Yorkville. Comparing measurements to model results, daytime emission rates for formic acid were increased by a factor, which yielded a profile closer to that which had been observed. Further, we investigated the increased deposition of formic acid at night, mimicking the potential removal of formic acid by dew formation, which further improved the predicted diurnal profile. Our findings indicate that direct emission and deposition can explain why the model exhibits the low bias.
Ancillary topics also evolved from this funding:
Chemical ionization mass spectrometers (CIMS) require a method to ionize reagent species. This is most often done with radioactive sources. Severe restrictions on the storage and transport of these sources, and the required training of personnel operating these instruments containing the sources, highly complicates field deployments. Through partial funding from this project two new methods were developed to minimize these issues.
Most I--CIMS (iodide-CIMS) for measurement of atmospheric trace gases, such as organic acids, utilize a radioactive ion source with an initial activity of 10 or 20 mCi of 210Po. Lee et al. (2020) characterized a 210Po ion source with an initial activity of 1.5 mCi that could be easily constructed from commercially available components. The low level of radioactive activity of this source significantly reduces complications with storage and shipping relative to higher activity sources. Ji et al. (2020) developed a new ion source (IS) utilizing vacuum ultraviolet (VUV) light and characterized its use with iodide- chemical ionization mass spectrometers (I--CIMS). The VUV-IS utilizes a compact krypton lamp that emits light in two wavelength bands corresponding to energies of ~10.0 and 10.6 eV. The VUV light photoionizes either methyl iodide (ionization potential, IP = 9.54 ± 0.02 eV) or benzene (IP = 9.24378 ± 0.00007 eV) to form cations and photoelectrons. The electrons react with methyl iodide to form I- which serves as the reagent ion for the CIMS. The VUV-IS is characterized by measuring the sensitivity of a quadrupole CIMS (Q-CIMS) to formic acid, molecular chlorine, and nitryl chloride under a variety of flow and pressure conditions. The sensitivity of the Q-CIMS, with the VUV-IS, reached up to ~700 Hz pptv-1, with detection limits of less than 1 pptv for a one-minute integration period. The reliability of the Q-CIMS with a VUV-IS was demonstrated with data from a month-long ground-based field campaign. The VUV-IS was further tested by operation on a high-resolution time-of-flight CIMS (TOF-CIMS). Sensitivities greater than 25 Hz pptv-1 were obtained for formic acid and molecular chlorine, which were similar to that obtained with a radioactive source. In addition, the mass spectra from sampling ambient air were cleaner with the VUV-IS on the TOF-CIMS compared to measurements using a radioactive source. These results demonstrate that the VUV lamp is a viable substitute for radioactive ion sources on I--CIMS systems for most applications. In addition, the VUV-IS can likely be extended to other reagent ions, such as SF6- which are formed from high IP electron attachers, by the use of absorbers such as benzene to serve as a source of photoelectrons.
The second spin-off study investigated the link between transition metal ions and aerosol pH (Wong et al. 2020). Transition metal ions, such as water-soluble iron (WS-Fe), are toxic components of fine particulate matter (PM2.5). In Atlanta from 1998 to 2013, WS-Fe was the PM2.5 species most associated with adverse cardiovascular outcomes in a previous study. We examined this data set to investigate the sources of WS- Fe and effects of air quality regulations on ambient levels of WS-Fe through particle water and pH. We find insoluble forms of iron in mineral and road dust combined with sulfate from coal-fired electrical generating units were converted to soluble forms by sulfate-driven acid-dissolution. Sulfate produced both the highly acidic aerosol (summer pH 1.5-2) and liquid water required for the aqueous phase acid- dissolution, but variability in WS-Fe was mainly driven by particle liquid water. These processes were more pronounced in summer when particles were most acidic, whereas in winter the relative importance of WS-Fe from combustion emissions increased. Although WS-Fe constituted a minute fraction of PM2.5 mass (0.15%), the WS-Fe-PM2.5 mass correlation was high (r=0.67) and may be explained by these formation routes, which in part, could account for observed associations between PM2.5 mass and adverse health seen in past studies. Similar processes are expected in many regions, implying these unexpected benefits from coal-burning reduction may be widespread.
