CHEMICAL COMPOSITION, CHARACTERISTICS, SOURCES, AND PROCESS OF FINE PARTICULATE MATTER IN THE CENTRAL VALLEY OF CALIFORNIA.

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 1002107
• Project Start Date: Feb 24, 2014
• Project End Date: Sep 30, 2018
• Program Code: [(N/A)]- (N/A)

Recipient Organization
UNIVERSITY OF CALIFORNIA, DAVIS
410 MRAK HALL
DAVIS,CA 95616-8671

Performing Department
Environmental Toxicology

Non Technical Summary
Atmospheric aerosol particles (a.k.a. particulate matter, PM) are a key determinant of air quality and an important player in the Earth's climate system. Yet, they represent some of the largest uncertainties that limit the understanding of climate change issues and complicate the assessment of air quality and energy policies. Properties that determine aerosol's impacts on climate, environment, and human health are directly linked to the composition of the PM. Specifically, there is critical need to understanding the organic fraction of PM in California in order to develop effective regulatory policies on air quality and emissions in the state. Over the years the state's emission control programs have not reduced the concentrations of ambient OA as rapidly as the reductions in inorganic particulates and black carbon. This means that further PM control may need to focus on OA. Evaluation and improvement of air quality and climate models, which guide the development of regulatory policies, require data-driven phenomenological PM descriptions. In this project, we will perform field and laboratory studies and integrated data analysis to study aerosol composition, sources and processes in the California's Central Valley and share such information publically. Our main objectives include 1) improving understanding of organic aerosol speciation and characterization using state-of-the-art aerosol instruments; 2) investigating the emission sources and life cycle processes of atmospheric fine PM; and 3) characterizing different source regimes of fine PM in the Central Valley, e.g., primary vs. secondary and urban vs. agricultural vs. biogenic vs. biomass burning; and 4) synthesizing our results for model improvement and validation. This research will provide useful new data on inorganic and organic PM in the Central Valley of California. From these data, important insights may be gained on the sources and fates of atmospheric PM. These results may be compared directly to findings from previous studies in the state, most of which were conducted in southern California for a better understanding of regional differences in OA characteristics, sources, and effects within California. Also importantly, since these data represent a self-consistent observation-based PM description, they will have broad application within regional air quality models used to predict the efficiency of emissions control programs. In summary, the results from this research will be of immediate value for developing air quality attainment strategies in California.

Animal Health Component

50%

Research Effort Categories

Basic

50%

Applied

50%

Developmental

0%

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
141	0499	2000	100%

Knowledge Area
141 - Air Resource Protection and Management;

Subject Of Investigation
0499 - Atmosphere, general/other;

Field Of Science
2000 - Chemistry;

Keywords

aerosol research

aerosol radiative forcing

air pollution

atmospheric chemistry

atmospheric transformation and evolution

atmospheric transport

emission sources

environmental chemistry

health effects

mass spectrometry

new particle formation and growth

secondary aerosol production/formation

Goals / Objectives
Atmospheric aerosol particles (a.k.a. particulate matter, PM) are a key determinant of air quality and an important player in the Earth's climate system. Yet, they represent some of the largest uncertainties that limit the understanding of climate change issues and complicate the assessment of air quality policies [IPCC, 2007]. Properties that determine aerosol's impacts on climate, environment, and human health are intrinsically linked to the chemical species composing the particles. Characterizing the chemical composition of atmospheric PM is thus vital to understanding the physico-chemical processes that govern aerosol properties pertinent to climate, air quality, and health. Organic aerosol (OA) represents a major mass fraction of fine PM in California and in many regions globally. But the emission sources, formation mechanisms, and evolution processes of atmospheric OA remain poorly characterized and this knowledge gap has contributed significantly to the very large uncertainties in current model simulations of aerosol climate and health effects. Because the results from model predictions usually guide emission control strategies, an improved understanding of atmospheric organic PM pollution is important to developing effective regulatory policies on air quality and emissions. This is directly relevant to California since over the years the state's emission control programs have not reduced OA loading as rapidly as the reductions in inorganic particulates and black carbon, which means that further fine particle control may need to focus on OA. Development, evaluation, and improvement of air quality and climate models require data-driven phenomenological PM descriptions, especially real time, quantitative, and size-resolved aerosol data such as those acquired with Aerosol Mass Spectrometers (AMS) and a Scanning Mobility Particle Sizer (SMPS). In this project, we will perform field and laboratory studies and integrated data analysis to study aerosol composition, sources and processes in the California's Central Valley. Our main objectives are: 1) Improve organic aerosol speciation and characterization using state-of-the-art aerosol instruments including a High-Resolution Time-of-Flight AMS (HR-ToF-AMS) and a SMPS; 2) Investigate photochemical processing and evolution of atmospheric primary and secondary organic aerosol components; 3) Examine the correlations and the ratios between important pairs of aerosol and gas phase pollutants to investigate different source regimes of fine PM in the Central Valley, e.g., primary vs. secondary, urban vs. agricultural vs. biogenic vs. biomass burning; and 4) Classify OA mass into source- and process-specific types suitable for model improvement and validation.

