Abstract View
Is It Possible to Overcome the Lack of Authentic Standards in Quantification of Biogenic Secondary Organic Aerosol Tracers?
DANIEL BRYANT, Alfred Mayhew, Sri Hapsari Budisulistiorini, David Topping, Andrew Rickard, Jacqueline Hamilton, University of York
Abstract Number: 38
Working Group: Aerosol Standards
Abstract
Biogenic secondary organic aerosol (BSOA) is a key contributor to organic aerosol and analysis at a molecular level allows a greater understanding of formation pathways and individual compound contributions. Liquid chromatography (LC)/high-resolution mass spectrometry (HRMS) is a powerful technique for targeted and non-targeted analysis of SOA. However, accurate quantification is reliant on authentic standards for which subsets of SOA such as BSOA are limited. Recent studies synthesising authentic BSOA standards show large differences in the ionisation efficiencies of BSOA tracers when using electrospray ionisation. This highlights an important issue with MS aerosol measurements, where direct-injection studies often assume equal ionisation efficiencies for identified species, while some LC-MS studies use proxy standards for different compound classes. Both could lead to significant under/overestimation of the contributions of individual BSOA tracers to aerosol metrics or average BSOA composition. This study aims to establish a method for more reliable quantification of BSOA species without the need for authentic standards.
This study proposes quantification based on the prediction of relative ionisation efficiency (RIE) factors established on chemical structure and properties. RIE’s were determined for 90 authentic standards across a broad range of functionalities, relative to pinonic acid. The RIE’s were coupled to structural descriptors and a random forest model developed to predict the RIE’s of BSOA compounds without authentic standards. BSOA species were then quantified using the predicted RIE factors in samples collected in Beijing. This resulted in a large reduction in the BSOA concentrations measured when compared to using cis-pinonic acid to calibrate the BSOA, with the impacts on common aerosol metrics (O:C, H:C, OSc) discussed. This study provides initial evidence that the structures of BSOA tracers can cause large variability in their ionisation efficiencies, and that future work is needed to develop alternative, synthesis free strategies.