Molecular Characterization of Compounds in Wildfire Smoke

The Science

An estimated 20 percent of phosphorus (P) emitted annually worldwide comes from naturally occurring fires. Although most of this P is not soluble in water directly upon combustion, the insoluble organic phosphorous compounds can take up oxidants as they move through the atmosphere, transforming them into soluble compounds in a process called atmospheric aging. Once the P becomes soluble, it can dramatically affect aquatic ecosystems, leading to algal blooms and oxygen depletion. Now, a team of researchers has determined the molecular composition of organophosphorus compounds in wildfire smoke, and by doing so, they have taken a critical first step in better understanding how wildfires may affect phosphorus cycling and the health of aquatic ecosystems. 

The Impact 

Even tiny changes to the amount of P available in surface waters can have a very large environmental impact. P is an essential nutrient in aquatic ecosystems, but too much P can create harmful algal blooms and cause oxygen depletion. P can only be used by aquatic organisms in certain molecular forms, so knowing the molecular composition of compounds deposited on surface waters has important implications for understanding the biogeochemistry of aquatic environments and their health. Wildfire-influenced aerosols are known to constitute a significant source of P in aquatic environments, but this is the first study to perform a molecular characterization of organophosphorus compounds in wildfire smoke. Because the occurrence of wildfires is predicted to increase with changes to climate and fuel availability, the importance of understanding which compounds are in wildfire-influenced aerosols and how they affect aquatic ecosystems is growing. 

Summary 

Previous studies have shown that significant amounts of phosphorus are emitted during large-scale biomass burning events like wildfires, but scientists have not been able to characterize the complete molecular makeup of biomass burning organic aerosols (BBOAs). One of the primary obstacles has been inadequate instrumentation for the low concentration of organophosphorus compounds in aerosols. To overcome that challenge, a team of researchers used an ultrahigh-resolution, custom-built mass spectrometer at EMSL, the Environmental Molecular Sciences Laboratory, a Department of Energy (DOE) Office of Science user facility. This instrument, a 21 Tesla Fourier transform ion cyclotron resonance (FTICR) mass spectrometer, has the highest field strength of any superconducting magnet-based FTICR mass spectrometer. Team members analyzed a sample of BBOAs collected downwind of wildfires in the Pacific Northwest with unprecedented resolution and sensitivity. They also subjected the sample to less powerful instrumentation and compared results. The more powerful mass spectrometer available from EMSL was able to identify environmentally relevant, phosphorus-bearing molecular groups that were not identified with the less powerful instrumentation. Although groups containing P were a small percentage of the formulas assigned, their identification is important because of how they can affect the biogeochemical balance of aquatic ecosystems. The successful characterization of organophosphorus compounds with EMSL’s instrumentation demonstrates the viability and advantage of ultrahigh-resolution tools for future studies on complex mixtures. 

Contacts 

Amna Ijaz, Michigan Tech University, aijaz@mtu.edu 

Lynn Mazzoleni, Michigan Tech University, lrmazzol@mtu.edu 

William Kew, Environmental Molecular Sciences Laboratory, william.kew@pnnl.gov 

Funding 

This research was performed on a large-scale research project award from the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility sponsored by the Biological and Environmental Research program. Additional support was provided by DOE. 

Publications 

A. Ijaz, et al., “Molecular Characterization of Organophosphorus Compounds in Wildfire Smoke Using 21-T Fourier Transform-Ion Cyclotron Resonance Mass Spectrometry.” Analytical Chemistry, 94 (42), 14537-14545 (2022). [DOI: 10.1021/acs.analchem.2c00916]