Project Methods
This project is three pronged. The first focus area of this project is performing detailed and advanced analyses of four highly time- and size-resolved aerosol chemistry datasets acquired with a high-resolution aerosol mass spectrometer (HR-AMS) and a scanning mobility particle sizer (SMPS) acquired recently by Dr. Qi Zhang's group in California:Winter 2010, Fresno, conducted as part of the EPA - the San Joaquin Valley Aerosol Health Effects Research Center (SAHERC) study on aerosol healthSummer 2010, Sacramento and Sierra foothills, conducted as part of DOE Carbonaceous Aerosols and Radiative Effects Study (CARES).Winter 2011, DavisWinter 2013, Fresno, conducted as part of a NASA Earth Venture program funded mission - Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ).Specifically, we will 1) analyze the high resolution mass spectra (HRMS) to determine the bulk chemical and elemental compositions of OA; 2) perform multivariate analyses to the HRMS, chemically-resolved size distributions, and volatility profiles; 3) deconvolute and determine distinct OA types; and 4) relate OA types to different sources and processes based on extensive examinations on their correlations with tracer compounds and other parameters. We will also investigate photochemical processing and evolution of OA properties characteristic to the Central Valley via integrated analyses and focused case studies. Backtrajectory or FLEXPART analyses will be performed to examine plume sources. Photochemical behavior of air-masses will be inferred using VOC oxidation clock and AMS internal indictors such as O/C ratio. Finally, we will collaborate with atmospheric modelers on improvement and validation of models.The second focus area of this project is conducting laboratory studies to identify chemical signatures of primary and secondary organic materials generated in particulate and aqueous phases under controlled experimental conditions. We will focus on characterizing condensed-phase organic substances obtained in controlled environments, e.g., secondary OA produced in smog chambers or via aqueous phase photoreactions of known precursor compounds and primary OA samples collected from known emission sources. These experiments will allow us to identify chemical signatures and reference spectra that may assist the interpretation of ambient measurement data.The final focus area is synthesizing the results and insights generated from the first two focus areas of this research to achieve a holistic understanding of the chemical and physical properties, sources, and transformation processes of fine PM in the Central Valley of California.

