Analysis of aerosol composition data for western United States wildfires between 2005 and 2015: Dust emissions, chloride depletion, and most enhanced aerosol constituents

Abstract

This study examines major wildfires in the western United States between 2005 and 2015 to determine which species exhibit the highest percent change in mass concentration on day of peak fire influence relative to preceding nonfire days. Forty‐one fires were examined using the Environmental Protection Agency (EPA) Interagency Monitoring of Protected Visual Environments (IMPROVE) data set. Organic carbon (OC) and elemental carbon (EC) constituents exhibited the highest percent change increase. The sharpest enhancements were for the volatile (OC1) and semivolatile (OC2) OC fractions, suggestive of secondary organic aerosol formation during plume transport. Of the noncarbonaceous constituents, Cl, P, K, NO3−, and Zn levels exhibited the highest percent change. Dust was significantly enhanced in wildfire plumes, based on significant enhancements in fine soil components (i.e., Si, Ca, Al, Fe, and Ti) and PMcoarse (i.e., PM10–PM2.5). A case study emphasized how transport of wildfire plumes significantly impacted downwind states, with higher levels of fine soil and PMcoarse at the downwind state (Arizona) as compared to the source of the fires (California). A global model (Navy Aerosol Analysis and Prediction System, NAAPS) did not capture the dust influence over California or Arizona during this case event because it is not designed to resolve dust dynamics in fires, which motivates improved treatment of such processes. Significant chloride depletion was observed on the peak EC day for almost a half of the fires examined. Size‐resolved measurements during two specific fires at a coastal California site revealed significant chloride reductions for particle aerodynamic diameters between 1 and 10 μm.

A Decadal Climatology of Chemical, Physical, and Optical Properties of Ambient Smoke in the Western and Southeastern United States

“…Chen et al (2010) showed the release of NO x was also related to combustion condition, with more NO x from the flaming phase and more NH 3 from the smoldering phase. Schlosser et al (2017) also found the concentrations of nitrate, fine soil, and coarse particles increased on peak EC days, that is, their defined smoke-impact days in the western United States from 2005 and 2015, consistent with our results. Other notable differences in the smoke aerosol composition between the two western regions and the SE are the sulfate and soil fractions.…”

“…This may also explain a greater enhancement of nitrate in the western regions (1.1% in the PW and 1.6% in the SW), where flaming fires may dominate, compared to the SE (0.69%). Schlosser et al (2017) determined smokeimpacted days as days with high EC (mean + 2σ for the 10-week period centered around this day), while our method uses the overlap with HMS and further restricts "smoky days" to the subset with high PM 2.5 loadings (> mean + σ for our selected April-September time frame). The sulfate fraction is 18% in the SE and only 1-3% in the two western regions, which may be due to fuel differences, as discussed earlier.…”

“…However, we are only aware of one study that quantifies a climatology of ambient smoke aerosol composition through long-term surface-based observations (Schlosser et al, 2017). Schlosser et al (2017) used longterm observations of Interagency Monitoring of Protected Visual Environments (IMPROVE) PM 2.5 speciation over the United States to analyze more than 40 fire cases in the western United States They showed that smoke-impacted measurements are associated with dust enhancement, chloride depletion, and enhancement of some other elements (P, K, nitrate, and Zn) along with the expected enhancements of carbonaceous species. However, similar to the remote-sensing studies described above, Schlosser et al (2017) did not isolate the smoke properties from the nonsmoke aerosol, and they only focused on large wildfires in the western United States…”

Characteristic Vertical Profiles of Cloud Water Composition in Marine Stratocumulus Clouds and Relationships With Precipitation

“…This study analyzes a comprehensive set of cloud water samples obtained in the stratocumulus cloud deck off the California coast during the months of July and August between 2011 and 2016. The Center for Interdisciplinary Remotely‐Piloted Aircraft Studies Twin Otter conducted flights in the following four campaigns from which data are analyzed: the Eastern Pacific Emitted Aerosol Cloud Experiment (E‐PEACE) (Russell et al, ; Wonaschütz et al, ), the Nucleation in California Experiment (NiCE) (Crosbie et al, ; Maudlin et al, ), the Biological and Oceanic Atmospheric Study (BOAS) (Wang et al, ), and the Fog and Stratocumulus Evolution (FASE) Experiment (Dadashazar et al, ; Schlosser et al, ). Table summarizes the dates and flights for these field experiments, while Figure shows the spatial area of the flight tracks during each experiment.…”

Development and characterisation of a high-efficiency, aircraft-based axial cyclone cloud water collector

“…The plume was transported offshore on a number of the flights and was likely to be a significant conduit for lofting near surface continental airmasses into the lower free troposphere, where it could later descend into the marine cloud deck. It is also known that fires 30 can locally drive substantial dust and soil emissions (Kavouras et al, 2012, Diapouli et al, 2014, Schlosser et al, 2017. Comparing the Ca 2+ :Na + ratio between probes shows that RF4 exhibits a marked difference in the relative abundance of non-sea salt calcium compared to the other flights.…”