Grantee Research Project Results
Final Report: Effects of Ammonia on Secondary Organic Aerosol Formation in a Changing Climate
EPA Grant Number: R835881Title: Effects of Ammonia on Secondary Organic Aerosol Formation in a Changing Climate
Investigators: Dabdub, Donald , Nizkorodov, Sergey
Institution: University of California - Irvine
EPA Project Officer: Chung, Serena
Project Period: January 1, 2016 through December 31, 2018 (Extended to December 31, 2021)
Project Amount: $701,304
RFA: Particulate Matter and Related Pollutants in a Changing World (2014) RFA Text | Recipients Lists
Research Category: Air , Climate Change
Objective:
- Study the reactive uptake of NH3 by SOA in chamber experiments and the effects of temperature, humidity, and NH3 levels on the yields of nitrogen-containing organic compounds (NOC)
- Conduct box model simulations of chamber experiments on NOC
- Introduce new mechanism of formation of NOC in an urban three-dimensional air quality model
- Quantify the effects of changing meteorological conditions and background concentrations due to climate change on SOA and brown carbon concentrations at urban level
- Introduce a simplified SOA chemical mechanism into a coupled meteorological-air quality model for the entire contiguous United States
- Quantify the effects of changing meteorological conditions and background concentrations due to climate change on SOA and NOC at continental scale and estimate the feedback effects of brown carbon on meteorological conditions
Summary/Accomplishments (Outputs/Outcomes):
Task 1: Study the reactive uptake of NH3 by SOA in chamber experiments. Teflon chamber experiments of oxidation of common anthropogenic organic compounds followed by uptake of ammonia or common amines were performed. In addition, uptake on aerosol produced by photooxidation of biogenic organic compounds was investigated. The effects of humidity in the presence of ammonia were studied.
Task 2: Conduct box model simulations of chamber experiments. Well-established existing box model (modules) were updated to reflect the findings from chamber experiments. Parameterization of reactive uptake of NH3 by SOA were added to modules to account for the formation of nitrogen-containing organic compounds.
Task 3: Introduce new mechanism of formation of nitrogen-containing organic compounds (NOC) in an urban three-dimensional air quality model. Updated computational modules were incorporated into urban air models. Modules were used to study systematically the impact of various parameters. The perturbation parameters considered included: (1) temperature; (2) absolute humidity; (3) biogenic VOC emissions due to temperature changes; and (4) boundary conditions.
Task 4: Quantify the effects of climate change on SOA and NOC concentrations at urban level. Simulations performed at the urban level show that NH3 emissions exhibit global implications. Furthermore, NH3 emissions have shown increasing trends over the last few decades and are expected to increase even more in the future. Our studies modeled several future scenarios based on various expected emission growth.
Task 5: Introduce a simplified SOA chemical mechanism into a coupled meteorological-air quality model. The potential meteorology and air quality impacts of the heterogeneous uptake of NH3 by SOA were investigated using the WRF-CMAQ two-way coupled model, which calculates the two-way radiative forcing feedback caused by aerosol between meteorology and chemistry in a single simulation.
Task 6: Quantify the effects of climate change on SOA and NOC concentrations in the entire US. We performed simulations with and without the NH3-SOA uptake over the contiguous US for July 2014 and July 2050 under the IPCC-predicted scenarios to study the potential impact of climate change. The impact of the uptake on fine atmospheric aerosols was quantified. As a result of uptake, NH3 levels were reduced. Thus, the study was able to quantify the impact of increases in particle acidity, which is itself produced by changes in climate when ammonia uptake is considered. Finally, we study the impact of ammonia uptake on other aspects of air pollution, such as ozone levels.
Conclusions:
Our experimental studies summarized in Smith et al. (2021) focused on the uptake of ammonia (NH3) or dimethylamine (DMA) by secondary organic aerosol (SOA) particles generated via photooxidation or ozonolysis of limonene and α-cedrene (biogenic VOCs) as well as SOA generated by photooxidation of toluene (anthropogenic VOC). In addition to the acid-base equilibrium uptake, NH3 and DMA can react with SOA carbonyl compounds converting them into nitrogen-containing organic compounds (NOCs). A clever approach was invented by us making it possible to quantify the rate of growth of NOC in particles by using organic seed particles containing nitrogen for internal calibration. The effective reactive uptake coefficients for the formation of NOCs from ammonia were measured on the order of 10-5. The observed DMA reactive uptake coefficients ranged from 10-5 to 10-4. Typically, the reactive uptake coefficient decreased with increasing relative humidity. Our experimental findings suggest that the reaction of NH3 with carbonyls in the SOA resulting in the loss of water is an important pathway in the uptake of NH3 by SOA. A side result of these studies was an important observation that the composition of low-NOx toluene SOA depends on the RH under which it is produced (Hinks et al. 2018). Oligomers produced by condensation reactions were observed in higher concentrations in the mass spectra of toluene SOA produced under low RH and were suppressed under high RH conditions.
