Dramatic shifts in the current hydrologic cycle of the western U.S., evidenced by higher average annual temperatures, earlier snowpack melting, and greater severity of droughts, has created conditions conducive to longer wildfire seasons with higher intensity burns. Every state in the western U.S. has experienced an increase in the average number of large wildfires per year during this decade when compared to the annual averages of the previous two decades. Wildfire events impact downwind air and water quality even across distances thousands of kilometers from the source and long time periods after the fire has stopped, sometimes exacerbating pollution from gas and aerosol emissions from fossil fuel combustion.

We developed a robust high-throughput analytical method for the detection of three monosaccharide anhydrides (MAs) - levoglucosan, mannosan, and galactosan - in low-volume snow, water, and aerosol deposit samples at part per trillion concentrations. This method uses evaporative concentration, derivatization, and gas chromatography tandem mass spectrometry (GC/MS/MS) analysis with isotopic dilution quantification. The three MAs are thermal degradation products of cellulose and hemicellulose generated via combustion of biomass and are widely used as molecular tracers of wildfire and agricultural burning events. These molecules can be transported for thousands of kilometers in the atmosphere (along with other combustion constituents) before dry or wet deposition processes return them to the terrestrial environment. Since these MAs are not generated from fossil fuel combustion, they allow for the specific detection of air masses containing wildfire constituents and appropriate sources of other fire-related atmospheric deposition constituents, such as organic acids, nutrients, and mercury, that affect terrestrial and aquatic ecosystems.

This analytical tool can be used to measure MA concentrations in precipitation and dry deposition samples monitored by the NADP network to help recognize and characterize biomass burning sources of organic acids, nutrients, base cations, and mercury also determined in NADP samples. This expanded analysis approach can be applied to the NADP network to connect atmospheric transport and deposition of key combustion-derived constituents to landscape.