Also related to pH, through partial funding from this project Lawal et al. (2018) investigated the effect of emission reductions in sulfur and nitrogen oxide in the USA on PM2.5 acidity through an extensive modeling study. The findings of this work supported an earlier study that showed these emission reductions have not significantly changed fine particle pH, however, it extended these findings to a larger geographical region. Battaglia et al. (2019) performed a detailed thermodynamic analysis of the effect of water- soluble organic carbon (WSOC) on aerosol pH, also through partial funding from this project. They found that the main effects of WSOC on pH are through particle water concentration and the H+ ion activity coefficient and that these two effects are largely offsetting making the effects of WSOC on pH minor in many regions.
References:
Battaglia Jr., M. A., Weber, R. J., Nenes, A., and Hennigan, C. J. Effects of water-soluble organic carbon on aerosol pH, 19, 14607–14620, https://doi.org/10.5194/acp-19-14607-2019, 2019.
Chen, Y., Takeuchi, M., Nah, T., Xu, L., Canagaratna, M. R., Stark, H., Baumann, K., Canonaco, F., Prévôt, A. S. H., Huey, L. G., Weber, R. J., and Ng, N. L. Chemical characterization of secondary organic aerosol at a rural site in the southeastern US: insights from simultaneous high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and FIGAERO chemical ionization mass spectrometer (CIMS) measurements, 20, 8421–8440, https://doi.org/10.5194/acp-20-8421-2020, 2020.
Chen, Y., H. Guo, T. Nah, D. J. Tanner, A. P. Sullivan, M. Takeuchi, Z. Gao, P. Vasilakos, A. G. Russell, K. Baumann, L. G. Huey, R. J. Weber, and N. L. Ng, Low-molecular-weight carboxylic acids in the Southeastern U. S.: Formation, partitioning, and implications for organic aerosol aging, Environ. Sci.
Technol. , in review, 2021.
Gao, Z., P. Vasilakos, T. Nah, M. Takeuchi, D. J. Tanner, N. L. Ng, L. G. Huey, R. J. Weber, and A. Russell, Emissions, reactions or bidirectional surface transfer to dew? Gas phase formic acid in the atmosphere, Atmos. Environ., in progress 2021.
Guo, H., Otjes, R., Schlag, P., Kiendler-Scharr, A., Nenes, A., and Weber, R. J. Effectiveness of ammonia reduction on control of fine particle nitrate, 18, 12241–12256, https://doi.org/10.5194/acp-18-12241-2018, 2018.
Ji, Y., Huey, G., Tanner, D. J., Lee, Y. R., Veres, P. R., Neuman, J. A., Wang, Y., and Wang, X. A vacuum ultraviolet ion source (VUV-IS) for iodide-chemical ionization mass spectrometry: a substitute for radioactive ion sources, Atmos. Meas. Tech., 13, 3683–3696, https://doi.org/10.5194/amt-13-3683-2020, 2020.
Lawal, A. S., Guan, X., Liu, C., Henneman, L. R. F., Vasilakos, P., Bhogineni, V., Weber, R. J., Nenes, A., and Russell, A. G. Linked response of aerosol acidity and ammonia to SO2 and NOx emissions reductions in the United States, Environ. Sci. Technol., 52, 9861–9873, https://doi.org/10.1021/acs.est.8b00711, 2018.
Lee, Y. R., Ji, Y., Tanner, D. J., and Huey, L. G. A low-activity ion source for measurement of atmospheric gases by chemical ionization mass spectrometry, Atmos. Meas. Tech., 13, 2473–2480, https://doi.org/10.5194/amt-13-2473-2020, 2020.
Nah, T., Ji, Y., Tanner, D. J., Guo, H., Sullivan, A. P., Ng, N. L., Weber, R. J., and Huey, L. G. Real-time measurements of gas-phase organic acids using SF6− chemical ionization mass spectrometry, 11, 5087–5104, https://doi.org/10.5194/amt-11-5087-2018, 2018a.
Nah, T., Guo, H., Sullivan, A. P., Chen, Y., Tanner, D. J., Nenes, A., Russell, A., Ng, N. L., Huey, L. G., and Weber, R. J. Characterization of aerosol composition, aerosol acidity, and organic acid partitioning at an agriculturally intensive rural southeastern US site, 18, 11471–11491, https://doi.org/10.5194/acp-18-11471-2018, 2018b.