Science learned from chamber experiments was implemented in computer models at various scales. Modeling efforts in this project have focused on the development and implementation of a novel chemical mechanism to simulate the reactive uptake of ammonia by SOA. This process has not been included in any previous air quality models (except ours). We used a variety of air quality modeling tools, including the UCI-CIT model to simulate air quality at the urban scale, CMAQ (version 5.2) model to simulate air quality at the continental scale, and WRF-CMAQ (version 5.2) two-way coupled model to simulate meteorological-air quality two-way feedbacks.
Our modeling work assumed that the yield of nitrogen-containing organic compounds (NOC) due to reactions between ammonia and SOA remain in the particles and do not cause a significant increase in the mass concentration of particulate organics. In these reactions, carbonyl groups are first converted into primary imines, and further reactions lead to more stable secondary imines and heterocyclic compounds (Laskin et al., 2015). The uptake of NH3 is accompanied by loss of one or several water molecules, and the molecular weight and volatility of the NOC product should not be too different from those of the starting SOA compound, as observed in laboratory experiments by Liu et al. (2015).
Based on this assumption, we modeled the bulk NH3 loss due to its uptake by SOA at the beginning of each model timestep without directly impacting SOA concentrations, leaving other gas-aerosol interactions to step in afterward. In our models, all particles were considered spherical and internally mixed, which implies a homogeneous distribution of all chemical substances within the particle. However, as the uptake coefficient used in this study was measured from pure SOA particles, how the uptake coefficient could be changed with SOA mass ratios within the particle is unknown. In the absence of better information, we assumed that the uptake coefficient is proportional to the SOA mass fraction within the particle. In general, the uptake of NH3 by SOA was calculated based on the representative wet surface area concentration of SOA (SSOA) and the reactive uptake coefficient γ . The calculation of SSOA is based on the SOA mass ratios within the particle. The detailed SSOA calculation can be found in our peer-reviewed publications: Horne et al. (2018) for the UCI-CIT model and Zhu et al. (2018) for the CMAQ model. The effective first-order rate constant for the NH3 uptake by SOA is calculated as follows:
k=γ×vNH3×SSOA/4
where vNH3 is the average speed of NH3 molecules (609 ms-1 at 298 K). This first-order rate constant is then multiplied by the gas-phase NH3 concentration to determine the loss rate of NH3 in each grid cell at each time step. At the start of the project, the existing laboratory data were still insufficient to determine the exact uptake coefficient for individual SOA species, a range of uptake coefficients γ was selected for sensitivity studies in our work: 10−5 to 10−2 for the UCI-CIT model, 10−5 to 10−3 for the CMAQ study and 10−3 for the WRF-CMAQ study. Specifically, we implemented the limitation that the yield of NOC from reactions between ammonia and SOA compounds cannot exceed 10%, based on laboratory evidence (Liu et al., 2015; Horne et al., 2018).
The NH3-SOA uptake mechanism was first integrated into the UCI-CIT model for a series of sensitivity tests over the South Coast Air Basin of California (SoCAB) with a 5 km x 5 km resolution for a 3-day episode (August 27-29). Results indicate that the chemical uptake of NH3 by SOA can reduce the concentration of gas-phase ammonia, thereby reducing the potential to form ammonium nitrate and ammonium sulfate in the particle phase, with peak reductions in PM2.5 concentrations ranging from 5 µg/m3 in the g=10-5 scenario to 15 µg/m3 in the g=10-2 scenario. This study has been published in Atmospheric Environment (Horne et al., 2018). Then, the same mechanism was incorporated into the AERO6 model of CMAQ (version 5.2) with CB06 as the gas-phase mechanism, and several sensitivity studies were conducted over the continental US (12km x 12 km) and China (27 km x 27 km) for two months in winter (January and February) and two months in summer (July and August) to study seasonal influence. Meteorological fields were downscaled from NCEP FNL reanalysis data (the year 2011 for US and 2017 for China) using the WRFv3.9.1 model. For the US study, emissions were generated based on the 2014 National Emissions Inventory (NEI) and processed by the SMOKEv4.5. Biogenic emissions were obtained from the BEIS3, and emissions from cars, trucks, and motorcycles were calculated with MOBILE6. For the China study, we used MEGANv2.1 for biogenic emission and the Multi-resolution Emission Inventory for China (MEIC, available at http://meicmodel.org/) 2016 for anthropogenic emission.