Progress 02/24/14 to 09/30/18

Outputs
Target Audience:Federal and state government agencies, such as National Science Foundation, Department of Energy, and California Air Resource Board and general public Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project provided training for three graduate students (Caroline Parworth, Lu Yu, and Wenqing Jiang) and two postdoctoral researchers (Hwajin Kim, Gauri Prabhakar) not only in terms of conducting scientific research but also opportunities to present their research at major scientific conferences. How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? The Central Valley (CV) of California experiences persistent air quality problems associated with elevated particulate matter (PM) concentrations due to anthropogenic emissions, topography, and meteorological conditions. Our goal is to elucidate the various sources and processes affecting the concentration and physico-chemical properties of PM in the CV, thus better inform pollution abatement strategies and improve parameterizations in air quality models. To achieve this goal, we performed five field campaigns in the CV and measured PM composition and physical properties using advanced instruments including a high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), a particle-into-liquid sampler (PILS) - ion chromatograph system, and a scanning mobility particle sizer (SMPS). The field studies were performed: 1) in Fresno during January 2010, as part of the San Joaquin Valley Aerosol Health Effects Research Center (SAHERC) study funded by EPA; 2) at Sacramento and the Sierra foothills during summer 2010, as part of the Carbonaceous Aerosols and Radiative Effects Study (CARES) funded by DOE; 3) in Davis during winter 2011, to study aqueous phase processing of PM; 4) in Fresno during January and February 2013, as part of the Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) campaign funded by NASA; and 5) in Fresno during Dec. 2014 to Jan. 2015, as part of the Brown Carbon and Climatic Effect project funded by the California Air Resources Board (CARB). During this report period (Feb. 24, 2014 - Sept. 30, 2018), we performed extensive analyses of these datasets and characterized the chemical composition and physical properties of fine PM as well as their dynamic variations. We determined the sources and atmospheric processes of PM and studied the atmospheric aging processes of organic aerosols (OA). Our results show that the CV region frequently violates National Ambient Air Quality Standard (NAAQS) for PM during wintertime and that particulate pollutants are comprised primarily of organic compounds and nitrate. High PM pollution during winter was mainly due to elevated OA emitted from primary sources such as vehicle emissions, cooking, and residential wood burning as well as active formation of secondary PM species, such as nitrate and oxygenated organic compounds formed via photochemical and aqueous-phase reactions. Organics account for nearly 50% of the PM mass during wintertime and usually over 80% during summer in the CV, highlighting the importance of understanding OA sources and processes in this region. We investigated the properties and sources of OA characteristic to the CV via integrated data analyses and focused case studies, e.g., via analyzing the source regions of polluted air masses and examining the photochemical behaviors of PM using oxidation clocks and indicators. By comparing observations of aerosol chemistry at Fresno during different winter, we observed large year-to-year variations mainly attributed to changes of meteorological conditions, which influenced primary emissions and secondary aerosol formation. For example, PM concentration in 2013 was on average nearly three times that in 2010 and PM composition was significantly different between the two winters. The much higher OA associated with residential wood combustion in winter 2013 was attributed to colder temperatures which resulted in increased biomass burning activities. In addition, stronger solar radiation in 2013 resulted in greater photochemical production of secondary aerosol species, leading to higher nitrate and secondary organic aerosol (SOA) concentrations. Furthermore, the influence from a nighttime formed residual layer that mixed down in the morning was found to be much more intense in 2013 than 2010, leading to sharp increases in concentrations of secondary aerosol species including nitrate, sulfate, and SOA, in the morning between 08:00 to 12:00. In particular, ammonium nitrate, which is an important fine PM component and contributes to the buildup and sustaining of severe pollution episodes in the CV during wintertime, was produced through both nighttime chemistry and daytime photochemistry. In order to elucidate processes that influence surface nitrate concentrations during pollution events, we analyzed the combined airborne and ground observations of air pollutants made during the DISCOVER-AQ campaign. Our results highlight an important role played by nocturnal chemical production of nitrate aloft in the residual layer (RL) on determining daytime surface-level ammonium nitrate concentrations. The observations also demonstrate that dynamics within the RL can influence the early morning vertical distribution of nitrate, despite low wintertime wind speeds. It is thus important to properly represent nighttime chemistry in air quality models to accurately forecast PM pollution in the CV. Through analyzing data acquired from the CARES study, we found that regional new particle formation and growth events (NPE) were common in the Sacramento and western Sierra Foothills area of California during summertime and that they were driven primarily by the formation of oxygenated organic species and, to a lesser extent, ammonium sulfate. Our study also revealed that the interaction of biogenic emissions in the region with urban plumes from Sacramento and the San Francisco Bay Area has significantly enhanced the NPE in Northern California. Another component of this project is our study on SOA formation from phenols through aqueous phase reactions. Phenols are a group of compounds that are emitted in large quantities from biomass burning. In this study, we investigate the chemical evolution of SOA formed through aqueous reactions of phenolic compounds. Changes in the molecular composition of SOA as a function of aging time are characterized using an offline nanospray desorption electrospray ionization mass spectrometer (nano-DESI MS) whereas the real-time evolution of SOA mass, elemental ratios, and average carbon oxidation state (OSC) are monitored using a HR-ToF-AMS. Our results indicate that oligomerization is an important aqueous reaction pathway for phenols, especially during the initial stage of photooxidation equivalent to ~ 2 hours irradiation under midday, winter solstice sunlight in northern California. At later reaction times functionalization (i.e., adding polar oxygenated functional groups to the molecule) and fragmentation (i.e., breaking of covalent bonds) become more important processes, forming a large variety of functionalized aromatic and open-ring products with higher degree of oxidation. Fragmentation reactions eventually dominate the photochemical evolution of phenolic SOA, forming a large number of highly oxygenated open-ring molecules with carbon numbers (nC) below 6. We also investigated the effects of sulfate and nitrate on the formation and evolution of SOA from photooxidation of phenolic carbonyls. While SOA was formed efficiently in both ammonium sulfate and ammonium nitrate solutions, degradation rates of syringaldehyde and acetosyringone in nitrate solutions were 1.5 and 3.5 times faster than rates in sulfate solutions, and SOA yields in nitrate experiments are twice as high as in sulfate experiments. This work highlights the importance of aerosol-phase nitrate in the formation of SOA by facilitating the degradation of organic precursors. The initially formed SOA had oxygen-to-carbon (O/C) ratios and OSC similar to the precursors, but much more oxidized SOA was formed over the course of photooxidiation, with O/C and OSC reaching 1.2 and 1.1, respectively. Functionalization and oligomerization dominated at the beginning of the reactions, with phenolic oligomers and their derivatives significantly contributing to SOA formation. Oxidation of the first-generation products led to an abundance of oxygenated ring-opening products.

