Regional Influence of Aerosol Emissions from Wildfires Driven by Combustion Efficiency

Zhang, Q., University of California, Davis

Aerosol Processes

Aerosol Processes

Collier S, S Zhou, T Onasch, D Jaffe, L Kleinman, A Sedlacek, N Briggs, J Hee, E Fortner, J Shilling, D Worsnop, R Yokelson, C Parworth, X Ge, J Xu, Z Butterfield, D Chand, M Dubey, M Pekour, S Springston, and Q Zhang. 2016. "Regional Influence of Aerosol Emissions from Wildfires Driven by Combustion Efficiency: Insights from the BBOP Campaign." Environmental Science & Technology, 50(16), 10.1021/acs.est.6b01617.


Map of the Pacific NW region with two major persistent wildfires highlighted by red circles. Also shown are the MBO ground site location and two G-1 flight tracks.


Organic aerosol emission and oxidation degree as a function of modified combustion efficiency (MCE) observed from MBO and G-1. O/C data is colored by approximate transport time. MCE is an index of combustion process of a fire: Flaming (> 0.9); Smoldering (< 0.9). A strong overlap between the results from MBO (representing more aged emissions) and from G-1 (representing fresher emissions) suggests that regional BBOA characteristics are strongly influenced by combustion processes at the source.


Map of the Pacific NW region with two major persistent wildfires highlighted by red circles. Also shown are the MBO ground site location and two G-1 flight tracks.

Organic aerosol emission and oxidation degree as a function of modified combustion efficiency (MCE) observed from MBO and G-1. O/C data is colored by approximate transport time. MCE is an index of combustion process of a fire: Flaming (> 0.9); Smoldering (< 0.9). A strong overlap between the results from MBO (representing more aged emissions) and from G-1 (representing fresher emissions) suggests that regional BBOA characteristics are strongly influenced by combustion processes at the source.

Science

During our study we found that combustion processes of wildfires strongly influence organic aerosol concentrations and properties on a regional scale and that more flaming burns emit less aerosol mass but more oxidized organic aerosol. We also found that secondary organic aerosol formation in wildfire plumes may have been balanced by primary organic aerosol evaporation, leading to more oxidized aerosol while not significantly enhancing organic mass.

Impact

A detailed understanding of the factors that strongly influence biomass burning emissions on a regional scale is critical in our ability to model it and predict air quality and climate effects more accurately. This is especially important for the Pacific Northwest region of the U.S., which experiences widespread wildfire events during dry and hot periods and is predicted to experience higher rates and intensities of wildfire occurrences in the future due to climate change.

Summary

In this study, the regional and nearfield influences of wildfire emissions on ambient aerosol concentration and chemical properties in the Pacific Northwest region of the United States were studied using real-time measurements from a fixed ground site (~ 2700 m a.s.l.) as well as near their sources using an aircraft. The regional characteristics of biomass burning aerosols were found to depend strongly on the modified combustion efficiency (MCE), an index of the combustion processes of a fire. Organic aerosol emissions had negative correlations with MCE, whereas the oxidation state of organic aerosol increased with MCE and plume aging. The relationships between the aerosol properties and MCE were consistent between fresh emissions (~1 hour old) and emissions sampled after atmospheric transport (6-45 hours), suggesting that biomass burning organic aerosol concentration and chemical properties were strongly influenced by combustion processes at the source and conserved to a significant extent during regional transport. These results suggest that MCE can be a useful metric for describing aerosol properties of wildfire emissions and their impacts on regional air quality and global climate.