Overall, the results from the CMAQ studies agree with those predicted by the UCI-CIT model, which showed that the uptake of NH3 by SOA can cause significant reductions in modeled gas-phase NH3 concentrations. Based on the coefficient range from 10-5 to 10-3, the corresponding spatially averaged reductions in gas-phase NH3 concentrations during the summer period were -8.7% to -67.0% for the US and -2% to - 27.5% for China. Similarly, during the winter period the reductions were -2.3% to ‑29.5% for the US and -4.8% to -19.0% for China. The largest reduction of NH3 and PM2.5 occurs over California's Central Valley for the US study and over the North China Plain for the China study. Moderate impacts of NH3 and PM2.5 can be observed over the upper Mississippi River Basin and North Carolina for the US study and the Sichuan Basin for the China study. Significant impacts on NH3 and PM2.5 concentration related to wildfire sources are also highlighted during the summer period in the US study. For model performance evaluation, after including the uptake mechanism, the overestimation of PM2.5 was reduced for the winter period of the US study and the summer period of the China study. Also, the best model performance of NH3 was found for the summer period US study when the uptake coefficient was set to 10-4. Moreover, significant increases in isoprene-epoxydiols derived SOA are observed due to the enhanced acid-catalyzed ring-opening reactions, especially over the southeastern US during the summer period. This is caused by increased particle acidity, as aerosol pH decreases due to the reduction in ammonium concentrations. The US study has been published in Atmospheric Chemistry and Physics, and the China study has been published in the Journal of Geophysical Research: Atmospheres.
Additional sensitivity studies were conducted based on the WRF-CMAQ two-way coupled model, which calculates the two-way radiative forcing feedback caused by aerosol between meteorology and chemistry in a single simulation. Simulations with and without the NH3-SOA uptake are performed over the contiguous US for July 2014 and July 2050 under the RCP 8.5 IPCC scenario to study the potential impact of climate change. A comparison with multiple observation network data shows that the NH3-SOA uptake improves the model performance for PM2.5 prediction (bias reduced from ‑22% to ‑17%), especially the underestimation of organic carbon over the Southeastern US (bias reduced from ‑17% to ‑7%). Secondly, the addition of the NH3-SOA chemistry significantly impacts the concentration of NH3 and NH4+, thus affecting the modeled particle acidity. Including the NH3-SOA uptake also impacts the meteorological conditions through the WRF-CMAQ two-way feedback. Moreover, the impact on meteorological conditions results in different windspeed or dispersion conditions, thus affecting air quality predictions. Finally, simulations including the NH3-SOA uptake under the warmer climate conditions of 2050 show a smaller impact on air quality predictions than under the current climate conditions. This study has been accepted for publication in Frontiers in Environmental Science.
California-based (4 km x 4 km) modeling studies were also conducted to improve the understanding between the emissions inventory, climate change and air quality impact. These studies included one sensitivity analysis to investigate the potential impact of an underestimated VOC inventory on air quality, especially for impacts on SOA concentrations which are the base for the NH3 uptake mechanism. The result of this study has been published in Atmospheric Environment. Additionally, a comprehensive study was conducted using the CMAQ model during the third period to quantify the effect of climate change on pollutant concentrations at a regional level under different mitigation policies. This study has been accepted for publication in in Environment International.
References:
Li, Yong Jie, Pengfei Liu, Zhaoheng Gong, Yan Wang, Adam P. Bateman, Clara Bergoend, Allan K. Bertram, and Scot T. Martin. 2015. “Chemical Reactivity and Liquid/Nonliquid States of Secondary Organic Material.” Environmental Science and Technology 49 (22): 13264–74. https://doi.org/10.1021/acs.est.5b03392.
Journal Articles on this Report : 4 Displayed | Download in RIS Format
Other project views: | All 47 publications | 12 publications in selected types | All 11 journal articles |
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Smith N, Montoya-Agullera J, Dabdub D, Nizkorondov S. Effect of Humidity on the Reactive Uptake of Ammonia and Dimethylamine by Nitrogen-Containing Secondary Organic Aerosol. ATMOSPHERE 2021;12(11):1502. |
R835881 (Final) |
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Yao Y, Dawson M, Dabdub D, Reimer N. Evaluating the Impacts of Cloud Processing on Respended Aerosol Particles After Cloud Evaporation using a Particle-Resolved Model. JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 2021;126(24):e2021JD034992. |
R835881 (Final) |
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Zhu S, Horne JR, Montoya-Aguilera J, Hinks ML, Nizkorodov SA, Dabdub D. Modeling reactive ammonia uptake by secondary organic aerosol in CMAQ:application to continental US. Atmospheric Chemistry and Physics 2018;18(5):3641-3657. |
R835881 (2017) R835881 (2018) R835881 (2020) R835881 (Final) |
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Zhu S, Wu K, Nizkorodov S, Dabdub D. Modeling Reactive Ammonia Uptake by Secondary Organic Aerosol in a Changing Climate:A WRF-CMAQ Evaluation. FRONTIERS IN ENVIRONMENTAL SCIENCE 2022;10:867908. |
R835881 (Final) |
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Supplemental Keywords:
air, ambient air, atmosphere, ozone, global climate, tropospheric, VOC, oxidants, nitrogen oxides, organic, environmental chemistry, engineering, modelingRelevant Websites:
None
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.
Project Research Results
- 2020 Progress Report
- 2019 Progress Report
- 2018 Progress Report
- 2017 Progress Report
- 2016 Progress Report
- Original Abstract
11 journal articles for this project