Publications

• Type: Journal Articles Status: Published Year Published: 2018 Citation: Huang, D., Zhang, Q.*, Cheung, H. H. Y., Yu, L., Zhou, S., Anastasio, C., Smith, J. D. and Chan, C. K. (2018) Formation and evolution of aqSOA from aqueous-phase reactions of phenolic carbonyls: comparison between ammonium sulfate and ammonium nitrate solutions, Environ. Sci. Technol. 52, 9215-9224, 19
• Type: Journal Articles Status: Published Year Published: 2014 Citation: Setyan, A., C. Song, M. Merkel, W. B. Knighton, T. B. Onasch, M. R. Canagaratna, D. R. Worsnop, A. Wiedensohler, J. E. Shilling, and Qi Zhang* (2014), Chemistry of new particle growth in mixed urban and biogenic emissions: insights from CARES, Atmos. Chem. Phys., 14, 6477-6494, 10.5194/acp-14-6477-2014
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Lupascu, A., Easter, R., Zaveri, R., Shrivastava, M., Pekour, M., Tomlinson, J., Yang, Q., Matsui, H., Hodzic, A., Zhang, Q., and Fast, J. D.* (2015) Modeling particle nucleation and growth over northern California during the 2010 CARES campaign, Atmos. Chem. Phys., 15, 12283-12313, 10.5194/acp-15-12283-2015
• Type: Journal Articles Status: Published Year Published: 2016 Citation: Zhang, X. L., Kim, H., Parworth, C. L., Young, D., Zhang, Q., Metcalf, A. R., Cappa, C. D.*, Optical Properties of Wintertime Aerosols from Residential Wood Burning in Fresno, CA: Results from DISCOVER-AQ 2013 (2016) Environmental Science and Technology, 50, 1681-1690, 10.1021/acs.est.5b04134.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: Collier, S., Williams, L. R., Onasch, T. B., Cappa, C. D., Zhang, X., Russell, L. M., Chen, C.-L., Sanchez, K. J., Worsnop, D. R., and Zhang, Q.* (2018) Influence of emissions and aqueous processing on particles containing black carbon in a polluted urban environment: Insights from a Soot Particle - Aerosol Mass Spectrometer, Journal of Geophysical Research: Atmospheres, 123, 6648-6666, 10.1002/2017JD027851.

Progress 10/01/16 to 09/30/17

Outputs
Target Audience:Federal and state government agencies, such as National Science Foundation, Department of Energy, and California Air Resource Board and general public. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project provided training for two graduate students (Caroline Parworth and Wenqing Jiang) and a postdoctoral researcher (Gauri Prabhakar not only in terms of conducting scientific research but also opportunities to present their research at major scientific conferences. How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals?We will complete the analysis of SP-AMS data on BC-containing particles

Impacts
What was accomplished under these goals? The San Joaquin Valley (SJV) in California experiences persistent air quality problems associated with elevated particulate matter (PM) concentrations due to anthropogenic emissions, topography, and meteorological conditions. It is important to unravel the various sources and processes affecting the physico-chemical properties of PM to better inform pollution abatement strategies and improve parameterizations in air quality models. During January and February 2013, we performed comprehensive, highly time resolved measurements of PM as part of the NASA's Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) campaign. Measurements were made using two real-time instruments including a High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and a particle-into-liquid sampler (PILS) coupled with two ion chromatographs. Our observations indicate that ammonium nitrate (NH4NO3) makes up a major fraction of fine particle mass in the SJV during wintertime and that both nighttime chemistry and daytime photochemistry can increase surface-level nitrate concentrations and contribute to the buildup and sustaining of severe pollution episodes in the region (Parworth et al., 2017;Young et al., 2016). In order to better understand the various processes that impact surface nitrate concentrations during pollution events, we have analyzed the combined airborne and ground observations of air pollutants made during the DISCOVER-AQ campaign. Our results highlight an important role played by nocturnal chemical production of nitrate aloft in the residual layer (RL) on determining daytime surface-level ammonium nitrate concentrations. The observations also demonstrate that dynamics within the RL can influence the early morning vertical distribution of nitrate, despite low wintertime wind speeds (Prabhakar et al., 2017). In December 2014 and January 2015, we performed another field study in Fresno, focusing on understanding the physical and chemical characteristics of atmospheric soot particles and their associated coatings using a soot-particle aerosol mass spectrometer (SP-AMS). This study was motivated by that fact that various combustion processes can emit inhalable particles containing black carbon (BC), a graphitic substance with properties highly relevant to climate change and respiratory health. Often BC particles are coated with other materials derived from the same combustion source or added in the atmosphere as these particles age. This coating material can have profound effects on the behavior, properties and longevity of BC. In this study we deployed the SP-AMS to selectively analyze particles containing BC and investigate their coating, concentration and composition in real-time in Fresno, CA in wintertime. Our results indicate that the properties of BC particles were found to be mainly controlled by emission sources but were also significantly influenced by humid meteorological conditions. This work was written in an article submitted to Journal of Geophysical Research - Atmospheres (Collier et al., 2017). During this report period, two manuscripts from above mentioned works have been published (Prabhakar et al., 2017;Parworth et al., 2017) and one was submitted for peer-review (Collier et al., 2017): References: Collier, S., Williams, L. R., Onasch, T. B., Cappa, C. D., Zhang, X., Russell, L. M., Chen, C.-L., Sanchez, K. J., Worsnop, D. R., and Zhang, Q.: Influence of emissions and atmospheric processing on particles containing black carbon in a polluted urban environment: Insights from a soot particle - aerosol mass spectrometer, Journal of Geophysical Research - Atmospheres (submitted), 2017. Parworth, C. L., Young, D. E., Kim, H., Zhang, X., Cappa, C. D., Collier, S., and Zhang, Q.: Wintertime water-soluble aerosol composition and particle water content in Fresno, California, Journal of Geophysical Research: Atmospheres, 122, 3155-3170, 10.1002/2016JD026173, 2017. Prabhakar, G., Parworth, C. L., Zhang, X., Kim, H., Young, D. E., Beyersdorf, A. J., Ziemba, L. D., Nowak, J. B., Bertram, T. H., Faloona, I. C., Zhang, Q., and Cappa, C. D.: Observational assessment of the role of nocturnal residual-layer chemistry in determining daytime surface particulate nitrateconcentrations, Atmos. Chem. Phys., 17, 14747-14770, 10.5194/acp-17-14747-2017, 2017. Young, D. E., Kim, H., Parworth, C., Zhou, S., Zhang, X., Cappa, C. D., Seco, R., Kim, S., and Zhang, Q.: Influences of emission sources and meteorology on aerosol chemistry in a polluted urban environment: results from DISCOVER-AQ California, Atmos. Chem. Phys., 16, 5427-5451, 10.5194/acp-16-5427-2016, 2016.

