Center for Environmental Research and Technology

Join us for a presentation and defense by Afsara Tasnia, as she defends her Ph.D. thesis at the Center for Environmental Research and Technology (CE-CERT).

Details: May 31st, 2024 @ 1:30 PM, CE-CERT RM 105 and Zoom (https://ucr.zoom.us/j/91274953047 Meeting ID: 912 7495 3047)

Title: From Climate Change in the Arctic to Urban Air Quality in the LA Basin: Using Advanced Chromatography to Fingerprint Biogenic and Anthropogenic Sources of Gaseous Organic Carbon

Abstract: Volatile organic compounds (VOCs) contribute to ozone (O3) and secondary organic aerosol (SOA) formation and thus contribute to poor air quality and play an important role in climate radiative forcing. The identities and quantities of VOCs depend largely on their sources and atmospheric conditions. The effects of VOCs on air quality and climate also depend on their relative reactivity with atmospheric oxidants. Developing unique VOC profiles, or fingerprints, across a range of environments will lead to better understanding of the sources and drivers of VOC emissions and their atmospheric feedbacks. A unifying focus of this research is the measurement and analysis of VOCs using two-dimensional gas chromatography with time-of-flight mass spectrometry (GCxGC-TOFMS) from three different regions:

(i) remote (North Slope Alaska). Ambient biogenic VOCs were identified and quantified in the Arctic. Samples were collected from Utqiagvik, Alaska for one week in summer 2022 and for one month in summer 2023. Quantified VOCs will be used in future modelling studies to predict O3 and OA formation from these species in this remote environment and to predict changes in biogenic VOCs, O3, and SOA with changing climate.

(ii) western pine forest (Blodgett Forest Research Station). VOCs from prescribed burns (pyrogenic VOCs) in a western pine forest were identified and quantified in samples collected over four days in spring 2021. Emission factors (EFs) were calculated and then compared with existing databases. Sensitivity tests were performed using a widely used fire and smoke model FOFEM. Model results were compared with measurements to evaluate and improve model capability to predict smoke emissions from prescribed burns.

(iii) urban (Los Angeles Basin). Anthropogenic and biogenic VOCs were identified and quantified from urban samples collected during the Los Angeles Air Quality Campaign (LAAQC). Samples were collected in Pasadena, CA from April-July 2020, covering the COVID-19 shelter-in-place orders, and again from April-August 2022 accounting for post COVID-19 restrictions. Speciated VOC data and supplementary meteorological data were used to evaluate changes in dominant emissions sources and to differentiate biogenic and anthropogenic sources of a family of compounds known as terpenoids.

Each of these measurement campaigns resulted in a unique GCxGC-TOFMS dataset that provided information about local emissions sources, chemistry, and atmospheric feedbacks. For example, in samples from the Arctic, biogenic terpenoids were identified, along with some unique compounds that are emitted by stressed plants. In samples from the Los Angeles Basin, compounds from anthropogenic and biogenic sources were observed and are likely to play a role in local chemistry. The emission factors calculated from the prescribed burn measurements were consistent with an existing database, but included four times more compounds than that database. Landcover based fuel loading inputs into the FOFEM fire model resulted in an underprediction of smoke emissions and input EFs introduced additional uncertainty for VOCs. The research conducted in the LA Basin provided robust observations of a shift in dominant combustion sources from on-road mobile to off-road mobile, and in an emerging area of research, provided evidence for biogenic and anthropogenic terpenoids in the LA Basin and insights in differentiating terpenoids from these sources.