Novel analytical approaches to characterizing the composition and source of aerosol brown carbon

Dr. Cora Young, Assistant Professor in the Department of Chemistry at York University, presented their research into the chemical drivers of climate and the fate and transport of contaminants at the SOCAAR Seminar held on January 10th, 2018. The talk gave insights on the molecular composition of brown carbon, aging, and the limitations of mass spectrometry in detection and characterization of brown carbon.

Brown carbon is the water soluble, wavelength-dependent component of aerosols. It can be detected from biomass burning aerosols but its chemical structure is largely uncharacterized. Consequently, climate models typically omit brown carbon because of its uncertainty in source.


Aerosol samples were collected from biomass burning plumes from Vancouver, British Columbia and St. John’s, Newfoundland. Background air aerosol samples from Alabama’s SOAS campaign were also collected for comparison. The brown carbon contained in these samples were analyzed for their structural characteristics using ultra-high resolution mass spectrometry, size-exclusion chromatography coupled to UV/vis and mass spectrometry.


This was the first study to apply size-exclusion chromatography-UV/vis to brown carbon samples and Young showed the prevalence of extremely low volatility organic compounds in brown carbon. She also suggested that most brown carbon is derived from biomass burning because the molecular size distribution of brown carbon compounds were conserved between aerosol samples taken from the different locations. Young conclude that aged brown carbon is dominated by large molecules while single aged biomass burning sample is enriched in submicron particles. The next steps in their research will be to conduct further analyses to understand the chemical composition of brown carbon, characterizing what the chemicals are.

In her talk, Young also spoke about the impact of policy on the arctic deposition of contaminants, specifically the Montreal Protocol that was enacted in 1987.

In the 1960s, there was large scale use of CFCs and they were confirmed to be destroying the stratospheric ozone layer. When the Montreal Protocol was enacted replacement compounds for CFCs, hydrochloric fluorocarbons and hydrofluorocarbons, were adopted. Since then these replacement compounds were also found to be bad for the environment and production on HCFC and HFC were reduced starting in the 2000s.

Young spoke about their study of the high arctic ice caps to understand the record of atmospheric pollution, specifically perfluorocarboxylic acids. They analyzed ice cores collected from the Devon Ice caps in 2015 and were dated back to 1977.

Perfluorocarboxylic acids (PFCAs) are persistent compounds that are found everywhere in the environment, even in the High Arctic which is far from known sources. PFCAs have the potential to impact the ecosystem and have negative health impacts as they are known to bioaccumulate and lead to endocrine disruption. PFCAs are largely produced for the nonstick industry and can be produced from the oxidation of commercial precursor compounds in the atmosphere.

Young concluded that the deposition short-chain PFCAs reflect the changes in emissions and mixing ratios of precursor compounds which are predominantly CFC replacements that are regulated by the Montreal Protocol. The increased regulation and replacement of HCFCs and HFCs through the Montreal Protocol is likely to influence the deposition in the high arctic.