Title: Observations of Peroxyacyl Nitrates in polluted and remote troposphere
Location: L1114 and https://gatech.zoom.us/j/93059161414 (https://bit.ly/3JO77sh)
Time: 11:00–13:00 Eastern Time, July 20th, 2023
Committee members: Dr. Greg Huey (Advisor), Dr. Nga Lee Ng, Dr, Pengfei Liu, Dr. Jennifer Kaiser and Dr. James Roberts
Abstract
Emissions of volatile organic compounds (VOCs) and their photooxidation with nitrogen oxides (NOx) play a significant role in atmospheric chemistry and have substantial effects on air quality. Understanding these processes in the ambient environments is a challenge, in part, due to uncertainties in emission sources and the complex chemical evolution of emissions. This dissertation leverages a comprehensive suite of ground-based and airborne observations to investigate the impacts of VOCs-NOx photochemistry on atmospheric trace gas compositions, both in heavily polluted and pristine environments. In particular, this work focuses on observations of peroxyacyl nitrates (PANs) to provide a detailed diagnosis of photochemistry in the regions discussed throughout the dissertation.
East Asian countries such as South Korea and China have experienced severe air pollution problems. In this work, extensive observations of primary and secondary pollutants were conducted in two locations: a remote ground site in the Yellow River Delta, China, during the Ozone Photochemistry and Export from China Experiment (OPECE) in 2018, and a petrochemical producing region in South Korea during the Korea-United States Air quality (KORUS-AQ) campaign in 2016. Our findings during the field observations indicated that both regions are characterized by heterogeneous VOC composition with substantial emissions of alkenes and aromatics. Photooxidation of these VOCs led to efficient ozone production in a radical-limited environment. In addition, elevated levels of peroxyacetic nitric anhydride (PAN), as well as rarely measured homologs such as peroxybenzoic nitric anhydride (PBzN) and peroxyacrylic nitric anhydride (APAN), illustrated the unique atmospheric chemistry in East Asian environments.
This dissertation presents global-scale airborne observations of PAN from the NASA DC-8 research aircraft during the ATmospheric Tomography (ATom) campaign. The focus of this investigation was on PAN observations in remote tropospheric regions such as over the Pacific and Atlantic Oceans. We found that PAN over remote oceans is significantly influenced by relatively simple sources including anthropogenic and biomass burning emissions. Notably, biomass burning has a dominant and persistent impact on the global distribution of PAN. Based on a diagnostic evaluation using observations, this work suggests that accurate model treatment of biomass burning can improve prediction of PAN in the remote troposphere.
Lastly, the characterization of a low-activity 210Po ion source with an initial activity of 1.5 mCi was performed for use with iodide-chemical ionization mass spectrometry (I--CIMS). We demonstrated that the low activity source is a viable substitute of higher activity radioactive source,
offering advantages in terms of reduced regulatory burden during storage and shipping. The performance of the low activity source is illustrated using airborne measurements of PANs during the ATom campaign.