Publications

• Type: Journal Articles Status: Published Year Published: 2017 Citation: Prabhakar, G., Parworth, C., Zhang, X., Kim, H., Young, D., Beyersdorf, A. J., Ziemba, L. D., Nowak, J. B., Bertram, T. H., Faloona, I. C., Zhang, Q., and Cappa, C. D.* (2017) Observational assessment of the role of nocturnal residual-layer chemistry in determining daytime surface particulate nitrate concentrations, Atmos. Chem. Phys., 17, 14747-14770, 10.5194/acp-17-14747-2017
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Parworth, C. L., Young, D. E., Kim, H., Zhang, X., Cappa, C. D., Collier, S., and Zhang, Q* (2017) Wintertime water-soluble aerosol composition and particle water content in Fresno, California: Results from DISCOVER-AQ 2013, Journal of Geophysical Research - Atmospheres, 122(5), 3155-3170, 10.1002/2016JD026173.

Progress 10/01/15 to 09/30/16

Outputs
Target Audience:Federal and state government agencies, such as National Science Foundation, Department of Energy, and California Air Resource Board and general public Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project provided training for two graduate students (Lu Yu and Caroline Parworth) and a postdoctoral researcher (Dominique Young) not only in terms of conducting scientific research but also opportunities to present their research at major scientific conferences. How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? The San Joaquin Valley (SJV) in California experiences persistent air quality problems associated with elevated particulate matter (PM) concentrations due to anthropogenic emissions, topography, and meteorological conditions. It is important to unravel the various sources and processes affecting the physico-chemical properties of PM to better inform pollution abatement strategies and improve parameterizations in air quality models. During January and February 2013, we installed a ground supersite at the Fresno-Garland California Air Resources Board (CARB) monitoring station and performed comprehensive, real-time measurements of PM using instruments including a High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and a particle-into-liquid sampler (PILS) coupled with two ion chromatographs as part of the NASA's Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) campaign. We determined that the average submicron aerosol (PM1) concentration was 31.0 µg m-3 and the mass was dominated by organic aerosols (OA, 55%) and ammonium nitrate (39%). High PM pollution events were commonly associated with elevated OA concentrations, mostly from primary sources such as vehicle emissions (9%), cooking (28%), and residential wood burning (33%). Oxygenated organic compounds formed via chemical reactions in the atmosphere contributed 40% to the total OA mass. Relatively strong solar radiation in the winter of 2013 resulted in greater photochemical production of secondary aerosol species, leading to higher nitrate and secondary organic aerosol (SOA) concentrations. As part of this project, the chemical composition and concentrations of water-soluble gases and ionic aerosol components were also measured using a Particle-Into-Liquid Sampler with Ion Chromatography (PILS-IC) and annular denuders. Particle water was calculated based on E-AIM thermodynamic prediction of inorganic particle water and κ-Köhler theory approximation of organic particle water. Our results show that ionic aerosol mass is dominated by NH4NO3 and that NH4NO3 production is limited by HNO3 availability. Residential wood burning is a source of ionic aerosols including K+ and glycolate, sea spray is a source of Na+, Cl-, and dimethylamine, and vehicles are a source for formate. Particle water is most abundant during early morning and night hours and is primarily controlled by inorganic composition and relative humidity. During this project period, we continued our study on SOA formation through aqueous phase reactions of phenols -- a group of compounds that are emitted in large quantities from biomass burning. Understanding these reactions is important for a predictive understanding of atmospheric aging of aerosols and their impacts on climate, air quality, and human health. In this study, we investigate the chemical evolution of aqueous secondary organic aerosol (aqSOA) formed during reactions of phenolic compounds with two oxidants - the triplet excited state of an aromatic carbonyl (3C*) and hydroxyl radical (•OH). Changes in the molecular composition of aqSOA as a function of aging time are characterized using an offline nanospray desorption electrospray ionization mass spectrometer (nano-DESI MS) whereas the real-time