Wong, J. P. S., Yang, Y., Fang, T., Mulholland, J. A., Russell, A. G., Ebelt, S., Nenes, A., and Weber, R. J. Fine particle iron in soils and road dust Is modulated by coal-fired power plant sulfur, Environ. Sci. Technol., 54, 7088–7096, https://doi.org/10.1021/acs.est.0c00483, 2020.
Journal Articles on this Report : 11 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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Chen Y, Guo H, Nah T, Tanner DJ, Sullivan AP, Takeuchi M, Gao Z, Vasilakos P, Russell AG, Baumann K, Huey LG, Weber RJ, Ng NL. Low-molecular-weight carboxylic acids in the southeastern U.S.: Formation, partitioning, and implications for organic aerosol aging. Environmental Science & Technology 2021. doi:10.1021/acs.est.1c01413. |
R835882 (Final) |
not available |
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Guo H, Otjes R, Schlag P, Kiendler-Scharr A, Nenes A, Weber RJ. Effectiveness of ammonia reduction on control of fine particle nitrate. Atmospheric Chemistry and Physics 2018;18:12241–56. doi:10.5194/acp-18-12241-2018. |
R835882 (Final) |
not available |
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Lawal AS, Guan X, Liu C, Henneman LRF, Vasilakos P, Bhogineni V, Weber RJ, Nenes A, Russell AG. Linked response of aerosol acidity and ammonia to SO2 and NOX emissions reductions in the United States. Environmental Science & Technology 2018;52(17):9861-9873. |
R835882 (Final) R835880 (2017) R835880 (2018) R835880 (Final) |
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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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Nenes A, Pandis SN, Kanakidou M, Russell AG, Song S, Vasilakos P, Weber RJ. Aerosol acidity and liquid water content regulate the dry deposition of inorganic reactive nitrogen. Atmospheric Chemistry and Physics 2021;21:6023–33. doi:10.5194/acp-21-6023-2021. |
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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Battaglia Jr MA, Weber RJ, Nenes A, Hennigan CJ. Effects of water-soluble organic carbon on aerosol pH. Atmospheric Chemistry and Physics 2019;19:14607–20. doi:10.5194/acp-19-14607-2019. |
R835882 (Final) |
Exit |
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Wong JPS, Yang Y, Fang T, Mulholland JA, Russell AG, Ebelt S, Nenes A, Weber RJ. Fine particle iron in soils and road dust Is modulated by coal-fired power plant sulfur. Environmental Science & Technology 2020;54:7088–96. doi:10.1021/acs.est.0c00483. |
R835882 (Final) |
Exit Exit |
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Lee YR, Ji Y, Tanner DJ, Huey LG. A low-activity ion source for measurement of atmospheric gases by chemical ionization mass spectrometry. Atmospheric Measurement Techniques 2020;13:2473–80. doi:10.5194/amt-13-2473-2020. |
R835882 (Final) |
Exit |
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Ji Y, Huey G, Tanner DJ, Lee YR, Veres PR, Neuman JA, Wang Y, Wang X. A vacuum ultraviolet ion source (VUV-IS) for iodide-chemical ionization mass spectrometry:a substitute for radioactive ion sources. Atmospheric Measurement Techniques 2020;13:3683–96. doi:10.5194/amt-13-3683-2020. |
R835882 (Final) |
Exit |
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Chen Y, Takeuchi M, Nah T, Xu L, Canagaratna MR, Stark H, Baumann K, Canonaco F, Prévôt ASH, Huey LG, Weber RJ, Ng NL. Chemical characterization of secondary organic aerosol at a rural site in the southeastern US:insights from simultaneous high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and FIGAERO chemical ionization mass spectrometer (CIMS) measurements. Atmospheric Chemistry and Physics 2020;20:8421–40. doi:10.5194/acp-20-8421-2020. |
R835882 (Final) |
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Supplemental Keywords:
aerosols, particles, pH, acidity, organic acids, CIMS, soluble metalsProgress 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.
Project Research Results
- 2019 Progress Report
- 2018 Progress Report
- 2017 Progress Report
- 2016 Progress Report
- Original Abstract
11 journal articles for this project