evolution of SOA mass, elemental ratios, and average carbon oxidation state (OSC) are monitored using an online aerosol mass spectrometer (AMS). Our results indicate that oligomerization is an important aqueous reaction pathway for phenols, especially during the initial stage of photooxidation equivalent to ~ 2 hours irradiation under midday, winter solstice sunlight in northern California. At later reaction times functionalization (i.e., adding polar oxygenated functional groups to the molecule) and fragmentation (i.e., breaking of covalent bonds) become more important processes, forming a large variety of functionalized aromatic and open-ring products with higher OSC values. Fragmentation reactions eventually dominate the photochemical evolution of phenolic aqSOA, forming a large number of highly oxygenated ring-opening molecules with carbon numbers (nC) below 6. The average nC of phenolic aqSOA decreases while average OSC increases over the course of photochemical aging. In addition, the saturation vapor pressures (C*) of dozens of the most abundant phenolic aqSOA molecules are estimated. A wide range of C* values is observed, varying from < 10-20 ?g m-3 for functionalized phenolic oligomers to > 10 ?g m-3 for small open-ring species. The detection of abundant extremely low volatile organic compounds (ELVOC) indicates that aqueous reactions of phenolic compounds are likely an important source of ELVOC in the atmosphere. Two manuscripts from these works have been published in the "Atmospheric Chemistry and Physics" journal in 2016: 1. Young, D., Kim, H. J., Parworth, C., Zhou, S., Zhang, X. L., Cappa, C., Seco, R., Kim, S., and Zhang, Q.: Influences of emission sources and meteorology on aerosol chemistry in a polluted urban environment: Results from DISCOVER-AQ California, Atmospheric Chemistry & Physics, 16, 5427-5451, 10.5194/acp-16-5427-2016. 2. Yu, L., Smith, J., Laskin, A., George, K. M., Anastasio, C., Laskin, J., Dillner, A. M., and Zhang, Q.: Molecular transformations of phenolic SOA during photochemical aging in the aqueous phase: Competition among oligomerization, functionalization, and fragmentation, Atmospheric Chemistry & Physics, 16, 4511-4527, 10.5194/acp-16-4511-2016. In addition, one manuscript was submitted to and is currently under review in the "Journal of Geophysical Research": Parworth, C. L., Young, D. E., Kim, H., Zhang, X., Cappa, C. D., Collier, S., and Zhang, Q.: Wintertime water-soluble aerosol composition and particle water content in fresno, california: Results from discover-aq 2013, Journal of Geophysical Research - Atmospheres (submitted), 2016.

Publications

• Type: Journal Articles Status: Published Year Published: 2016 Citation: Young, D., Kim, H. J., Parworth, C., Zhou, S., Zhang, X. L., Cappa, C., Seco, R., Kim, S., and Zhang, Q.* (2016) Influences of emission sources and meteorology on aerosol chemistry in a polluted urban environment: Results from DISCOVER-AQ California, Atmospheric Chemistry & Physics, 16, 5427-5451, 10.5194/acp-16-5427-2016. http://www.atmos-chem-phys.net/16/5427/2016/acp-16-5427-2016.pdf
• Type: Journal Articles Status: Published Year Published: 2016 Citation: Yu, L., Smith, J., Laskin, A., George, K. M., Anastasio, C., Laskin, J., Dillner, A. M., and Zhang, Q.* (2016) Molecular transformations of phenolic SOA during photochemical aging in the aqueous phase: Competition among oligomerization, functionalization, and fragmentation. Atmospheric Chemistry & Physics, 16, 4511-4527, 10.5194/acp-16-4511-2016
• Type: Journal Articles Status: Under Review Year Published: 2017 Citation: Parworth, C. L., Young, D. E., Kim, H., Zhang, X., Cappa, C. D., Collier, S., and Zhang, Q*.: Wintertime water-soluble aerosol composition and particle water content in Fresno, California: Results from DISCOVER-AQ 2013, Journal of Geophysical Research - Atmospheres (submitted), 2016.

Progress 10/01/14 to 09/30/15

Outputs
Target Audience:Federal and state government agencies, such as National Science Foundation, Department of Energy, and California Air Resource Board and general public Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project has provided training for a graduate student (Lu Yu) and a postdoctoral researcher (Dominique Young) not only in terms of conducting scientific research but also opportunities to present their research at major scientific conferences. How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals?We will continue to study the chemical properties of atmospheric particles and fog waters in the Central Valley of California in order to better understand the air pollution problem in the region.

Impacts
What was accomplished under these goals? The San Joaquin Valley (SJV) in California experiences persistent air quality problems associated with elevated particulate matter (PM) concentrations due to anthropogenic emissions, topography, and meteorological conditions, thus it is important to unravel the various sources and processes affecting the physico-chemical properties of PM in order to better inform pollution abatement strategies and improve parameterizations in air quality models. During January and February 2013, we installed a ground supersite at the Fresno-Garland California Air Resources Board (CARB) monitoring station and performed comprehensive, real-time measurements of PM using instruments including a High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and a particle-into-liquid sampler (PILS) coupled with two ion chromatographs as part of the NASA's Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) campaign. We determined that the average submicron aerosol (PM1) concentration was 31.0 µg m-3 and that the total mass was dominated by organic aerosols (OA, 55%), followed by nitrate (27%). High PM pollution events were commonly associated with elevated OA concentrations, mostly from primary sources such as vehicle emissions (9%), cooking (28%), and residential wood burning (33%). We also found that oxygenated organic compounds were formed via chemical reactions in the atmosphere and that these compounds contributed 40% to the total OA mass. By comparing to observations of aerosol chemistry at Fresno in winter 2010, which had been performed at a nearby location with partial support from AES, we found that aerosol concentration was nearly three times higher in 2013 than 2010. These variations were attributed to differences in the meteorological conditions between 2010 and 2013 which influenced primary emissions and secondary aerosol formation. In particular, PM concentrations from cooking and residential wood combustion were greater in 2013 than 2010, where colder temperatures in 2013 likely resulted in increased biomass burning activities. Stronger solar radiation in 2013 resulted in greater photochemical production of secondary aerosol species, leading to higher nitrate and secondary organic aerosol (SOA) concentrations. In addition, the influence from a nighttime formed residual layer that mixed down in the morning was found to be much more intense in 2013 than 2010, leading to sharp increases in concentrations of secondary aerosol species including nitrate, sulfate, and SOA, in the morning between 08:00 to 12:00. This is an indication that nighttime chemistry might be also higher in 2013. During this project period, we continued our study on SOA formation through aqueous phase reactions of phenols -- a group of compounds that are emitted in large quantities from biomass burning. Understanding these reactions is important for a predictive understanding of atmospheric aging of aerosols and their impacts on climate, air quality, and human health. In this study, we investigate the chemical evolution of aqueous secondary organic aerosol (aqSOA) formed during reactions of phenolic compounds with two oxidants - the triplet excited state of an aromatic carbonyl (3C*) and hydroxyl radical (•OH). Changes in the molecular composition of aqSOA as a function of aging time are characterized using an offline nanospray desorption electrospray ionization mass spectrometer (nano-DESI MS) whereas the real-time evolution of SOA mass, elemental ratios, and average carbon oxidation state (OSC) are monitored using an online aerosol mass spectrometer (AMS). Our results indicate that oligomerization is an important aqueous reaction pathway for phenols, especially during the initial stage of photooxidation equivalent to ~ 2 hours irradiation under midday, winter solstice sunlight in northern California. At later reaction times functionalization (i.e., adding polar oxygenated functional groups to the molecule) and fragmentation (i.e., breaking of covalent bonds) become more important processes, forming a large variety of functionalized aromatic and open-ring products with higher OSC values. Fragmentation reactions eventually dominate the photochemical evolution of phenolic aqSOA, forming a large number of highly oxygenated open-ring molecules with carbon numbers (nC) below 6. The average nC of phenolic aqSOA decreases while average OSC increases over the course of photochemical aging. In addition, the saturation vapor pressures (C*) of dozens of the most abundant phenolic aqSOA molecules are estimated. A wide range of C* values is observed, varying from < 10-20 mg m-3 for functionalized phenolic oligomers to > 10 mg m-3 for small open-ring species. The detection of abundant extremely low volatile organic compounds (ELVOC) indicates that aqueous reactions of phenolic compounds are likely an important source of ELVOC in the atmosphere. Two manuscripts from these works have been completed and are currently under review for publication in the "Atmospheric Chemistry and Physics" journal: 1. Young, D., Kim, H. J., Parworth, C., Zhou, S., Zhang, X. L., Cappa, C., Seco, R., Kim, S., and Zhang, Q.: Influences of emission sources and meteorology on aerosol chemistry in a polluted urban environment: Results from DISCOVER-AQ California, Atmospheric Chemistry & Physics Discussions, 15, 35057-35115, 10.5194/acpd-15-35057-2015, 2015. 2. Yu, L., Smith, J., Laskin, A., George, K. M., Anastasio, C., Laskin, J., Dillner, A. M., and Zhang, Q.: Molecular transformations of phenolic SOA during photochemical aging in the aqueous phase: Competition among oligomerization, functionalization, and fragmentation, Atmospheric Chemistry & Physics Discussions, 15, 29673-29704, 10.5194/acpd-15-29673-2015, 2015.

Publications

• Type: Journal Articles Status: Under Review Year Published: 2015 Citation: Young, D., Kim, H. J., Parworth, C., Zhou, S., Zhang, X. L., Cappa, C., Seco, R., Kim, S., and Zhang, Q.: Influences of emission sources and meteorology on aerosol chemistry in a polluted urban environment: Results from DISCOVER-AQ California, Atmospheric Chemistry & Physics Discussions, 15, 35057-35115, 10.5194/acpd-15-35057-2015, 2015.
• Type: Journal Articles Status: Under Review Year Published: 2015 Citation: Yu, L., Smith, J., Laskin, A., George, K. M., Anastasio, C., Laskin, J., Dillner, A. M., and Zhang, Q.: Molecular transformations of phenolic SOA during photochemical aging in the aqueous phase: Competition among oligomerization, functionalization, and fragmentation Atmospheric Chemistry & Physics Discussions, 15, 29673-29704, 10.5194/acpd-15-29673-2015, 2015.

Progress 02/24/14 to 09/30/14

Outputs
Target Audience: Federal and state government agencies, such as National Science Foundation, Department of Energy, and California Air Resource Board and general public Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? This project has provided training for a graduate student (Lu Yu) and a postdoctoral researcher (Sonya Collier) not only in terms of conducting scientific research but also opportunities to present their research at major scientific conferences. How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals? We will continue to study the aqueous phase chemistry of phenolic compounds under atmospheric relevant conditions. A near term goal is to understand the atmospheric aging and chemical illumination of phenolic secondary organic aerosols in fog and cloud waters.

Impacts
What was accomplished under these goals? Biomass burning is an important source of air pollutants including primary particulate matter (PM) and chemical precursors of ozone (O3) and secondary PM. Emissions from wildfires and residential wood combustion are particularly intense in California during summer and winter, respectively, affecting air quality on both local and regional scales. Phenolic compounds are emitted in large amounts from biomass burning. These compounds have high Henry's Law constants and can partition significantly into atmospheric aqueous phases which include cloud and fog drops and water-containing aerosol. Once in aqueous phase, phenols can undergo fast reactions to form secondary organic aerosol (aqSOA) with close to 100% mas yield. For these reactions, aqueous phase reactions of phenolic compounds may play crucial roles controlling the concentration, composition, physical and chemical properties, and toxicity of atmospheric PM, especially during periods influenced by biomass burning emissions. During this project period, we thoroughly characterized the chemical composition and studied the volatility and optical properties of phenolic aqSOA formed via reactions with two different oxidants: 3C* and •OH. Elemental analysis indicates that all phenolic aqSOA are highly oxidized (O/C ratios: 0.85-1.23), despite the fact that some of the reactions were very fast (t1/2 < 1 hr for syringol). For the same oxidant, the oxidation degree of the aqSOA formed at t1/2 follows the order: phenol > guaiacol > syringol. A large number of aqSOA molecules are identified, including oligomers (up to hexamers) and their derivatives with varying numbers of carbonyl, carboxyl, ester, and hydroxyl groups. A large number of ring-opening species (nC < 6) including small organic acids (e.g., oxalate, formate, and acetate) are also identified. The physical properties, such as volatility and light absorptivity, of the phenolic aqSOA depend on their chemical compositions. Our thermodenuder experiments indicate that the volatility profiles of phenolic aqSOA are influenced by both oligomer contents and average oxidation degree. In addition, the formation of aqSOA species with enhanced conjugated double bonds is probably responsible for the significant light absorption in the actinic region, suggesting that aqueous-phase reactions of phenols are an important source of brown carbon in the atmosphere. Overall, our results indicate that aqueous-phase processing of phenols represents an important pathway for the production of low-volatility, highly oxygenated and high molecular weight species, which remain in the particle phase after water evaporation. Since phenolic aqSOA is both water soluble and light absorbing, understanding the impacts of these reactions on the chemical and physical properties, and thus the climatic and health effects, of atmospheric particles may be important, especially in regions influenced by biomass burning emissions A manuscript that describes this work was published in the "Atmospheric Chemistry and Physics" journal: "Yu, L., Smith, J., Laskin, A., Anastasio, C., Laskin, J., and Zhang, Q.: Chemical characterization of SOA formed from aqueous-phase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical, Atmos. Chem. Phys., 14, 13801-13816, 10.5194/acp-14-13801-2014, 2014." We disseminated our findings by participating and presenting at an international conference - the 2014 American Association of Aerosol Research conference at Orlando, FL

Publications

• Type: Journal Articles Status: Published Year Published: 2014 Citation: Yu, L., Smith, J., Laskin, A., Anastasio, C., Laskin, J., and Zhang, Q.: Chemical characterization of soa formed from aqueous-phase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical, Atmos. Chem. Phys., 14, 13801-13816, 10.5194/acp-14-13801-2014, 2014.